Design and development of detector signal conditioning electronics for SST-1 Thomson scattering system

An IR enhanced thermoelectrically cooled Si-avalanche photodiode (Si-APD) module is used for detection of scattered photons from plasma electrons. Present design of signal conditioning electronics for the APD has fast (50 MHz) and slow (500 kHz) channels to measure scattered and plasma background light, respectively. We report design analysis for different stages and their performance. The performance of fast channel is analyzed for two different group delays, speed, linearity, and its cross-talk with slow channel. Temperature dependence of APD's responsivity is studied in the wavelength range of 900-1060 nm. A minimum detection of ∼25 photoelectrons (with S/N=1) in the range of 5 to 25 deg. C is achieved at an APD gain of 75 in the present design.