The U.S. Navy considers 30 kilowatts enough power for a weapon capable of engaging drones and small boats, as the LAAWS laser deployed on the USS Ponce demonstrated.
The term laser is an acronym for Light Amplification by Stimulated Emission of Radiation. Although true amplification of light has been achieved using a laser, its greatest use has been as an optical oscillator; that is, as a source of coherent radiation in the visible portion of the electromagnetic spectrum. The meaning of the term laser will be probed more extensively later. The concept of the laser, which is a further extension of the principles of the maser (Microwave Amplification by Stimulated Emission of Radiation), was first discussed by Charles Townes and Arthur Schawlow (then of Columbia University and Bell Telephone Laboratories, respoctively) in 1958. The first operating laser using ruby an the active material was developed in mid-1960 by Theodore Maiman of Hughes Aircraft Company. Since that time, various types of lasers using different crystals, glasses, gaser, and semiconductors have been developed.
One of the key properties of lasers is that the output beam is highly directional. Typical laser beams have a divergence of less than a milliradian, and some systems can be designed to have sub-microradian divergences. Because of their small size, semiconductor diode lasers usually have divergences measured in degrees, expanding rapidly. However, this beam divergence can be substantially reduced by using external optics.
The laser was quickly employed as an aid to other weapon systems. Innovative scientists and engineers used the beam to point at a target and generate an aim-point that could be used to guide a bomb precisely to the target. As a type of precision guided munitions (PGM), the PAVE (—Precision Avionics Vectoring Equipment“) series of laser target designators (LTD) and the associated PAVEWAY laser-guided bombs (LGB) have been tremendously useful in conflicts from the Vietnam War to the Gulf War. Fielded military laser systems also include highly accurate range-finders and secure communication systems. Lasers have also been very useful for training aids such as the MILES system, the military equivalent of —laser tag“ available now to the general public. Recently, laser spotlights have provided both visible and infrared illumination for improved use of night vision devices (NVD).
Since the early 1960s, the complexity of the military missions has dramatically increased, with more diverse theaters of operation, expanded spectrums of conflict, and tremendously increased requirements for information delivered in almost immediately to the warfighter. It would be impossible in a short report to comprehensively address all the unique aspects of lasers in the space environment as well as the potential military applications.
Both laser technology and space operations have matured substantially in the recent decades, offering synergistic possibilities of using lasers from space-based platforms to improve US military capabilities. Coherent laser light offers a number of unique advantages as does the space environment, permitting speed-of-light applications such as optical communication, illumination, target designation, active remote sensing and high-energy weapons. Many of these concepts have been discussed in recent strategic studies, but it will take innovative leadership and close cooperation between researchers and operators to bring the concepts from the laboratory to the field.
The damage threshold for "soft“ targets like paper or skin is roughly one Joule per square centimeter, assuming a one-second exposure. Wood surfaces are damaged at approximately 10 J/cm2 while metal surfaces are damaged in the range of 100 J/cm2.
The process of generating the highly coherent laser beam is usually very inefficient. The Nd:YAG laser is only about one percent efficient, while the popular heliumneon laser is only about 0.001 percent efficient. The unique features of the output beam make these inefficiencies bearable. Fortuitously, semiconductor lasers, which generate light by direct conversion of electrical current to photons, are very efficient, achieving 20 to 50 percent efficiencies. At present, these systems do not produce the power levels necessary for high-energy laser weapons. But a laser, such as the carbon dioxide laser (used in the Airborne Laser Laboratory (ALL) to shoot down several Sidewinder missiles), has an efficiency on the order of 20 to 30 percent, which can achieve output powers of hundreds of kilowatts. The chemical efficiency of hydrogen fluoride (HF) lasers, being considered for space-based laser weapons, can be up to 20 percent or more, while the electrical efficiencies can exceed 150 percent, because the energy in the beam comes from a highly exothermic chemical reaction.
The High Energy Laser Joint Technology Office (HEL JTO) supports all of the Services under Office of the Secretary of Defense (OSD) leadership by translating requirements into technology. The HEL JTO is a key enabler to the HEL community at the component level for laser sources, beam control, lethality, and modeling and simulation. Several advances in the development of high power laser devices like the 100 kilowatt, laboratory-scale Joint High Power Solid State Laser and the Robust Electric Laser Initiative would not have occurred without HEL JTO leadership, joint service collaboration, and adequate funding. The HEL JTO is also developing the Advanced Beam Control for Locating and Engagement program that will advance pointing and tracking through the use of improved sensors and adaptive optics. The Services are leveraging these components and designs for inclusion in future weapon systems.
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