Friday, April 19, 2024

Directed Energy Weapons: Less-Lethal Laser Weapons

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Under directed energy weapons, so far we have covered particle beam weapons and high-power microwaves. Let us now take a look at some less-lethal laser weapons.

Directed energy laser systems are generally categorised as non-lethal or, more appropriately, less-lethal directed energy laser weapons and lethal high-energy laser weapons. These include laser dazzlers used in anti-personnel applications for anti-terrorist and counter-insurgency operations and lethal high-energy laser weapons system aimed at inflicting structural damage to the intended targets at tactical and strategic ranges. High-energy lasers used in anti-sensor applications as a part of electro-optic counter measure equipment also come under less-lethal directed energy laser systems.

Another important application of high-energy directed energy laser systems, when operated at relatively-lower power levels, is in safe neutralisation of unexploded ordnances with minimised collateral damage. These systems, generally configured around kilowatt-class bulk solid-state lasers or high-power fibre lasers, have amply demonstrated their efficacy in the disposal of unexploded ordnances including improvised explosive devices from a safe distance.

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Less-lethal laser dazzlers

Response of human eye to different wavelengths
Fig. 1: Response of human eye to different wavelengths

A low-intensity conflict (LIC) is the most common form of warfare today, and is likely to be so in the foreseeable future. Data suggests that more than 75 percent of the armed conflicts since World War II have been of the low-intensity variety. An LIC operation is a military term used for deployment and use of troops and/or assets in situations other than conventional war.

Laser dazzler (Laser weapons) for close-combat operation
Fig. 2: Laser dazzler for close-combat operation

As compared to a conventional war, in the case of LIC operations, armed forces engaged in the conflict operate at a greatly-reduced tempo, generally with fewer soldiers, reduced range of tactical equipment and limited scope to operate in military manner. Also, use of artillery is avoided in the case of conflicts in urban territories, and use of air power is often restricted to surveillance and transportation of personnel and equipment.

LICs, which pose an alarming threat to national security, is an area of concern for the whole of international community, today. Its scope extends from emergency preparedness and response to domestic intelligence activities to riot and mob control, from combating illegal drug trafficking to protection of critical infrastructure, from handling counter-insurgency and anti-terrorist operations to detection of concealed laser weapons, from detection and identification of chemical and biological warfare agents to detection of explosive materials.

Laser and optoelectronics technologies play an important role in handling LIC situations. Key advantages of the use of laser weapons technology in such applications are near-zero collateral damage, speed-of-light delivery and potential for building non-lethal laser weapons. Some of the well-established laser devices in LIC applications include laser dazzlers for close-combat operations, mob/riot control and protection of critical infrastructures from aerial threats.

Operational parameters for Laser Weapons

Vehicle-mounted laser dazzler for crowd-control application
Fig. 3: Vehicle-mounted laser dazzler for crowd-control application

A laser dazzler emits a high-intensity laser beam in the visible band, usually in the blue-green region, to temporarily impair the vision of the adversary without causing any permanent or lasting injury or adverse effect to the subject’s eyes. Depending upon intended application, laser dazzlers come in a variety of package styles, mounting configurations and performance specifications. These devices can be handheld or weapon-mountable for versatility, convenience and ease of use. Some laser dazzlers have adjustable beam divergence that allows these to vary the spot size. While using a broader beam allows these a larger swath path needed to effectively produce a tactical advantage, tighter beams allow longer range and increased efficacy at longer distances.

Choice of operating parameters such as laser power, spot size at the target, laser power density and others are driven by the nature of deployment. Beam-shaping and directing optics are designed to achieve the desired value of nominal ocular hazard distance (NOHD) and a laser power density that does not exceed the maximum permissible exposure (MPE) figure dictated by American National Standards Institute (ANSI) standards for eye safety.

MPE, expressed as power density, is dependent on wavelength and exposure time. At 532nm, maximum permissible power density equals 2.5mW/cm2 for 0.25-second exposure and 1.0mW/cm2 for an exposure time of ten seconds.

Laser dazzler in homeland security
Fig. 4: Laser dazzler in homeland security

Blue-green region is the chosen wavelength band as the human eye is most sensitive to green light. Relative spectral response (Fig. 1) is used in determining lumens of a light source and thus how bright the light will appear in terms of lux. For a red light to appear as bright as a green light, the red light must emit more radiation than the green light because humans are not as sensitive to red light.

Most-commonly-employed wavelength from laser weapons for the purpose is 532nm, usually generated by using either laser diodes or frequency doubling Nd-YAG lasers. These devices usually produce a randomly-pulsed output in the range of 10Hz to 20Hz, riding a DC level for better overall effect. DC level is usually kept at 30 per cent to 50 per cent of peak intensity level. Night-time maximum operational range is typically three to four times the maximum day-time range.

To know more about laser weapons, turn to page 2.


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