LASER DAMAGE WEAPONS

INTRODUCTION
1. Although the vast number of low powered Laser illuminators, Rangefinders, LADAR and other devices are not specifically designed to be weapons, if observed by the unprotected human eye, they can produce temporary or even permanent blindness. Although banned by international protocol, purpose built Laser Dazzle weapons have been developed and deployed in the field. Additionally, higher-powered Lasers of varying power and complexity have been developed to cause actual physical damage. It is very important to be aware of the threat posed by such weapons and their future potential.

OBJECTIVE
1. The objective for this section is to explain the operation of high and low-power military Laser systems. The following subjects will be covered:
a. Classes of Laser.
b. Dazzle Weapons.
c. High Energy Systems
(1) Land Based Systems.
(2) Airborne systems.
d. Adaptive Optics.
CLASSES OF LASER
2. Lasers can be grouped into certain classes based upon their power and potential for physical damage to the human eye or skin. A term commonly referred to is ‘Aversion’ which is man’s instinctive reaction to “blink “ when illuminated by a high power light or Laser. The Classes are shown in the table below:
Class Power Rating Hazard
1 µ watts Not Hazardous within Aversion response time
2 m watts Hazardous if viewer overcomes Adversion
3 M watts - Watts Causes injury faster than Adversion response
4 Watts Cause skin damage
4. For all Laser systems, including those not designed as Dazzle weapons, there exists what is known as the Normalised Ocular Hazard Distance (NOHD). This is defined as the range where the signal strength from a Laser has reduced to a level considered to be eye safe.
5. The NOHD depends upon the Class of Laser, its wavelength and pulse rate. Typically for a Nd YAG Laser the NOHD is 1 km. During peace time operations there are strict controls on the use of military Laser systems.
DAZZLE WEAPONS
6. It has been a natural and fairly easy step for existing Lasers systems to be developed into Dazzle weapons. A Laser Rifle developed in the US came from a medical Laser. Information about such weapons is very highly classified and difficult to obtain. Damage to the eye can be either temporary or permanent depending upon the class of Laser and type of exposure the eye has received. Brief descriptions of several Dazzle systems follow:
7. The US Army Laser Rifle was developed during the 1980’s. In 1993 it is believed that 1100 Rifles were tested and can cause either temporary or permanent damage. The Beamwidth is assessed as being 0.5 metres at 1 km. However little is known about ranges or the NOHD. The figure below shows a diagram of the Rifle.

8. A Laser weapon known as Stingray was fitted to 2 Bradley Armoured Personnel Carriers and deployed to Saudi Arabia during the Gulf War. The system designator is AN/VLQ-7. Designed to scan the battlefield with an eye safe Laser, the Stingray detects reflections from optical devices such as periscopes and Binoculars. It then illuminates these with a narrow-beam high-power Laser that blinds anyone looking through the targeted optic. The system can operate in automatic, Semi-automatic or manual modes.

9. An example of a naval system can be found in the Royal Navy Dazzler found on some UK warships. The only details available are photographs.

HIGH ENERGY LASER SYSTEMS
10. The Laser is a very attractive alternative weapon system offering several advantages over conventional weapons. These are:
a. Almost zero time of flight.

b. The beam travels in a straight line.


11. However there are also limitations:

a. Very high-energy requirements.

b. Complex technology.

c. Expensive

12. Due to the classification of many of the HEL projects it is again difficult to get reliable information about each of the various systems. However their development can be traced through unclassified sources. The first hint of any such systems can be found in the late 1060’s and 1970’s, but the first major publicity of their existence came about with the US Strategic Defence Initiative SDI of the 1980’s. Recent years have produced much more open discussion with the emphasis being placed on Lasers being used purely as a defensive weapon to shoot down SCUD missiles. It is still a very sensitive area as recently witnessed with the widespread criticism of USA proposal to use Lasers as protection against ICBM’s.
13. Initial attempts at producing HEL weapons resulted in large devices with low power and poor beam quality. The beams were also degraded by atmospheric distortion, a phenomenon not overcome for many years with the introduction of adaptive optical systems. (Covered later in these notes). Early HEL employed gas lasers while more recent systems use chemical lasers to generate more power. Two examples of this are the Mid IR Advanced Chemical Laser (MIRACL) and the Chemical Oxygen Iodine Laser (COIL), both of which are used in present day systems. We shall now look at specific examples of Land and Airborne systems.
LAND BASED HEL
14. Developed initially as a naval initiative the US has developed the SeaLite 400 kW Laser that used IR and Visible sensors to track targets. It reportedly shot down a TOW ATGM in flight. In 1980 it was used to destroy a tethered and stationary UH-1 helicopter. Eventually funding was lost for this system but it was later resurrected as the Multi Purpose Chemical Laser (MPCL) producing the 1986 10 MW LATEX Laser.

