Dependence of polarisation of radiation of a linear Nd:YAG laser on the pump radiation polarisation

Abstract

The aim of this paper is to investigate the relative influence of geometrical and order parameters on diffuse -ED intensities. In most diffuse LEED studies relative to molecules adsorbed at single crystal surfaces, there are probably several chemisorption sites or several adsorbedspecies. Forthisreason, thissituation isexamined indetail here. Theelasticdiffuse LEED intensity from a single crystal surface Pt(ll1) partially covered with CO molecules is calculated for different valuesof the parameters which characterize the adsorbatelsubstrate model. These parameters are separated into: geometrical parameters related to the local arrangement of atoms near chemisorption sites, and order parameters related to the statistical distribution of the occupied chemisorption sites. In the present case, the geometrical parameters are the C-Pt and the C-0 bond lengths and the location in the 2D unit cell of the surface lattice (bridge and top sites). The order parameters are the site occupancy pair correlation functions or the quantities which determine them: surface coverage. surface temperature, pair interaction potential between adsorbates. etc. Even in thecaseof ashortrangeorder, thesensitivitiesofdiffuseintensitiesto bothkindsofparametersarefoundvery similar. On the other hand, in thesituation where several kinds ofchemisorption sitesexist, the diffuse LEED intensity is not the product of a form factor and a structure factor. So the use ofthe Yfunctionmethod,which avoidsthestructure factor determination, is not possible.Thus, a determination of the statistical distribution of adsorbates at the substrate surface cannot be circumvented,

Polarization properties of laser-diode-pumped micro-grained Nd:YAG ceramic lasers

“…A similar bistability of the left and right quasi-circularly polarized laser fields oscillating at slightly different optical frequencies, with a phase difference of π, has been predicted for a quasi-isotropic longitudinally monomode Nd:YAG single-crystalline laser [9]. The observed polarization property of the Nd:YAG micro-grained ceramic laser in the isotropic laser cavity is similar to that of the Nd:YAG single-crystalline laser [6]. This result suggests that the anisotropy of amplification is caused by the angular distribution of population inversions resulting from the saturation of the population inversions by the polarized radiation rather than the local electric field of compensating charges of Nd ions in the local D2 (orthorhombic) symmetry [1,2] because crystal axes are randomly distributed in micro-grained ceramic samples.…”

“…As for polarization of radiations, two lasers exhibited different properties. In the external cavity laser, linearly-polarized single-frequency oscillations whose direction coincided with that of pump polarization were obtained similar to the Nd:YAG single-crystalline laser in the isotropic resonator [6]. Pump-dependent oscillation spectra are depicted in the inset of Fig.…”

“…This result suggests that the anisotropy of amplification is caused by the angular distribution of population inversions resulting from the saturation of the population inversions by the polarized radiation rather than the local electric field of compensating charges of Nd ions in the local D2 (orthorhombic) symmetry [1,2] because crystal axes are randomly distributed in micro-grained ceramic samples. The angular inhomogeneity depends on the orientation of the polarization plane of laser radiation from that of pump radiation and the polarization state is considered to be almost completely determined by polarization of pump radiation for the isotropic cavity [6,12].…”

“…Different polarization properties have been reported experimentally in LD-pumped microchip Nd:YAG single crystalline lasers. These include linear polarization oscillations along the polarization direction of the LD pump light in the case of an isotropic laser cavity [6] and orthogonal linear polarization (i.e., dual-polarization) oscillations in the case of quasi-anisotropic laser cavity [3,7]. As for Nd:YAG ceramic lasers that consist of small single-crystalline grains with distributed crystal axes, on the other hand, polarization properties have been demonstrated to depend on the average grain size with respect to the lasing beam diameters [7].…”

Polarization Properties of Laser-Diode-Pumped Microchip Nd:YAG Ceramic Lasers

“…Note that linearly polarized emissions predominate and DPO appears with increasing pump power in lowpower LD end-pumped Nd-doped fiber lasers in the absence of thermal birefringence (Bielawski, 1992). Such a lasing polarization property has been well explained theoretically in terms of the polarization-selective gain, namely pumping anisotropy, in which the polarization-selective gain occurs because both the interactions between the polarized pump and the ions, and that between the ion and the fields along each direction of polarization depend on the local field experienced by the ion (Bielawski, 1992;Kravtsov et al, 2004). The observed polarization properties, which follow the pump polarization, in micro-grained ceramic lasers could be interpreted in terms of the pumping anisotropy in isotropic lasing media.…”