Abstract
In order to avoid the influence of shot noise due to the powerful local oscillator (LO) in traditional heterodyne detection, the signal-to-noise ratio (SNR) was analyzed for laser heterodyne detection with a weak LO at the photon level. First, the expression for the SNR with a pulsed laser was applied to the condition of partial CW and weak LO laser heterodyne detection, the spectrum of the heterodyne signal with the center frequency 212 kHz was obtained, and the theoretical value of the SNR found to be in agreement with experiment. Second, the techniques of data segment fractionizing and power spectral sensity (PSD) averaging were used to investigate the SNR. The results show that the volume of the data required can be decreased by a factor of 10 compared with the traditional PSD averaging, the data resource is fully used while signal processing, and the signal-to-noise improved ratio (SNIR) nearly obeys the rule (m is the averaging time) under a small quantity of data segments. Finally, the limiting factors about the SNIR during the PSD averaging have been determined so that good use can be made of the data.
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