F

Failsafe interlock

An interlock whereby the failure of a single mechanical or electrical component of the interlock will cause the system to go into, or remain in, a safe mode.

Femtoseconds

Ten to the negative 15th seconds.

Fiber coupling

A method of directing a laser’s output into a single mode or multi-mode fiber optic.

Fiberoptics

A system of flexible quartz or glass fibers with internal reflective surfaces that pass light through thousands of glancing (total internal) reflections.

Flashlamp

A tube typically filled with Krypton or Xenon. Produces a high intensity white light in short duration pulses.

Fluorescence

The emission of light of a particular wavelength resulting from absorption of energy typically from light of shorter wavelengths.

Flux

The radiant, or luminous, power of a light beam. The time rate of the flow of radiant energy across a given surface.

F-number

The focal length of lens divided by its useable diameter. In the case of a laser, the useable diameter is the diameter of the laser beam or a smaller aperture that restricts a laser beam.

Focal length

Distance between the center of a lens and the point on the optical axis to which parallel rays of light are converged by the laser. The effective focal length (EFL) is the distance from the principal point to the focal point. The back focal length (BFL) is the distance from the vertex of the last lens to the second focal point. The front focal length (FFL) is the distance from the first lens surface to the first focal point.

Focal point

That distance from the focusing lens where the laser beam has the smallest diameter.

Focus

As a noun, the point where rays of light meet that have been reflected by a mirror or refracted by a lens, giving rise to an image of the source. As a verb, to adjust focal length for the clearest image and smallest spot size.

Folded resonator

Construction in which the interior optical path is bent by mirrors. Permits compact packaging of a long laser cavity.

Frequency

The number of light waves passing a fixed point in a given unit of time, or the number of complete vibrations in that period of time.