Laser applications

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The benefits of lasers in various applications stems from their properties such as coherency, high monochromaticity, and ability to reach extremely high powers. For instance, a highly coherent laser beam can be focused down to its diffraction limit, which at visible wavelengths is only a few hundred nanometers. This property allows:-

In reality however, perfect focusing of a beam to its diffraction limit is somewhat difficult.

Contents

[edit] Scientific

In science, lasers are used in many ways, including:-

[edit] Spectroscopy

Most types of laser are an inherently pure source of light; they emit near-monochromatic light with a very well defined range of wavelengths. By careful design of the laser components, it is possible to improve the purity of the laser light (measured as the linewidth) beyond that of any other light source. This makes the laser a very useful source for spectroscopy. The high intensity of light that can be achieved in a small, well collimated beam can also be used to induce a nonlinear optical effect in a sample, which makes techniques such as Raman spectroscopy possible. Other spectroscopic techniques based on lasers can be used to make extremely sensitive detectors of various molecules, able to measure molecular concentrations in the parts-per-trillion (ppt) level. Due to the high power densities achievable by lasers, beam induced atomic emission is possible, this technique is termed Laser induced breakdown spectroscopy (LIBS).

Lasers may also be indirectly used in spectroscopy as a micro-sampling system, a technique termed Laser ablation (LA), which is typically applied to ICP-MS apparatus resulting in the powerful LA-ICP-MS.

[edit] Lunar laser ranging

Main article: Lunar laser ranging experiment

When the Apollo astronauts visited the moon, they planted retroreflector arrays to make possible the Lunar Laser Ranging Experiment. Laser beams are focused through large telescopes on Earth aimed toward the arrays, and the time taken for the beam to be reflected back to Earth measured to determine the distance between the Earth and Moon with high precision.

[edit] Photochemistry

Some laser systems, through the process of modelocking, can produce extremely brief pulses of light - as short as picoseconds or femtoseconds (10-12 - 10-15 seconds). Such pulses can be used to initiate and analyse chemical reactions, a technique known as photochemistry. The short pulses can be used to probe the process of the reaction at a very high temporal resolution, allowing the detection of short-lived intermediate molecules. This method is particularly useful in biochemistry, where it is used to analyse details of protein folding and function.

[edit] Laser cooling

A technique that has had recent success is laser cooling. This involves ion trapping or atom trapping, a method where a number of ions or atoms are confined in a specially shaped arrangement of electric and magnetic fields. Shining particular wavelengths of laser light at the ions or atoms slows them down, thus cooling them. If this process is continued, eventually they all are slowed and have the same energy level, forming an unusual arrangement of matter known as a Bose-Einstein condensate.

[edit] Nuclear fusion

Lasers are used in certain types of thermonuclear fusion reactors. Perhaps the most extravagant use of lasers in science is in the field of fusion research. Some of the world's most powerful and complex arrangements of multiple lasers and optical amplifiers are used to produce extremely high intensity pulses of light of extremely short duration. These pulses are arranged such that they impact pellets of tritium-deuterium simultaneously from all directions, hoping that the squeezing effect of the impacts will induce atomic fusion in the pellets. This technique, known as inertial confinement fusion so-far has not been able to achieve breakeven, that is, less power is generated by the fusion reaction than is used to power the lasers, but research continues.

[edit] As a finderscope for amateur telescopes

With the advent of higher power green laser pointers came a new product line for observational astronomers -- the laser finder. Akin to the laser sighting device used in military rifles, a green laser mounted to the tube of a telescope and properly collimated can reveal the precise location in the sky that the telescope is pointed. In most outdoor night locales, the green beam of the laser is visible to the eye. By moving the telescope (and the laser beam) to the proper location in the sky, observers can more easily locate the intended celestial target.

[edit] Microscopy

Confocal laser scanning microscopy and Two-photon excitation microscopy make use of lasers to obtain blur-free images of thick specimens at various depths.

