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 bulky and 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 several 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 appeared on sale.
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 “button” batteries and, as of April 2012, cost about 1-5 US dollars. Powerful red pointers (wavelength 650-660 nm) with a power of several hundred milliwatts to a watt, capable of igniting materials that absorb radiation well, cost about $50-500.
Rarer red laser pointers use a diode-pumped solid-state laser. Diode-pumped solid-state laser, DPSS) and operate at a wavelength of 671 nm. They differ from laser diode pointers in having a round beam cross-section (in a conventional laser pointer, the beam is flattened due to the astigmatism of the laser diode resonator).
Green laser pointers (510-530nm)
First, a powerful (usually 200-1000 mW) infrared laser diode with λ = 808 nm is pumped into a neodymium-doped yttrium orthovanadate crystal (Nd:YVO 4), where the radiation is converted to 1064 nm. Then, passing through a crystal of potassium titanyl phosphate (KTiOPO 4, abbreviated KTP), the frequency of the radiation doubles (1064 nm → 532 nm) and visible green light is obtained. The generation and output of green radiation is provided by mirrors, one of which completely reflects radiation with wavelengths of 1064 and 532 nm and completely transmits pump radiation at 808 nm, and the other completely reflects radiation at 1064 nm, but completely transmits 532 nm. The pump radiation is also partially reflected.
In most modern green laser pointers, yttrium vanadate and KTP crystals, together with resonator mirrors, are combined into a so-called “microchip” - a gluing of two crystals with mirrors deposited on the edges. To generate laser radiation, it is sufficient to focus the radiation of a pump laser diode inside the Nd:YVO 4 crystal.
The efficiency of the circuit strongly depends on the pump power and can reach no more than 20%. In addition to green light, such a laser emits significant power in IR at wavelengths of 808 and 1064 nm, so it is necessary to install an infrared filter (IR filter) in such pointers to remove residual IR radiation and avoid damage to vision. In inexpensive versions of green pointers, such a filter may not be installed; in this case, even a pointer with a power of 1-5 mW poses a serious danger to vision, since the power of IR radiation can reach tens of milliwatts. The 1064 nm radiation is focused almost as well as green and poses a hazard if it enters the eye even at long distances, while the 808 nm pump radiation is highly unfocused and not concentrated along the beam, presenting a hazard up to several meters away.
It is worth noting the high energy consumption of green lasers - the current consumption reaches hundreds of milliamps. Since the generation and doubling efficiency increases rapidly with pump power, increasing the output power from 5 to 100 mW requires only approximately doubling the current consumption.
The small size of the green laser pointer does not allow installing a system for stabilizing the temperature of the laser diode and active media. Temperature has a particularly strong effect on the wavelength emitted by a laser diode, which leads to its departure from the maximum of the neodymium absorption line and a drop in output power. This leads to the fact that such pointers operate unstable when the temperature changes. This drawback is partially eliminated by stabilizing the radiation power at the laser output. To do this, a beam splitter is installed at the output (the role of which is played by an IR filter, from which part of the radiation is reflected) and a photodiode, and negative feedback is introduced. The disadvantage of this solution is the possibility of failure of the laser diode with a significant temperature deviation, at which the stabilization system, compensating for the drop in output power, is forced to significantly increase the current through it.
Blue laser pointers (473 nm)
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 yttrium aluminum garnet crystal with neodymium additives (Nd:YAG) is used.
Blue laser pointers (445 nm)
In these laser pointers, light is emitted from a powerful 1-5 W blue laser diode. Most of these pointers belong to laser hazard class 4 and pose a very serious danger to the eyes and skin, both directly and in the form of radiation scattered by the surface.
Blue pointers have become increasingly widespread due to the serial production of powerful laser diodes, mainly for compact LED projectors, for example Casio Slim.
Purple laser pointers (405nm)
The light in the purple pointers is generated by a laser diode emitting a beam with a wavelength of 405 nm. These lasers are used in Blu-ray Disc record players. The wavelength of 405 nm is at the edge of the range perceived
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 enormous 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 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.
