Analysis of solid-state saturable absorbers with temperature dependent absorption cross-sections

• Published in: Optical materials Vol. 31; no. 4; pp. 598 - 603
• Main Authors: Sennaroglu, Alphan, Coskun, Ahmet Faruk, Demirbas, Umit
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier B.V 01.02.2009; Elsevier
• Subjects: Exact sciences and technology; Fundamental areas of phenomenology (including applications); Nonlinear optical crystals; Optical materials; Optics; Physics; Temperature dependence; Saturable absorbers; Non linear material; Energy levels; Refractive index; Doped materials; Forsterite; Chromium additions; Radiative lifetimes; Excited state absorption; Temperature effects; Transition elements; Differential equations; Rate equation; Optical materials; Magnesium Silicates
• ISSN: 0925-3467; 1873-1252
• DOI: 10.1016/j.optmat.2008.06.012

We describe a comprehensive model which can be used in the continuous-wave (cw) analysis of solid-state transition metal-doped saturable absorbers, which, in addition to the commonly observed temperature dependence of the refractive index and fluorescence lifetime, also exhibit a temperature dependent absorption cross-section. By using a rate equation analysis, two coupled differential equations are derived for the beam power and the q-parameter of the pump beam. To test the validity of the model, we analyzed the cw and pulsed saturation data taken with Cr 4+:forsterite crystals which are subject to these three thermal effects at 1064 nm. Data for electric field parallel to the crystal b-axis ( E ‖ b ) and c-axis ( E ‖ c ) were analyzed. Results indicate that when thermal loading effects are taken into account, better agreement is obtained between the cross-section results of the cw and pulsed saturation data. In particular, inclusion of thermal effects reduced the fractional deviation between the average cw and pulsed cross-section values from 23% to 2% and from 34% to 29% for the E ‖ c and E ‖ b cases, respectively. In the E ‖ b case, the average absorption cross-section and the normalized strength of excited-state absorption were further determined to be 5.98 × 10 −19 cm 2 and 0.45, respectively. The presented model can be readily extended to analyze other thermal effects or other media with different energy-level schemes.