C

Calorimeter

An instrument that measures energy, usually as heat generated by absorption of the laser beam.

Carbon dioxide

Molecule used as a laser medium. Emits far infrared energy at 10,600 nm (10.6 micrometers).

Cathode

A negatively-charged electrical element providing electrons for an electrical discharge.

Charge-coupled device (CCD)

An image-sensing detector that consists of a matrix of microscopic sensing elements, each of which corresponds to an image pixel. The CCD converts an optical image into electrical signals that represent the information contained within each pixel. These signals may be extracted sequentially and stored, or they may otherwise be processed in digital format for the purpose of transmitting or storing a digital representation of the optical image.

CIE

Abbreviation for Commission International de L’Eclairage, the French translation for International Commission on Illumination.

Cladding

One or more layers of material of lower refractive index that surround the core of an optical fiber. Works to contain core light and protect against surface contaminant scattering.

Clear aperture (CA)

Also known as free aperture or objective aperture. The opening in the mount of an optical system or its components that restricts the extent of the bundle of rays incident on the given surface. It is usually circular and specified by its diameter.

Closed installation

Any location where lasers are used that will be closed to unprotected personnel during laser operation.

CO₂ laser

A widely used laser in which the primary lasing medium is carbon dioxide gas. The output wavelength is 10.6 micrometers in the far infrared spectrum. It can be operated in either CW or pulsed mode.

Coaxial gas

A shield of inert gas flowing over the target material to prevent plasma oxidation and absorption, to blow away debris, and to control heat reaction. The gas jet has the same axis as the beam, so the two can be aimed together.

Coherence

Pertains to two or more waves that have a fixed phase relationship over time. When wave crests simultaneously meet other crests, while troughs meet other troughs, the waves are deemed to be in phase. When the crests of one wave simultaneously meet the troughs of another, they are out of phase. When crests and troughs meet randomly, they are deemed incoherent.

Coherence length

The distance over which energy in two separate waves remain in phase.

Collimation

The process by which divergent beams are converted into parallel beams (coherent light).

Collimated light

Light in which all of the rays are considered to be parallel to one another.

Combiner mirror

The mirror in a laser that combines two or more wavelengths into a coaxial beam.

Convergence

In optics, the bending of light rays toward one another.

Constant current mode

Laser diode drivers operating in this mode do not utilize a photodiode. Instead, they provide a set level of current to the diode. The diode output power will drift when the temperature changes due to the inherent properties of the semiconductor material. A thermoelectric cooler can help prevent power and wavelength drift by stabilizing the operating temperature of the laser diode.

Continuous wave (CW) laser modules

These modules emit energy continuously rather than in short pulses. Continuous wave applications require the laser to be on 100% of the time.

Continuous mode

The duration of laser exposure is controlled by the user (by foot or hand switch).

Convergence

The bending of light rays toward each other, as by a positive (convex) lens.

Corrected lens

A compound lens that is made measurably free of aberrations through the careful selection of its dimensions and materials.

Crystal

A solid with a regular array of atoms. Sapphire (ruby laser) and YAG (Nd:YAG laser) are two crystalline materials used as laser sources.

Current regulation

Laser system regulation in which discharge current is kept constant.

Current saturation

The maximum flow of electric current in a conductor. In a laser, the point at which further electrical input will not increase laser output.