What is laser radiation? Laser radiation: its sources and protection from it. nm – violet

Laser safety knowledge

1. What is a laser?
A laser device that emits light (electromagnetic radiation) through a process of optical amplification based on stimulated emission of photons. The term "laser" originated as an abbreviation for stimulated emission of light amplification. The laser radiation emitted has a high degree of spatial and temporal coherence, unattainable with other technologies.

2. Laser pointer Block diagram


3. What is laser application?
Lasers are widely used in everyday life. Lasers are most applicable in presentations for pointing out objects, construction and project approvals, medical treatment for cosmetic and surgical procedures. The lower laser power indicator is ideal for presentations and stargazing astronomy. A higher laser pointer power of up to 100 mW would be great for a combustion experiment. High power class IV laser is used for experiment, scientific research, military, etc. targeting

4. What is wavelength?
Our eyes are sensitive to light that is in a very small region of the electromagnetic spectrum labeled "visible light." This visible light corresponds to a wavelength range of 400 - 700 nanometers (nm) and a color range from violet to red. The human eye is unable to “see” radiation with wavelengths outside the visible spectrum. The visible colors of the shortest wavelengths to the longest are: violet, blue, green, yellow, orange and red. Ultraviolet radiation has a shorter wavelength than visible violet light. Infrared radiation has a wavelength than visible red light. White light is a mixture of colors in the visible spectrum. Black is the complete absence of light.

Spectral colors and wavelengths

This graph shows the colors of the visible light spectrum and associated 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 mode?


The transverse electromagnetic mode (TEM) structure of a laser beam describes the power distribution across the beam cross section. Most laser applications will require a fundamental beam mode (TEM00) with a Gaussian power distribution across the beam cross section, as shown in the figure to the right. This fundamental results in the smallest beam diameter and beam divergence mode and can be concentrated to the smallest possible spot size.
Other higher-power applications are available in the first order mode (TEM01*), or even the higher order mode. Laser power having a structure mode above the fundamental is usually called multitransverse mode (MTM). The mode of laser production structure can be changed simply by changing the mirrors.

6. Different classifications of lasers

Class I

Inherently safe, there is no possibility of eye damage. This may be either due to low power output (in case of eye damage not possible even after several hours of exposure), or due to the cabinet preventing users from accessing the laser beam during normal operation, such as CD players or laser printers.

Class II

The human eye's blink reflex (aversion response) will prevent eye damage if a person intentionally stares into a beam for an extended period. Output power can be up to 1 mW. This class includes only lasers that emit visible light. Most laser pointers and commercial scanners are laser in this category.

Class IIIa

Lasers in this class are primarily dangerous when combined with optical instruments that alter beam diameter or power density, although even without an optical instrument, increased direct contact with the eye for two minutes can cause severe retinal damage. Output power does not exceed 5 mW. The radiation power density does not exceed 2.5 mW/cm2 unless the device is labeled with a "caution" warning label, otherwise a "hazard" warning label is not required. Many laser sights for firearms and laser pointers are in this category.

Class IIIb

Lasers in this class can cause damage if the beam hits the eye directly. Typically this applies to lasers powered from 5-500 mW. Lasers in this category can cause permanent eye damage with an exposure of 1/100th of a second or less depending on the strength of the laser. Diffuse reflections are generally not dangerous, but specular reflections can be just as dangerous as direct reflections. Safety glasses are recommended when direct viewing of a Class IIIb laser beam may occur. High-end lasers in this class may also present a fire hazard and may slightly burn the skin.

Class IV

Lasers in this class have an output power greater than 500 mW per beam and can cause severe, irreversible damage to the eyes or skin without enhanced eye optics or instrumentation. Diffuse reflection of the laser beam may be hazardous to the skin or eyes within the rated hazard zone. Many industrial, scientific, military and medical lasers are in this category.

