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Journal of Modern Optics

Ultra-high-frequency Beats Produced by Laser Modes at the Single-photon Level

P. Hariharan, Ninita H. Brown, Ichiro Fujima, Barry C. Sanders

Published Mar 1, 1995• 4 citations
Publisher

Abstract

A helium-neon laser operating in two or more axial modes generates beat signals in the ultra-high frequency (UHF) range at a photodetector. An analysis of earlier data obtained at very low light levels shows that such UHF beats can be observed even when the mean time interval between the arrival of successive photons at the photodetector is greater than the period of the beat. This is because the beat is actually a sinusoidal modulation of a random carrier.

DOI
10.1080/09500349514550521

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A helium-neon laser operating in two or more axial modes generates beat signals in the ultra-high frequency (UHF) range at a photodetector. An analysis of earlier data obtained at very low light levels shows that such UHF beats can be observed even when the mean time interval between the arrival of successive photons at the photodetector is greater than the period of the beat. This is because the beat is actually a sinusoidal modulation of a random carrier.
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A helium-neon laser operating in three or more axial modes can generate, at a photo detector with a nonlinear response to intensity, beat signals with frequencies corresponding to the second differences between the frequencies of these modes. This paper presents a quantum-field theoretical treatment of the formation of such low-frequency beats, as well as experimental data demonstrating that interference effects corresponding to the production of such beats can be observed even at light levels at which the probability of at least one photon from each of the three modes being present simultaneously in the optical path is negligible.
Optical heterodyning has been observed at the single-photon level by recording the sinusoidal variation in the probability for detection of a photoelectron from a photomultiplier tube illuminated with a FM laser and a local oscillator laser. The single-photon character of the heterodyne process was demonstrated by observation of beat signals at total power levels down to6 \times 10^{-15}W where the spacing between photons emitted from the source laser was\sim40 000times greater than their transit time through the apparatus.