Transformation of Photon Statistics in Second Harmonic Generation: AN Experimental Investigation

In this dissertation, we have studied the photon statistics of second harmonic generation (SHG). We have experimentally investigated the transformation of photon statistics of a single mode laser near threshold in SHG. Two -photon bunching and correlation effects in second harmonic generation with a single mode laser near threshold were directly observed. As the operating point of the laser changes from below to above threshold, the statistical properties of the laser change from thermal to coherent. Our experimental results on the efficiency of SHG clearly show that photons in thermal light are more bunched than photons in coherent light. Therefore, thermal light is more efficient in SHG than coherent light for the same mean intensity. SHG with multimode laser beams was also studied. The number of modes was systematically varied from 1 to 7 and the dependence of the efficiency of SHG on the number of modes in the fundamental beam was studied. Experimental results clearly demonstrate the increasing degree of photon bunching in the fundamental beam as the number of modes increases. We also present a new method for determining higher order moments and higher order correlation functions of an optical field using SHG. This method was used to study three- and four photon bunching in a single mode laser. Higher order intensity correlation functions and correlation times for photon bunching were measured. Photon counting statistics of second harmonic photons generated by the single mode laser operating near threshold were investigated by means of photoelectric counting measurements. Second harmonic photons display superthermal fluctuations below threshold where pump statistics are thermal. Above threshold, as the pump field becomes coherent, second harmonic photons exhibit Poisson statistics. These measurements, interpreted as two-photon statistics of the fundamental beam, provide the first experimental evidence for the dependence of the fluctuation properties of a light beam on the process of detection.