[edit] Military

Military uses of lasers include use as target designators for other weapons; their use as directed-energy weapons is currently under research. Laser weapon systems under development include the airborne laser, the advanced tactical laser, the Tactical High Energy Laser, the High Energy Liquid Laser Area Defense System, and the MIRACL, or Mid-Infrared Advanced Chemical Laser.

[edit] Defensive applications

Recently, some progress has been made in the use of the laser as a directed energy weapon, mostly in defensive applications. By using a chemical laser, one in which the laser operation is powered by an energetic chemical reaction, the requirement for generating and storing a large amount of electrical energy (which directly or indirectly is used to power most high-power lasers) is removed. This makes the laser system much more compact, and easier to transport. One example is a laser system which is designed to destroy missiles in flight. It is mounted in a converted commercial airliner, and could be used, for example, to protect assets such as AWACS aircraft or to destroy ballistic missiles (see Airborne Laser). However, the practical problems of reliably generating and aiming the laser beam remain formidable.

The Mobile Tactical High-Energy Laser (MTHEL) is another defensive laser system under development; this is envisioned as a field-deployable weapon system able to track incoming artillery projectiles and cruise missiles by radar and destroy them with a powerful deuterium fluoride laser.

For information and a list of laser-based weapon systems, see also Directed Energy Weapon (Lasers).

[edit] Strategic Defense Initiative

Another example of direct use of a laser as a defensive weapon was researched for the Strategic Defense Initiative (SDI, nicknamed "Star Wars"), and its successor programs. This project would use ground-based or space-based laser systems to destroy incoming intercontinental ballistic missiles (ICBMs). Again, the practical problems of using and aiming these systems would be many; particularly the problem of destroying ICBMs at the most opportune moment, the boost phase just after launch. This would involve directing a laser through a large distance in the atmosphere, which, due to optical scattering and refraction, would bend and distort the laser beam, complicating the aiming of the laser and reducing its efficiency.

Another idea to come from the SDI project was the nuclear-pumped X-ray laser. This was essentially an orbiting atomic bomb, surrounded by laser media in the form of glass rods; when the bomb exploded, the rods would be bombarded with highly-energetic gamma-ray photons, causing spontaneous and stimulated emission of X-ray photons in the atoms making up the rods. This would lead to optical amplification of the X-ray photons, producing an X-ray laser beam which would be minimally affected by atmospheric distortion and capable of destroying ICBMs in flight. The X-ray laser would be a strictly one-shot device, destroying itself on activation. Some initial tests of this concept were performed with underground nuclear testing, however, the results were not encouraging. Research into this approach to missile defense was discontinued after the cancellation of the SDI program.

In recent years, the United States Air Force has begun experimenting with using lasers combined with high-altitude airships as a potential means for a missile defense shield but also as a means to destroy enemy spacecraft or satellites in low-earth orbit. For more information, see Evolutionary Air and Space Global Laser Engagement.

[edit] Laser sight

The laser has in most military applications been used as a tool to enhance the targeting of other weapon systems. For example, a laser sight is a small, usually visible-light laser placed on a handgun or rifle aligned to emit a beam parallel to the barrel. Since a laser beam typically has low divergence, the laser light appears as a small spot even at long distances; the user simply places the spot on the desired target and the barrel of the gun is aligned. Recent studies (2001) have shown that laser sight has become an effective deterring tool for law enforcement. Criminals are more likely to surrender without resistance when they find a red laser dot on their chest.

Most laser sights utilize a red (670–633 nm) diode, with the 633–635 nm diodes being an estimated 10 times as bright as their 670 nm counterparts. Some laser sights used an infrared diode, which produced a dot invisible to the naked human eye, but would show up when special optics were employed by the user. In the late 1990s, green DPSS laser sights (532 nm) became available.

Modern laser sights are so small that they can be installed below the barrel as part of the gun, instead of being a separate attachment. Some laser sights, such as ones produced by LaserMax, are actually integrated into a unit that replaces the entire guide rod of a pistol, thus adding no bulk to the weapon. Others, like Crimson Trace Lasergrips, are built into the grip so that activation is automatic whenever the weapon is held.

