Doctoral Thesis / Dissertation from the year 2022 in the subject Physics - Other, grade: PhD, , language: English, abstract: This work presents a Thermal Lens spectrometry model based on Laguerre–Gaussian excitation of sample. We calculated refractive index and temperature gradient profiles and compare with the results obtained by fundamental Gaussian mode. Our results show remarkable change of the refractive index around propagation axis and an increase along radial direction that can be crucial for increasing the sensitivity of the technique. Furthermore a modified general dual beam Z-scan model and its exact solution have been presented. The comparison with the previous model of Z-scan has been briefly discussed. The dependence of pinhole size and sample to detector distance in Thermal Lense signal for Z-scan is critical, which was ignored in previous models. The experimental validity of the presented model for thermal diffusivity and absorption coefficient of distilled water is also part of our research work.