TAC (time-to-amplitude converter)

An instrument that outputs the time difference between two pulse signals as a pulse amplitude (height).

Terahertz wave

Electromagnetic waves at frequencies around 1 THz (wavelength: 300 um). Terahertz waves transmit through paper, wood, and plastic but do not transmit through metal and water. The terahertz band is called the fingerprint region of substances, and their applications are recently being developed along with progress made from basic research.

Terminal capacitance (Ct)

In a photodiode, the PN junction can be considered as a type of capacitor. This capacitance is termed the junction capacitance and is an important parameter in determining the response speed. In current-to-voltage conversion circuits using an op amp, the junction capacitance might cause gain peaking. At HAMAMATSU, we specify the terminal capacitance including this junction capacitance plus the package stray capacitance.


A thermally sensitive resistor that greatly changes its electrical resistance as the temperature changes. Thermistors are used for temperature sensing.

Thermoelectric cooling element

When an electric current flows through the junction of two dissimilar electric conductors, heat absorption (or heat generation) occurs on one side while heat generation (or heat absorption) occurs on the other side. Thermoelectric cooling elements make use of this effect (known as Peltier effect). Reversing the direction of the electric current reverses the relation between the heat absorption and generation.


An arrangement of two or more photosensors in a tile configuration to have a wider active area. Also called “edge-to-edge butted.”

Tracking detector (vertex detector)

A detector mainly used in elementary particle energy physics experiments for the purpose of tracking the traveling direction and decay processes of secondary particles generated as a result of high energy particle collisions. Tracking detectors are installed at positions surrounding the point where the particles collide.

Transimpedance amplifier (TIA)

An amplifier which converts a small photocurrent to a voltage. The gain of the amplifier is usually given as the transimpedance gain in units of volts/amp.

Transit time

The electron transit time is the time interval between the arrival of a delta function light pulse (pulse width less than 50 ps) at the photocathode and the instant when the anode output pulse reaches its peak amplitude.

Transit time spread (TTS)

Transit time spread is a result of different electron trajectories inside a PMT and different initial velocities of photoelectrons leaving the cathode. The effect is a fluctuation or jitter in the transit time and a broadening of the pulse. The spread is defined as the FWHM of the probability distribution of these fluctuations.

Transition frequency

This originally meant the frequency at which the current gain (hfe) of an emitter-grounded transistor is 1, but now indicates the frequency at which the gain of an amplifying element becomes 1.

Tunable laser

Light sources for multiple-wavelength transmission systems.