Another type of optical sight is the reflex, or red dot sight. This gives the illusion of a red dot being projected onto the target when the shooter looks through the sight, but the dot is only visible to the user. This has advantages where multiple weapons are aimed at the same target, and it is also more visible than a conventional laser in bright sunny conditions.

[edit] Satellite obstruction

According to a report issued by the Pentagon, China is developing a laser which could blind low-Earth-orbiting satellites. [1]

[edit] Illuminator

Saber 203 Laser Illuminator (U.S. Air Force)
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Saber 203 Laser Illuminator (U.S. Air Force)

This non-lethal laser weapon, shown in the accompanying photo attached to an M16 rifle, was developed by the U.S. Air Force to temporarily impair an adversary’s ability to fire a weapon or to otherwise threaten enemy forces. The Saber 203 briefly illuminates an opponent with harmless, low-power laser light. Realizing he has been targeted, the aggressor hides or flees rather than risk death by aiming his weapon and attracting defensive fire.

[edit] Rangefinder

Main article: Laser range-finder

A laser range-finder is a device consisting of a pulsed laser and a light detector. By measuring the time taken for light to reflect off a far object, and knowing the speed of light, the range to the object can be found. A laser rangefinder is thus a simple form of LIDAR. The distance to the target can then be used to aim a weapon such as a tank's main gun.

[edit] Target designator

Main article: Laser designator

Another military use of lasers is as a laser target designator. This is a low-power laser pointer used to indicate a target for a precision-guided munition, typically launched from an aircraft. The guided munition adjusts its flight-path to home in to the laser light reflected by the target, enabling a great precision in aiming. The beam of the laser target designator is set to a pulse rate that matches that set on the guided munition to ensure munitions strike their designated targets and do not follow other laser beams which may be in use in the area. The laser designator can be shone onto the target by an aircraft or nearby infantry. Lasers used for this purpose are usually infrared lasers, to prevent easy detection of the guiding laser light by the enemy.

[edit] Death ray

Not yet made practical: The first role envisioned for the laser in military applications was as a "death ray": a hand-held device that might replace the gun as a weapon for infantry, or a vehicle-mounted "laser cannon" able to destroy tanks, ships and aircraft. However, practical considerations have severely constrained these ideas; any laser capable of seriously wounding a human would (with its requisite power supply) be inevitably too heavy for a single soldier to lift, and a high-power laser capable of burning through tank armour would be extremely complex and very sensitive to misalignment from any knocks or vibration it might suffer, making it unsuitable for field deployment.

[edit] Fictional military use

Such uses are very common in fiction: see raygun.

[edit] Recent real developments

In 1980, the US Air Force managed to shoot down missiles configured as target practice drones. Results were sporadic at best, but they showed definitively that aircraft could be shot down by a static ground laser. Further tests and calculations showed that there was a "light at the end of a the tunnel", but that it would not be easy.

One of the pillars of long range lasers is the flexible mirror. A laser travels in a straight line depending on many of its qualities, but also on distorting atmospheric conditions. In the 1990's, astronomers managed to compensate for atmospheric distortion by placing a deformable mirror or variable refractive index device between light emitter and optical sensor (eye, CCD, etc). In effect, this flexi-mirror makes the opposite of the atmospheric distortion and reduces the distortion (by cancellation of two opposite distortions), of the light rays to the sensor from the emitter (which here was a stellar object).

In parallel, lasers were growing increasingly powerful. Some lasers can emit a very brief but extremely powerful pulse of light energy, which vaporises a layer of the target material, ejecting gases at such a high speed that they are equivalent to a local explosion on the surface of the target. They were using this principle since quite some time in the medical field to break apart bladder stones without surgery, by sending a small probe up the urinary tract, which could guide the laser to the surface of the stone and break it apart by pulsing a powerful burst on its surface. Lasers can function continuously if properly cooled, and continuous lasers are used to cut metals and other materials.

