UC Berkeley Berkeley Scientific Journal Title Light Wars: The Bright Future of Laser Weapons Permalink https://escholarship.org/uc/item/2v1656tz Journal Berkeley Scientific Journal, 12(1) ISSN 1097-0967 Author Mistry, Hemma Publication Date 2009 DOI 10.5070/BS3121007589 Peer reviewed|Undergraduate eScholarship.org Powered by the California Digital Library University of California WAR TECH • SPRING 2008 • WAR TECH Light Wars: The Bright Future of Laser Weapons by Hemma Mistry Lasers as directed energy weapons: this idea may fying light through the process of stimulated emission. In sound like the ray guns and light sabers of a science fiction 1916, Albert Einstein first theorized stimulated emission as writer’s dreams, but the idea of incorporating lasers into one of the three processes by which light can interact with military technology has been pursued since lasers were first matter (Perram, et al. 2004). In this process, a photon of invented. The U.S. government has spent millions of dol- light hits an electron in an excited, high energy state, caus- lars attempting to make laser weaponry a reality. In 1983, ing the electron to fall to a lower energy state which releas- the Reagan administration initiated an ambitious effort to es a photon of light with the same wavelength, phase, and create missile defense systems using lasers in space, nick- direction as the incident light. Mirrors are then used to named “Star Wars.” Although these systems were never amplify the emitted light, resulting in a beam of monochro- realized, the “Star Wars” program paved the way for future matic, coherent, directed laser light. laser research. The Clinton administration continued the This diagram shows the basic components of a laser. effort for missile defense laser weaponry with an agreement The gain medium, or amplifying medium, contains atoms with the Israeli government in 1996. Currently there are whose electrons are stimulated to emit light. Mirrors on several U.S. military funded programs developing laser either end of the optical cavity reflect the light back several weapons. times through the gain medium, amplifying the beam. An energy input is also required to excite the electrons in the What is a Laser? gain medium into a high energy state so that stimulated h 5 t / t i p m emission can occur. : a / g / e c s o / r F d i . g o 0 r 5 g - Military Interest in Lasers / 0 s 1 t . e g p i _ f o n l i n e The characteristics of laser light give lasers the / s t 1 - potential to make effective weapons. Because a laser beam is focused in one direction, laser weapons have the poten- The basic components of a laser tial to be extremely accurate in hitting targets. In combat, Lasers can serve as a valuable technology in warfare this accuracy would minimize the destruction of surround- because the light they emit has important and useful quali- ing area that is caused by more imprecise weapons such as ties. Laser light is monochromatic and coherent, which explosives. The precise aim of the weapon and the mini- means that not only does the light have a uniform wave- mal destruction would also reduce the harm caused to civil- length, but also the light waves maintain the same phase ians and other unintended targets. Lasers would also relationships over time. The waves also propagate in a def- enable the military to attack targets from far away, provided inite direction. These properties allow laser light to carry a that there is an unobstructed path for the laser’s beam to large amount of energy travel between the that can be applied in a weapon and target. specific direction, which Lasers could be used to destroy satel- Since the beam would is highly advantageous lites in space, or conversely, space-based travel at the speed of for a weapon. lasers could attack targets on the ground. light, the weapon would The word laser be effective on these is actually an acronym distant targets almost for “Light Amplification by Stimulated Emission of instantaneously. This long-range capability of lasers also Radiation,” and as the name implies, lasers work by ampli- means that a laser attack could be carried out covertly from 5 WAR TECH • SPRING 2008 • WAR TECH a great distance. have so far failed to reduce the system to a reasonable Since its invention in 1960 by Arthur Shawlow and size, which means that its portability would be an issue for Charles Townes, the U.S. military has been interested in military use. Another concern is the THEL’s enormous applying laser technology to military use (Perram et al. fuel requirement and furthermore, the storage and supply 2004). For defense purposes, lasers could be implemented of this fuel. The performance of the THEL is also unsatis- in ships, planes, or in ground-based systems to destroy