Efficient, low threshold, cryogenic Ho:YAG laser

Abstract

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A cryogenic silicon interferometer for gravitational-wave detection

“…Two basic laser architectures are available: optical fiber [117] and free-space [118] lasers. These architectures are not necessarily incompatible and the final system may contain a low-power free-space master oscillator (MO) followed by some combination of power oscillators and fiber amplifiers.…”

High power cryogenic Ho:YAG laser

“…The spectral widths of the Ho:YAG absorption lines in the 1905-1911 nm region are approximately 0.3 nm [12], which compares favorably with the <0.15 nm line-width of the high power TDFLs used [21,22]. Both the 1907 nm and 1908 nm absorption strengths are high and not influenced by atmospheric water absorption.…”

“…Early work reported a cryogenically cooled Ho:YAG laser for medical applications demonstrating near 4-level lasing at up to 50W, but the laser was lamp pumped, required precooled liquid oxygen and had low efficiency [4]; furthermore no spectroscopy or beam quality was reported. Comparing more recent results at RT [3,[8][9][10] with those at cryogenic temperatures (CT) [5,11,12] demonstrates the substantial differences in threshold. In particular, the lowering of the laser threshold at CT allows for a lower pump intensity, thus enabling a larger laser mode volume to be exploited, while maintaining overall efficiency.…”

“…Ho:YAG was selected as the gain medium based on our previous results and the availability of suitable high power pump lasers. To achieve the maximum benefits of cryogenic cooling of the YAG host, the dopant concentration of Ho 3+ must be kept low, thereby promoting an end-pumped configuration with a long absorption length and large cooling surfaces [12]. The thulium fibre pump laser must provide high power in a narrow line-width with excellent wavelength stability and beam quality suitable for mode-matched end-pumping of the laser crystal.…”

“…Our present work seeks to address these issues and demonstrate the scalability of the CC of Ho:YAG lasers using liquid nitrogen (LN 2 ). In the work reported in [12] we presented the possibility of lasing using the absorption bands of Ho:YAG at 1907 nm and 1908 nm at cryogenic temperatures. These bands are narrow, but have high absorption coefficients.…”