Lasers. Nm - Green

1. Passage of monochromatic light through a transparent environment.

2. Creating an inverse population. Methods of pumping.

3. The principle of the laser. Types of lasers.

4. Features of laser radiation.

5. Characteristics of laser radiation used in medicine.

6. Changes in the properties of tissue and its temperature under the action of continuous powerful laser radiation.

7. The use of laser radiation in medicine.

8. Basic concepts and formulas.

9. Tasks.

We know that the light is emitted by separate portions - photons, each of which arises as a result of the radiative transition of an atom, molecules or ion. Natural light is a set of a huge number of such photons that differ in frequency and phase emitted at random moments of time in random directions. Obtaining powerful beams of monochromatic light using natural sources - the task is practically unresolved. At the same time, the need for such bundles was felt both physicists and specialists of many applied sciences. The creation of a laser allowed to solve this task.

Laser- A device generating coherent electromagnetic waves due to the forced radiation of microparticles of the medium in which a high degree of excitation of one of the energy levels is created.

Laser Laser Light AMPLIFICATION by Stimulated Of Emission Radiation) is an increase in light with forced radiation.

The intensity of laser radiation (Li) is many times greater than the intensity of natural light sources, and the divergence of the laser beam is less than one angular minute (10 -4 rad).

31.1. Passage of monochromatic light through a transparent environment

In lecture, we found out that the passage of light through the substance is accompanied as photon excitationits particles and acts forced radiation.Consider the dynamics of these processes. Suppose in the environment applies monochromaticthe light whose frequency (ν) corresponds to the transition of particles of this medium from the main level (E 1) to the excited (E 2):

Photons falling into particles in the main state will be absorband the particles themselves will switch to the excited state E 2 (see Fig. 27.4). Photons that fall into excited particles, initiate a forced radiation (see Fig. 27.5). At the same time, photon doubling occurs.

In a state of thermal equilibrium, the ratio between the number of excited (N 2) and the unexcited (N 1) particles is obeying the distribution of the Boltzmann:

where k is the boltzmann constant, T is an absolute temperature.

In this case, N 1\u003e N 2 and the absorption dominates the doubling. Consequently, the intensity of the emerging light I will be less than the intensity of the incident light I 0 (Fig. 31.1).

Fig. 31.1.Weakening of light passing through the medium in which the degree of excitation is less than 50% (N 1\u003e N 2)

As light absorbs, the degree of excitement will grow. When it reaches 50% (N 1 \u003d N 2), between absorptionand doublingequilibrium will be established, since the probabilities of photons entering the excited and unexcited particles will become the same. If the medium illumination stops, after a while, the medium will return to the initial state corresponding to the Boltzmann distribution (N 1\u003e N 2). Make a preliminary conclusion:

When illuminated by monochromatic light (31.1) it is impossible to achieve this state of the medium in which the degree of excitation exceeds 50%. And yet let's consider the question of passing light through the medium in which the state of N 2\u003e N 1 was achieved in some way. This condition is called a state with inverse population(from lat. inversio.- turning).

Inverse population- This is a state of the medium in which the number of particles on one of the upper levels is greater than on the bottom.

In an inverse population medium, the probability of photon entering the excited particle is greater than in an unexcited. Therefore, the doubling process dominates the absorption process and takes place gain lights (Fig. 31.2).

As light passes through the medium with inverse population, the degree of excitation will decrease. When it reaches 50%

Fig. 31.2.Strengthening light passing through a medium with inverse population (N 2\u003e N 1)

(N 1 \u003d N 2), between absorptionand doublingequilibrium and the effect of light gain will disappear. If the medium illumination stops, after a while, the medium returns to a state corresponding to the combat distribution (N 1\u003e N 2).

If all this energy is highlighted in radiative transitions, we will get a light pulse of a huge power. True, it will not have the required coherence and orientation, but will be highly monochromatic (HV \u003d E 2 - E 1). This is not a laser, but something close.

31.2. Creating an inverse population. Methods of pumping

So is it possible to achieve inverse population? It turns out, you can, if using threeenergy levels with the following configuration (Fig. 31.3).

Let the medium illuminates a powerful flash of light. A part of the radiation spectrum will be absorbed in the transition from the main level E 1 to a wide level of E 3. Recall that wideit is an energy level with a small relaxation time. Therefore, the majority of particles falling on the level of excitation E 3, it is imperceptibly moving into a narrow metastable level E 2, where their accumulation occurs. Due to the narrowness of this level, only a small share of flash photons

Fig. 31.3.Creating an inverse population on a metastable level

capably cause a forced transition E 2 → E 1. This provides conditions for creating an inverse population.

The process of creating an inverse population is called pumped.In modern lasers, various types of pumping are used.

Optical pumping transparent active media uses light pulses from an external source.

Electrical pumping gas active media uses an electric discharge.

Injection pumping semiconductor active media uses electric current.

Chemical pumping active Environment From the mixture of gases uses the energy of the chemical reaction between the components of the mixture.

31.3. Principle of laser operation. Types of lasers

The laser functional diagram is shown in Fig. 31.4. The working fluid (active medium) is a long narrow cylinder, the ends of which are closed with two mirrors. One of the mirrors (1) is translucent. Such a system is called an optical resonator.

The pumping system translates particles from the main level E 1 to the absorption level E 3, from which they are idle to the metastable level E 2, creating its inverse population. After that, spontaneous emitting transitions E 2 → E 1 begins with the emission of monochromatic photons:

Fig. 31.4.Schematic laser device

Photons of spontaneous radiation emitted at an angle to the axis of the resonator go through the side surface and do not participate in the generation process. Their flow quickly dries.

Photons that, after spontaneous radiation move along the axis of the resonator, repeatedly pass through the working fluid, reflecting from the mirrors. At the same time, they interact with excited particles, initiating forced radiation. Due to this, the "avalanche-like" increase in induced photons moving in the same direction occurs. Recently reinforced photon flow comes through a translucent mirror, creating a powerful beam of almost parallel coherent rays. In fact, laser radiation is generated firstspontaneous photon, which moves along the resonator axis. This ensures radiation coherence.

Thus, the laser converts the energy of the pump source into the energy of monochromatic coherent light. The effectiveness of such a transformation, i.e. The efficiency depends on the type of laser and lies in the range of percentage of up to several tens of percent. Most of the tramp lasers are 0.1-1%.

Types of lasers

The first created laser (1960) used ruby \u200b\u200band optical pumping system as a working fluid. Ruby is a crystalline aluminum oxide A1 2 O 3, containing about 0.05% of the chromium atoms (it is chrome that gives rubbing pink color). Chromium atoms embedded in a crystal lattice are an active medium.

with the configuration of the energy levels shown in Fig. 31.3. Ruby laser radiation wavelength equal λ \u003d 694.3 nm. Then there appeared lasers using other active media.

Depending on the type of working body, the lasers are divided into gas, solid-state, liquid, semiconductor. In solid-state lasers, the active element is usually made in the form of a cylinder, the length of which is much larger than its diameter. Gas and liquid active mediums are placed in a cylindrical cuvette.

Depending on the pumping method, it is possible to obtain continuous and impulse generation of laser radiation. With a continuous pumping system, the inversion of the population is maintained for a long time due to an external energy source. For example, continuous excitation by electrical discharge in the gas environment. With a pulsed pumping system, the inversion of the population is created in a pulse mode. Frequency of pulses from 10 -3

Hz up to 10 3 Hz.

