Research Of Third Optical Nonlinearity Measuring Sensitivity Based On Special Gaussian Beam

Since the invention of laser, the interactions between light and matter have beenfurther developed, thus advanced nonlinear optical developmeat. There is no doubt thatthe investigation of nonlinear materials is an important aspect of nonlinear optics.Meanwhile, it is of great significance to research third-order nonlinear refraction of thematerials. In general, Z-scan technique is the most common method to characterize thethird-order nonlinear refraction of the materials. However, it is needed in increasinglyimproving the measuring sensitivity to attain the small third-order nonlinearcoefficients of nonlinear materials. To this end, various new light sources areintroduced. The main purpose in this thesis is to explore how to enhance the measuringsensitivity with the application of several of special Gaussian-type beams.We researched the characterization of optical nonlinearity by using theLaguerre-Gaussian (LG) beams with different orders and the dependence of themeasuring sensitivity on these kinds of beams. Firstly, the spot area distributions of theLG beams with various radial and azimuthal orders are discussed. Subsequently, thetransversal distributions of irradiance of LG beams with different orders in the vicinityof focus are analyzed. Base on Z-scan measuring technique, the effects of LG beamswith different orders on the sensitivity are described by virtue of numerical simulation,as well as the modulation function of phase object is illuminated. Finally, the analyticalexpressions of the low order LG beams to characterize the third-order optical nonlinearrefractive index are deduced. The results show that, compared with the numericalsolution, it is more prominent for the enhancement of the sensitivity and moremeaningful for the practical applications.The dependence of the measurement sensitivity on Hollow Gaussian (HG) beamsare researched. HG beams have distinct intensity distributions in contrast to other lightbeam sources, thus it may incarnate different measurement sensitivities in the Z-scanmeasuring system. The facula areas of the HG beams with different orders are profiled.Also, the intensity distributions of the HG beams with different orders are explored indetail. Furthermore, the investigation of the optical nonlinearity by using HG beamswith different orders is simulated numerically. More importantly, the analyticalformulas of the low-order (e. g. n=1) HG beams to examine the third-ordernonlinearity are derived, and the comparison of the sensitivity for HG beams, LGbeams and Gaussian beam are given.We study the effects of the measurement sensitivity on Bessel Gaussian (BG)beam.It is well known that the central intensity distribution of zero-order BG beam is decided different with high-order BG beams. It is obvious that the spot areas changefor focused BG beams with various orders. Likewise, the sensitivity of the system isexplored by a series of BG beams on the basis of Z-scan technique. By analyzing theeffects of the different orders of the BG beams on the nonlinear absorption andnonlinear refraction curves, which makes a relativity high sensitivity become possible.