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We report on an in-band pumped SESAM mode-locked Ho:CALGO bulk laser with a record-high average power of 8.7 W and an optical-to-optical efficiency of 38.2% at a central wavelength of 2.1 um. At this power level, the bulk laser generates pulses with a duration of 369 fs at 84.4-MHz repetition rate, corresponding to a pulse energy of 103 nJ and a peak power of 246 kW. To the best of our knowledge, this is the highest average power and pulse energy directly generated from a mode-locked bulk laser in the 2-3 um wavelength region. Our current results indicate that Ho:CALGO is a competitive candidate for average power scaling of 2 um femtosecond lasers., 9 pages, 5 figures

We report on high-power mode-locked femtosecond Ho:CALGO laser at 2.1 µm. The laser generates a record-high average output power of 8.7 W (369 fs) with SESAM mode-locking and 1.2 W (152 fs) with Kerr-lens mode-locking.

A detailed study of thermo-optic properties of 1.5 at.% Yb:Lu2O3 single crystal is performed. Thermo-optic dispersion formulas are derived for dn/dT coefficient and thermal coefficient of the optical path. At the wavelength of 1.03 μm, dn/dT = 5.8 × 10−6 K−1. High-precision temperature-dependent measurements of the thermal expansion coefficient α are performed. At the room temperature (RT), α = 5.880 ± 0.014 × 10−6 K−1. Temperature dependence of the bandgap is analyzed, yielding RT value of E g = 5.15 eV and dE g/dT = –3.7 × 10−4 eV/K. Sensitivity factor of the thermal lens is calculated for a diode-pumped Yb:Lu2O3 crystal versus the pump spot radius and crystal temperature.

Absorption, stimulated-emission and gain cross-sections are determined for 3 at.% Tm:CaGdAlO4. This crystal is employed in a microchip laser diode-pumped at 802 nm. In the continuous-wave (CW) regime, this laser generates 1.16 W at 1883-1893 nm with a slope efficiency of 32% with respect to the absorbed pump power. Using a special "bandpass" output coupler, vibronic CW laser operation up to 2043 nm is achieved. For passive Q-switching of the Tm:CaGdAlO4 laser-saturable absorbers (SAs) based on CVD-grown graphene and randomly-oriented arc-discharge single-walled carbon nanotubes (SWCNTs) in a PMMA film. The SWCNT-SA demonstrates superior performance. The laser produced a maximum average output power of 245 mW at 1844 nm with a slope efficiency of 8%. The latter corresponds to a pulse energy and duration of 6 μJ and 138 ns, respectively, at a repetition rate of 41 kHz. Using the graphene-SA, 2.8 μJ, 490 ns pulses are obtained at a repetition rate of 86 kHz.

We report on, to the best of our knowledge, the first fs-laser-written waveguide laser in Yb3+:CaGdAlO4 (Yb:CALGO). With Yb:CALGO crystals grown in our labs, we obtained a slope efficiency of 69% and up to 2.4 W of continuous wave (cw) output power in a waveguide-laser configuration. Moreover, bulk laser experiments with Yb:CALGO were performed, and slope efficiencies up to 73%, optical-to-optical efficiencies of 65%, and maximum cw output powers of 3.3 W were reached. These are the highest efficiencies in the laser configuration with Yb:CALGO.

We studied the refractive index and dispersive properties of the tetragonal rare-earth calcium aluminates, CaLnAlOsub4/sub(Ln=Gd or Y). Sellmeier equations were derived for the spectral range of 0.35-2.1 μm. The group velocity dispersion (GVD) in CaGdAlOsub4/subis positive at ∼1 μm, 95 fssup2/sup/mm and negative at ∼2 μm, -40 fssup2/sup/mm. The GVD values for CaYAlOsub4/subare similar. In addition, thermo-optic coefficients, dn/dT, and thermal coefficients of the optical path were determined for CaYAlOsub4/sub. dn/dT is negative at ∼1 μm, dnsubo/sub/dT=-7.8, and dnsube/sub/dT=-8.7×10sup-6/sup Ksup-1/sup. Thermo-optic dispersion formulas were constructed. The obtained data are of key importance to the design of high-power mode-locked oscillators at ∼1 and ∼2 μm based on such laser hosts.

We report on, to the best of our knowledge, the first fs-laser-written waveguide laser in Yb3+:CaGdAlO4 (Yb:CALGO). With Yb:CALGO crystals grown in our labs, we obtained a slope efficiency of 69% and up to 2.4 W of continuous wave (cw) output power in a waveguide-laser configuration. Moreover, bulk laser experiments with Yb:CALGO were performed, and slope efficiencies up to 73%, optical-to-optical efficiencies of 65%, and maximum cw output powers of 3.3 W were reached. These are the highest efficiencies in the laser configuration with Yb:CALGO.