title: Amplification characteristics of a cryogenic Yb³⁺:YAG total-reflection active-mirror laser.
abstract: We have studied the amplification characteristics of a cryogenically cooled Yb³⁺:YAG total-reflection active-mirror (TRAM) ceramic laser including wavefront distortion, birefringence loss, small signal gain (SSG), and temperature rise for developing high-performance master oscillator power amplifier (MOPA) systems. A 0.6 mm thick Yb³⁺:YAG ceramic sample was used, and maximum pump intensity ~10  kW/cm² was reached. The transmitted wavefront was measured by using a Shack-Hartmann wavefront sensor, and we evaluated the thermal lens focal length and Strehl ratio for different pump conditions. We have also observed a butterfly-like leakage profile of thermally induced birefringence loss at the maximum pump intensity. From SSG measurements, we obtained moderate laser gain of G=3 for one bounce with a near aberration-free wavefront. Gain calculations, which included also temperature dependence of the emission cross section and reabsorption of Yb³⁺:YAG, were in good agreement with the experiments. These experimental results will be useful as benchmark data for numerical simulations of temperature distribution in TRAM and for designing multikilowatt-class high-performance MOPA systems.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Furuse
authors.forename: Toshimitsu
authors.initials: T
authors.lastname: Sakurai
authors.forename: Haik
authors.initials: H
authors.lastname: Chosrowjan
authors.forename: Junji
authors.initials: J
authors.lastname: Kawanaka
authors.forename: Noriaki
authors.initials: N
authors.lastname: Miyanaga
authors.forename: Masayuki
authors.initials: M
authors.lastname: Fujita
authors.forename: Shinya
authors.initials: S
authors.lastname: Ishii
authors.forename: Yasukazu
authors.initials: Y
authors.lastname: Izawa