Coherent nonlinear optical spectroscopy using photon-number squeezed light

Summary form only given. The photon-number squeezed light generated by an injection-locked quantum-well laser is used as the probe field in a nondegenerate (CW) differential-transmission (pump-probe) spectroscopy measurement of the Urbach tail and exciton resonances in a GaAs multiple quantum-well sample. Because of the nonclassical intensity fluctuations of the probe field, the measurement sensitivity in this experiment is 1.0 dB (20%) below the semiclassical shot noise limit (SNL). This measured quantum noise level is nearly one-third (below the SNL) of the fundamental nonclassical sensitivity limit (5.2 dB below the SNL) set by vacuum field fluctuations that enter through background losses (30%) in the sample.