INVESTIGATION OF CORRELATION EFFECTS IN NONLINEAR OPTICS (QUANTUM OPTICS, THREE-WAVE MIXING, PARAMETRIC DOWN CONVERSION, PHOTON STATISTICS)

This thesis deals with intensity correlation measurement methods as they apply to the study of light generated by a parametric downconversion process. The correlation properties of light can be used to distinguish between quantum mechanical light and classical light, where quantum mechanical light is electromagnetic radiation that can be accurately described only by a theory that quantizes the field. Spontaneous parametric downconversion produces quantum mechanical light, and we investigate some of its properties.;The normalized cross-correlation functions for spontaneous downconversion are inversely dependent on intensity, but the normalized auto-correlations are independent of intensity. Measurements of the magnitude of the cross-correlations for several different pump beam intensities confirm this relationship. One of the inequalities imposed by classical theory relates the magnitude of the auto-correlations to the magnitude of the cross-correlations. Because of the inverse intensity dependence, this inequality is violated, thereby showing the quantum mechanical nature of the downconverted light.;As an application of the large cross-correlations in downconversion, we apply the process to an optical communication channel which transmits information via coincidences between two light beams. Because of the strong discrimination against background provided by this technique, the channel can operate with large amounts of background light. A demonstration experiment of this communication channel is described. A signal transmitted by intensity modulation of the downconverted light is received perfectly by a coincidence counter, but is invisible to a photon counter.;Also, a new correlator has been designed and constructed to measure intensity correlation functions. It has been used to measure the correlation properties of a standing-wave, single-mode, inhomogeneously-broadened He:Ne laser as a function of detuning. Results show that detuning of the laser alters the correlation properties in a way that can not be accounted for by merely a change in the pump parameter. These effects should therefore be taken into account when measurements of the statistical properties of the light are made whenever the laser intensity is controlled by detuning.;A unique aspect of downconverted light is that pairs of photons are emitted in an interval that can be made smaller than the resolving time of any photon counting apparatus. Our experiments indicate that the interval is not affected by the bandwidth of the pump laser, nor by the length of the crystal. It is apparently determined only by the bandwidth of the detection apparatus, which in our experiment implies that the photons are produced in less than 1 psec, which is much shorter than the 100 psec resolution of our detection apparatus.