31.4. Features of laser radiation

Laser radiation in its properties is significantly different from radiation of conventional light sources. We note its characteristic features.

1. Coherence.Radiation is high-coherentwhat is due to the properties of forced radiation. In this case, not only temporary, but also spatial coherence: the phase difference at two points of the plane perpendicular to the direction of propagation is maintained by constant (Fig. 31.5, a).

2. Collimation.Laser radiation is collimatedthose. All rays in the beam are almost parallel to each other (Fig. 31.5, b). At a high distance, the laser beam is only slightly increased in diameter. Since the corner of divergence φ small, the intensity of the laser beam is weakly decreasing with distance. This allows you to transmit signals for huge distances at a low weakening of their intensity.

3. Monochromatism.Laser radiation is in high degree monochromaticthose. contains waves of almost the same frequency (the width of the spectral line is Δλ ≈0.01 nm). On the

figure 31.5, in a schematic comparison of the laser beam lines width and a ray of ordinary light.

Fig. 31.5.Coherence (a), collimacy (b), monochromaticity (c) laser radiation

Prior to the appearance of lasers, radiation with some degree of monochromaticity was able to obtain with devices - monochromators excreted from a solid spectrum narrow spectral intervals (narrow wavelength bands), but the power of light in such lanes is small.

4. High power.With the help of a laser, it is possible to ensure a very high power of monochromatic radiation - up to 10 5 W in continuous mode. The power of pulse lasers is several orders of magnitude higher. Thus, the neodymium laser generates a pulse with an energy E \u003d 75 J, the duration of which T \u003d 3x10 -12 p. The power in the impulse is p \u003d e / t \u003d 2.5x10 13 W (for comparison: the power of hydroelectric power is p ~ 10 9 W).

5. High intensity.In pulsed lasers, the intensity of laser radiation is very high and can reach i \u003d 10 14 -10 16 W / cm 2 (cf. intensity sunlight near the ground surface i \u003d 0.1 w / cm 2).

6. High brightness.In the lasers working in the visible range, brightnesslaser radiation (the power of light from the surface unit) is very large. Even the weakest lasers have a brightness of 10 15 kD / m 2 (for comparison: the brightness of the sun L ~ 10 9 kD / m 2).

7. Pressure.When the laser beam falls on the surface of the body is created pressure(D). With full absorption of laser radiation, falling perpendicular to the surface, a pressure d \u003d I / C is created, where the radiation value of the radiation, C - the speed of light in vacuum. With full reflection, the pressure is twice as much. For the intensity i \u003d 10 14 W / cm 2 \u003d 10 18 W / m 2; D \u003d 3.3x10 9 Pa \u003d 33,000 atm.

8. Polarizedness.Laser radiation completely polarized.

31.5. Characteristics of laser radiation used in medicine

Lena wavelength

The radiation wavelengths (λ) of the medical lasers lie in the range of 0.2 -10 μm, i.e. From ultraviolet to the far infrared area.

Radiation power

The radiation power (P) of medical lasers varies in a wide range defined by the use objectives. Lasers with continuous pumping p \u003d 0.01-100 W. Pulse lasers are characterized by power in the impulse P and and the pulse duration τ and

For surgical lasers P and \u003d 10 3 -10 8 W, and the pulse duration T and \u003d 10 -9 -10 -3 s.

Energy in radiation pulse

The energy of one pulse of laser radiation (E and) is determined by the relation E and \u003d p and, and, where t and is the duration of the radiation pulse (usually t and \u003d 10 -9 -10 -3 s). For surgical lasers E and \u003d 0.1-10 J.

Frequency of impulses

This characteristic (f) of pulse lasers shows the number of radiation pulses generated by a laser for 1 s. For therapeutic lasers f \u003d 10-3 000 Hz, for surgical F \u003d 1-100 Hz.

The average power of radiation

This characteristic (p of CP) of pulse-periodic lasers shows what energy the laser emitters for 1 s, and is determined by the following ratio:

Intensity (power density)

This characteristic (i) is defined as the ratio of the power of laser radiation to the cross-sectional area of \u200b\u200bthe beam. For continuous lasers i \u003d p / s. In the case of impulse lasers distinguish intensity in impulseI and \u003d p and / s and the average intensity I cf \u003d p cf / s.

The intensity of surgical lasers and pressure generated by their radiation have the following values:

for continuous lasers I ~ 10 3 W / cm 2, d \u003d 0.033 Pa;

for pulse lasers I and ~ 10 5 -10 11 W / cm 2, d \u003d 3.3 - 3.3x10 6 Pa.

Energy Density in Pulse

This value (W) characterizes the energy that falls on a unit of the irradiated surface area for one pulse and is determined by the ratio W \u003d E and / S, where S (cm 2) is the area of \u200b\u200bthe light spot (i.e. cross-section of the laser beam) on the surface Biotani. In the lasers used in surgery, W ≈ 100 J / cm 2.

The parameter W can be considered as a dose of radiation D for 1 pulse.

31.6. Changes in the properties of the tissue and its temperature under the action of continuous powerful laser radiation

Change temperature and fabric properties

under the action of continuous laser radiation

The absorption of powerful laser radiation by biological tissue is accompanied by the release of heat. To calculate the highlighted heat use a special value - volumetric density of heat(q).

The release of heat is accompanied by an increase in temperature and the following processes proceed in tissues:

at 40-60 ° C, the activation of enzymes, the formation of swelling, change, and depending on the period of action of the death of cell denaturation of protein, the beginning of coagulation and necrosis;

at 60-80 ° C - denaturation of collagen, membrane defects; at 100 ° C - dehydration, evaporation of tissue water; Over 150 ° C - charring;

over 300 ° C - Fabric evaporation, gas formation. The dynamics of these processes are depicted in Fig. 31.6.

Fig. 31.6.Dynamics of the temperature of the fabric under the influence of continuous laser radiation

1 phase.First, the temperature of the fabric rises from 37 to 100 ° C. In this temperature range, the thermodynamic properties of the tissue remain almost unchanged, and the linear temperature increases occurs with the time (α \u003d const and i \u003d const).

2 phase.At a temperature of 100 ° C, the evaporation of the tissue water begins, and until the end of this process, the temperature remains constant.

3 phase.After evaporation of water, the temperature again begins to grow, but slower than in section 1, since the dehydrated tissue absorbs energy is weaker than normal.

4 phase.Upon reaching the temperature of T ≈ 150 ° C, the coagulation process begins and, consequently, the "blackening" of biites. In this case, the absorption coefficient α increases. Therefore, there is a nonlinear, accelerating temperature increase over time.

5 phase.Upon reaching the temperature of T ≈ 300 ° C, the process of evaporation of dehydrated charred biycleanis begins and the temperature rise again stops. It is at this moment that the laser beam disks (removes) the cloth, i.e. becomes a scalpel.

The degree of temperature increase depends on the depth of the tissue (Fig. 31.7).

Fig. 31.7.Processes occurring in irradiated tissues at different depths: but- In the surface layer, the fabric heats up to several hundred degrees and evaporates; b.- The power of radiation, weakened by the upper layer, is insufficient for evaporation of the tissue. Fabric coagulation occurs (sometimes together with the char harness - a black bold line); in- tissue heating due to heat transfer from the zone (b)

The length of individual zones is determined by both the characteristics of laser radiation and the properties of the tissue itself (primarily the absorption and thermal conductivity coefficients).

