What is a Laser?

Light Amplification by Stimulated Emission of Radiation


A laser, short for Light Amplification by Stimulated Emission of Radiation, is a very intense, highly directional beam of light. A laser is commonly produced by "exciting" the atoms or molecules in a material in a very controlled manner until they emit photons, or packets of light, in a very organized or coherent fashion. In chemical lasers, the excited species are formed by a chemical reaction and the energy provided to the system is stored as chemicals. In a solid state laser, the excited species is formed by optical excitation and the energy is provided to the system electrically. This electrical energy can be stored in batteries, flywheels or in fuel for generators. In both cases a population inversion is formed, which allows stimulated emission. Optical extraction occurs using an optical resonator, which can be as simple as a pair of mirrors surrounding the excited gain medium.

A laser is to a common light bulb what a marching band is to a random group of people. A laser's light waves are coherent, i.e., they travel in the same direction at the same time with the same wavelength, allowing the beam to propagate great distances across space with minimal "spreading out" or loss of intensity. With the aid of high precision optical systems, high-energy lasers can deposit intense amounts of light energy (heat) on objects at distances up to thousands of kilometers away.

Chemical Lasers

Chemical lasers are devices whose excited species are formed by chemical reactions. Northrop Grumman has developed two types of chemical lasers – hydrogen fluoride/deuterium fluoride (HF/DF) and chemical oxygen iodine laser (COIL). Both types of lasers have demonstrated significant power levels and are being or will be operated at megawatt-class output power. These types of lasers release their waste heat with their effluent and their beam quality is excellent.

Solid State Lasers

Solid-state lasers (SSLs) use a crystalline or glass material doped with an ion, which is the lasing species. These lasers use flashlamps or diodes to pump the ions to excited levels, which then emit radiation. The first laser, a ruby laser, is an SSL. Recently, these lasers have been scaled to higher power levels for a variety of government and commercial applications. The most common SSL is based on neodymium (Nd) doped into crystals such as Yttrium Aluminum Garnet (YAG). Nd:YAG lasers emit radiation at 1.06 m m, an excellent wavelength for transmission through the atmosphere.

Although currently not as powerful as their chemical counterparts, solid-state lasers are well-suited to a wide variety of defense missions - from destroying incoming threats to illuminating targets, from air defense to mine destruction, from ship protection to electronic warfare. This versatile technology also simplifies field logistics and operations, and is readily adapted for use aboard a wide range of air-, land-, sea-, and space-based platforms