Measurement of the phase fluctuations in a He-Ne Zeeman laser

The measurement of the phase fluctuations caused by spontaneous emission in the oscillation of a He-Ne laser operating at 1.15 μ is reported. The frequency fluctuations in the signal resulting from heterodyning two independent modes in the laser were measured as f²(ν) =(9.6±2)×10^-2 Hz²/Hz for 1.65×10⁷ stored photons per mode and f²(ν) =(2.7±0.3)×10^-1 Hz²/Hz for 6.2×10⁶ stored photons per mode. These values are to be compared with the theoretical minima for these cases, which are calculated to be f²(ν) =5.1×10^-2 Hz²/Hz and f²(ν) =1.4×10^-1 Hz²/Hz, respectively.