factory, considering the time and money spent building it. missiles or rockets. Lasers could also be used to destroy After investing over $300 million in this program, the satellites in space, or conversely, space-based lasers could Pentagon decided to drop THEL in September 2005 attack targets on the ground. Lasers could also be built because of these problems, as writer William J. Broad into army vehicles or even planes as offensive weapons explains in an article on the program (New York Times, that could target large areas (Dunn 2005). July 30, 2006). A chemical laser program that is showing some Progress with Chemical Lasers promise, however, is the Airborne Laser (ABL), also developed by Northrop Grumman. The goal of ABL is to The mili- fit a Boeing 747 airplane with an oxygen iodine laser h t t p tary has : weapon so that it can detect and shoot down missiles soon / / w w invested w after they are launched. However, like THEL, ABL is not . a f a . in the o progressing as hoped – the team has yet to install the laser r g / m develop- a in the aircraft. Operational setbacks mean that the pro- g a z i ment of n posed date for the first missile test, 2008, will probably be e / d e several c further postponed. 2 0 0 2 / different 1 2 0 2 a types of t Solid-State Lasers Hold Promise t a c k lasers, 6 . j The Tactical High Energy Laser (THEL) at the U.S. p and the Army Missile Range at White Sands, New Mexico g While scientists are struggling to successfully main dif- incorporate chemical lasers into missile defense systems, ferences between these lasers are the source of electrons solid-state lasers are holding much more promise. Instead and the source of power. The most advanced military of chemicals, these lasers use a ruby or crystal to produce lasers currently are chemical lasers, which were invented light. Most commonly, these lasers use crystal yttrium in 1965 by George C. Pimentel (Perram et al. 2004). aluminum garnet (YAG). Ions of usually neodymium or Chemical lasers obtain energy from an exothermic chemi- ytterbium are dropped into the crystal, and the process of cal reaction. This energy excites the electrons in the gain stimulated emission occurs on these atoms. The energy medium, which is usually a low pressure gas. For exam- used to excite the electrons in these ions comes from elec- ple, the reaction of fluorine atoms with hydrogen mole- tricity, specifically flashlamps or diodes. cules produces hydrogen fluoride molecules and releas- es excess energy. These molecules of hydrogen fluo- ride become the gain medium, and the excess energy The goal of ABL is to fit a Boeing 747 is used to raise electrons into an excited state. airplane with a laser weapon so that it can Chemical lasers are the most developed and detect and shoot down missiles soon after most advanced lasers used for military application. They are also capable of generating the highest power they are launched. of any kind of laser – over 1 megawatt. The most advanced chemical laser defense system currently is the Solid-state lasers hold several advantages over Tactical High Energy Laser (THEL), which is a deuteri- chemical lasers. Because they are powered by electricity, um-fluoride laser. In 1996, Northrop Grumman, a corpo- there is no need for expensive and bulky chemical fuels. ration providing defense technology, received $89 million They can also produce wavelengths of light that transmit to design and build this system for the US and Israeli gov- well through the atmosphere, unperturbed by interference. ernments. The system shot down its first Katyusha rocket However, solid-state lasers can only operate at a fraction in 2000, and since then it has successfully shot down mul- of the power of chemical lasers. The military would like tiple test rockets, mortar shells, and other missiles (Hecht to see a 100kW solid-state laser because this is the energy 2006). required to destroy mortars and artillery rockets Despite its operational successes, the THEL has (Shachtman 2006). serious drawbacks. The whole laser system is about the The build-up of heat is a problem in solid-state size of six buses placed side-by-side, and the developers lasers because the diodes produce a lot of heat but only 6 7 - - of need to be acceler , This laser has achieved 14.2kW . WAR TECH WAR Madey at Stanford University (Dylla and • John Solid-state lasers and chemical lasers have certain Unlike chemical and solid-state lasers, free-electron The U.S. Navy has invested in the Free-Electron http://tr.wikipedia.org/wiki/Absinthe and expensive. , by stimulated emission can only produce certain discrete lthough it has not achieved the power level of LLNL’s The Future of Free-Electron Lasers limitations on the power and quality of beam that they can Aachieve.