LASER: Light Amplification by Stimulated Emission of Radiation.

The formal definition: A device that converts some form of energy (electrical, optical, chemical, etc.) into a narrow beam of light which is monochromatic (single pure color) and coherent (all waves in step with one another).

Monochromatic means that it consist of one single color or wavelength. Even though some lasers can generator more than one wavelength, the light is extreme "pure" and consists of a very narrow spectral range.

Directional means that the beam is very well collimated and travels over long distances with very little spread in diameter.

Coherent means that all individual waves of light are moving precisely together through time and space, or are in phase. The effect of one wave enhances the strength of every other wave, so that the overall effect of coherent light is much greater than if the waves were not in phase.

Because of these properties laser light can be focused to an extremely small spot, which results in a very large power density which produces a very high temperature.

Lasers come in many different types, each with a different power level and wavelength (color). Some are so weak that you cannot feel the beam on your hand (i.e., supermarket scanners), while others might have an invisible beam that can burn a hole through a steel plate (large CO2 laser).

DPSSL is the brief for Diode-Pumped Solid-State Laser. It is an exciting new tool for OEM applications that combines the beam quality of a gas laser and the small size and efficiency of a diode laser with single-line output in the blue (457nm), green (532nm), or infrared (1064nm).

L's, shown in the picture below, start with a standard diode laser operating at for example 808nm, the most common source. The output of this laser is focused into a small chip of neodymium-doped YAG or vanadate (the lasing medium) producing laser output at 914nm or 1064nm, depending on the basic configuration. To obtain blue or green ligth, a frequency-doubling crystal is inserted into the laser cavity. Finally, extracavity beam conditioning optics are added to enlarge and collimate the beam.

Green laser is also a primary color and is aesthetically attractive. Because of that it is widely used in laser shows and as stage lighting. Green laser light sources are also popular in medical devices and biological research. In recent years, diode-pumped solid-state () lasers have become an attractive alternative to aircooled argon ion lasers and green helium neon (HeNe) lasers in many applications. lasers, which, depending upon the configuration, produce output in the infrared (1064nm) or green (532 nm), combine high output power with long operating life. They exhibit excellent output stability, exceptional mode purity, and extremely low power consumption, and are ideal for both laboratory and OEM applications.

The fundamental TEM₀₀ mode is only one of many transverse modes that satisfy the round-trip propagation criteria. The figure below shows examples of the primary lower-order Hermite-Gaussian (rectangular) solutions to the propagation equation.

Note that the subscripts n and m in the Eigenmode TEM _nm are correlated to the number of nodes in the x and y directions. In each case, adjacent lobes of the mode are 180° out of phase.

The propagation equation can also be written in cylindrical form in terms of radius (r) and angle (f). The eigenmodes (E_rf) for this equation are a series of axially symmetric modes, which, for stable resonators, are closely approximated by Laguerre-Gaussian functions, denoted by TEM_rf. For the lowest order mode, TEM₀₀, the Hermite-Gaussian and Laguerre-Gaussian functions are identical, but for higher order modes, they differ significantly, as shown in the figure below.

The mode, TEM₀₁*, also known as the "bagel" or "doughnut" mode, is considered to be a superposition of the Hermite-Gaussian TEM₁₀ and TEM₀₁ modes, locked in phase quadrature.

In real-world lasers, the Hermite-Gaussian modes predominate since strain, slight misalignment, or contamination on the optics tends to drive the system toward rectangular coordinates. Nonetheless, the Laguerre-Gaussian TEM₁₀ "target" or "bulls-eye" mode is clearly observed in well-aligned gas-ion and helium neon lasers with the appropriate limiting apertures.