The effect of a powerful focused beam of laser radiation is accompanied by the occurrence of shock waves, which can cause mechanical damage to the adjacent tissues.

Ablation of tissue under the influence of powerful pulsed laser radiation

When exposed to the fabric of short pulses of laser radiation with high energy density, another mechanism of dissection and detection of biological entry is implemented. In this case, there is a very quick heating of the tissue fluid to the temperature of T\u003e T of instrumentation. In this case, the tissue fluid turns out to be in a metastable overheated state. Then there is an "explosive" boiling of the tissue fluid, which is accompanied by the removal of fabric without charring. This phenomenon is called ablation.Ablation is accompanied by the generation of mechanical shock waves capable of causing mechanical damage to the tissues in the vicinity of the zone of laser exposure. This fact must be taken into account when selecting the parameters of pulse laser radiation, for example, when skin grinding, drilling teeth, or with laser correction of visual acuity.

31.7. Using laser radiation in medicine

The processes characterizing the interaction of laser radiation (Li) with bio-objects can be divided into 3 groups:

impact effect(which does not have a noticeable effect on the bio object);

photochemical action(an excited particle with a laser or herself takes part in the corresponding chemical reactions, or transfers its excitation to another particle involved in the chemical reaction);

photoint evidence(by highlighting heat or shock waves).

Laser diagnosis

Laser diagnostics is a non-viable effect on bio-object using coherencelaser radiation. We list the basic diagnostic methods.

Interferometry.Under the reflection of laser radiation from the rough surface, secondary waves occur, which interferred with each other. As a result, a picture of dark and light spots (speckles) is formed, the location of which gives information about the surface of the bio-object (the method of singing interferometry).

Holography.Using laser radiation, a 3-dimensional image of an object is obtained. In medicine, this method allows you to receive volumetric images of the internal cavities of the stomach, eyes, etc.

Light scattering.When passing a sharply directed laser beam through a transparent object, light scattering occurs. Registration of the angular dependence of the intensity of the scattered light (method of oil meterometry) allows to determine the dimensions of the particles of the medium (from 0.02 to 300 microns) and the degree of their deformation.

When scattered, the polarization of light may vary, which is also used in the diagnosis (polarization neophelometry method).

Doppler effect.This method is based on the measurement of the Doppler shift of the frequency of whether, which occurs when the light is reflected even from slowly moving particles (anenterometry method). In this way, the speed of blood flow in vessels, the mobility of bacteria, etc.

Quasi-elastic scattering.With such scattering, there is a slight change in the wavelength of probing whether. The reason for this is a change in the process of measuring the scattering properties (configurations, particle conformation). The time changes in the parameters of the scattering surface are manifested in the change in the scattering spectrum compared with the spectrum of the supply radiation (the spectrum of scattering is either interrupted or additional maxima appear in it). This method Allows you to obtain information about changing characteristics of the scatterer: diffusion coefficient, directional velocity, sizes. This is the diagnosis of protein macromolecules.

Laser mass spectroscopy.This method is used to research. chemical composition object. Powerful laser radiation beams evaporate the substance from the surface of the biobject. Couples are subjected to mass-spectral analysis, according to the results of which they judge the composition of the substance.

Laser blood test.Laser beam, passed through a narrow quartz capillary, according to which specially treated blood pumps, causes fluorescence of its cells. Fluorescent glow is then captured by a sensitive sensor. This glow is specific for each type of cells, passing by one by the section of the laser beam. The total number of cells in the specified blood volume is calculated. The exact quantitative indicators for each cell type are defined.

Method of photovolving.It is used to study the surface compositionobject. Powerful beams are allowed to take microprobes from the surface of bio-object by evaporating the substance and the subsequent mass spectral analysis of this steam.

Using laser radiation in therapy

In therapy, low-intensity lasers are used (intensity 0.1-10 W / cm 2). Low-intensity radiation does not cause a noticeable destructive action on the tissue directly during irradiation. In the visible and ultraviolet areas of the spectrum, irradiation effects are due to photochemical reactions and do not differ from the effects caused by monochromatic light obtained from conventional non-coherent sources. In these cases, lasers are simply convenient monochromatic light sources,

Fig. 31.8.Scheme of the application of a laser source for intravascular irradiation of blood

accurate localization and dosage of exposure. As an example in Fig. 31.8 shows the scheme of using a source of laser radiation for intravascular blood irradiation in patients with heart failure.

Below are the most common methods of laser therapy.

Therapy with red light.The radiation of the non-NE laser with a wavelength of 632.8 nm is used with an anti-inflammatory target for the treatment of wounds, ulcers, ischemic heart disease. Therapeutic effect is associated with the effect of the light of this wavelength on the proliferative activity of the cell. The light acts as a regulator of cell metabolism.

Therapy with blue light.Laser radiation with a wavelength in a blue region of visible light is used, for example, for the treatment of jaundice newborns. This disease is a consequence of a sharp increase in the body of a bilirubin concentration, which has a maximum absorption in the blue area. If they irradiate children with laser radiation of this range, then bilirubin breaks down, forming water-soluble products.

Laselophysiotherapy -the use of laser radiation with a combination with various methods of electrophysitherapy. Some lasers have magnetic nozzles for a combined effect of laser radiation and a magnetic field - magnetoveser and therapy. These include the magnetic infrared laser therapeutic apparatus of Morta.

The efficiency of laser and therapy increases with compinite effects with drugs, pre-applied to the irradiated zone (laser formulation).

Photodynamic tumor therapy.Photodynamic therapy (PDT) is used to remove tumors available for irradiation with light. FDT is based on the use of photosensitizers in tumors, increasing tissue sensitivity when they

subsequent irradiation of visible light. The destruction of tumors at PDT is based on three effects: 1) direct photochemical destruction of tumor cells; 2) damage to the blood vessels of the tumor, leading to the ischemia and the death of the tumor; 3) the emergence of an inflammatory reaction that mobilizing the antitumor immune protection of the body tissues.

For irradiation of tumors containing photosensitizers, laser radiation with a wavelength of 600-850 nm is used. In this area of \u200b\u200bthe spectrum, the depth of the penetration of light into biological tissue is maximal.

Photodynamic therapy is used in the treatment of skin tumors, internal organs: lungs, esophagus (with the internal organs, laser radiation is delivered using light guides).

Using laser radiation in surgery

In surgery, high-intensity lasers are used to disseminate tissues, removing pathological sites, stopping bleeding, beycle welding. Choosing a proper wavelength of radiation, its intensity and duration of exposure can be obtained by various surgical effects. Thus, for cutting biological tissues, a focused beam of a continuous CO 2 is used, having a wavelength λ \u003d 10.6 μm, a power of 2x10 3 W / cm 2.

The use of the laser beam in surgery provides selective and controlled impact. Laser surgery has several advantages:

Contactlessness, giving absolute sterility;

Selectivity that allows the choice of radiation wavelength to dispense pathological tissues, without affecting those surrounding healthy fabrics;

Becability (due to coagulation of proteins);

The possibility of microsurgical effects, due to the high degree of focusing of the beam.

We indicate some areas of surgical application of lasers.

