Amplitude-squeezed light is light with an intensity noise level below the shot noise level, i.e. below the standard quantum limit. This reduced intensity noise can be obtained only at the expense of increased phase noise. In a phase space representation (see Figure 1), the uncertainty region becomes squeezed in the sense that it becomes narrower in the amplitude direction and wider in the phase direction. This is one form of squeezed states of light.
Amplitude-squeezed light can be generated in different ways. One possibility is to drive a laser diode with a very quiet electric current [4, 7], and typically also to operate it at a very low temperature. In other cases, optical nonlinearities are exploited. For example, amplitude-squeezed light can be generated in a doubly resonant [5, 6] or singly resonant  frequency doubler.
|||D. Walls, “Squeezed states of light”, Nature 306, 141 (1983), doi:10.1038/306141a0|
|||Y. Yamamoto et al., “Amplitude squeezing in a pump-noise-suppressed laser oscillator”, Phys. Rev. A 34 (5), 4025 (1986), doi:10.1103/PhysRevA.34.4025|
|||H. J. Kimble and D. Walls (eds.), Special Issue on squeezed light, J. Opt. Soc. Am B 4 (10) (1987)|
|||S. Machida et al., “Observation of amplitude squeezing in a constant-current-driven semiconductor laser”, Phys. Rev. Lett. 58 (10), 1000 (1987), doi:10.1103/PhysRevLett.58.1000|
|||S. F. Pereira et al., “Generation of squeezed light by intracavity frequency doubling”, Phys. Rev. A 38 (9), 4931 (1988), doi:10.1103/PhysRevA.38.4931|
|||A. Sizmann et al., “Observation of amplitude squeezing of the up-converted mode in second harmonic generation”, Opt. Commun. 80 (2), 138 (1990), doi:10.1016/0030-4018(90)90375-4|
|||W. H. Richardson et al., “Squeezed photon-number noise and sub-Poissonian electrical partition noise in a semiconductor laser”, Phys. Rev. Lett. 66 (22), 2867 (1991), doi:10.1103/PhysRevLett.66.2867|
|||R. Paschotta et al., “Bright squeezed light from a singly-resonant frequency doubler”, Phys. Rev. Lett. 72 (24), 3807 (1994), doi:10.1103/PhysRevLett.72.3807|