7. What is laser safety knowledge?
Even the first laser was recognized as potentially dangerous. Theodore Maiman characterized the first laser as having the power of a single "Gillette", just as it could burn through a single Gillette razor blade. Today it is generally accepted that even low-power lasers with only a few milliwatts of power can be dangerous to human vision when the beam of such a laser hits the eyes directly or after reflection from a shiny surface. At wavelengths that the cornea and lens can focus on well, the consistency and low divergence of laser light means that it can be aimed at the eye into a very small spot on the retina, resulting in localized burning and damage within seconds or even less time. Lasers are usually designated by a number of safety classes, which determine how dangerous the laser is:

. Class I/1 are inherently safe, usually because of the light contained in the housing, such as CD players.
. Class II/2 is safe during normal use; the blinking reflex from the eyes will prevent damage. Typically up to 1 mW, for pointers such as lasers.
. Class IIIa/3A Lasers are typically up to 5 mW and carry a small risk of eye damage during the blink reflex. Staring at such a beam for several seconds can damage the spot on the retina.
. Class IIIb/3B may cause immediate eye damage upon exposure.
. Class IV/4 Lasers can burn the skin, and in some cases even stray light can cause eye irritation and/or skin damage. Many industrial and scientific lasers are in this class. Specified powers are for visible light, continuous lasers. For pulsed lasers and invisible waves, different power limits apply.

People working with Class 3B and Class 4 lasers can protect their eyes with safety glasses, which are designed to absorb light of a specific wavelength.

Some infrared lasers with wavelengths beyond about 1.4 micrometers are often referred to as "eye-safe". This is because the internal molecular vibrations of water molecules very strongly absorb light in this part of the spectrum, and thus laser beams at these wavelengths is attenuated so much as it passes through the cornea of ​​the eye that no light remains to be focused on the lens onto the retina. The label "eye-safe" can be misleading, however, as it only applies to relatively low-power continuous wave beams of any high power. or Q-switched lasers at these wavelengths can burn the cornea, causing serious eye damage.

8. Dangers of Laser Radiation
Laser pointers have been widely used since its first appearance. Lasers are mainly used as a presentation tool in teaching, stargazing astronomy, and meetings. However, these lasers are gradually being owned by laser fans and enthusiasts including children due to low cost and countless suppliers, and are being used in ways not intended by the manufacturers. As a result, it is seriously important to understand the dangers of laser pointers before actually owning a laser pointer.

Laser danger
Laser radiation predominantly causes damage through thermal effects. Even moderate laser power can cause eye injury. High power lasers can also burn the skin. Some lasers are so powerful that even diffuse reflection from a surface can be dangerous to the eyes.

Although there is a potential hazard to the retina, not all visible beam lasers are likely to cause permanent retinal damage. Exposure to looking at a laser pointer beam is most likely the cause of image retention, flash blindness and glare. Temporary pain in the retina will recover in a few minutes.

The low divergence angle of the laser light and the focusing mechanism on the eye mean that the laser light can be concentrated into a very small spot on the retina. If the laser is powerful enough, permanent damage can occur within a fraction of a second, literally faster than the blink of an eye. Sufficiently powerful visible to near-infrared laser radiation (400-1400nm) will penetrate the eyeball and can lead to heating of the retina, while exposure to laser radiation with wavelengths less than 400 nm and greater than 1400 nm is mainly absorbed by the cornea and lens. leads to the development of cataracts or burns.

Infrared lasers are especially dangerous because the body's protective "blink reflex" response is triggered only by visible light. For example, some people exposed to high power Nd:YAG lasers with invisible 1064 radiation may not feel pain or notice immediate damage to their vision. A pop or clicking sound emanating from the eyeball may be the only indication that retinal damage has occurred i.e. the retina is heated to 100°C resulting in a localized explosive effervescence followed by the immediate creation of a permanent blind spot.

Responsible laser owners must fully understand the dangers of laser radiation, and acknowledge the FAA regulations associated with the use of a laser pointer. Safety glasses are usually required when direct observation of a powerful beam is likely to occur.

9. How to protect yourself from laser danger?
This is essential for adopting effective methods to prevent Class 3B or Class IIIb damage. Laser safety glasses are the premier eye protection accessory on the market today. Different selection of laser sensors, glasses must be selected for a specific type to block the appropriate wavelength. For example, a 532 point absorber usually has orange points.

Directly looking at laser pointers is strictly prohibited under any conditions. Remember to wear safety glasses before using the laser pointer.

Laser pointer safety tips:

● Place the laser out of the reach of minors. Do not allow minors (under 18 years of age) to purchase or use a laser pointer under any supervision. Only adults may use laser pointers after they have understood the safety and hazards of laser products.

