Abstract
We present spectroscopic measurements focusing on a detailed investigation of temperature dependence of absorption, emission and gain in the uniaxial Yb:YLF laser gain medium. Measurements are carried out in the 78–300 K range, but we especially targeted our attention to the 78–150 K interval, which is the desired working range of liquid nitrogen cooled cryogenic Yb:YLF lasers/amplifiers. A tunable (770–1110 nm) Cr:LiSAF laser with around 100 mW continuous-wave output power and sub-0.2 nm bandwidth is used as an excitation source. 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, while the measured temperature dependent small-signal gain profile provided a second independent confirmation. The acquired absorption cross section curves match the previous literature quite well, 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 single pass gain values above 50 have been measured for the 995 nm transition of E//c axis at 78 K. We further provide simple analytic formulas for the measured temperature dependence of absorption and emission cross section. We hope the presented results to be useful for the development of next generation of cryogenic Yb:YLF laser and amplifier systems.
Highlights
High-average and peak power laser and amplifier systems based on ytterbium-doped gain media are interesting tools for many applications including nonlinear pulse compression [1], optical parametric chirped-pulse amplification [2], parametric-waveform synthesis [3], and table-top electron acceleration [4]
We present spectroscopic measurements focusing on a detailed investigation of temperature dependence of absorption, emission and gain in the uniaxial Yb:YLF laser gain medium
In our design/simulation attempts [31], we have realized that, the literature lacks temperature dependence of data even in these basic parameters: (i) data is plotted in small graphs with limited spatial resolution, (ii) the data is taken with low spectral resolution, (iii) the data is only given for a few selected temperatures, (iv) the data is only given in arbitrary units, and (v) sometimes the data available from variable sources conflict with each other
Summary
High-average and peak power laser and amplifier systems based on ytterbium-doped gain media are interesting tools for many applications including nonlinear pulse compression [1], optical parametric chirped-pulse amplification [2], parametric-waveform synthesis [3], and table-top electron acceleration [4]. It is important to investigate the temperature variation of absorption, emission and gain in Yb:YLF carefully (especially in the 78–150 K range [30]), for the successful development of generation of cryogenic Yb:YLF laser and amplifier systems which could potentially reach kW level average powers along with pulsewidths in the sub-250-fs range Such spectroscopic information could be useful for the optical refrigeration community (that partially base their efforts on anti-Stokes emission of Yb:YLF crystals) [32,33,34,35,36,37,38], in their attempts to develop nanometer scale quantum optical devices [36].
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