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 problem is that the parallel laser beam is focused by the eye onto a 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 clots. You can hit a blood vessel with a point and block it, you can get into a blind spot, where nerves from all over the eye go to the brain, you can burn out a line of “pixels”... And then the damaged retina can begin to peel off, and this is the path to complete and irreversible loss vision. And the most unpleasant thing is that you won’t notice any damage at first: there are no pain receptors there, the brain completes objects in the damaged areas (so to speak, remapping dead pixels), and only when the damaged area becomes large enough can you notice that objects disappear when they get into it . You won’t see any black areas in your field of vision – there will simply be nothing here and there, but it’s not noticeable. Only an ophthalmologist can see damage in the first stages.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 camera (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
This is perhaps the most common type of laser on the Internet, and all because every DVD-RW has one with a power of 150-250 mW (the higher the recording speed, the higher). At 650 nm, the sensitivity of the eye is not very good, because even though the dot is dazzlingly bright at 100-200 mW, the beam is only barely visible during the day (at night, of course, it is visible better). Starting from 20-50 mW, such a laser begins to “burn” - but only if its focus can be changed to focus the spot into a tiny point. At 200 mW it burns very quickly, but again you need focus. Balls, cardboard, gray paper...
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 heaps 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 supply: 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
They have a complex structure - these are so-called DPSS lasers: The first laser, infrared at 808 nm, shines into an Nd:YVO4 crystal - laser radiation at 1064 nm is obtained. It hits the “frequency doubler” crystal - the so-called. KTP, and we get 532nm. It's not easy to grow all these crystals, which is why DPSS lasers were damn expensive for a long time. But thanks to the hard work of our Chinese comrades, they have now become quite affordable - from $7 a piece. In any case, these are mechanically complex devices, they are afraid of falls and sudden temperature changes. Be careful.
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
This is more like near ultraviolet. Most diodes emit 405nm directly. The problem with them is that the eye has a sensitivity at 405nm of about 0.01%, i.e. a speck of 200 mW laser seems tiny, but in fact it is damn dangerous and blindingly bright - it damages the retina for the entire 200 mW. Another problem is that the human eye is accustomed to focusing “under green” light, and the 405nm spot will always be out of focus - not a very pleasant feeling. But there is a good side - many objects fluoresce, for example paper, with a bright blue light, which is the only thing that saves these lasers from oblivion by the mass public. But then again, they're not that fun. Although the harness is 200 mW, be healthy, due to the difficulty of focusing the laser on a point, it is more difficult than with red ones. Also, photoresists are sensitive to 405nm, and anyone who works with them can figure out why this might be needed ;-)780nm – infrared
Such lasers are in CD-RW and as a second diode in DVD-RW. The problem is that the human eye cannot see the beam, and therefore such lasers are very dangerous. You can burn your retina and not notice it. The only way to work with them is to use a camera without an infrared filter (it’s easy to get in web cameras, for example) - then both the beam and the spot will be visible. IR lasers can probably only be used in homemade laser “machines”; I would not recommend messing around with them.Also, IR lasers are found in laser printers along with a scanning circuit - a 4- or 6-sided rotating mirror + optics.
10µm – infrared, CO2
This is the most popular type of laser in the industry. Its main advantages are low price (tubes from $100-200), high power (100W - routine), high efficiency. They cut metal and plywood. Engrave etc. If you want to make a laser machine yourself, then in China (alibaba.com) you can buy ready-made tubes of the required power and assemble only a cooling and power system for them. However, special craftsmen also make tubes at home, although it is very difficult (the problem is in mirrors and optics - 10-μm glass does not transmit radiation - only optics made of silicon, germanium and some salts are suitable here).Applications of lasers
Mainly used for presentations, playing with cats/dogs (5mW, green/red), astronomers pointing to constellations (green 5mW and higher). Homemade machines - operate from 200 mW on thin black surfaces. CO2 lasers can cut almost anything. It’s just difficult to cut a printed circuit board - copper reflects radiation longer than 350 nm very well (that’s why in production, if you really want to, they use expensive 355 nm DPSS lasers). Well, standard entertainment on YouTube - popping balloons, cutting paper and cardboard - any lasers from 20-50 mW, provided it is possible to focus to a point.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!