● Be especially careful if you are using high power laser radiation. You should never try to point your laser pointer at any person and animals, airplane pilot and moving vehicles, or you will be jailed in prison for misuse of laser devices.

● Keep away from high-power lasers. Please always keep yourself away from powerful lasers such as laser burning. They differ significantly from formal presentation lasers. Never try to buy a laser without any indication of class and power.

10. How powerful will laser pointers be?

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

Continuous or medium power required for some applications:
Power usage
1-5 mW laser pointer
5 mW CD
5-10 mW DVD player or DVDs
100 mW high speed CD-RW burner
250 mW consumer 16x DVD-R burner
400 mW combustion through the disc case including for 4 seconds
1 W Green Laser in Current Holographic Universal Development Prototype Disc
1-20 W Output of most commercially available solid state lasers used for micro-machining
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 by 1 cm bar laser diode
100 KW Claimed power CO2 laser being developed by Northrop Grumman for military (weapons) applications

11. What's laser service?

Proper maintenance of your laser will greatly extend its life. We just need to follow the following tips:

What you need:
1. Microfiber cloth
Please make sure the microfiber cloth is specifically designed for cleaning lenses. You can find this at your local camera or glasses store.
2. Q-tip or tooth choice
You will need to fold the fabric over one of them to be able to reach the lens correctly.
3. Solution cleaning lens (optional)
Use the lens cleaning solution only if the lens cannot be cleaned with a microfiber cloth alone. Please ensure that the cleaning solution is formulated specifically for cleaning the lens.
*Caution: Do not use water.

Procedure:
1. Wash your hands with soap and water. Make sure to dry them properly.
2. Fold the microfiber cloth over the toothpick or handle part of the Q-Tip. Make sure you don't touch the part of the cloth that will be cleaning the lenses. You probably won't be able to fold the fabric in half, so you have to be very careful not to press too hard on the lens.
3. Gently move the fabric into the hole as it makes contact with the lens. Rub it from side to side, but don't press too hard. Gently rotate the fabric in a back and forth rotation motion. Repeat this procedure until your laser lens is clean.
4. Turn your laser unit to see if the lens is clean.

Still dirty? Try using a lens cleaning solution.
Apply 1 drop at a time to only the part of the cloth that will be cleaning the lenses, follow the same procedure as above. You'll want to finish by using a dry piece of cloth to wipe the lens dry, this should take one pass side to side or gently rotate.

In many online stores, the power of portable lasers and laser pointers is unreasonably inflated for commercial gain. It is quite difficult for the average buyer to understand this issue and determine how much the power of the purchased portable laser or laser pointer corresponds to reality. In this regard, we suggest reading this article, in which we will talk about what powers portable lasers and laser pointers have, as well as how power is measured in our online store.

Power of portable lasers and laser pointers

At the moment, the most powerful representatives of portable lasers are blue lasers with a wavelength of 445-450 nm. Some self-assembled models, using several laser diodes and beam convergence, reach a power of 6.3 W. However, the power of existing individual laser diodes does not exceed 3.5 W. It is important to note that the power data was obtained at abnormally high currents, for which these diodes are not designed. Maximum output power, at which the blue portable laser will work stably at the moment does not exceed 2000mW(2000 milliwatts = 2W, 2000mW).

The next most powerful are red (650-660nm) and violet (405nm) portable lasers. Their power does not exceed 1000mW.

Finally, the most popular and brightest green (532nm) lasers have maximum power 750mW. It is important to note that green lasers differ in operating principle from blue and red ones: green 532nm lasers are diode-pumped semiconductor lasers. Therefore, the power of a green laser consists of three components: infrared 808 nm (laser pump diode), 1064 nm (laser radiation from yttrium aluminum garnet, (“YAG”, Y 3 Al 5 O 12) doped with neodymium (Nd) ions) and 532 nm (green laser light after frequency doubling in a KTP crystal). To obtain 750 mW of output power from a green 532 nm laser, you need more 5W power 808nm pump diode! When checking the power of a green laser with a wattmeter, you need to make sure that it has a filter that can cut off infrared wavelengths. Otherwise, the wattmeter will show the total laser power (of which only 10-15% is at 532nm).

About power measurement in the LaserMag online store

Our online store has a unique opportunity to check the optical power of portable lasers and laser pointers thanks to a special optical wattmeter.

