Investigation of spectral characteristics and coherence properties of optical systems in the presence of fluctuating drives

Abstract

The theoretical part of the thesis has been centered on the study of newlinephase and intensity fluctuations of electromagnetic fields and the resulting newlinespectral profiles for different systems of interest. We have chosen a gas newlinelaser as one of the systems under study in this thesis. The existing theories newlineof gas lasers did not take into account the effect of atomic collisions in 8 newlinemicroscopic way and the spectral profile used to be written as a Voigt profile newline(8 convolution of the Gaussian velocity distribution and a Lorentzian newlineassociated with each velocity subclass of atoms). This description is not very newlineaccurate and we have attempted to provide a microscopic theory of the newlinephenomenon. Unlike some other recent studies of collisional effects, viz., in newlinenonlinear mixing signal line-shapes, in our case, the system is closed (selfconsistent), newlineand thus the approach to the problem is different. The study of newlinethe nonlinear response of an atomic ensemble as 8 function of noise properties newlineof the fields has recently acquired much importance in the light of its newlinepotential application in ultrafast (sub-picosecond) life-time measurements. newlineThe second class of systems studied in this thesis use the nonlinear optical newlineprocess of four-wave mixing (FWM). The dependence of the nonlinear signal on newlinethe noise properties of the pump fields is studied numerically. This newlinepre~1llY study is directed towards finding a nonperturbative solution to newlinethe problem so that the case of FWM with two strong pump beams can be treated newlinesatisfactorily. The experimental work involves the study of characteristics of newlinethe signal generated in the degenerate FWM process in a resonant material of newlinevii newlineviii newlineltiye-doped boric acid glass. These materials are useful for basic studies as newlinethey are easy to prepare, and have a high resonant third-order susceptibility newlinearising from a long upper-state life-time of the dye. It is this long lifetime newlineon the other hand that makes these «slow· samples not technologicaUy newlineuseful.