15. In 1989 the SeaLite aiming and tracking system was used in conjunction with the MIRACL to produce the highest power, 2.2 MW Deuterium Fluoride, operational Laser. This is base at the High Energy Laser Systems Test Facility. (HELSTF) based at White Sands in the USA. This system has reportedly engaged a Vandal supersonic missile and shot down 5 Firebee drones.

16. In 1996 the US Army Nautilus project used the MIRACL at low power to shoot down a short-range rocket in flight. In 1997 it was reportedly fired at a satellite. The success of this project led to the forming of a joint US / Israeli project know as the Tactical High Energy Laser (THEL). This system, which is mobile, is designed to engage tactical battlefield weapons with a Deuterium Fluoride Laser. A fixed site demonstrator has been built that has demonstrated a capability to shoot down several ‘small’ Targets. However it has proven to be delicate, unreliable and requiring too much maintenance. An updated system, now called the Mobile THEL (MTHEL), is currently under development. The range of potential targets has been expanded and it is planned that each system, presently consisting of 3 units, will be reduced to one vehicle easily transportable by C-130. This reduction in size may be achieved by the use of a new solid-state Laser.

17. Additional projects in development by the US include an Army 10 kW solid-state Laser which they hope to develop to 100 kW operational system by 2006. The USA is also developing the airborne Advanced Tactical Laser. (ATL)
AIRBORNE HEL
18. There is much activity in the development of airborne Laser applications both as high power damage systems and as lower power non-lethal systems for use in IRCM. The US Army is developing the non-lethal HELSTAR system using a COIL similar in design to the highly publicised Airborne Laser Project. (ABL). Designed for helicopters, the HELSTAR is 50 – 70 kW in power and has a range of only a few kilometres.
19. The USA first trialed airborne Laser technology in the 1980’s with the creation of the Airborne Laser Laboratory (ALL). This converted KC-135 was fitted with a 10.6 micron system that successfully shot down 5 sidewinder missiles. It did however highlight the problem of how the atmosphere makes the Laser wavefront go out -of- phase with a resultant drop in power. This effect has now been overcome by the use of adaptive optics, basically a combination of computer controlled deformable mirrors, which transmit a shaped wavefront that becomes in-phase after transmission through the atmosphere. This technique was first developed to remove star scintillation caused by the variable refractive index of the atmosphere.

20. The ABL project uses a converted Boeing-747 equipped with a COIL plus 3 other low-power Lasers for tracking of the target. The system is designed to engage ICBM’s as they break cloud cover above their launch site. The coil can engage at ranges up to 450 nm and provides for 45 seconds to destroy the target, fairly slow in this phase of its flight, which has not had time to deploy decoys or multiple re-entry vehicle warheads. If the engagement is successful, there is an added bonus of the debris falling back upon the launch area. Space based Lasers are prohibited by international treaty which this system does not require as it is fired from within the atmosphere. The project should be completed by 2003 and operational by 2007.


SUMMARY

21. As it should be evident from these notes, there is evidence of many developments in the use of Laser weapons in a wide variety of applications. The technology now exists to create a Laser of low or high-power specifically designed to match a particular requirement or function. Lasers are capable of being used as low-power dazzle weapons, medium-power for IRCM applications or high power anti-missile systems.
22. Breakthroughs in solid state laser technology are resulting in successful projects such as the mobile THEL; directed energy weapons could be installed in aircraft by 2010 and be the future of precision strikes and defence against missiles.
23. The ABL is conducting evaluation trials (Nov 2002); AAR procedures are being evaluated and the IR targeting sensors monitored a US ballistic missile launch from a range of 300nm.