Laser welding of fabrics.The connection of dissected tissues is the necessary stage of many operations. Figure 31.9 shows how to weld one of the trunks of a large nerve is carried out in the contact mode using solder, which

Fig. 31.9.Nerva welding with a laser beam

pipette drops are served at the location of the lazing.

Destruction of pigmented areas.Lasers operating in pulse mode are used to destroy pigmented areas. This method (phototermolysis)used for the treatment of angioma, tattoos, sclerotic plaques in blood vessels, etc.

Laser endoscopy.The introduction of endoscopy produced a native coup in operational medicine. To avoid large open operations, laser radiation is delivered to the place of exposure using fiber-optic light guides, which make it possible to supply laser radiation to biotmates of internal hollow organs. At the same time, the risk of infection and the emergence of postoperative complications is significantly reduced.

Laser breakdown.Short-pulse lasers in combination with fiber films are used to remove plaques in vessels, stones in the bustling bubble and kidneys.

Lasers in ophthalmology.The use of lasers in ophthalmology allows to perform bloodless operational interventions without disrupting the integrity of the eyeball. These are operations on the vitreous body; welding of peeling retinal; Treatment of glaucoma by "piercing" with a laser beam of holes (with a diameter of 50 ÷ 100 μm) for outflow of intraocular fluid. The layer ablation of the tissues of the cornea is used for vision correction.

31.8. Basic concepts and formulas

Ending table

31.9. Tasks

1. In the phenylalanine molecule, the difference in the main and excited states is ΔЕ \u003d 0.1 eV. Find the ratio between the population of these levels at T \u003d 300 K.

Answer:n \u003d 3.5 * 10 18.

Lasers are becoming increasingly important tools for research in the field of medicine, physics, chemistry, geology, biology and technology. With incorrect use, they can dazzle and apply injuries (including burns and electricians) operators and other personnel, including random visitors to the laboratory, as well as cause significant damage to property. Users of these devices must fully understand and apply the necessary security measures when contacting them.

What is a laser?

The word "laser" (eng. Laser, Light Amplification by Stimulated Emission of Radiation) is an abbreviation that is decoded as "linge of light by induced radiation". The radiation frequency generated by the laser is within or close to the visible part of the electromagnetic spectrum. Energy is enhanced to a state of extremely high intensity using a process that is called "Laser induced" radiation.

The term "radiation" is often understood incorrectly, because it is also used when describing in this context it means energy transmission. Energy is transferred from one place to another by means of conductivity, convection and radiation.

There are many different types of lasers working in different environments. Gases are used as a working medium (for example, an argon or a mixture of helium with neon), solid crystals (for example, ruby) or liquid dyes. When the energy is fed into the working medium, it goes into an excited state and releases the energy as particles of light (photons).

A pair of mirrors at both ends of the sealed tube either reflects, or transmits light as a concentrated flow called a laser beam. Each working medium produces a beam of a unique wavelength and color.

Laser light color, as a rule, is expressed by a wavelength. It is non-ionizing and includes ultraviolet (100-400 nm), visible (400-700 nm) and infrared (700 nm - 1 mm) part of the spectrum.

Electromagnetic spectrum

Each electromagnetic wave has a unique frequency and length associated with this parameter. Similarly, the red light has its own frequency and wavelength, and all other colors - orange, yellow, green and blue - have unique frequencies and wavelengths. People are able to perceive these electromagnetic waves, but not able to see the rest of the spectrum.

Ultraviolet have the greatest frequency. Infrared, microwave radiation and radio waves occupy the lower frequencies of the spectrum. Visible light is located in a very narrow range between them.

Impact on man

The laser produces an intense directed beam of light. If it is directed, reflect or focus on the object, the beam will be partially absorbing, increasing the surface temperature and the inner part of the object, which can cause a change or deformation of the material. These qualities that have found use in laser surgery and processing materials can be dangerous for human tissues.

In addition to radiation that has a thermal effect on tissue, dangerously laser radiation producing a photochemical effect. Its condition is quite short, i.e. ultraviolet or blue part of the spectrum. Modern devices Laser radiation is produced, the impact on the person whose person is minimized. The energies of low-power lasers are not enough to apply harm, and they do not represent the dangers.

Human fabric is sensitive to energy effects, and under certain circumstances electromagnetic radiation, Laser including, can damage the eyes and skin. Studies of threshold levels of traumatic radiation were conducted.

Danger for eyes

The human eye is more susceptible to injury than skin. The cornea (transparent outer front surface of the eye), unlike the dermis, does not have an outer layer of dead cells protecting against exposure ambient. Laser and absorbed by the cornea of \u200b\u200bthe eye, which can harm it. Injury is accompanied by an e-epithelium and erosion, and with heavy damage - turbidity of the anterior chamber.

The crystal of the eye can also be injured when various laser radiation is affected - infrared and ultraviolet.

The greatest danger, however, represents the effect of the laser on the retina in the visible part of the optical spectrum - from 400 nm (violet) to 1400 nm (near infrared). Within this area of \u200b\u200bthe spectrum, the collimated rays focus on very small retinal areas. The most unfavorable impact option occurs when the eye looks into the distance and the straight or reflected beam falls into it. In this case, its retina concentration reaches 100,000 times.

Thus, the visible bundle with a capacity of 10 MW / cm 2 acts on the retina of the eye with a power of 1000 W / cm 2. This is more than enough to cause damage. If the eye does not look into the distance, or if the beam is reflected from the diffuse, not a mirror surface, a significantly more powerful radiation leads to injury. Laser impact The skin is devoid of focusing effect, so it is much less susceptible to injuries at these wavelengths.

X-rays

Some high-voltage systems with a voltage of more than 15 kV can generate X-rays of significant power: laser radiation whose sources are powerful with electronic pumping, as well as plasma systems and sources of ions. These devices must be verified on including to ensure proper shielding.

Classification

Depending on the power or energy of the beam and the wavelength of the radiation, the lasers are divided into several classes. The classification is based on the potential ability of the device to cause immediate injury to the eye, skin, ignition with direct exposure to the beam or when reflected from diffuse reflective surfaces. All commercial lasers are identified using labels applied on them. If the device was manufactured at home or otherwise not marked, you should get advice on the appropriate classification and labeling. Lasers differ in power, wavelength and exposure duration.

Safe devices

First-class devices generate low-intensity laser radiation. It cannot achieve a dangerous level, so the sources are exempt from most control measures or other observation forms. Example: Laser printers and CD players.

Conditionally safe devices

Second-class lasers emit in the visible part of the spectrum. This laser radiation, the sources of which cause a normal reaction to a normal reaction to too bright light (blinker reflex). When exposed to the beam, the human eye blinks through 0.25 s, which ensures sufficient protection. However, the laser radiation in the visible range is capable of damaging the eyes at constant exposure. Examples: laser pointers, geodesic lasers.

Lasers 2A-Class are devices special purpose With an output capacity of less than 1 MW. These devices cause damage only with direct impact for more than 1000 s for an 8-hour working day. Example: barcode reading devices.

Dangerous lasers

The class 3a includes devices that are not injured with short-term exposure to unprotected eyes. Can be dangerous when using focusing optics, such as telescopes, microscopes or binoculars. Examples: Helium-neon laser with a capacity of 1-5 MW, some laser pointers and building levels.

Laser Class 3B Laser can cause injury with direct effects or when it is mirror reflected. Example: helium-neon laser with a capacity of 5-500 MW, many research and therapeutic lasers.

