A terahertz system using semi-large emitters: noise and performance characteristics

We have built a relatively simple, highly efficient, terahertz (THz) emission and detection system centred around a 15 fs Ti:sapphire laser. In the system, 200 mW of laser power is focused on a 120 microm diameter spot between two silverpaint electrodes on the surface of a semi-insulating GaAs crystal, kept at a temperature near 300 K, biased with a 50 kHz, +/- 400 V square wave. Using rapid delay scanning and lock-in detection at 50 kHz, we obtain probe laser quantum-noise limited signals using a standard electro-optic detection scheme with a 1 mm thick (110) oriented ZnTe crystal. The maximum THz-induced differential signal that we observe is deltaP/P = 7 x 10(-3), corresponding to a THz peak amplitude of 95 V cm(-1). The THz average power was measured to be about 40 microW, to our knowledge the highest power reported so far generated with Ti:sapphire oscillators as a pump source. The system uses off-the-shelf electronics and requires no microfabrication techniques.