LASER THEORY

LASER THEORY

INTRODUCTION

1. The use of Lasers both commercially and by the military is very wide-ranging. Commercial applications find Lasers in industrial and medical cutting equipment, CD players and Laser pointers to name only a few. In military use, Lasers are used for:
a. Range finding.
b. Target designation / illumination.
c. Missile guidance.
d. Laser radar.
e. Directed Laser Energy Weapons.
2. As the enemy is highly likely to employ an array of Laser systems against you, there is a need to understand and be able to exploit and counter such systems. Indeed one of the fastest growing areas of industry is in Laser Warning Receivers as many countries try to give their platforms some protection against such systems. The word Laser comes from Light Amplification by the Stimulated Emission of Radiation. A Laser is a device that generates and amplifies coherent light radiation in the Ultra Violet, Visible and InfraRed parts of the EO spectrum. Lasers operate at selected discrete wavelengths dependant on the selection of material used as the Lasing medium.
OBJECTIVE
3. The objective for this section is to explain the basics of Laser theory, explain how a simple system operates and different types of laser have different properties. The following areas will be covered:
a. Basic theory.
(1) Electron States.
(2) Excitation.
(3) Coherency.
(4) Divergence.
b. The requirements of a simple Laser system
c. Types of Laser system.
d. Laser propagation
BASIC LASER THEORY

4. To understand how a laser operates you need to have an understanding of molecular theory. Energy is stored in electrons that exist in differing bands around the nucleus of an atom, as shown in figure below.



Movement of electrons between the bands or levels can occur, and when an electron drops from a higher level (further away from the nucleus) to a lower level, a photon of light is given off. It is the harnessing of these photons that forms the basis of all Laser systems.

5. In its normal state the electrons of a particular substance are situated in specific bands around its nucleus. In order for the electrons to move to higher levels they must either collide with another moving particle or absorb a photon of radiated energy. This process is known as Excitation and the device that performs this in a Lasing system is called a ‘Pump’. Figure shows an electron decaying and emitting a photon of light energy.



The wavelengths of the energy given off in this manner cover from IR through Visual to the UV wavelengths. The wavelength is directly proportional to the difference between energy levels. This process does not have to be man-made and occurs naturally in some materials where electrons decay back to their ground state emitting the light in a process known as spontaneous decay. An example of this can be found in naturally fluorescent materials.

6. Another property of these materials is that, if you stimulate these materials with a stream of photons and raise the electron states to higher levels, as the electrons at a higher state decay they emit another photons with exactly the same properties as the incident photon. These then combine together and increase the strength of the light. The figure below illustrates this process for a single electron. Note how the resultant photon has the same wavelength and is in phase with the original.




7. To create a large enough flow of energy a population inversion has to be created where electrons in a higher state exceed the thermal Equilibrium State. Stimulated emissions then exceed spontaneous emissions. In a practical laser more than two energy levels are used with three or four being common. The figure below





8. shows electron energy levels E1 and E2 for a normal disposition and also an example of a population inversion.




9. The process of flooding the Lasing material with photons to create the population inversion is known as ‘pumping’. There are three methods of pumping Optical, Electrical or Chemical. Optical pumping uses a tube containing a quartz iodine compound and a Nd/YAG crystal is excited by a light from a high energy lamp or low power Laser. Electrical pumping applies a charge between two electrodes in a gaseous or semiconductor material, while in Chemical pumping a chemical reaction between two materials raises electrons to a higher state. The reaction between Hydrogen and Fluorine produces excited 2HF molecules while Carbon Monoxide and Oxygen produce excited CO2 molecules.

REQUIREMENTS FOR A SIMPLE LASER SYSTEM
10. A Laser system requires the following components:

a. A medium with a suitable energy level system.

b. A source of energy to produce the required population inversion.

c. An optical resonator to amplify the signal and produce the output beam.

