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THz - Detectors

 





Basics

These types of pyroelectric detectors are optimized for application in THz region. The detectors are small, have a large active area and a short response time.

The basic principle of pyroelectric detection is that the radiation pulse coming from a pulsed laser or a chopped cw-laser is absorbed in an absorber sheet. From there the heat energy is transferred to the pyroelectric sensor material by heat conduction. For all types of THz detectors a broadband metallic absorber is used. For realizing broadband absorption a partial absorption of nearly 50 % is realized, whereas 25% are reflected and the 25% transmitted radiation is absorbed in a dump.  A temperature change of the sensor material leads to a generation of a free charge at two opposite surfaces of the sensor. The thermal time constant (τtherm) describes the relaxation of the sensor temperature to the ambient temperature. 

The THz detection system consists of a detector and a current preamplifier. It is optimized for application in connection with cw- lasers and a chopper.

The response of a pyroelectric detector can be very fast, but for a reduction of noise the bandwidth of the preamplifier is limited. A further reduction of noise is possible by using detectors with smaller active area. The actual bandwidth depends on the frequency limit and is given in the preamplifier datasheet. Two possibilities for a Signal/Noise improvement for continuously repeated signals are often used:

-Averaging

-Lock in amplification.

 

Calibration:

All detectors are calibrated from PTB Germany at a wavelength of 2.52 THz in combination with a preamplifier. Other conditions on request.

The calibration of the detector is done without any window. Under these conditions any movement of air must be avoided. We deliver the detector with a protection cap having a THz transparent insert. This cap can be used for avoiding any type of disturbance from moving air or fans. You have to check if this cap can be used for your wavelength and have in mind that the calibration is done without this cap. Furthermore it is advisable to tilt the detector a little bit against the optical axes for avoiding reflexions back to the source.

 

 




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