The subject matter or figure imaged by, or seen through, an optical system.

Optical Density

Abbreviated OD.  The logarithm to the base ten of the reciprocal of the transmittance at a particular wavelength, where: Dλ = log10 (1/τ λ) where τ λ is the transmittance at the wavelength of interest. Symbol: D(λ), D λ or OD. Optical Density is commonly used to describe the protection factor provided by a filter (such as used in eyewear, viewing windows, etc.) at a specific wavelength. Each incremental unit of OD (1, 2, 3….etc.) represents a 10x increase in protection.

Light Transmission and OD Calculation

Optical Fiber

Filament of quartz or other optical material capable of transmitting light along its conformation and emitting it at the end.

Output Power

The energy per second emitted from the laser in the form of coherent light, usually measured in watts for continuous-wave operation and joules for pulsed operation.

Oxygen Assist

In certain cutting operations, coaxial oxygen initiates an exothermic reaction to enhance the cutting rate for thick metals; in other words, oxygen actually does the cutting, with the reaction being maintained by the laser beam.