Comparative investigation of lasing and amplification performance in cryogenic Yb:YLF systems

Abstract

We present detailed experimental results with cryogenic Yb:YLF gain media in rod-geometry. We have comparatively investigated continuous-wave (cw) lasing and regenerative amplification performance under different experimental conditions. In the cw lasing experiments effect of crystal doping, cw laser cavity geometry and pump wavelength on lasing performance were explored. Regenerative amplification behavior was analyzed and the role of depolarization losses on performance was investigated. A recently developed temperature estimation method was also employed for the first time in estimating average crystal temperature under lasing conditions. It is shown that the thermal lens induced by transverse temperature gradients is the main limiting factor and strategies for future improvements are discussed. To the best of our knowledge, the achieved results in this study (375 W in cw, and 90 W in regenerative amplification) are the highest average powers ever obtained from this system via employing the broadband E//a axis.

Recent progress in cryogenic Yb:YLF laser technology

“…A 2 kW 960 nm fiber coupled module is used for pumping, and the pump beam is imaged to the same spot size at the center of the crystals using appropriate pump lenses (f1-f3). Details of these cavities can be found in our recent publications 51,52 . Figure 4 (a) shows the measured cw performance of the Yb:YLF laser using both the E//a and E//c configuration.…”

“…Mode-locking with a SESAM/SBR, 3-ps pulses with 28 W average power and tuning in the 1013.5-1019 nm range is achieved in the cryogenically cooled system 48,49 . We have further developed multi-kHz repetition rate regenerative amplifiers with 20 mJ pulse energy, sub-ps pulsewidth and up to 370 W average power at 78% extraction efficiency [50][51][52] . Initial multi-pass amplification efforts resulted in pulse energies exceeding 300 mJ level at 10 Hz 53,54 .…”

Error analysis of contactless optical temperature probing methods for cryogenic Yb:YAG

“…The variation of pump absorption at 1030 nm with temperature was employed in estimating Yb:YAG thin-disk temperatures in the 40-300 K range by Petrov et al [22]. We have recently investigated different spectral methods for temperature estimation of cryogenic Yb:YLF samples and demonstrated a temperature estimation accuracy below ± 1 K in the 78-300 K region [23], and used this for analyzing laser performance [24,25]. Similar methods had already been in use for temperature estimation of Yb:YLF and Yb:YAG by the cryogenic optical refrigeration community [26][27][28][29][30].…”

Highly efficient cryogenic Yb:YLF regenerative amplifier with 250 W average power

“…Interestingly, as it is underlined by Kawanaka et al in their pioneering work [1], the Yb:YLF gain media possess broad emission bands even at cryogenic temperatures [8][9][10]. Especially, the a-axis of Yb:YLF, which has a transition centered around 1016-1017 nm with a FWHM of 11 nm at 125 K (typical operation temperature of Yb:YLF amplifiers under thermal load [11]), could ideally support generation and amplification of sub-250-fs pulses [3]. Because of its broad emission profile, almost all cryogenic amplification studies with Yb:YLF so far had employed the a-axis, and amplification of sub-ps pulses with energies up to 300 mJ, and average powers up to 100 W was already demonstrated [12][13][14][15][16].…”