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Important Laser Research

Beginnings

The Directed Energy Directorate, Laser Division of the Air Force Research Laboratory, High Power Gas Laser Branch at Kirtland AFB, NM created the first chemical oxygen-iodine laser (COIL) in 1977, but a few more have been developed since that time. The early version only reached a mere .01 Watts of total power. The modern version, the research assessment device improvement chemical laser (RADICL) is underway testing ejector nozzle array technology and iodine-atom generation/injection.

Started in 1995, this new RADICL puts out 20KW; a supersonic COIL powered by a rotating-disk oxygen generator hooked to a Mach 2 single-slit portal (nozzle). Research in illuminator functions was enabled on this superior chemical efficicient test platform, but now that work is concentrating on making numerous shapes that the ejector nozzle array can accept. This research has resulted in the newest one --the advanced coil test stand (ACTS). The ultimate aim is cutting through harder stuff faster. There are three parts to this chemical laser that makes laser photons out of chemical reactions' energy.

Parts of the COIL

1. Singlet delta oxygen generator (SOG)

The generator is composed of a singlet-delta oxygen energy vehicle which is excited molecules from the aqueus combination of (watch out, boys and girls, do not try this at home or your now bleached hair will also explode!) potassium hydroxide and peroxide - basic hydrogen peroside (BHF), and mixed with gas-phase chlorine (and do not put this in your swimming pools, you would-be Buster Crabbs, and Esther Williams.) This is a tremendous exothermic reaction, heating up the soup, and leaving only a residue of potassium chloride, (probably not a good table salt.) Now, here is where the iodine comes in, it is injected into the air flow upstream of the supersonic nozzle to make the lasing action possible because oxygen has too much stability in this generator. The dissociation of the iodine molecules into atoms allows rapid transfer of energy. But, there are still power losses that further research seeks to remedy utilizing direct injection of iodine atoms.

2. Supersonic Nozzle

The purpose of the supersonic nozzle is to reduce the temperature in the laser cavity by means of supersonic expansion. Typical gas temperatures from chemical reactions in the COIL reach 180 degrees, Kelvin and is the source of potential inefficiencies.

3. The laser cavity

This is the place where the reaction takes place using little over 1 percent of iodine is added to the oxygen. The passing excited iodine atoms through the cavity become stimulated -- giving the lasing results.

Advanced COIL test program

Researchers are looking for ways to improve chemical efficiency and pressure recovery. This includes the iodine atom generation/injection, ejector nozzle technologies and supersonic nozzles. The current helium diluent, low pressured COILs need large vacuum systems to boost nozzle exit pressure, but the new ejector experiments could allow their use at lower altitudes.

Downstream Iodine Molecular Injection

The Three Methods

Ejector nozzle bank experiments where the laser active medium of separated singlet-delta oxygen and nitrogen in a supersonic diffuser result in more pressure and less loss. The oxygen flows from a jet-type SOG into a nozzle bank through the cavity-mixing chamber at Mach 1, and after the N2 gets in there reaching Mach 2, we increase to three flows with the introduction of the iodine in the downstream. The math has been done, and the position of the injections is crucial in this laser induced fluorescence.

Streamwise Vortices

Tabs are used to introduce fluid dynamics at the ejector nozzle creating streamwise vortices -- to improve the melange. The ACTS will try to understand the difference between different directorates' nozzles.

Generating Atomic Iodine

Methods

  1. Chemical
  2. Photolytic
  3. Electrical

Results of ACTS

This testing on nozzles and chemical mixing is continuing to gain the 25% power improvement over traditional COILS. This will implement their use for high-speed drilling and cutting, major quarrying and processing and power plant and nuclear warhead plant demolition.

Source: AFRL Technology Horizons, December 2001

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