Its operating principle is based on a thermoelement that absorbs laser radiation and generates an electrical signal. The electrical signal enters the DAC (Digital to Analog Converter). Next, using a special program supplied with an optical wattmeter, a dynamic power characteristic (power versus time) is displayed on the computer screen. If the client wishes, we are ready to provide a power graph of any purchased laser.

You all love lasers. I know, I’m more obsessed with them than you are. And if someone doesn’t love it, then they simply haven’t seen the dance of sparkling dust particles or how a dazzling tiny light gnaws through the plywood

It all started with an article from the Young Technician in 1991 about the creation of a dye laser - then it was simply unrealistic for a simple schoolchild to repeat the design... Now, fortunately, the situation with lasers is simpler - they can be taken out of broken equipment, they can be bought ready-made, they can be assembled from parts... The lasers that are closest to reality will be discussed today, as well as the methods of their application. But first of all about safety and danger.

Why lasers are dangerous

The danger of lasers is considered based on whether they can cause damage before the eye reflexively blinks - and a power of 5 mW for visible radiation is considered not too dangerous. Therefore, infrared lasers are extremely dangerous (and partly violet lasers - they are simply very hard to see) - you can get damaged and never see that the laser is shining directly into your eye.

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

Also, never, under any circumstances, look into the “exit” of the laser. If it seems to you that “something is not working” or “somehow weak” - look through a webcam/point-and-shoot (not through a DSLR!). This will also allow you to see the IR radiation.

Of course, there are safety glasses, but there are a lot of subtleties. For example, on the DX website there are glasses against green lasers, but they transmit IR radiation and, on the contrary, increase the danger. So be careful.

PS. Well, of course, I distinguished myself once - I accidentally burned my beard with a laser ;-)

650nm – red

You can buy them ready-made (for example, the one in the first photo is red). They also sell small lasers “wholesale” - real little ones, although they have everything like an adult - a power system, an adjustable focus - what is needed for robots and automation.

And most importantly, such lasers can be carefully removed from DVD-RW (but remember that there is also an infrared diode there, you need to be extremely careful with it, more on that below). (By the way, in service centers there are piles of out-of-warranty DVD-RWs - I took 20 of them, I couldn’t bring any more). Laser diodes die very quickly from overheating, and from exceeding the maximum luminous flux - instantly. Exceeding the rated current by half (provided the luminous flux is not exceeded) reduces the service life by 100-1000 times (so be careful with “overclocking”).

Power: there are 3 main circuits: the most primitive, with a resistor, with a current stabilizer (on LM317, 1117), and the most advanced - using feedback through a photodiode.

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

The second scheme is easy to implement and provides good stability, especially if you leave a small power reserve (~10-30%). This is exactly what I would recommend doing - a linear stabilizer is one of the most popular parts, and in any radio store, even the smallest one, there are analogues of LM317 or 1117.

The simplest circuit with a resistor described in the previous article is only a little simpler, but with it it’s easy to kill the diode. The fact is that in this case, the current/power through the laser diode will greatly depend on temperature. If, for example, at 20C you get a current of 50mA and the diode does not burn out, and then during operation the diode heats up to 80C, the current will increase (they are so insidious, these semiconductors), and having reached, say, 120mA the diode begins to shine only with black light. Those. Such a scheme can still be used if you leave at least a three to four times power reserve.

And finally, you should debug the circuit with a regular red LED, and solder the laser diode at the very end. Cooling is a must! The diode “on the wires” will burn out instantly! Also, do not wipe or touch the optics of lasers with your hands (at least >5mW) - any damage will “burn out”, so if necessary, we blow it with a blower and that’s it.

And here's what a laser diode looks like up close in operation. The dents show how close I was to failure when removing it from the plastic mount. This photo wasn't easy for me either.

532nm – green

The main advantage of green lasers is that 532nm is very close to the maximum sensitivity of the eye, and both the dot and the beam itself are very visible. I would say that a 5mW green laser shines brighter than a 200mW red laser (in the first photo there are 5mW green, 200mW red and 200mW purple). Therefore, I would not recommend buying a green laser more powerful than 5 mW: the first green one I bought was 150 mW and it’s a real mess - you can’t do anything with it without glasses, even the reflected light is blinding and leaves an unpleasant feeling.

