Lasers

Lasers Revisited: New Outlook at Directed Energy

Word Laser means Light Amplification by Stimulated Emission of Radiation. Laser ray is produced when electrons in special glasses or gases emit light photons when excited by an electromagnetic pulse. The two major characteristics of laser pulse is wavelength coherence and wave uniformity: the light wave's crests and troughs of light will always be the in lock step, being equal frequency and wavelength. Partially reflecting mirrors over triangular crystals must be used in order to compound impulse power on top of each other: while the flash of light coming one way is reflected 90 degrees, another impulse is being added through the transparent one-sided mirror coming right through and doubling the energy of the impulse. The laser flashes last only microseconds but are extremely powerful. For example, laser beam used to measure long distances will run perfectly straight for millions of miles. The beam bounces off the moon and is received back on earth without getting distorted. Wave coherence affords to focus light with great precision. Many materials are used now days to generate laser light: ruby crystals for short pulse are called solid state laser; helium-neon gas, or liquid dye lasers,are used to generate continuous beam of light.

National Ignition Facility

The biggest laser in the world is located in NIF, that is National Ignition Facility, and you better believe these guys know how set things on fire, hotter than the sun! In NIF, intense pulses of light from hundreds of giant lamps pump electrons in slabs of special glass in order to compound the power of many independent flashes of light. Sets of laser glasses placed on a straight line allows the impulses to travel with minimum distortion and a system of mirrors at both ends of the laser glass bounces the light forth and back causing tremendous amount of photons to accumulate in one spot at a time. This level of density causes more electrons to get involved in the process of producing photons – they get stimulated and emit even more coherent photons; it's called Amplification. Essentially incoming photons clone themselves by causing glass electrons to emit coherent, or absolutely identical wavelength and direction, photons. In NIF, a number of amplifiers increase the initially weak pulse of light quadrillions times creating extremely tight and dense laser beams capable to produce temperatures and pressures comparable to those inside the stars. 

Ruby Laser

Ruby is an aluminum oxide crystal with atoms of chromium partially replacing atoms of aluminum. Chromium gives ruby its red color by absorbing all green and blue light. In laser, ruby crystal has to be shaped as a cylinder in order to produce a beam. It is wrapped with spiral light diodes and capped with fully reflecting mirror on one end of the cylinder to bounce all the photons back inside the crystal. Partially reflecting mirror is placed on the other end to let the energy out. Ruby laser was invented in 1960s.

Solid State Lasers: Ground Military Applications

Recently, multiple independent developments, sponsored by the US Government, have been taking place to implement previously overlooked solid-state laser technology. It used to be considered that solid state lasers are inherently weak for military application;however, in 2006 Boeing has proved that solid-state laser technology is mature enough to consider its use in weapon applications.

As you can see on two pictures field tests have been successfully performed to prove that this technology is finally suitable for military use. The system was called Avenger and was able to successfully disarm and detonate roadside bombs and unexploded ammunition from safe distance.

Solid State Lasers: Airborne Applications

Now that we have entered second decade of the twenty first century, the US Defense Department have finally been able to visualize their goals and to finalize their requirements. Among few other programs, the High Energy Liquid Laser Area Defense System (HELLADS) program was set to reach 150 kW energy output level. The weight per one kilowatt of produced power must not exceed 12 pounds (5 kilo) - that’s a lot to ask! Already, in 2009 couple independent research teams were able to produce beam of almost 35 kW, but 100-150 kW is the bottom threshold power output below which military application of laser becomes unreliable since it can’t guaranty target destruction anymore. Since 2009 a lot of progress has been accomplished and we can be confident that production airborne laser application is behind the corner. The goal of the program was to design and produce such a compact laser module, powered by the aircraft produced power that fits inside the bomb bay of conventional fighter jet enabling it to shoot down tactical targets such as surface-to-air missiles as well as ground human targets. Speed of light warfare has arrived.

 

Solid State Lasers: US Navy Demonstrates Directed Energy Weapon at Sea

Meantime US Navy is not wasting their time either. In October 2010 the U.S. Office of Naval Research has announced that they have successfully disabled a target boat using laser beam. Stemming from Joint High Power Solid State Laser Program, another DARPA's programs, Maritime Laser Demonstrator was placed on the deck of the test ship the USS Paul Foster. The solid-state laser system made by Northrop Grumman's Aerospace Systems was fully integrated and synchronized with ship's navigation and targeting platforms, displaying that Navy is strategical about the project. The system was tested at high power more than 35 times that year and was able to withstand stress of ocean wave heights up to almost eight feet. Recent experiments involve shooting down model UAV (please see the video at the end of the article). US Navy intends to implement the laser weapon systems on eight classes of war ships. The directed energy program leaders believe that the technology is mature enough to transition to the fleet, but is seen as complimentary, rather than replacement for conventional weapons.

Directed Energy Weapon Outlook

The US will definitely keep focusing on directed energy weapon programs to weaken efforts to restrict US Military freedom of movement. The increasing accessibility of precision-guided missiles and unmanned aircraft will be presenting bigger and bigger problem in near future, since more and more world hostile elements will be receiving access to cheap, precise and effective weaponry. Instead of relying on expensive Kinetic Missile Interceptor systems, the US should invest in defensive and also offensive directed energy weapons providing "nearly unlimited magazines to counter incoming missiles at a negligible cost per shot". The vision of nuclear drone loaded with compact direct energy module, capable to stop any missile or evaporate human target from 15,000 feet altitude while remaining in the midair for few months at a time is a dream of many proactive minds, however the political reality of a nuclear reactor in the mid-air makes this proposition a very long stretch.

 

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