Tag Archives: TEM

The term “Laser” is an acronym which stands for “Light Amplification by Stimulated Emission of Radiation“ and is basically a device that converts energy into light. A laser typically consists of a laser cavity or resonator. In its simplest form a laser cavity is made up of two mirrors: a total reflector and a partial reflector (also called output coupler) between which light bounces back and forth. Some of this light escapes the cavity through the output coupler producing an output beam. This laser beam, as opposed to ordinary light sources, is monochromatic, directional and coherent. These properties allow for lasers to be projected over long distances thanks to their extreme brightness without spreading significantly and to be focused to a very small spot, which results in a very large power density, acting almost as a true point source.

Inside the laser cavity light gains intensity by oscillating through the gain medium (also called the lasing medium). In most lasers this medium consists of atoms which have been “excited” by means of an electrical current or light (e.g. by a flash lamp). Gain medium can be of any state: gas, liquid, solid, or plasma. This process of transforming atoms into their excited states is called “pumping”. Once excited, atoms convert this stored energy into light in a process known as “stimulated emission”. Light then travels back and forth between the two reflecting mirrors and is reinforced by constructive interference only at specific wavelengths, called longitudinal modes of the cavity. The exact wavelength(s) at which emission occurs are determined by the gain bandwidth of the gain medium, the spectral characteristics of the cavity mirrors and the longitudinal modes of the cavity at which constructive interference occurs. The cavity also controls the so-called transverse modes, i.e. the electromagnetic field pattern of radiation measured in a plane perpendicular to the propagation direction of the beam. Lasers can emit any number of transverse modes, of which TEM00 is usually the most desirable. Laser output is, in fact, usually described as what percentage of the total beam intensity is in the form of TEM00. Continue reading →