Green lasers also have a great danger: 808 and especially 1064 nm infrared radiation comes out of the laser, and in most cases there is more of it than green. Some lasers have an infrared filter, but most green lasers under $100 do not. Those. The “damaging” ability of a laser to the eye is much greater than it seems - and this is another reason not to buy a green laser more powerful than 5 mW.

Of course, it is possible to burn with green lasers, but again you need a power of 50 mW + if the side infrared beam “helps” near you, then with distance it will quickly become “out of focus”. And considering how blinding it is, nothing fun will come of it.

405nm – violet

780nm – infrared

Also, IR lasers are found in laser printers along with a scanning circuit - a 4- or 6-sided rotating mirror + optics.

10µm – infrared, CO2

Applications of lasers

On the more serious side - target designators for weapons (green), you can make holograms at home (semiconductor lasers are more than enough for this), you can print 3D objects from UV-sensitive plastic, you can expose photoresist without a template, you can shine it on a corner reflector on the moon , and in 3 seconds you will see the answer, you can build a 10 Mbit laser communication line... The scope for creativity is unlimited

So, if you are still thinking about what kind of laser to buy, take the 5mW green one :-) (well, and the 200mW red one if you want to burn)

Questions/opinions/comments - go to the studio!

Tags:

• laser
• dvd-rw
• dealextreme

Duration of laser radiation

The duration is determined by the design of the laser. The following typical modes of radiation distribution over time can be distinguished:

Continuous mode;

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

Q-switching mode of the resonator (the duration of the radiation pulse is determined by the excess of pumping above the lasing threshold and the speed and speed of switching on the Q factor, the typical duration lies in the range of 10-9 - 10-8 s, this is the so-called nanosecond range of radiation durations);

Synchronization mode and longitudinal modes in the resonator (radiation pulse duration Dfl ~ 10-11 s - picosecond range of radiation durations);

Various modes of forced shortening of radiation pulses (Dfl ~ 10-12 s).

Radiation power density

Laser radiation can be concentrated into a narrow beam with a high power density.

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

Accordingly, the radiation energy density Ws is determined by the ratio of the energy passing through the cross-section of the laser beam to the cross-sectional area and has the dimension J cm-2

The power density in a laser beam reaches large values ​​due to the addition of the energy of a huge number of coherent radiations of individual atoms arriving at a selected point in space in the same phase.

Using an optical lens system, coherent laser radiation can be focused onto a small area comparable to the wavelength on the surface of the object.

The power density of laser radiation at this site reaches enormous values. In the center of the site the power density is:

where P is the output power of laser radiation;

D is the diameter of the lens of the optical system;

l - wavelength;

f is the focal length of the optical system.

Laser radiation with a huge power density, affecting various materials, destroys and even evaporates them in the area of ​​incident focused radiation. At the same time, in the area of ​​incidence of laser radiation on the surface of the material, a light pressure of hundreds of thousands of megapascals is created on it.

As a result, we note that by focusing the laser radiation to a spot whose diameter is approximately equal to the radiation wavelength, it is possible to obtain a light pressure of 106 MPa, as well as enormous radiation power densities reaching values ​​of 1014-1016 W.cm-2, while temperatures up to several million kelvin.

Block diagram of an optical quantum resonator

The laser consists of three main parts: the active medium, the pump device and the optical cavity. Sometimes a thermal stabilization device is also added.

Figure 3 - Laser block diagram

1) Active medium.

For resonant absorption and amplification due to stimulated emission, it is necessary that the wave passes through a material whose atoms or systems of atoms are “tuned” to the desired frequency. In other words, the difference in energy levels E2 - E1 for the atoms of the material must be equal to the frequency of the electromagnetic wave multiplied by Planck's constant: E2 - E1 = hn. Further, in order for stimulated emission to prevail over absorption, there must be more atoms at the upper energy level than at the lower one. This usually doesn't happen. Moreover, any system of atoms, left to itself for a sufficiently long time, comes into equilibrium with its environment at a low temperature, i.e. reaches a state of lowest energy. At elevated temperatures, some of the atoms of the system are excited by thermal motion. At an infinitely high temperature, all quantum states would be equally filled. But since the temperature is always finite, the predominant proportion of atoms are in the lowest state, and the higher the states, the less filled they are. If at absolute temperature T there are n0 atoms in the lowest state, then the number of atoms in the excited state, the energy of which exceeds the energy of the lowest state by an amount E, is given by the Boltzmann distribution: n=n0e-E/kT, where k is the Boltzmann constant. Since there are always more atoms in lower states under equilibrium conditions than in higher ones, under such conditions absorption always predominates rather than amplification due to stimulated emission. An excess of atoms in a certain excited state can be created and maintained only by artificially transferring them to this state, and faster than they return to thermal equilibrium. A system in which there is an excess of excited atoms tends to thermal equilibrium, and it must be maintained in a nonequilibrium state by creating such atoms in it.