11. Making the emitted photons travel parallel to an optical axis within a device called a Cavity Resonator can create a Laser beam. The parallel photons are then made to travel back and forth as they are reflected by two mirrors, one of which is only 50% reflecting, at either end of an optical cavity. The beam continues to build in strength until it is of sufficient to pass through the 50% mirror and thus is emitted as the Laser beam as shown in figure below.


1. Alternately, instead of mirrors, some systems use the polished ends of a crystal (Ruby Laser), the two faces of a semiconductor or rotating rather than fixed mirrors. The use of a rotating mirror to replace the 50% transmission mirror allows for the laser signal to be pulsed.

LASER PROPAGATION

12. One of the main features of Lasers is that they produce a narrow parallel beam with very little divergence or spreading out of the shape. This is known as a collimated beam. If this beam travels thorough Space or a vacuum then there is very little if any divergence and absorption of the beam.

13. However this is not the case through the Earth’s atmosphere where the beam will be absorbed and scattered. The main losses are caused by:

a. Absorption and Scattering.

b. Beam Jitter caused by inconsistent output and vibration from servo-controlled tracking systems.

c. Atmospheric Turbulence produces variable refractive indexes that cause beam steering problems.

d. Beam Divergence (small).

TYPES OF LASER
14. There are five main types of Laser:

a. Solid state.

b. Gas.

c. Semiconductor or diode.

d. Liquid.

e. Chemical.

15. Solid state lasers use a solid rod made up of a crystal or a special glass that contains atoms of the lasing medium. Characteristics of the laser depend on the active material used as well as the substrate or host material. Materials include chromium, erbium, titanium and neodymium.

16. Nd-YAG has widespread applications including range finders and target designators. They can be battery powered, small and light. They are rugged and resistant to temperature variations.

17. Gas Lasers use a pure gas or a mixture of gasses as the lasing medium. to produce the different wavelengths as shown in the table below. CO2 used for research in HEL systems. Helium-neon lasers are small, cheap, simple and can be used for long periods. They are used by the military for ring gyros. They can use the IR, UV and visible bands as shown below.

GAS COLOUR WAVELENTH
Helium / Neon Visible Red 0.628 μm
Argon Visible Green 0.55 μm
Carbon Dioxide IR 10.6 μm

19. Liquid Lasers use an organic dye solvents as the lasing medium. These low powered lasers are widely used in medical research. They can be tuned to produce Lasers with wavelengths from 0.34 to 1.17 µm.

20. Semi-conductor/Diode lasers. An example of a Semiconductor Laser is one made from Gallium Arsenide. The beam produced is rectangular and diverges and expands rapidly making it ideal for use with fibre optic communications. Also used in CD players and DVDs.

21. Chemical lasers. Energy required provided by a chemical reaction between 2 elements. Suitable for use in HELs. Elements commonly used Hydrogen fluoride ( 2.5 – 3.0 ), Deuterium fluoride ( 3.5 –4.0 ) and Oxygen iodide ( 1.315 )

22. When selecting a Laser for a particular task, there are many factors that have to be considered such as platform size, cost and complexity. However the main constraint is that as the power rises, the efficiency of the system decreases. The table below shows various different types of Laser and their power and efficiency. The ultimate challenge in Laser technology is to produce high-power high-efficiency systems.


Type of Laser Power Efficiency
Gas Watts to Kilowatts 20%
Liquid Megawatts 25%
Solid Ruby Gigawatts 1%
Solid Nd/YAG Kilowatts 2%
Solid Semiconductor Low 2%


SUMMARY

23. In order to produce a Laser you output you require to have a suitable Lasing material that can produce a satisfactory population inversion of electrons. There must be more atoms, ions or molecules in the excited state than there are in the lower ground stable state. This permits the emission of large numbers of light photons that are combined to produce the Laser beam.
24. Some form of a ‘Pump’ is normally required to achieve this population inversion and amplification of the emissions requires a cavity or optical resonator.
25. Most Lasers are inefficient and require large amounts of power. Depending upon the requirement of producing equipment for a particular role or mission, the system designer can select from Gas, Liquid or Solid- state Lasers. Generally Gas and Liquid Lasers are more efficient than Solid-state Lasers but tend to be larger and more expensive. Solid-state lasers are inefficient but tend to be cheaper and smaller, making them very suitable for low power devices.
26. The main property of a Laser is that being Collimated and Coherent, high levels of accuracy can be achieved. However the beams travel will be altered by bending and propagation losses through the Earth’s atmosphere.

