Lambda quantum-beat laser with another laser cascaded

In this paper we investigate the quantum statistical properties in a cascad e laser system with the lower transition being in a Lambda quantum-beat con figuration It is shown that a type of three-mode squeezing may be generated . The fluctuations of the intensity difference between the sum-mode from th e quantum-beat and the cascade single mode may be reduced below the shot-no ise limit. The best achievable noise reduction is up to 50%. Good squeezing occurs when the sum mode and the cascade single mode have normalized inten sities much larger than unity and the intensity difference is much smaller than the respective intensity.