2) Resonator.

An optical resonator is a system of specially matched two mirrors, selected in such a way that weak stimulated emission arising in the resonator due to spontaneous transitions is amplified many times over, passing through an active medium placed between the mirrors. Due to multiple reflections of radiation between the mirrors, an elongation of the active medium occurs in the direction of the resonator axis, which determines the high directivity of laser radiation. More complex lasers use four or more mirrors to form a cavity. The quality of the manufacturing and installation of these mirrors is critical to the quality of the resulting laser system. Also, additional devices can be mounted in the laser system to achieve various effects, such as rotating mirrors, modulators, filters and absorbers. Their use allows you to change the laser radiation parameters, for example, wavelength, pulse duration, etc.

The resonator is the main determining factor of the operating wavelength, as well as other properties of the laser. There are hundreds or even thousands of different working fluids on which a laser can be built. The working fluid is “pumped” to obtain the effect of electron population inversion, which causes stimulated emission of photons and an optical amplification effect. The following working fluids are used in lasers.

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

Gases such as carbon dioxide, argon, krypton or mixtures such as in helium-neon lasers. Such lasers are most often pumped by electrical discharges.

Solids such as crystals and glass. The solid material is usually doped (activated) by adding small amounts of chromium, neodymium, erbium or titanium ions. Typical crystals used are aluminum garnet (YAG), yttrium lithium fluoride (YLF), sapphire (aluminum oxide), and silicate glass. The most common options are Nd:YAG, titanium sapphire, chromium sapphire (also known as ruby), chromium doped strontium lithium aluminum fluoride (Cr:LiSAF), Er:YLF and Nd:glass (neodymium glass). Solid-state lasers are usually pumped by a flash lamp or other laser.

Semiconductors. A material in which the transition of electrons between energy levels can be accompanied by radiation. Semiconductor lasers are very compact and pumped with electric current, allowing them to be used in consumer devices such as CD players.

3) Pumping device.

The pump source supplies energy to the system. This could be an electrical spark gap, a flash lamp, an arc lamp, another laser, a chemical reaction, or even an explosive. The type of pumping device 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 a helium-neon gas mixture, and lasers based on neodymium-doped yttrium aluminum garnet (Nd:YAG lasers) use focused light from a xenon flash lamp, and excimer lasers use the energy of chemical reactions.

In a narrow beam, a biconvex collimator lens is usually used. However, with high-quality focusing of the beam (which can be done independently by tightening the lens clamping nut), the pointer can be used to conduct experiments with a laser beam (for example, to study interference). The power of the most common laser pointers is 0.1-50 mW; more powerful ones up to 2000 mW are also available for sale. In most of them, the laser diode is not closed, so they must be disassembled with extreme caution. Over time, the open laser diode “burns out,” causing its power to decrease. Over time, such a pointer will practically stop shining, regardless of the battery level. Green laser pointers have a complex structure and are more reminiscent of real lasers in design.

Laser pointer

Types of laser pointers

Early models of laser pointers used helium-neon (HeNe) gas lasers and emitted radiation in the 633 nm range. They had a power of no more than 1 mW and were very expensive. Nowadays, laser pointers typically use less expensive red diodes with a wavelength of 650-670 nm. Slightly more expensive pointers use orange-red diodes with λ=635 nm, which make them brighter to the eye, since the human eye sees light with λ=635 nm better than light with λ=670 nm. Laser pointers of other colors are also produced; for example, a green pointer with λ=532 nm is a good alternative to a red one with λ=635 nm, since the human eye is approximately 6 times more sensitive to green light compared to red. Recently, yellow-orange pointers with λ=593.5 nm and blue laser pointers with λ=473 nm have been gaining popularity.