Class 4 includes devices with power levels of more than 500 MW. They are dangerous for eyes, skin, as well as fires. The effect of a beam, its mirror or diffuse reflections can cause eye and skin injuries. All security measures should be taken. Example: nd: yag lasers, displays, surgery, metal cutting.

Laser radiation: Protection

Each laboratory should provide appropriate protection for persons working with lasers. The windows of the premises through which radiation of devices 2, 3 or 4 classes can be done with damage to uncontrolled areas, should be coated or otherwise protected during the operation of such an instrument. To ensure maximum eye protection, the following is recommended.

• A bundle must be concluded in a non-combustible non-combustible protective shell to minimize the risk of accidental impact or fire. To equalize the beam, use luminescent screens or secondary visiers; Avoid direct impact on the eyes.
• For the leak alignment procedure, use the smallest power. If possible, use low-class devices for preliminary alignment procedures. Avoid the presence of unnecessary reflective objects in the zone of the laser.
• Limit the passage of the beam in the danger zone at no time using dampers and other obstacles. Do not use the walls of the room for alignment of the lasers of class 3B and 4 lasers.
• Use non-reflective tools. Some inventory that does not reflect the visible light becomes mirrored in the invisible area of \u200b\u200bthe spectrum.
• Do not wear reflective jewelry. Metal decorations also increase the danger of electric shock.

Protective glasses

When working with 4 class lasers with an open dangerous zone or at risk of reflection, use protective glasses. Their type depends on the type of radiation. Points need to be chosen to protect against reflections, especially diffuse, as well as to ensure protection to a level when a natural protective reflex can prevent eye injury. Such optical devices will retain some visibility of the beam, prevent skin burns, reduce the possibility of other accidents.

Factors that should be considered when choosing safety glasses:

• wavelength or radiation spectrum area;
• optical density at a certain wavelength;
• maximum illumination (W / cm 2) or beam power (W);
• type of laser system;
• power mode - pulse laser radiation or continuous mode;
• reflection capabilities - mirror and diffuse;
• line of sight;
• the presence of corrective lenses or sufficient size allowing wearing glasses for vision correction;
• comfort;
• the presence of fanning holes that prevent fogging;
• influence on color vision;
• impact resistance;
• the ability to perform the necessary tasks.

Since safety glasses are subject to damage and wear, the laboratory security program should include periodic checks of these protective elements.

Laser Radiation Duration

Duration is determined by the laser design. The following typical radiation distribution modes can be distinguished in time:

Continuous mode;

Pulse mode, the pulse duration is determined by the duration of the flash of the pump lamp, the typical duration of DFL ~ 10-3C;

The modulation mode of the resonator (the duration of the radiation pulse is determined by the excess of pumping over the generation threshold and the speed and speed of the goodness, the typical duration lies in the range of 10-9 - 10-8 s, this is the so-called nanosecond radiation duration range);

The synchronization mode and longitudinal modes in the resonator (the duration of the radiation pulse of the DFL ~ 10-11c - the picosecond range of radiation durations);

Various modes of forced shortening radiation pulses (DFL ~ 10-12C).

Radiation power density

Laser radiation can be concentrated in a narrow-controlled beam with a high power density.

The density PS power of the radiation is determined by the ratio of the radiation power passing through the section of the laser beam, to the cross-section area and has the dimension of W cm-2.

Accordingly, the radiation energy density of the radiation energy is determined by the ratio of the energy passing through the section of the laser beam, to the section cross section and has the dimension of JM-2

The power density in the laser beam reaches large quantities due to the addition of the energy of a huge set of coherent emissions of individual atoms coming in the selected point of space in the same phase.

Coherent radiation of the laser using an optical lenses system can be focused on a small, comparable with a wavelength on the surface of the object.

The power density of laser radiation on this site reaches a huge amount. In the center of the site Power density:

where P is the output power of laser radiation;

D - the diameter of the optical system lens;

l - wavelength;

f - focal length of the optical system.

The radiation of the laser with a huge power density, affecting various materials, destroys and even evaporates them in the area of \u200b\u200bfalling focused radiation. At the same time, in the field of falling laser radiation on the surface of the material, it creates light pressure in hundreds of thousands of megapascals.

As a result, we note that focusing the radiation of the OCG to a stain, the diameter of which is approximately equal to the length of the radiation wave, it is possible to obtain light pressure in 106MP, as well as the huge radiation power densities reaching the values \u200b\u200bof 1014-1016W. CM-2, while temperatures up to several occur Million Celvin.

Block diagram of optical quantum resonator

The laser consists of three main parts: active medium, pumping device and optical resonator. Sometimes the thermal stabilization device is added.

Figure 3 - Laser flowchart

1) active medium.

For resonant absorption and reinforcement due to the forced radiation, it is necessary that the wave pass through the material, the atoms or systems of the atoms of which are "configured" to the desired frequency. In other words, the difference in energy levels E2 - E1 for the material atoms must be equal to the frequency electromagnetic wavemultiplied by a permanent bar: E2 - E1 \u003d HN. Further, in order for forced radiation to prevail over the absorption, atoms at the upper energy level should be greater than on the bottom. Usually it does not happen. Moreover, any system of atoms, for quite a long time granted to itself, comes to balance with its surroundings at low temperatures, i.e. Reaches the state of lowest energy. At elevated temperatures, part of the system atoms is excited by thermal motion. With an infinitely high temperature, all quantum states would be equally filled. But since the temperature is always finite, the predominant proportion of atoms is in the lowest state, and the higher the state, the less they are filled. If at an absolute temperature t in the low state is N0 atoms, the number of atoms in the excited state, the energy of which by the value of E exceeds the energy of the lower state, is given by the Boltzmann distribution: N \u003d N0E-E / KT, where k is the boltzmann. Since atoms in lower conditions, in equilibrium, there are always greater than in higher, in such conditions, absorption always prevails, and not strengthening due to the forced radiation. Excess atoms in a certain excited state can be created and maintained, only artificially transferring them to this condition, and faster than they return to thermal equilibrium. A system in which there is an excess of excited atoms, strives for thermal equilibrium, and it must be maintained in a non-equilibrium state, creating such atoms in it.

2) Resonator.

The optical resonator is a system of specially agreed two mirrors, selected in such a way that the weak disreamant arising in the resonator due to spontaneous transitions is repeatedly intensified by passing through the active medium placed between the mirrors. Due to multiple reflections of radiation between mirrors, there is a lengthening of the active medium in the direction of the resonator axis, which determines the high orientation of the laser radiation. In more complex lasers, four or more mirrors forming the resonator are used. The quality of manufacture and installation of these mirrors is for the quality of the obtained laser system. Also, additional devices can be mounted in the laser system, the length of obtaining different effects, such as rotating mirrors, modulators, filters and absorbers. Their use allows you to change the parameters of the laser radiation, for example, wavelength, pulse duration, etc.

The resonator is the main defining factor of the working wavelength, as well as the other properties of the laser. There are hundreds or even thousands of different working bodies, on the basis of which you can build a laser. The working body is subjected to "pumping" to obtain the effect of inversion of electronic populations, which causes forced radiation of photons and the effect of optical amplification. The lasers use the following working bodies.

The liquid, for example, in dye lasers, consists of an organic solvent, such as methanol, ethanol or ethylene glycol, in which chemical dyes are dissolved, such as coumarin or rhodamine. The configuration of the dye molecules determines the wavelength.

