Modeling of the 3D spatio-temporal thermal profile of joule-class -based laser amplifiers

Abstract

Thermal profile modification of an active material in a laser amplifier via optical pumping results in a change in the material’s refractive index, and causes thermal expansion and stress, eventually leading to spatial phase aberrations, or even permanent material damage. For this purpose, knowledge of the 3D spatio-temporal thermal profile, which can currently only be retrieved via numerical simulations, is critical for joule-class laser amplifiers to reveal potentially dangerous thermal features within the pumped active materials. In this investigation, a detailed, spatio-temporal numerical simulation was constructed and tested for accuracy against surface thermal measurements of various end-pumped $\text{Yb}^{3+}$ -doped laser-active materials. The measurements and simulations show an excellent agreement and the model was successfully applied to a joule-class $\text{Yb}^{3+}$ -based amplifier currently operating in the POLARIS laser system at the Friedrich-Schiller-University and Helmholtz-Institute Jena in Germany.

Thermal lens analysis in a diode-pumped 10 Hz 100 mJ Yb:YAG amplifier

“…where T is the temperature, S(r, z, t) stands for the heat source term and K c and C p are the thermal conductivity and the heat capacity, respectively. This equation was solved numerically by many groups, using commercial or in-house computational codes [17,[22][23][24][25][26][27] . Isotropic and anisotropic crystals were considered in different pumping schemes and boundary conditions.…”

A model for pumping optimization in edge-pumped disk amplifiers

“…Titanium sapphire lasers are extensively used in ultrashort pulse and extreme intensities applications and are becoming available with increasing repetition rate, up to 10 Hz or higher, and higher average power [8] and are now aiming at a multi kW average power operation [9]. Scaling of laser drivers for the specifications required by future plasma accelerators, however, will require kHz [10] and beyond, and higher efficiency systems with possible novel gain media [11,12]. These systems rely on compact amplifiers with efficient diode pumping and effective heat extraction.…”

A Yb:KGW dual-crystal regenerative amplifier

“…The Yb-ion has a long storage time, which is suitable for adopting a diode laser as a pump. Ytterbium-doped lasers have been developed to exhibit high pulse energy and power [13][14][15][16][17][18][19][20][21][22][23][24][25][26] .…”

“…The Petawatt Optical Laser Amplifier for Radiation Intensive Experiments (POLARIS) project based on the Yb:glass amplifier, which aimed to achieve a petawatt peak power output with a sub-hertz repetition rate, was started in 1999, and has demonstrated 54 J pulse energy [13][14][15] . Meanwhile, the Petawatt Energy Efficient Laser for Optical Plasma Experiments (PENELOPE) project with designed parameters of 150 J/150 fs/1 PW/1 Hz based on the Yb:CaF 2 crystal amplifier is under development [16] .…”