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- laser
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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 of these two lines and emits photons of 593.5 nm (the total energy of 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
Since the creation of solid-state lasers and to the present day, there has been a continuous increase in the power of their radiation. However, if in the early years the growth rates were approximately the same for all main types of solid-state lasers, then recently there has been a noticeable decrease in the growth rates of the radiation power of ruby and garnet lasers compared to neodymium glass lasers.
Laser emission is due to stimulated emission, as a result of which the emission of photons is partially synchronized. The degree of synchronization and the number of quanta emitted at any time are characterized by statistical parameters, such as the average number of emitted photons and the average emission intensity. Therefore, the power spectrum of the laser radiation turns out to be more or less narrow and its autocorrelation function behaves like the autocorrelation function of a sinusoidal oscillation generator, the output signal of which is unstable in phase and amplitude.
This is mainly explained by the fact that gas lasers with acceptable parameters are produced by domestic and foreign industry and can practically be used by telegraph operators. However, these lasers have a limited number of discrete wavelengths suitable for capturing monochrome and color holographic images. The choice of wavelength is determined not only by the laser radiation power at this wavelength, but also by the possibility of maximum matching of recording and playback wavelengths from the point of view of creating an optimal image for the subjective perception of the viewer.
In Fig. 147, b shows options for placing sensors when implementing this measurement method. When using one sensor for measurement, it is advisable to place it in the place of the diffraction pattern corresponding to point A. However, in the case of using one sensor, the measurement result is strongly influenced by the instability of the laser radiation power and the uneven intensity distribution in the cross section of the beam, which manifests itself with the lateral displacement of the measured product.
Their properties are discussed above. The number of types produced commercially amounts to many dozens. The wavelength range of their radiation covers the UV, VI and IR spectral ranges. The radiation power of lasers ranges from 0 1 mW to 10 W.
Microfluorescence uses laser excitation, which naturally has advantages over excitation with conventional light sources. The high coherence and directivity of laser radiation makes it possible to achieve extremely high radiation power densities. In table Figure 8.2 compares the power densities achieved by different sources. Laser illumination is the most intense, and due to the high power density of lasers, microfluorescence analysis has several advantages.
However, most of them have been studied in solutions, and only a few detailed studies with polarization measurements have been performed on single crystals. The situation has completely changed with the advent of a continuous-wave laser, whose collimated, polarized and practically monochromatic radiation is ideal for Raman spectroscopy of even small single crystals. Immediately after the discovery of the Raman effect, the importance of measuring the Raman anisotropy of crystals for the attribution of vibrations became clear. However, such studies could only become routine after lasers were used as a radiation source. Beam collimation is more important than laser power, and the latter is often less than the power of good Toronto-type lamps, the use of which stimulated the development of Raman spectroscopy during the 50s and early 60s.
To increase the number of atoms participating almost simultaneously in enhancing the light flux, it is necessary to delay the onset of generation in order to accumulate as many excited atoms as possible, creating an inverted population, for which it is necessary to raise the laser generation threshold and reduce the quality factor. For example, the parallelism of the mirrors can be disrupted, which will sharply reduce the quality factor of the system. If pumping is started in such a situation, then even with a significant inversion of the level population, generation does not begin, since the generation threshold is high. Rotating the mirror to a position parallel to another mirror increases the quality factor of the system and thereby lowers the lasing threshold. Therefore, the laser radiation power increases greatly. This method of controlling laser generation is called the Q-switched method.
This possibility is realized in practice by switching the Q factor of the laser. This is done as follows. Imagine that one of the laser cavity mirrors is removed. The laser is pumped using illumination, and the population of the upper level reaches its maximum value, but there is no stimulated emission yet. While the population is still inverted, the previously removed mirror is quickly moved into place. In this case, stimulated emission occurs, a rapid decrease in the population of the upper level occurs, and a giant pulse appears with a duration of only 10 - 8 s. With 25 J of energy emitted in a pulse, the laser radiation power is 2 5 - 109 W - a very impressive value, approximately equal to the power of a large power plant. True, the power plant operates at this power level all year round, and not 10 - - 8 s. In the first laser models, mirrors were moved mechanically, but now this is done electro-optically using a Kerr or Pockels cell.