Gas, for example, carbon dioxide, argon, crypton or mixtures, such as in helium neon lasers. Such lasers are most often pumped by electrical discharges.

Solid bodies, such as crystals and glass. The solid material is usually allocated (activated) by adding a small number of chromium ions, neodymium, erbium or titanium. Typical crystals used: aluminum grenade (YAG), lithium-yttrium fluoride (YLF), sapphire (aluminum oxide) and silicate glass. The most common options are: ND: YAG, titanium sapphire, chromium sapphire (also known as ruby), doped with chromium strontium lithium-aluminum fluoride (Cr: Lisaf), ER: YLF and ND: Glass (neodymium glass). Solid-state lasers are usually pumped with a pulsed lamp or another laser.

Semiconductors. The material in which the transition of electrons between the energy levels may be accompanied by radiation. Semiconductor lasers are very compact, pumped up with electric shock, which allows them to be used in household devices, such as CD players.

3) pumping device.

The pump source consists of energy. It can be an electrical discharger, a pulse lamp, an arc lamp, another laser, chemical reaction or even an explosive. The type of pump used directly depends on the working fluid used, and also determines the method of supplying energy to the system. For example, helium neon lasers use electrical discharges in the helium-neon gas mixture, and lasers based on alumo-yttrium grenade with neodymium doping (ND: YAG lasers) - focused light of xenon pulse lamp, excimer lasers - chemical reaction energy.

Laser safety knowledge

1. What is a laser?
Laser device that emits light (electromagnetic radiation) in the process of optical amplification based on the forced radiation of photons. The term "laser" appeared as an abbreviation amplification of light with forced radiation. Emitted laser radiation is different high degree Spatial and temporal coherence, unattainable with the help of other technologies.

2. Laser Pointer Structural Scheme


3. What is laser application?
Lasers were widely used in everyday life. Lasers are the most applicable presentation for indicating objects, coordination for construction and project, medical treatment for cosmetic and surgical procedures. The lower laser power index is ideal for presentations and astronomy of starstel. The higher power of the laser pointer up to 100 MW would be great for burning the experiment. High power class IV laser is used for experiment, scientific research, Military, etc. Targeting

4. What is the wavelength?
Our eyes are sensitive to light, which is located in a very small area of \u200b\u200bthe electromagnetic spectrum with the inscription "visible light". This visible light corresponds to the wavelength range of 400 - 700 nanometers (NM) and the color GNMU purple to red. The human eye is not able to "see" radiation with wavelengths outside the visible spectrum. Visible color from the shortest length long wavelength are: purple, blue, green, yellow, orange and red. Ultraviolet radiation has a shorter wavelength than Violet Visible Light. Infrared radiation has a wavelength than visible red light. White light is a mixture of visible spectrum colors. Black is a complete lack of light.

Spectral colors and wavelengths

This schedule shows the colors of the visible spectrum of light and associated with wavelengths in nanometers. Ranges are traditionally given as:
ultraviolet light, 100 nm, 400 nm;
visible light, 400 NM-750NM;
infrared light, 750 NM-1 NM.

5. What is laser transverse fashion?


Transverse electromagnetic mode (TEM) The structure of the laser beam describes the power distribution over the beam cross section. Most laser applications require the fundamental ray mode (TEM00) with a Gaussian power distribution by a beam cross section, as shown in the figure on the right. These are fundamental results in the smallest diameter of the beam and the beam divergence and can be focused to the smallest possible spot size.
Other income applications with high power are available in the first order (TEM01 *), or even a high-order mod. The power of the laser with the structure of the structure over fundamental is commonly called Multitra NSverse mode (MTM). The mode of the laser production structure can be changed by simply changing the mirrors.

6. Various classifications of lasers

Class I.

In essence, safe, there is no possibility of eye damage. It can be either due to low output power (in case of damage to the eye, it is impossible even after several hours of exposure), or due to the cabinet to prevent user access to the laser beam during normal operation, such as CD players or laser printers.

Class II.

Reflex of the blinking of the human eye (disgust answer) will prevent eye damage if a person deliberately looks in a beam for a long period. Output power can be up to 1 mw. This class includes only lasers that emit visible light. Most laser pointers and co-mechanical laser scanners in this category.

Class IIIa

Lasers of this class are mainly dangerous in combination with optical tools that change the diameter of the beam or power density, although even without an optical tool for increasing direct contact with the eye for two minutes, it may result in serious damage to the retina. Output power does not exceed 5 MW. The radiation power density does not exceed 2.5 MW / sq. CM if the device is not marked with "caution" a warning sign, otherwise "hazard" warning label is required. Many landmarks are laser for firearms and laser pointers in this category.

Class IIIB

Lasers in this class may damage if the beam falls into the eye directly. As a rule, this refers to lasers is powered by 5-500 MW. Lasers in this category may result in irreversible eye damage from exposure 1 / 100th second or less depending on the strength of the laser. Diffuse reflection is usually not dangerous, but mirror reflections can be as dangerous as direct influences. Protective glasses recommended when viewing a class IIIB laser beam can occur. Lasers at the high end power of this class can also represent the risk of fire and can slightly burn the skin.

Class IV

Lasers in this class have an output power of more than 500 MW in a beam and can cause heavy, irreversible damage to the eyes or skin without increasing eye optics or appliances. The diffuse reflection of the laser beam can be dangerous to the skin or eye over the nominal danger area. Many industrial, scientific, military and medical lasers in this category.

7. What is laser safety knowledge?
Even the first laser was recognized as potentially dangerous. Theodore Meiman is characterized by the first laser as having the power of one "Gillette", as it could burn through one gillette razor blade. Today it is believed that even low-power lasers with the help of only a few milliwatts of power can be vision dangerous for a person when the beam of such a laser enters the eyes directly or after reflection from the shiny surface. At wavelengths, the cornea and lens can focus well, consistency and low divergence of laser light means that it can be directed to the eye into a very small spot on the retina of the eye, which leads to localized burning and damage for seconds or even less time. Lasers are usually indicated by a series of security class, which determines how dangerous laser:

. Class I / 1 In essence, it is generally safe, because the light contained in the case, for example, CD players.
. Class II / 2 is safe at normal operation; Reflex blinking from the eye will prevent damage. Usually up to 1 MW, for the signs for example a laser.
. Class IIIA / 3A Lasers, as a rule, up to 5 mW and attract a small risk of eye damage during the morgue reflex. Looking at such a beam for a few seconds can damage the spots on the retina.
. Class IIIB / 3B may result in immediate eye damage when exposed.
. Class IV / 4 Lasers can burn the skin, and in some cases even scattered light can cause eye irritation and / or skin damage. Many industrial and scientific lasers in this class. Specified powers for visible light, continuously lasers. For pulse lasers and invisible waves, other capacity limitations are applied.

People working with a class 3B and 4 class of lasers can protect their eyes protective glasses, which are designed for absorbing the light of a certain wavelength.

Some infrared lasers with a wavelength outside of about 1.4 micrometers are often referred to as "eye safe." This is because the inner molecular oscillations of water molecules are very highly absorbed in this part of the spectrum, and thus the laser beam on these wavelengths. It is weakened as much as it passes through the cornea of \u200b\u200bthe eye, that there is no light remains to be focused on the lens on the retina. The "safe for eye" label can be misleading, however, as it applies only to the relatively low power of continuous beams of waves, any high power Or modulation of the quality of the laser on these wavelengths can burn the cornea, causing serious eye damage.

