Theoretical and experimental investigation of polarization spectroscopy

Abstract

The physics of polarization spectroscopy has been studied theoretically and experimentally. Theoretically, the dependence of saturated polarization spectroscopy signal has been studied using the direct numerical integration code (DNI) of the time-dependent density matrix equations. Understanding the saturation behavior of polarization spectroscopy signals is a vital task for the development of this method as a potential diagnostics method. However, the underlying equations for this method are complicated. A model has been developed in this work to describe the curve shape of polarization spectroscopy power-dependence scans in both the saturated and the unsaturated regimes. The results have been compared to experimental results performed in Lund Institute, Sweden. Polarization spectroscopy saturation curves in the co-propagating beam geometry from the excitation of OH A ²[]⁺-X²[] (0,0) at the Q₂(8) line for sub-atmospheric pressures have been fitted to the proposed model. The model proposed in this work provides excellent fits to polarization spectroscopy saturation curves for absorption lines dominated by homogeneous broadening and for narrow-bandwidth excitation sources. The model does not provide an adequate description for inhomogeneous broadened lines when compared to experimental data. For this case an empirical equation is proposed. The proposed model offers a starting point for simplification of the underlying polarization spectroscopy theory and provides new opportunities for further development of this theory. Experimentally, the effect of pump beam polarization is investigated in a co-propagating geometry. The behavior of the polarization spectroscopy signal for linear and circular pump polarization for different transitions and different levels of saturation is studied.