Abstract

We present new results for the quantum noise reduction owing to the mth harmonic generation (m = ½, 2, 3) in a laser. Study of such a source of light with noise beyond the quantum limit is now in progress.^1,2 We consider this problem for both the laser with conventional random pumping and the laser with reduced pump noise, i.e., the sub-Poissonian laser. In the case of the laser with a conventional pump, the noise in the mth harmonic can be suppressed by m times as compared to the shot noise limit. For the sub-Poissonian laser, perfect noise reduction can be achieved in any harmonic mode. Cross correlations between the fundamental mode and the harmonic mode lead to the quantum noise interference effect, which manifests itself in the noise of the total photon flux from the laser. The system with two nonlinear crystals inside the laser cavity can serve as a source of two perfectly squeezed modes with divisible frequencies. The first crystal is driven by the external field of frequency 2ω. This field is downconverted in the crystal to the frequency ω, which is the frequency of lasing. In the second crystal the lasing field is again downconverted to the frequency ω/2. The lasing mode m and the subharmonic mode ω/2 from such a laser can be perfectly squeezed; that means complete quantumnoise reduction of these two modes if mixing with local oscillators of phase shifts π/2 is used.

© 1990 Optical Society of America