On the theory of polarization effects in gas lasers

Abstract

Starting from a theory in which laser operation is described as the excitation of the natural-modes of an open-resonator system, the case of a Fabry-Perot resonator with plane-parallel mirrors is investigated. It is shown that, in the case of weakly anisotropic mirrors, the natural-modes can be grouped in pairs, such that each pair corresponds to one scalar longitudinal mode. In that case, laser operation can and will be described in terms of these longitudinal modes, which then possess a vectorial field amplitude, in agreement with the usual formalism.The polarization preference in a single-mode gas laser, operating on a transition between a singlet and a triplet state is investigated, taking into account different relaxation constants for the density matrix. A calculation of the effect on the relaxation constants due to interatomic collisions leads to the conclusion that theory and experiment are in good agreement with each other.Equations describing the time evolution of the polarization parameters of both modes in a two-mode operating gas laser are derived. It is found as a general rule that mode-mode interaction results in modes whose polarizations are mutually orthogonal.An exception to this rule is found in the case in which the single-mode preference is for circular polarization. The influence of two specific mirror anisotropies is discussed.The polarizing behaviour of a single-mode gas laser in the presence of (partly) applied, transverse magnetic fields is extensively dealt with. It appears to be essential to distinguish between the case in which the magnetic field is applied only to a fraction of the active medium and the case in which the magnetic field is uniform in the entire medium. This distinction is shown to lead to a satisfactory theoretical description of a certain class of experiments. In the case of two other experiments, good agreement with the theory is obtained, by assuming the presence of mirror anisotropies of acceptable kind and size. Finally, the influence of small anisotropies on the degree of polarization of a single-mode gas laser is theoretically investigated, when the latter is polarized by means of a transverse magnetic field. CONTENTS

Polarization dynamics of longitudinally monomode bipolarized microchip solid-state lasers

“…Since all these effects are small, the lasers with Fabry-Perot cavities are quasi-isotropic and orthogonally polarized modes with the same longitudinal index have equal lasing thresholds and similar lasing frequencies, and under these conditions unstable lasing is possible [5,11]. Similar problems have already been considered in a variety of situations, mostly for He-Ne [14][15][16][17][18][19][20] and then YAG [21,22] and diode [23,24] lasers and more recently Vertical Cavity Surface Emitting Lasers (VCSEL) [12]. As far as microchip lasers are concerned, there have been few systematic studies of their polarization dynamics.…”

Phase Correlations and Polarization Characteristics of Dye-Solution Laser Radiation

“…Precisely such a quantity is measured experimentally in the majority of cases [1,2,5,6,14]. In selecting an axis along the pumping radiation polarization vector, the definition given by (7) coincides with the technique by which we find the polarization degree in terms of the Stokesian parameters P = S 1 ⁄ S 0 , and it is reduced to the value of P 0 if radiation has only linearly polarized components.…”

<title>Nonlinear dynamics of lasers considering the vector character of the emitted field</title>

“…Often it is convenient to choose a basic set of operators in accordance with the transformation properties under three-dimensional rotations7 15. 16 To define the response of the active medium one should take into account the presence of 72 polarization modes and magiietic field. Our purpose in this work is to show the influence of the decay rate Yf on laser dynamics rather then a detail investigation of the behavior of electromagnetic field emitted by a particular laser.…”