Radian

A unit of angular measurement equal to the angle subtended at the center of a circle by an arc whose length is equal to the radius of the circle.
Example: 1 radian = ~ 57.3 degrees; 2π radians = 360 degrees

Raman Effect

Part of the energy in a photon is transferred to (or from) the vibrational/rotational energy of a molecule.

Ramper

Power controls for accomplishing the ramping steps; may be computer-controlled.

Refraction

The change of direction of propagation of any wave, such as an electromagnetic wave, when it passes from one medium to another in which the wave velocity is different. Simply put, the bending of incident rays as they pass from one medium to another, such as air to water.

Resolution

Resolving power, or the quantitative measure of the ability of an optical instrument to produce separable images of different points on an object; the capability of making distinguishable the individual parts of an object, closely adjacent images, or sources of light.

Resonator

The mirrors (or reflectors) making up the laser cavity containing the laser rod or tube. The mirrors reflect light back and forth to build up amplification under an external stimulus. Emission is through one of them, called a coupler, which is partially transmissive.

RMS

Abbreviation for Root-Mean-Square. Units of electronic noise.

Rockwell C

A scale or test used to define hardness in metals, particularly steel and titanium.

Rotating Lens

Beam delivery in a circular movement for cutting large-diameter holes. (De-focusing the beam for this lowers power density and increases drilling time.)