Further Measurements of Quantum Phase Noise in a He–Ne Laser

Kenneth R. Manes, Anthony E.. Siegman

By heterodyning together the outputs from two stable He-Ne $3.39\ensuremath{-}\ensuremath{\mu}$ lasers, we have measured the power spectrum of the laser field over a wide range of output powers. By combining this high-gain laser transition with a very lossy laser cavity, the quantum phase noise contribution to the laser linewidth could be made dominant at low output powers. The laser spectrum was then found to be nearly Lorentzian with a bandwidth inversely proportional to output power, in good agreement with a modified form of the Schawlow-Townes laser linewidth formula. Weak quantum-noise-excited sidebands were also observed in the beat spectrum of a He-Xe $3.508\ensuremath{-}\ensuremath{\mu}$ laser. These were identified with a resonance in the He-Xe laser amplitude-fluctuation spectrum.

Anthony E.. Siegman, Raymond Arrathoon

Chien Chou, Hui-Kang Teng, Chien-Chung Tsai +1 more

A differential-phase decoder (DPD) together with a polarization common-path optical heterodyne interferometer is set up. Based on this interferometric configuration and a novel balanced-detector scheme, the performance of the quantum-noise-limited differential-phase decoder is demonstrated and analyzed. The minimum-detectable differential phase is on the order of 10(-7) rad/sqrt Hz when a 2.5 mW He-Ne laser is used. Verified experimentally, the DPD is immune to the common-phase noise induced by an electro-optic phase modulator or by thermal disturbance within the interferometer. This signifies that the minimum-detectable differential phase can become 10(-8) rad/sqrt Hz if a 300 mW continuous wave laser is employed instead.

Raymond Arrathoon, Anthony E.. Siegman

Harald Gerhardt, H. Welling, A. Güttner

Salim N. Jabr

The spectrum of the stimulated electronic Raman gain at 650 nm in Ne I, pumped by a 633-nm He-Ne cw laser in the same cavity, is derived. The question of the proper Raman-gain linewidth is addressed. It is shown that the gain has a nearly Doppler-free component whose width is measured as 30 +/- 10 MHz (FWHM) at 6 Torr. This value agrees reasonably well with the residual Doppler broadening but not with collisional broadening rates. A simple calculation is included that shows the quantum-limited frequency uncertainty of the 650-nm laser to be higher by a factor of 1.5 than the frequency uncertainty of the 633-nm laser at equal power.