Optical superheterodyne spectrum analyzer with a triggered photon counting method

A photocounting spectroscopic method with the advantage of optical superheterodyne techniques is discussed, and experimental results are presented. This method can give the spectrum due to only the thermal field without any data processing even when the local oscillator is weak. In the present optical superheterodyne system, the triggered photon counting rate exhibits a Fourier spectrum of incident thermal field. The homodyne component is involved in a dc level, and it is distinguished from the heterodyne component. Therefore, it is postulated that only the heterodyne component can be detected, even when the intensity of the local oscillator is not great. When non-Gaussian light is mixed with thermal light and the second-order correlation function is explained by the sum of Gaussian and non-Gaussian terms such as concentration fluctuations, only the thermal light can be measured