Transmittivity measurements by means of squeezed vacuum light
  A method for measuring the transmittivity of optical samples by using squeezed--vacuum radiation is illustrated. A squeezed vacuum field generated by a below--threshold optical parametric oscillator is propagated through a nondispersive medium and detected by a homodyne apparatus. The variance of the detected quadrature is used for measuring the transmittivity. With this method it is drastically reduced the number of photons passing through the sample during the measurement interval. The results of some tests are reported. 
V. D'Auria, C. de Lisio, A. Porzio, S. Solimeno, M. G. A. Paris