Red laser pointers

The most common type of laser pointer. These pointers use laser diodes with a collimator. Power varies from approximately one milliwatt to a watt. Low-power pointers in the form factor of a key fob are powered by small “tablet” batteries and today (April 2012) cost about $1. Powerful red pointers are among the cheapest in terms of price/power ratio. Thus, a focusable laser pointer with a power of 200 mW, capable of igniting materials that absorb radiation well (matches, electrical tape, dark plastic, etc.), costs about $20-30. Wavelength is approximately 650 nm.

Rarer red laser pointers use a diode-pumped solid-state (DPSS) laser and operate at a wavelength of 671 nm.

Green laser pointers

Green laser pointer device, DPSS type, wavelength 532nm.

A 100mW laser pointer beam aimed at the night sky.

Green laser pointers began being sold in 2000. The most common type of diode pumped solid state (DPSS) laser. Green laser diodes are not produced, so a different circuit is used. The device is much more complex than conventional red pointers, and the green light is obtained in a rather cumbersome manner.

First, a neodymium-doped yttrium orthovanadate crystal (Nd:YVO 4) is pumped by a powerful (usually >100 mW) infrared laser diode with λ=808 nm, where the radiation is converted to 1064 nm. Then, passing through a crystal of potassium titanyl phosphate (KTiOPO 4, abbreviated KTP), the radiation frequency doubles (1064 nm → 532 nm) and visible green light is obtained. The efficiency of the circuit is about 20%, most of which comes from a combination of 808 and 1064 nm IR. On powerful pointers >50 mW, an infrared filter (IR filter) must be installed to remove residual IR radiation and avoid damage to vision. It is also worth noting the high energy consumption of green lasers - most use two AA/AAA/CR123 batteries.

473 nm (turquoise color)

These laser pointers appeared in 2006 and have a similar operating principle to green laser pointers. 473 nm light is typically produced by doubling the frequency of 946 nm laser light. To obtain 946 nm, a crystal of yttrium aluminum garnet with neodymium additives (Nd:YAG) is used.

445 nm (blue)

In these laser pointers, light is emitted from a powerful blue laser diode. Most of these pointers belong to laser hazard class 4 and pose a very serious danger to the eyes and skin. They began to actively spread in connection with the release by Casio of projectors that use powerful laser diodes instead of conventional lamps.

Purple laser pointers

The light in the purple pointers is generated by a laser diode emitting a beam with a wavelength of 405 nm. The wavelength of 405 nm is at the limit of the range perceived by human vision and therefore the laser radiation from such pointers appears dim. However, the light from the pointer causes some of the objects it is aimed at to fluoresce, which is brighter to the eye than the brightness of the laser itself.

Purple laser pointers appeared immediately after the advent of Blu-ray drives, in connection with the start of mass production of 405 nm laser diodes.

Yellow laser pointers

Yellow laser pointers use a DPSS laser that emits two lines simultaneously: 1064 nm and 1342 nm. This radiation enters a nonlinear crystal, which absorbs photons from these two lines and emits 593.5 nm photons (the total energy of the 1064 and 1342 nm photons is equal to the energy of the 593.5 nm photon). The efficiency of such yellow lasers is about 1%.

Using laser pointers

Safety

Laser radiation is dangerous if it comes into contact with the eyes.

Conventional laser pointers have a power of 1-5 mW and belong to hazard class 2 - 3A and can pose a danger if the beam is directed into the human eye for a long enough time or through optical devices. Laser pointers with a power of 50-300 mW belong to class 3B and are capable of causing severe damage to the retina of the eye even when briefly exposed to a direct laser beam, as well as a specular or diffusely reflected one.

At best, laser pointers are only irritating. But the consequences will be dangerous if the beam hits someone's eye or is aimed at a driver or pilot and can distract them or even blind them. If this leads to an accident, it will entail criminal liability.

Increasingly numerous “laser incidents” are causing demands in Russia, Canada, the USA and the UK to limit or ban laser pointers. Already in New South Wales there is a fine for possessing a laser pointer, and for “laser attack” - a prison term of up to 14 years.

It is also important to consider that most cheap Chinese lasers that operate on the pump principle (that is, green, yellow and orange) do not have an IR filter for reasons of economy, and such lasers actually pose a greater danger to the eyes than stated by the manufacturers.

Notes

Links

• Laser Pointer Safety website Includes safety data