A Tm-doped mixed sesquioxide ceramic laser is mode-locked near 2 µm using InGaAsSb quantum-well semiconductor saturable absorber and chirped mirrors for dispersion compensation. Maximum average ...output power of 175 mW is achieved for a pulse duration of 230 fs at a repetition rate of 78.9 MHz with a 3% output coupler. Applying a 0.2% output coupler pulses as short as 63 fs are generated at 2.057 µm.
Cubic sesquioxides, RE 2 O 3 , where RE = Y, Lu or Sc, are attractive host crystals for thulium (Tm 3+ ) doping. A comparison of the spectroscopic properties of Tm 3+ :RE 2 O 3 crystals in terms of ...transition cross sections and cross-relaxation (CR) efficiency required for efficient upconversion pumping is presented. Thermo-optic properties of Tm 3+ :RE 2 O 3 crystals (thermal lensing, fractional heat loading, and thermo-optic coefficients) are described. The positive thermal lens, broadband emission, and efficient CR of the Tm:RE 2 O 3 crystals enable the development of compact, highly efficient and power-scalable lasers operating above 2 μm, based on thermal guiding. Nowadays, Tm:Lu 2 O 3 microchip lasers are capable of generating nearly 5 W of output power at ~2.06 μm with a slope efficiency η of 67% and in a rod geometry-up to 47.5 W with η of 59%. For multiwatt output at even longer wavelengths around 2.15 μm, Tm:Sc 2 O 3 is an interesting candidate.
We report on the continuous-wave and passively Q-switched operation of a compositionally “mixed” heavily doped 16.6 at.% Yb:(Y,Lu)
3
Al
5
O
12
garnet crystal at cryogenic temperatures (100–200 K), ...pumped by a volume Bragg grating stabilized diode laser emitting at 969 nm. At 140 K, in the continuous-wave regime, a maximum output power of 10.65 W was achieved at ~ 1029 nm with a slope efficiency of 56% (versus the incident pump power), a laser threshold of 1.05 W and excellent beam quality. Using Cr
4+
:YAG as a saturable absorber, the passively Q-switched laser generated pulses with an energy/duration of 0.15 mJ/201 ns, respectively, at a repetition rate of 39.7 kHz, corresponding to a peak power of 0.39 kW.
We demonstrate the suitability of monoclinic double tungstates (MDTs), KRE(WO 4 ) 2 , where RE = Gd, Y or Lu, doped with Nd 3+ , Yb 3+ , Tm 3+ , or Ho 3+ ions and co-doped with Yb 3+ -Tm 3+ , or Tm ...3+ -Ho 3+ ion couples, for highly efficient micro-lasers at ~1 μm and at ~2 μm. This is facilitated by the use of high rare-earth doping levels (up to 15 at.% for Tm, 10 at.% for Nd, and 25 at.% for Yb) and a special crystal cut along the Ng-axis providing the thermal guiding. Record slope efficiencies for bulk MDT lasers are achieved for each studied ion. A 15 at.% Tm:KLu(WO 4 ) 2 laser generated 785 mW at 1957...1965 nm with a slope efficiency η = 77%. The quantum efficiency for Tm 3+ ions amounted to η q = 1.98±0.02. With a 0.9 mm-thick 25 at.% Yb:KLuW micro-laser, η = 91% is achieved, approaching the theoretical limit set by the Stokes shift.
Energy-transfer processes strongly affect the performance of lanthanide-doped photonic devices. In this work, we introduce a simple stochastic model of energy-transfer processes and successfully ...apply it to the example of cross-relaxation (CR) and energy-transfer upconversion (ETU) in amorphous Al2O3:Tm3+ waveguides on silicon intended for lasers operating at ∼2 μm. The stochastic model is based on the rate-equation formalism and considers two spectroscopically distinct ion classes, namely single ions and ions with neighbors (pairs and clusters), with the corresponding ion fractions being dependent on the doping concentration. We prove that a more accurate description of the luminescence properties of amorphous Al2O3:Tm3+ is obtained when accounting for the presence of these distinct ion classes. Based on the developed model, we derive microscopic CR and ETU parameters of C CR = 5.83 × 10–38 cm6 s–1, C ETU1 = 0.93 × 10–40 cm6 s–1, and C ETU2 = 7.81 × 10–40 cm6 s–1, and determine the laser quantum efficiency ηq of excitation of Tm3+ ions in the upper laser level. For the maximum Tm3+ concentration of 5.0 × 1020 cm–3 studied experimentally in this investigation, ηq reaches 1.73. Furthermore, the transition cross sections at the pump and laser wavelengths are determined. For the 3H6 → 3F4 transition, the maximum stimulated-emission cross section is σe = 0.47 × 10–20 cm2 at 1808 nm.
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