laser in military application

LASER IN MILITARY APPLICATIONS

INTRODUCTION

1. In recent years the Laser has seen widespread use especially in the Ranging and Designation for Laser Guided Bombs and Missiles. The features of a Laser including its very narrow beamwidth, highly monochromatic and source brightness make it a very powerful tool for such operations where it has advantages over and complements conventional Radar.
AIM
2. The aim of this section is to explain the design and operation of military Laser systems. The following subjects will be covered:
a. Laser Rangefinders.
b. Target Designators.
c. Target Illuminators.
d. Laser Guidance / Tracking Systems.
e. Laser Communication Systems.
f. Laser Radar LADAR.
LASER RANGEFINDERS

3. A Laser rangefinder transmits an intense highly collimated beam of short pulses. The time taken for a single pulse to travel to the target and back is recorded. Because we know the sped of light, a simple calculation will provide us with the range to the Target. If c = speed of light and T = time taken back and forth then:

Range = cT / 2

4. Early Rangefinders were made from Ruby Lasers which were then replaced by Nd/YAG systems which had the advantage of being invisible, therefore could not be seen by the enemy, and less dangerous to the human eye. More recent Rangefinders use Carbon Dioxide which has better penetration in adverse weather conditions and has four times less eye hazard than Nd/YAG. This means that Rangefinding can safely be conducted in training exercises without the fear of causing unintentional eye damage. Most Rangefinders have operational ranges of 5 to 10 Km although some have ranges greater than this. The figure below shows the basic operation of a Laser Rangefinder in an airborne scenario although the same principal applies to any platform such as the man-portable system shown in figure.

TARGET DESIGNATION

5. The principle of Designation is that the target is illuminated by Laser beam and a detector in the host platform, or weapon system, homes in onto reflected light from the target. The Lasers very narrow beam width ensures very accurate and selective marking of the target at ranges of up to 10 Km. Unless the enemy has lots of Laser Warning Receivers (LWR’s) it will not know who is being targeted. In most modern systems once the returning laser signals have been acquired, automatic tracking of the signal takes place. All the operator has to do is to keep the target illuminated and the weapon should home to the correct target. Accurate targeting information is then supplied to the aircraft or weapon systems, navigation and weapon aiming systems. Examples of Targeting systems include Litening and TIALD targeting pods which both include a Laser Designator as well as various FLIR and visual TV cameras.

The basic principal of operation of a Laser Designator is shown in the figure below.


TARGET ILLUMINATION


6. Target illumination can be used to improve the performance of Image Intensifiers. Here the Designator is used in the same manner as a torch producing reflections off the target that are large enough to be picked up by the Image Intensifier.

LADAR (LASER RADAR)

7. A Laser Radar generates very narrow beam widths which greatly improves covertness and resistance to jamming.

8. Optical Radar (LIDAR) employs visible wavelengths.
Laser Radar (LADAR) generally refers to systems employing other wavelengths.

9. The characteristics of LADAR greatly improve target profiling, definition, signature and tracking accuracy.

10. When using wavelengths in the UV band the high frequencies induce target fluorescence which improves signature analysis.

11. LADAR systems are used in;

a. Atmospheric Ozone detection.

b. Submarine detection.

c. Rangefinding.

d. As a Missile Seeker head.

12. Low Cost Autonomous Attack System (LOCAAS) – utilises LADAR technology.The purpose of this development was to illustrate that an autonomous low cost attack munition could be integrated into an air vehicle powered by a miniature turbojet engine.This would be integrated on the F-22, F-22X and JSF aircraft or a UAV as an autonomous system.



13. The vehicle would consist of a Multi-Mode Warhead (expanding rod, fragmentation) coupled to a solid state radar (LADAR) seeker with Autonomous Target Recognition (ATR) and INS/GPS midcourse guidance in a manoeuvrable airframe.

14. The LADAR allows target aim point and warhead selection to be determined automatically.

15. Endurance 30 min; Range >100km; Cost $33K/unit.