Modelling and measurement of thermal stress-induced depolarisation in high energy, high repetition rate diode-pumped Yb:YAG lasers

Abstract

In this paper, we present a model to predict thermal stress-induced birefringence in high energy, high repetition rate diode-pumped Yb:YAG lasers. The model calculates thermal depolarisation as a function of gain medium geometry, pump power, cooling parameters, and input polarisation state. We show that model predictions are in good agreement with experimental observations carried out on a DiPOLE 100 J, 10 Hz laser amplifier. We show that single-pass depolarisation strongly depends on input polarisation state and pumping parameters. In the absence of any depolarisation compensation scheme, depolarisation varies over a range between 5% and 40%. The strong dependence of thermal stress-induced depolarisation on input polarisation indicates that, in the case of multipass amplifiers, the use of waveplates after every pass can reduce depolarisation losses significantly. We expect that this study will assist in the design and optimisation of Yb:YAG lasers.

High‐Power Laser Systems

“…[68,164,[167][168][169][170] For the suppression of ASE, the primary purpose is to limit the oscillation of SE. The main methods currently used are anti-ASE cap, [155,156,169,[171][172][173] absorber cladding, [90,[174][175][176][177][178][179][180][181][182][183][184] beveling angle, [67,69,163] and nonlinear gradient doping. [185][186][187][188] The abovementioned DiPOLE laser system applied an absorber cladding.…”

Thermal-stress-induced birefringence management of complex laser systems by means of polarimetry

“…Another deleterious effect of the thermally induced polarization change is the degradation of the beam profile when the beam passes through any diattenuator, typically linear polarizer. It has been shown recently, that the losses can be substantially mitigated by the optimization of input linear or circular polarization state 5 , by the proper design of the laser amplifiers and their cooling 6 , 7 , by the mutual compensation of thermally induced birefringence realized between multiple passes through the same heated optical elements 8 – 10 , by proper orientation of the input linear polarization in square-shaped amplifiers 11 , or by the suitable crystal orientation of the amplifiers 12 . Even so, the methods based on the results referenced above are usually not sufficient to keep the power losses at acceptable values allowing efficient laser system operation.…”

Numerical Simulation of Thermo-Optic Effects in an Nd: Glass Slab with Low Thermally Induced Wavefront Distortion

“…Actually, the size of the pump area is usually smaller than the gain medium when considering the coupling efficiency and experimental operation difficulty. Some numerical analyses and experimental studies for already-existing configurations have been developed [26], and the preliminary optimization of cladding geometry for reducing thermal stress-induced depolarization in high-energy, high-repetition-rate, diode-pumped Yb: YAG lasers is also included in the literature [27]. The results show that the design for the cladding is effective to reduce thermal depolarization.…”