Open literature typically does not discuss the real power of modern lasers, as this is usually a closely guarded military secret. One thing that can be assumed, is that they are relatively powerful. Not enough to vaporise an army tank, perhaps, but powerful and practical enough to be deployed in cutting of the aluminium panels of aircraft from long range, or to penetrate modern body armour and inflict fatal wounds, otherwise, technological limitations would have been realised, and military pursuit of real-world applications would have been (at least temporarily) put on hiatus.

The third pillar is tracking. Well-explored technology in the radar field allows a high-speed aircraft to be easily tracked to the nearest ten meters or so. Extending this principle to laser tracking, meant that the accuracy of tracking was improved to the nearest meter, because tracking depends on the tracking beam being able to be very narrow. And as may be seen in toy lasers, they keep a narrow beam to very large distances.

Also, high-speed cameras and image processing algorithms allow an acquisition track, another term to denote the first approximate position to start high-precision laser tracking of a target. This is similar to the routine performed when using a binocular. First you get the approximate position of your target by looking at it directly, then you get a precision observation by placing the binoculars in the same axis as your observed target. If you were to look for something ("scanning") with the binoculars directly, you would waste a lot of time and would end up with a headache.

So the modern military ray guns have a minimum of three lasers and one initial track acquisition device.

  • 0: The initial track device gives the approximate position of the target,and other relevant information,such as speed altitude,predicted impact point, estimated launch position etc.
  • 1: The first laser (low power) then starts scanning the approximate position of the target until it acquires its precise coordinates.
  • 2: The second laser (low power) then performs measurements on the target, including:-
    • Atmospheric distortion measurements. This lets the shooter adjust a flexi-mirror to compensate for the deviations, with counter deviations in the final third laser.
    • Vibration analysis. This very important vibration analysis gives the shooter a complementary key information about the target: its mechanical resonance vibration modes. The second measurement laser can give information about the natural frequency of that part of the target where it shines.
  • 3: Finally, the third laser send powerful repetitive pulses at the natural frequency of the target, complete with distortion correction. This causes structural shock to the body of the missile, without considering other devastating thermal effects of the heating ability of a powerful laser. Usually flying machines are very fragile,and sudden thermal and physical shocks causes it to break apart.

Given these capacities, "ray-guns" are not technically impossible.

The only major limitation is that heavy vehicles like tanks would not suffer any significant effect when hit with a laser. Most probably the operator would notice that the side armour was vibrating, feel an increase in ambient temperature and no more. The only truly noticeable effect would be that a tank equipped with, reactive armour would start burning, with an outer extreme being low power, non damaging explosions.

[edit] To affect eyesight

There remains the possibility of using lasers to blind, since this requires much lower power levels, and is easily achievable in a man portable unit. However, most nations regard the deliberate blinding of the enemy as forbidden by the rules of war. Russia, China, and Jordan possess such weapons [citation needed], which were banned in most western countries in 1980. See Protocol on Blinding Laser Weapons.

[edit] Medical

[edit] Industrial & commercial

Lasers used for visual effects during a musical performance. (A laser light show.)
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Lasers used for visual effects during a musical performance. (A laser light show.)

[edit] In consumer products

In consumer electronics, telecommunications, and data communications, lasers are used as the transmitters in optical communications over optical fiber and free space.

[edit] Law enforcement

In law enforcement the most widely known use of lasers is for lidar, to detect the speed of vehicles.

The surface of a test target is instantly vaporized and bursts into flame upon irradiation by a high power continuous wave carbon dioxide laser emitting tens of kilowatts of far infrared light. Note the operator is standing behind sheets of plexiglass, which is opaque in the far infrared.
Enlarge
The surface of a test target is instantly vaporized and bursts into flame upon irradiation by a high power continuous wave carbon dioxide laser emitting tens of kilowatts of far infrared light. Note the operator is standing behind sheets of plexiglass, which is opaque in the far infrared.

[edit] Images

Lasers were used in the 2005 Classical Spectacular concert

A laser harp

[edit] References

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