Circuit to Use a Photon Correlator as a Fast Analog Correlator

A simple voltage-to-frequency converter has been made which has a 1-µs sampling time, generates a 25-MHz TTL pulse corresponding to a 10-V analog input, and responds up to a high-cutoff-frequency of 570 kHz. By processing an analog signal with it, a photon correlator has been used as a high-speed analog correlator. Observations of the analog correlation functions of sinusoidal signals and the Johson noise are given.