SM3F.8.pdf CLEO:2014 © 2014 OSA Passive Q-switching of a diode-pumped Tm,Ho:YLF laser using Cr:ZnSe saturable absorber Bozhidar Oreshkov, 1,2 Antonio Gianfrate, 1,3 Stefano Veronesi, 3 Valentin Petrov, 1,* Uwe Griebner, 1 Haohai Yu, 1 Ivan Buchvarov, 2 Daniela Parisi, 3 and Mauro Tonelli 3 1 Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, 2A Max-Born Str., D-12489 Berlin, Germany, 2 Faculty of Physics, Sofia University, 5 James Bourchier Blvd., BG-1164 Sofia, Bulgaria, 3 Dipartimento di Fisica dell’Università di Pisa, Largo B. Pontecorvo 3, I-56127 Pisa, Italy *Corresponding author: petrov@mbi-berlin.de Abstract: We report on passive Q-switching of a Tm,Ho:LiYF 4 laser with Cr:ZnSe saturable absorber achieving for the first time short (~50 ns) pulse durations and high (~640 W) peak power from such a diode-pumped Ho-laser. ©2014 Optical Society of America OCIS codes: (140.5680) Rare earth and transition metal solid-state lasers; (140.3540) Lasers, Q-switched; (140.3480) Lasers, diode-pumped Due to strong water absorption, the eye-safe emission of Tm 3+ -doped, Ho 3+ -doped, or Tm 3+ , Ho 3+ -co-doped lasers around 2 µm is interesting for many medical applications, remote sensing (LIDAR) as well as for pumping optical parametric oscillators (OPOs) for efficient frequency down-conversion into the mid-IR [1]. High pulse energy and peak power are advantageous for these applications since they can be achieved at relatively low average power if compared to continuous-wave (CW) regime of operation. For medical applications, the pulse duration and repetition rate are essential parameters that determine the interaction mechanisms with the tissue. Depending on the diagnostic findings and the art of therapy, most medical treatments are carried out either with a Tm- or a Ho-laser. Ho-lasers, both single and co-doped, have slightly longer emission wavelength than Tm-lasers, the difference is typically 50- 150 nm. Although small, this difference results in quite different penetration depth in soft tissue, which could be, e.g., 3-4 times larger for Ho-lasers [1]. Taking advantage of the absorption band of Tm 3+ ions around 800 nm and the efficient energy transfer between Tm 3+ and Ho 3+ ions, Tm, Ho-co-doped laser media can be diode-pumped (DP) by well established AlGaAs laser diodes designed for Nd 3+ -ion pumping. Passive Q-switching of such DP solid-state lasers (DPSSL) by an intracavity saturable absorber (SA) is a common technique to generate short and high peak power pulses, mainly due to the simplicity and low cost. Combining those advantages a DP passively Q-switched (PQS) Tm, Ho-co-doped laser is a simple, inexpensive and reliable source of short pulses slightly above 2 μm. In contrast to DP PQS Tm-lasers, where sub-10-ns pulses with energies >1 mJ were achieved [2], we are aware of only one demonstration of sub-1-µs DP PQS Tm, Ho-co-doped laser, where pulses as short as 354 ns were generated with cryogenically cooled Tm,Ho:GdVO 4 and the maximum pulse energy reached 70.5 µJ [3]. The situation is quite unsatisfactory and difficult to explain because such pulse durations are much longer than typically achieved with active Q-switching. Here we report on a Tm 3+ , Ho 3+ -co-doped LiYF 4 (Tm,Ho:YLF) laser, PQS with Cr 2+ :ZnSe SA. YLF belongs to the family of fluoride crystals which exhibit longest energy storage times (~10 ms for the 2-µm Tm- and Ho-laser transitions) and with which we obtained the best results for Tm-based PQS DP lasers using Cr 2+ :ZnS SAs [2,4]. With Tm,Ho:YLF we were now able to achieve stable Q-switching at 2051 nm with pulse durations as short as 40 ns and peak powers 3 to 200 times higher than in previous work on such co-doped lasers. (a) (b) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0.0 0.1 0.2 0.3 0.4 0.5 CW slope 42.6% PQS slope 10.9% P output (W) P absorbed (W) Fig. 1. (a) Setup of the PQS Tm,Ho:YLF laser. M1: dichroic pump mirror, M2: HR-laser, HT-pump mirror, M3: output coupler. (b) Output power vs. absorbed pump power for 5.8% OC in CW and PQS regimes.