T

TEM

Abbreviation for transverse electro-magnetic modes. Used to designate the cross-sectional shape of the beam.

TEM₀₀ mode

Fundamental (lowest order standing wave) transverse electromagnetic mode in a laser. With TEM modes, both the electric and magnetic field vectors are normal to the propagation of the beam. The TEM₀₀ mode has a Gaussian energy distribution across the beam.

Thermal relaxation time

The time to dissipate the heat absorbed during a laser pulse.

Thermoelectric (TE) cooler

A device that helps maintain a cool, stable temperature for a laser diode. The benefits of temperature control include prolonging the life of the laser diode, maintaining a stable output power, and promoting wavelength stability.

Threshold current (Ith)

The minimum driving current required to stimulate laser output.

Transmission

Passage of electromagnetic radiation through a medium.

Transmittance

The ratio of transmitted radiant energy to incident radiant energy, or the fraction of light that passes through a medium.

Transverse mode

Mode that has a field vector normal to the direction of propagation. In TE (transverse electric) mode, the electric field vector is normal. That is, the electric field is perpendicular to the direction of propagation. In TM (transverse magnetic) mode, the magnetic field vector is normal, meaning that it is perpendicular to the direction of propagation. In TEM (transverse electomagnetic) mode, both field vectors are normal to the direction of propagation. The lowest order transverse mode of a laser is the Gaussian TEM₀₀.

Tunable dye laser

A laser whose active medium is a liquid dye, pumped by another laser or flashlamps, to produce various colors of light. The color of light may be tuned by adjusting optical tuning elements and/or changing the dye used.

Tunable laser

A laser system that can be “tuned” to emit laser light over a continuous range of wavelengths or frequencies.

TTL modulation

Type of modulation that requires a 0 or 5VDC, TTL-compatible input signal to control laser output. Unlike analog modulated lasers, TTL modulated lasers cannot produce any level of fractional power. They are either ON or OFF. A benefit of TTL modulation is that users can program it to enable, inhibit, or modulate a laser, making it an excellent resource for synchronized applications.