8. Danger of laser radiation
Laser pointers have been widely used from its first appearance. Lasers are mainly applicable as a tool for presenting in teaching, astronomy of stars, and meetings. However, these lasers gradually owned by laser fans and enthusiasts, including children due to low cost and countless suppliers, and are used in the way not provided by manufacturers. As a result, it is seriously important to understand the dangers of laser pointers before the real possession of a laser pointer.

Laser danger
Laser radiation mainly causes damage by thermal exposure. Even moderately nutrition of the laser can lead to eye injury. High power lasers can also burn the skin. Some lasers are so powerful that even diffuse reflection from the surface can be dangerous to the eyes.

Although there is a potential danger to the retina, not all the visible beam lasers are likely to lead to irreversible damage to the retina. The impact is to look at the laser pointer beam, most likely the cause of the residual image, flash blindness and glare. The retina temporary pain will be recovered in a few minutes.

The low angle of divergence of laser light and the mechanism of focusing on the eyes means that laser light can be concentrated in a very small spot on the retina. If the laser is quite powerful, permanent damage can occur within a fraction of a second, literally faster than the blink of an eye. The Eye Apple will penetrate the eye apple visible to near IR with laser radiation and can lead to the heating of the retina, while the exposure to laser radiation with a wavelength of less than 400 nm and more than 1400nm is mainly absorbed by the cornea and lens, leads to the development of cataracts or burns.

Infrared lasers are especially dangerous, since the protective bodies of the "Reflex Morgania" response only the visible light. For example, some people are exposed to high ND power: YAG laser with invisible 1064 radiation cannot feel pain or notice direct damage to their vision. Pop music or the sound of a click arising from the eyeball can be the only sign that the retina damage occurred that is, the retina was heated to 100 ° C. As a result of localized explosive boobies, an immediate creation of a constant blind spot is accompanied.

Responsible owners of laser must fully understand the dangers of laser radiation, and recognize the FAA rules related to the use of laser pointer. Protective glasses are usually required when direct observation is a powerful beam can occur.

9. How to protect yourself from laser danger?
This is very important for adoption. effective methods Prevent damage from class 3B or class IIIB. Laser protective glasses are the main accessory to protect the eye in the market at present. Various selection of laser sensors, glasses must be selected for a specific type to block the corresponding wavelength. For example, absorbing 532 points usually has orange glasses.

Immediately looking at laser pointers is strictly prohibited in any conditions. Do not forget to wear safety glasses before using a laser pointer.

Safety Tips Laser P2:

● Put a laser in an unavailable for minors. Do not allow minors (up to 18 years) to acquire and use by a laser pointer under any supervision. Only adults can use laser pointers after they understood the knowledge of the safety and risk of laser products.

● Be especially careful if you use high laser radiation power. You should never try to specify your laser pointer on any person and animals, airplane pilot and moving vehicle, Or you will be imprisoned in prison for improper use of laser devices.

● Store away from powerful lasers. Please always keep yourself away from powerful laser, such as laser burning. They differ significantly from formal lasers for the presentation. Never try to buy a laser without identifying a class and power.

10. How will powerful laser pointers be?

Various applications must be lasers with different output power. Lasers that produce a continuous beam or a series of short pulses can be compared based on their average power. Lasers that produce impulses can be characterized on the basis of the peak power of each pulse. The peak power of the pulse laser is many orders of magnitude greater than its average power. The average output power is always less than power consumption.

Continuous or middle power required for some applications:
Power use
1-5 MW laser pointer
5 MW CDs
5-10 MW DVD Player or DVDs
100 MW high-speed CD-RW burner
250 MW consumer 16x DVD-R burners
400 MW burning through a disk case including within 4 seconds
1 W green laser in the current holographic universal development prototype disk
1-20 W Weekend most cochnishly available solid-state lasers used for micro-processing
30-100 W Typical Sealed CO2 Surgical Lasers
100-3000 W Typical sealed CO2 lasers used in industrial laser cutting
5 kW output power is achieved due to 1 cm bar laser diode
100 KW Studed CO2 Laser Power Developed by Northrop Grumman for Military (Weapons) Applications

11. What is laser services?

Proper maintenance of your laser perfectly extend its service life. We just need to follow the following advice:

What do you need:
1. Microfiber napkin
Please make sure that the microfiber fabric is specifically designed to clean the lenses. You can find it in your local camera or shop glasses.
2. Q-tip or tooth selection
You will need to fold the fabric over one of them to be able to achieve the lenses correctly.
3. Lens of cleaning of solutions (optional)
Use the solution to clean the lenses only if the lens is not cleaned with the microfiber napkin alone. Please make sure the cleaning solution is designed specifically for cleaning the lens.
* ATTENTION: Do not use water.

Procedure:
1. Wash your hands with soap and water. Make sure to dry them properly.
2. Fold the cloth from the microfiber on the toothpick or the handle part Q-Tip. Make sure you do not touch the fabric part that will clean the lenses. You probably will not be able to fold the cloth twice, so you should be very careful not to press too much on the lens.
3. Gently move the fabric into the hole until it comes into contact with the lens. Stit it from side to the side, but do not press too much. Smoothly turn the fabric in rotational motion back and forth. Repeat this procedure while your laser lens is clean.
4. Turn your laser block to see if the lens is clean.

Nevertheless dirty? Try using a solution for cleaning the lens.
Only part of the tissue, which will clean the lenses, follow the same procedure as above. You want to finish with a dry part of a cloth for wiping the lens dry, it should take one pass side to the side or gently rotate.

You all love lasers. I know, I'm getting out of them more than yours. And if someone does not like - he simply did not see the dance of sparkling dust or how the dazzling tiny light threatens Faneru

It all started from the article from a young technique for the 91st year about creating a laser on dyes - then repeat the design for a simple schoolchildren was simply unreal ... Now, fortunately with lasers, the situation is simpler - they can be taken from broken technology, they can be bought ready, their You can collect from the details ... about the most close to the reality of the lasers and today we are speech, as well as how to use them. But first of all about security and danger.

Why lasers are dangerous

The problem is that the parallel beam of the laser focuses on the eye to the point on the retina. And if it takes 200 degrees to ignite paper, only 50 is enough to damage the retina so that the blood flies. You can get a point in the blood vessel and clog it, you can get into the blind spot, where the nerves from all over the eyes go to the brain, you can smear the line of "pixels" ... And then the damaged retina can start peeling, and this is the path to full and irreversible loss. vision. And the most unpleasant -We will not notice at the beginning of any damage: there are no pain receptors there, the brain is completing objects in damaged areas (I can say that Irapping broken pixels), and only when the damaged area becomes quite big you may notice that items disappear when it gets into it . You will not see any black areas in the field of view - just something will not be anything, but it is nothing noticeable. Only an ophthalmologist can see damage at the first stages.

The danger of lasers is considered to be based whether it can cause damage before the eye is reflexively blinking - and it is considered not too dangerous power to 5 MW for visible radiation. Therefore, infrared lasers are extremely dangerous (well, in part purple - they are simply very badly visible) - you can get damaged, and never see that the laser is shining right in the eye.

Therefore, I repeat, it is better to avoid lasers more powerful than 5 MW and any infrared lasers.

