Studies On The Mid-infrared Photon Localization In Random Media And The Z-scan Technique

The dissertation, for the first time to our knowledge, establishes a systematic theory of mid-infrared photon localization for three kinds of random media in view of the properties of the mid-infrared materials, explains an interesting phenomenon newly found by the author, studies comprehensively the characteristics of Z-scan transmittance curves for the materials with a large nonlinear absorption in connection with the practical applications of Z-scan technique, researches numerically into the quantitative influence of the aperture size and nonlinear absorption on the profile of the Z-scan transmittance curves. Several creative achievements in respect of science and technique are contained in this dissertation, and summarized as follows:First, the author points out, for the first time to our knowledge, that several mid-infrared materials with large refractive index and low absorption and some transparent matrices in the mid-infrared can be used for the investigations on the mid-infrared photon localization, and breaks the idea that only Germanium (Ge) is the best material for experiments searching the photon localization.Second, in the theory of mid-infrared photon localization in the random media with high-refractive-index and lossless scatterers, which is called the first kind of random media, the author finds out that a negative-value region of the asymmetric scattering factor appears in the vicinity of Mie-resonant scattering peaks when the relative refractive index of the scatterer to the matrix is larger than 3.1, and breaks the conventional physical concept that Mie scattering is predominant in the forward direction. The study indicates that ideal photon localization establishes when the relative refractive index of the scatterer is larger than 3.8 and the concentration of the scatterers is as low as 10% using the Mie scattering theory and the low concentration approximation. In the meanwhile, a new concept called effective scattering cross section saturation is put forward, and the difficulty of perfect localization of mid-infrared radiation is discussed if effective scattering cross section may become saturate.Third, in the theory of mid-infrared photon localization hi the random media with anomalous dispersive dielectric scatterers, which is called the second kind of random media by our group, the author finds numerically out that mid-infrared photon localization hi a sense may establish in this kind of random medium, and the localization frequencies are in the reststrahlen band of the anomalous dispersive scatterer. For the first time, it is found that the influence of the refractive index of the background matrix on the photon localization in the first kind of random medium is very different from the one in the second kind of random medium.Forth, in the theory of mid-infrared photon localization in the random media using metal particles as random scatterers, which is called the third kind of random media, the author finds out that the scattering behavior of every metal in mid-infrared region is similar to each other, and all types of metal particles are low-efficiency scatterers but with high extinction albedo. When the concentration of the metal particles is 10%, 6.6 is the smallest value of the localization parameter, therefore photon localization can not be attained in this kind of random medium although the scattering is also strong and low-absorptive. It is revealed that this system has an intrinsic relationship with the one with high-refractive-index and low-absorptive scatterers, and influence of the refractive index of the matrix on the photon localization in this kind is very different from the other two, that is, the localization parameter be independent of the refractive index of the lossless matrix used commonly.Fifth, when studying closed-aperture Z-scan experimental transmittance curve of the materials with relatively large third-order nonlinear absorption, the author finds out that the well-known peak-valley or valley-peak structure is dependent on the relative value p...