Orientation ofNd3+dipoles in yttrium aluminum garnet: Experiment and model

Abstract

We report an experimental study of the 1.064 µm transition dipoles in neodymium doped yttrium aluminium garnet (Nd-YAG) by measuring the coupling constant between two orthogonal modes of a laser cavity for different cuts of the YAG gain crystal. We propose a theoretical model in which the transition dipoles, slightly elliptic, are oriented along the crystallographic axes. Our experimental measurements show a very good quantitative agreement with this model, and predict a dipole ellipticity between 2% and 3%. This work provides an experimental evidence for the simple description in which transition dipoles and crystallographic axes are collinear in Nd-YAG (with an accuracy better than 1 deg), a point that has been discussed for years. PACS numbers: 42.70.Hj, 42.55.Rz While Nd-YAG is one of the most (if not the most) commonly used solid-state laser crystals, the exact orientation of transition dipoles within it is still, paradoxically, an unresolved problem. This is probably owing to the fact that for most applications it is sufficient to consider the Nd-YAG crystal (usually grown along the 111 crystallographic axis) as isotropic, although it has been known for long [1,2] that Nd 3+ ions in this configuration rather see a D 2 symmetry, with six possible dodecahedral orientations. The influence of crystal symmetry on dipole orientations has been previously studied in saturable absorbers such as Cr-YAG [3,4,5] and Tm-YAG [6,7]. In the first case, it has been clearly established that transition dipoles were aligned with the crystal axes (labeled 100 , 010 and 001 ) [4,5] while in the second case it has been found that they were rather collinear with the 110 , 011 and 101 directions [7]. In the case of Nd-YAG, the answer to this question is still unclear in spite of several previous studies involving in particular dynamical polarization effects in Nd-YAG lasers [8,9,10,11].In this paper, we propose a new approach to probe the orientation of transition dipoles in Nd-YAG, by measuring the coupling constant between two linearly-polarized orthogonal modes of a laser cavity for different cuts of the gain crystal, using a steady-state method similar to the one described in [12]. The measured coupling constant is a dimensionless ratio between cross-saturation and selfsaturation coefficients, which is relatively independent of most laser parameters (pumping rate, birefringence,. . .), hence a good indicator for testing the validity of theoretical models. Our study deals for the most part with the 1064.15 nm emission line, sometimes referred to as R2, between the upper doublet of 4 F 3/2 and the Y3 level of 4 I 11/2 . As a matter of fact, it is known from previous studies [13,14] that the R1 line at 1064.4 nm (between the lower doublet of 4 F 3/2 and the Y2 level of 4 I 11/2 ) has a very small contribution to the overall gain, especially at low pumping rates.The paper is organized as follows. We first propose a theoretical model for calculating the coupling constant between two orthogonal modes of a Nd-YAG laser cavity, on t...

Experimental and theoretical studies of a dual-frequency laser free from anti-phase noise

“…1(a). As expected, for this orientation which is close to = 0° and for which the coupling is expected to be minimum [2], the anti-phase peak becomes so small that it disappears below the noise floor.…”

“…The nonlinear coupling constant in this laser being adjustable, we present how the spectral correlation between the intensity noises of the two orthogonally polarized modes behaves according to the coupling constant. It is has recently been shown that, in Nd:YAG, the emitting dipoles behave as if they were aligned along the crystallographic axes of the matrix [2]. In particular, by choosing a (100)-cut Nd:YAG crystal instead of the more common (111) cut, it was demonstrated that almost complete decoupling of two perpendicularly polarized laser modes could be obtained by aligning them with the (010) and (001) crystallographic axes.…”

Experimental demonstration of a dual-frequency laser free from antiphase noise

“…This is consistent with the fact that the laser behaves as if the emitting dipoles were aligned along the crystallographic axes, like in Ref. [15]. In the interesting situations corresponding to α = −2…”

“…The question now is how should we choose our active medium in order to uncouple the two polarization modes, i. e., in order to minimize cross-saturation effects among our two modes ? It has recently been shown that, in Nd:YAG, the emitting dipoles behave as if they were aligned along the crystallographic axes of the matrix [15]. In particular, by choosing a (100)-cut Nd:YAG crystal instead of the more common (111) cut, it was shown that almost complete decoupling of two perpendicularly polarized modes could be obtained by aligning them with the (010) and (001) crystallographic axes.…”

Numerical Analysis of Laser Diode Longitudinally Pumped Solid‐state Laser Generation Dynamics Using Traveling Wave Model

“…The influence of Cr:YAG crystal orientation on the generation dynamics was studied in [14,15,16] using PLM. Recently analogous generalization of orientation of Nd 3+ dipoles was proposed for Nd:YAG laser medium [29]. In this paper for the simplicity we will use only parallel orientation of polarization with crystal axis f j (θ) = (ĵê) 2 ≡ 1 and will not take into account the same possibility for Nd 3+ dipoles.…”