Q-switching of a Tm,Ho:KLu(WO₄)₂microchip laser by a graphene-based saturable absorber

Abstract

The first Ho microchip laser passively Q-switched using a graphene-based saturable absorber is demonstrated based on a Tm,Ho:KLu(WO4)2 crystal cut along the Ng-axis. A maximum average output power of 74 mW is extracted from the diode-pumped laser at 2061 nm with a slope efficiency of 4%. Pulses as short as 200 ns with an energy of ~0.2 μJ are obtained at a repetition rate of 340 kHz. The energy transfer (ET), 3F4 (Tm3+) ↔ 5I7 (Ho3+) is studied, yielding ET parameters of P28 = 1.69 and P71 = 0.15 × 10−22 cm3 μs−1, revealing the strong prevalence of direct ET.

Passive Q-switching of a Tm,Ho:KLu(WO_4)_2 microchip laser by a Cr:ZnS saturable absorber

“…With higher modulation depth of the SA (α 0 SA 3.5%), a pulse duration of 9 ns was achieved, the shortest ever reported for a PQS Tm,Ho-doped laser. At a pulse energy of 10.4 μJ, this corresponds to a record peak power of 1.15 kW, the highest ever extracted from a room-temperature PQS Tm,Ho laser, exceeding >50 times the previous results [19][20][21][22][23]. A theoretical model of a quasi-three-level laser system PQS with a "slow" SA is developed.…”

“…Passive Q-switched laser operation at room temperature is more favorable to benefit from the compactness of the cavity. A comparison of passively Q-switched Tm,Ho bulk lasers reported so far [19][20][21][22][23] is presented in Table 2. Two types of SAs were employed in these lasers, namely, Cr:ZnS and carbon nanostructures (graphene and single-walled carbon nanotubes, SWCNTs).…”

“…% Tm, 0.5 at. % Ho:KLuWO 4 2 or Tm,Ho:KLuW for short was grown by the top-seeded solution growth slow-cooling method and potassium ditungstate K 2 W 2 O 7 was used as a solvent; details about the growth procedure can be found in [13] [19] (expressed by an equilibrium constant, θ 0.089) which prevented unwanted colasing of both ions [26]. The latter, in turn, could be the main limitation for a stable Q-switched operation with this crystal.…”

“…We are aware of only one report on a PQS Tm,Ho microchip laser [19]. However, due to one particular limitation of the SA used in [19] (single-layer graphene), namely, the low modulation depth, this laser generated 200 ns∕ 0.2 μJ pulses with a peak power of only ∼1 W. Several previous studies were devoted to PQS Tm,Ho bulk lasers using LiYF 4 , LiLuF 4 , YAlO 3 , and YVO 4 host crystals and Cr 2 :ZnS or carbon nanostructures as SAs [20][21][22][23]. However, in such lasers, the typical pulse durations were still a few hundred nanoseconds (ns) and the peak power did not exceed a few tens of watts (W).…”

Graphene Q-switched Tm:KY(WO4)2waveguide laser

“…The laser is based on a buried 3 at.% Tm [28] may enable the generation of ns pulses at wavelengths longer than ~2 µm. Indeed, graphene PQS of a bulk Tm,Ho:KLuW laser has been already demonstrated [29]. a LPE-liquid-phase epitaxy, fs-femtosecond-written.…”