Also, never under any circumstances are not looking "in the output" of the laser. If it seems to you that "something does not work" or "somehow poorly" - see through the webcam / soap (only not through the mirror!). It will also allow you to see IR radiation.

There are of course protective glasses, but there are many subtleties. For example, on the DX website there are glasses against a green laser, but they miss the IR radiation, and vice versa increase the danger. So be careful.

PS. Well, I certainly distinguished himself once - I am inappropriate to myself a beard with a laser populated ;-)

650nm - red

This is probably the most common laser type on the Internet, and all because in each DVD-RW there is such a power of 150-250mW (the greater the recording speed is the higher). On 650nm, the sensitivity of the eye is not very, because even a point and dazzlingly bright 100-200mW, the beam is only barely seen (you can see certainly better at night). Starting from 20-50mW, such a laser begins to "burn" - but only if it is possible to change its focus to focus the stain into a tiny point. By 200 MW, burns very tightly, but again the focus is needed. Balls, cardboard, gray paper ...

You can buy them ready (for example, such on the first photo is red). There are also small Laser Laser "Wholesale" - real babes, although they have everything in an adult - a power system, customizable focus - what is needed for robots, automation.

And most importantly - such lasers can be carefully taken from DVD-RW (but remember that there is still an infrared diode, it is necessary to be extremely gently with it, about it below). (By the way, in service centers there are non-warranty DVD-RW heaps lie - I buried 20 pieces, it was no longer conveyed). Laser diodes will very quickly die from overheating, from exceeding the maximum light flux - instantly. Excess the rated current is twice (provided that the light flux is not exceeded) reduces the service life of 100-1000 times (so carefully with "acceleration").

Meals: There are 3 basic schemes: primitive, with a resistor, with a current stabilizer (on LM317, 1117), and the highest pilot machine - using feedback through a photodiode.

In normal factory laser pointers, the 3rd scheme usually applies - it gives the maximum stability of output power and the maximum diode service life.

The second scheme is easy to implement, and provides good stability, especially if you leave a small supply for power (~ 10-30%). It was her that I would recommend to do - a linear stabilizer is one of the most popular details, and in any, even the most small radio car market there are analogues of LM317 or 1117.

The simplest scheme with a resistor described in the previous article is just a little simpler, but to kill the diode elementary. The fact is that in this case the current / power through the laser diode will be highly dependent on temperature. If, for example, at 20c, you turned out the current 50mA and the diode does not burn, and then during operation the diode will warm up to 80s, the current will increase (they are cunning, these semiconductors), and reaching the 120 mA diode starts shining only with black light. Those. Such a scheme is still possible to use if you leave at least three-four-fold power supply.

And on the last, it is worth debugging the scheme with a conventional red LED, and the laser diode is soldered at the very end. Cooling necessarily! The diode "on the conduction" burns instantly! Also do not rub and do not touch the optics of lasers (at least\u003e 5mW) - any damage will be "burn out", so we blow the pear if everything is necessary.

But what a laser diode looks nearby. The dents can be seen how close I was to fail, getting it out of plastic fastening. This photo also did not give me easy

532nm - green

They are difficult - these are the so-called DPSS lasers: the first laser, infrared on 808nm, shines in the ND: YVO4 crystal - the laser radiation is obtained by 1064НМ. It falls on the crystal "Frequency Doubleness" - so-called. KTP, and get 532nm. The crystals are not easy to grow, because for a long time DPSS lasers were damn roads. But thanks to the shock work of Chinese comrades, now they have become intimidated - from $ 7. In any case, mechanically this complex devices are afraid of drops, sharp temperature drops. Be careful.

The main plus of green lasers - 532nm is very close to the maximum sensitivity of the eye, and both the point and the beam itself is very clearly visible. I would say 5mwt green laser shines brighter than 200 MW red (on the first photo just 5MW green, 200 mW red and 200 mwt purple). Therefore, I would not recommend buying a green laser more powerful than 5MW: the first green I bought for 150mW and this is a real tin - nothing can be done with it without glasses, even reflected light blindness, and leaves unpleasant sensations.

Also, green lasers have a big danger: 808 and especially 1064nm infrared radiation comes out of the laser, and in most cases it is more than green. In some lasers there is an infrared filter, but in most green lasers up to $ 100 there is no it. Those. The "striking" ability of the laser for the eye is much larger than it seems - and this is another reason not to buy a green laser more powerful than 5 MW.

Burn green lasers of course you can, but you need power again from 50mW + if near the side infrared ray will "help", then with the distance he will quickly become "not in focus". And considering how it is blind - nothing comes.

405nm - purple

It is rather a near ultraviolet. Most diodes - emit 405nm directly. The problem with them is that the eye has a sensitivity to 405nm about 0.01%, i.e. The spot 200 MW laser seems dead, but in fact it is damn dangerous and dazzling-bright - the retina damages for all 200 MW. Another problem - the person's eye is used to focusing "under green" light, and the 405nm stain will always not be in focus - not a very pleasant feeling. But there is a good side - many objects fluoresce, such as paper - bright blue light, only this saves these lasers from oblivion to the mass public. But again, with them not so fun. Although 200 mW hide is healthy, due to the complexity of the focusing of the laser to the point it is more difficult than with red. Also, photoresists are sensitive to 405nm, and who works with them, may come up with why it may be needed ;-)

780NM - infrared

Lasers in CD-RW and as a second diode in DVD-RW. The problem is that the human eye does not see the beam, and therefore such lasers are very dangerous. You can burn your retina and not to notice it. The only way to work with them is to use the camera without an infrared filter (in webcams it is easy to get it for example) - then the beam, and the stain will be visible. IK Lasers can be used perhaps only in homemade laser "machines", I would not have recommended to indulge with them.

Also, IR lasers are in laser printers, together with the scanning scheme - 4 or 6-and graded rotating mirror + optics.

10mkm - infrared, CO2

This is the most popular laser type in industry. The main advantages are low price (tubes from $ 100-200), high power (100W - routine), high efficiency. They cut metal, Phaneur. Engraving and so on. If you yourself want to make a laser machine - then in China (alibaba.com) you can buy finished tubes of the desired power and assemble only the cooling and nutrition system. However, special craftsmen make the tubes at home, even though it is very difficult (the problem in mirrors and optics - the glass 10MKM radiation does not miss - only optics from silicon, Germany and some salts are suitable here.

Applications of lasers

Basically - used on presentations, play with cats / dogs (5mW, green / red), astronomers point to constellations (green 5mW and higher). Homemade machines - work from 200 MW on thin black surfaces. CO2 lasers cut almost anything. But the printed fee is difficult to cut - copper very well reflects the radiation longer than 350nm (because in production, if you really want to - use expensive 355nm DPSS lasers). Well, standard entertainment on YouTube is the span of balls, cutting paper and cardboard - any lasers from 20-50mW, subject to the possibility of focusing to the point.

From the more serious - the goalkens for weapons (green), you can at home to make holograms (semiconductor lasers for this more than enough), you can print 3D objects from plastic sensitive to UV, you can exhibit a photoresist without a template, you can unite , and after 3 seconds to see the answer, you can build a laser line of communication at 10mbit ... Scrost for creativity is unlimited

So, if you still think, how to buy a laser - take the 5MW green :-) (well, and 200mwt red, if you want to burn)

Questions / Opinions / Comments - in Studio!

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