Phase Correlations and Polarization Characteristics of Dye-Solution Laser Radiation

Abstract

The influence of phase correlations of components on the energy and polarization parameters of output radiation have been calculated within the framework of the formalism of polarization components. It is shown that these correlations have a marked effect only on the energy characteristics. At the same time, an analysis of the polarization characteristics of a probe wave provides rich information for the analysis of the phase-polarization structure of radiation. An analysis of experimental data allows the inference that the correlation of components is relatively weak even for lasers with a high-Q resonator and at a high excess of threshold values. Introduction.In a series of works [1-4], a new generalized approach to the description of formation of polarized radiation in a dye-solution laser was suggested and developed. It is based on the representation of laser radiation in the form of a superposition of polarized components, the polarization vectors of which encompass the entire set of possible polarization states. Based on the method of polarization components, a number of characteristic features in the dependences of the energy, polarization, and statistical characteristics of a dye-solution laser near the lasing threshold have been explained.The calculations [2-4] were based on the assumption of statistical independence of the polarization components, which is quite explicable from the viewpoint of the physical mechanism underlying the start-up of the process of lasing as a successive strengthening of spontaneous emission. It was assumed that the statistical independence of polarization components may be considered as the first approximation, and in the process of lasing build-up the phase correlation of polarization components may arise (spontaneously or as a result of any induced processes) and successively become stronger because of the presence of strong feedbacks. Strictly speaking, the method of polarization modes [5, 6], which rather adequately describes the characteristic features of the emission of polarized dye-solution laser radiation upon substantial excess over the threshold, is based on the assumption that the state of radiation polarization can generally be elliptic, i.e., the phase of a light wave is quite a definite one. In other words, the polarization modes are "pure" orthogonal states, the superposition of which completely describes polarized laser radiation.From the viewpoint of the adequacy of this approach, of certain interest are the results of [7,8], in which a change in the polarization of a scanning wave passing through the couvette of a dye-solution laser pumped by a highpower linearly polarized radiation was investigated. Actually, these experiments to a certain extent repeat the classical scheme of nonlinear polarization spectroscopy [9], and, to interpret the results, the basic elements of the corresponding theory of [10] were used: on excitation by a linearly polarized radiation, an orientational anisotropy is created in a molecular medium, and a scanning linearly polarized w...

Polarization component method for calculation of the multiple-frequency lasing regime

“…In a series of papers [1][2][3][4][5], a new generalized approach was proposed and developed to describing the formation of polarized radiation in laser systems. It was based on the idea of laser emission as the superposition of polarization components whose polarization vectors span the entire set of possible polarized states.…”

“…It was based on the idea of laser emission as the superposition of polarization components whose polarization vectors span the entire set of possible polarized states. Based on the polarization component method, it was possible to explain a number of characteristic features on the energy and polarization characteristics of a liquid dye laser near the lasing threshold [1,2,5], and also to derive analytical relationships to describe their statistical properties [4]. In particular, distribution functions of the degree of polarization of the output radiation were found [4], and their variation as a function of the laser system parameters was studied.…”

“…Averaging over fast fluctuations leads to the fact that the resultant broadening of the spectral components is considerably less than the spectral interval ⏐ω χ − ω χ′ ⏐ between them (which, strictly speaking, also requires condition (1)) even in the case when spectral broadening of individual polarization components is comparable to or even greater than this value (the possibility of such a situation was indicated in [3]). At the same time, the assumption of statistical independence of the polarization components is satisfied over quite a broad range [3][4][5]. So the expansion (2) may be independently satisfied for any spectral component, while Eq.…”

“…(3) for the case of an R6G liquid dye laser, which made it possible to compare with the results for the single-frequency model [2][3][4][5]. The gain and the luminescent term were calculated within a 4-level model, and it was assumed that the characteristic time for a change in the fields was much longer than the time to establish an equilibrium distribution over the levels in the medium.…”

“…In the calculations, gain saturation effects were taken into account both for the gain and for the luminescent term; the loss coefficient was considered as orientationally isotropic and spectrally homogeneous. The basic numerical data were taken for a standard reference solution of rhodamine 6G as in [2][3][4][5].…”