23-μm Tm^3+:YLF laser passively Q-switched with a Cr^2+:ZnSe saturable absorber

Abstract

We report, what is to our knowledge, the first passively Q-switched operation of a 2.3-μm Tm³⁺:YLF laser by using a Cr²⁺:ZnSe saturable absorber. In the experiments, a tunable Ti³⁺:sapphire laser was used to end pump the Tm³⁺:YLF gain medium inside an x cavity. A Cr²⁺:ZnSe saturable absorber was also included in the cavity to initiate passive Q switching. At all pump power levels above lasing threshold, passively Q-switched operation of the Tm³⁺:YLF laser could be obtained at 2309 nm with pulse durations and repetition frequencies in the ranges of 1.2-1.4 μs and 0.3-2.1 kHz, respectively. Analysis of power dependent repetition rate data further gave an estimated value of 3.1% for the round-trip saturable loss of the Cr²⁺:ZnSe saturable absorber.

Efficient Tm:LiYF4 Lasers at ${\sim}2.3~\mu$ m: Effect of Energy-Transfer Upconversion

“…A diode-pumped Yb,Tm:LiYF 4 laser generated 0.45 W at 2.30-2.32 µm (broadband emission) with a slope efficiency of 18% (with 65% pump absorption) [22]. Pulsed laser operation in the passively Q-switched (PQS) [20] and mode-locked (ML) [26,27] regimes has been also achieved for ~2.3 µm bulk Tm lasers. The first ML ~2.3 µm bulk Tm laser using SEmiconductor Saturable Absorber Mirror (SESAM) generated 94 ps pulses at 2305.9 nm [27].…”

“…Among fluoride crystals, tetragonal lithium yttrium fluoride (LiYF 4 ) has been considered for ~2.3 µm lasers [17,19,20]. This crystal is well-known for Tm 3+ doping and it provides highly efficient laser operation at the 3 F 4 → 3 H 6 transition [33,34].…”

“…However, the doping cannot be too low to keep a reasonable pump absorption efficiency. As a result of such considerations, ~2.3 µm Tm:LiYF 4 lasers reported to date were based on crystals with low doping levels, about 1-2 at.% [17,19,20,25].…”

“…Further studies were performed with laser-pumping (using Alexandrite [19] and Ti:Sapphire [17,20] lasers) allowing for selective excitation to the 3 H 4 state. As gain materials, Tm 3+doped fluoride LiYF 4 and oxide Y 3 Al 5 O 12 or Lu 3 Al 5 O 12 crystals were employed.…”

“…A Ti:Sapphire pumped Tm:LiYF 4 laser generated 0.22 W at 2.30 µm with a slope efficiency of 15 % (versus the incident pump power, with 80% absorption) and a continuous tuning of the emission wavelength from 2.20 to 2.46 µm was also demonstrated [18]. Slightly higher slope efficiency was reported [20] (Table I) whilst still being lower than the Stokes efficiency for the 3…”