Characteristics of an intracavity method for reception of infrared optical signals in the atmosphere and increase of its noise immunity

An experimental comparison was made of intracavity and heterodyne methods of reception of weak optical signals. The efficiencies of the two reception methods were compared over a 200-m atmospheric path at the optical signal wavelength of 10.6 μ. The efficiency (signal/noise ratio) was the same for both reception methods, but the sensitivity was higher in the intracavity case. It was also found that signal fading, observed in the intracavity reception case due to fluctuations of the optical path length, could be readily compensated in the case of phase modulation by ensuring a sufficiently wide reception pass band.