Detailed investigation of absorption, emission and gain in Yb:YLF in the 78–300 K range
Umıt Demırbas, Jelto Thesinga, Martin Kellert, Franz X. Kärtner, Mikhail Pergament
Abstract
We present spectroscopic measurements focusing on a detailed investigation oftemperature dependence of absorption, emission and gain in the uniaxial Yb:YLF laser gainmedium. Measurements are carried out in the 78–300 K range, but we especially targeted ourattention to the 78–150 K interval, which is the desired working range of liquid nitrogen cooledcryogenic Yb:YLF lasers/amplifiers. A tunable (770–1110 nm) Cr:LiSAF laser with around100 mW continuous-wave output power and sub-0.2 nm bandwidth is used as an excitationsource. The average power of the Cr:LiSAF laser is low enough to prevent heating of the sample,and its spectral flux (W/nm) is high enough to enable large signal-to-noise ratio measurements.Measured absorption data is used to cross-check the validity of the emission measurements, whilethe measured temperature dependent small-signal gain profile provided a second independentconfirmation. The acquired absorption cross section curves match the previous literature quitewell, whereas the measured strength of c-axis emission is stronger than some of the earlier reports.Direct measurements of small signal gain confirmed the emission cross section data, where singlepass gain values above 50 have been measured for the 995 nm transition of E//c axis at 78 K. Wefurther provide simple analytic formulas for the measured temperature dependence of absorptionand emission cross section. We hope the presented results to be useful for the development ofnext generation of cryogenic Yb:YLF laser and amplifier systems.