The theory of the hyper-Raman effect in molecular gases is reviewed. In order to calculate relative intensities of vibration-rotation lines in hyper-Raman spectra, line strengths are introduced and these are calculated using the method of irreducible spherical tensors. It transpires that the hyper-Raman effect caused by scattering of a quasi-monochromatic light beam can be fully described by five independent line strength expressions. Rotational and vibrational selection rules as well as depolarization ratios for linearly, circularly and naturally polarized incident light are derived and discussed. The angular dependence of the scattered intensity is also given in the form of polar diagrams. To some extent the paper presented here parallels that published by Placzek and Tellers4 in 1933 on the rotational structure of vibrational bands in conventional Raman spectra caused by a spontaneous two-photon scattering process.
The particle picture presented by the author in the paper "A particle picture of the optical resonator" [K. Altmann, ASSL 2014 Conference Paper ATu2A.29], which shows that the probability density of a photon propagating with a Gaussian wave can be computed by the use of a Schrödinger equation, is generalized to the case of a wave with arbitrary shape of the phase front. Based on a consideration of the changing propagation direction of the relativistic mass density propagating with the electromagnetic wave, a transverse force acting on the photon is derived. The expression obtained for this force makes it possible to show that the photon moves within a transverse potential that in combination with a Schrödinger equation allows to describe the transverse quantum mechanical motion of the photon by the use of matter wave theory, even though the photon has no rest mass. The obtained results are verified for the plane, the spherical, and the Gaussian wave. Additional verification could be provided also by the fact that the mathematical equation describing the Guoy phase shift could be derived from this particle picture in full agreement with wave optics. One more verification could be obtained by the fact that within the range of the validity of paraxial wave optics, Snell's law could also be derived from this particle picture. Numerical validation of the obtained results for the case of the general wave is under development.
We derive a new model and simulation technique called "Dynamic Multimode Analysis (DMA)" to simulate the 3-dimensional dynamic behavior of a laser. A Gaussian mode analysis is used to obtain resonator eigenmodes taking into account thermal aberrations. These modes are coupled by a set of rate equations to describe the dynamic behavior of the individual modes for cw and Q-switched lasers. Our approach analyzes mode competition and provides a detailed description of the laser beam in terms of output power, beam quality factor M(2), and pulse shape. Comparison of experimental data with our simulation results provides new insight into the effect of mode competition and the operation of Q-switched lasers.
A new method for computing eigenmodes of a laser resonator by the use of finite element analysis is presented. For this purpose, the scalar wave equation (delta + k2)E(x, y, z) = 0 is transformed into a solvable three-dimensional eigenvalue problem by the separation of the propagation factor exp(-ikz) from the phasor amplitude E(x, y, z) of the time-harmonic electrical field. For standing wave resonators, the beam inside the cavity is represented by a two-wave ansatz. For cavities with parabolic optical elements, the new approach has successfully been verified by the use of the Gaussian mode algorithm. For a diode-pumped solid-state laser with a thermally lensing crystal inside the cavity, the expected deviation between Gaussian approximation and numerical solution could be demonstrated clearly.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.