Deep-red laser operation of cleaved single-crystal plates of Eu:CsGd(MoO4)2 molybdate.

We report on the first deep-red laser operation of a heavily Eu3+-doped cesium gadolinium double molybdate crystal with a perfect cleavage. A 17 at. % Eu:CsGd(MoO4)2 laser based on cleaved single-crystal plates generated a maximum continuous-wave output power of 212 mW at 703.1 nm (5D0 → 7F4 transition) with a slope efficiency of 30.1%, a low laser threshold of 51 mW, linear polarization, and a beam quality factor M2 = 1.6-1.7. This monoclinic crystal is promising for deep-red microchip lasers.

Efficient continuous-wave Tm,Ho:CaF2 laser at 2.1µm.

We report on the first, to the best of our knowledge, continuous-wave laser operation of a Tm3+,Ho3+-codoped calcium fluoride crystal at ∼2.1 µm. Tm,Ho:CaF2 crystals were grown by the Bridgman method, and their spectroscopic properties were studied. The stimulated-emission cross section for the 5I7 → 5I8 Ho3+ transition is 0.72 × 10-20 cm2 at 2025 nm, and the thermal equilibrium decay time is 11.0 ms. A 3 at. % Tm, 0.3 at. % Ho:CaF2 laser generated 737 mW at 2062-2088 nm with a slope efficiency of 28.0% and a laser threshold of 133 mW. Continuous wavelength tuning between 1985 and 2114 nm (tuning range: 129 nm) was demonstrated. The Tm,Ho:CaF2 crystals are promising for ultrashort pulse generation at ∼2 µm.

In-band pumped Tm,Ho:LiYF4 waveguide laser.

A 4.5 at.% Tm, 0.5 at.% Ho:LiYF4 planar waveguide (thickness: 25 µm) grown by Liquid Phase Epitaxy is in-band pumped by a Raman fiber laser at 1679 nm (the 3H6 → 3F4 Tm3+ transition). A continuous-wave waveguide laser generates a maximum output power of 540 mW at 2051nm with a slope efficiency of 32.6%, a laser threshold of 337 mW and a linear laser polarization (π). This represents the highest output power extracted from any Tm,Ho waveguide laser. No parasitic Tm3+ colasing is observed. The waveguide propagation losses are determined to be as low as 0.19 dB/cm.

Channel waveguide lasers in bulk Tm:LiYF4 produced by deep diamond-saw dicing.

We report on a novel approach to fabricate channel (ridge) waveguides (WGs) in bulk crystals using precision diamond saw dicing. The channels feature a high depth-to-width aspect ratio (deep dicing). The proof-of-the-concept is shown for a Tm3+:LiYF4 fluoride crystal. Channels with a depth of 200 µm and widths of 10-50 µm are diced and characterized by confocal laser microscopy revealing a r.m.s. roughness of the walls well below 100 nm. The channels obtained possess waveguiding properties at ∼815 nm with almost no leakage of the guided mode having a vertical stripe intensity profile into the bulk crystal volume and relatively low propagation losses (0.20-0.43 dB/cm). Laser operation is achieved in quasi-CW regime by pumping at 780 nm. The maximum peak output power reaches 0.68 W at ∼1.91 µm with a slope efficiency of 53.3% (in σ-polarization). The proposed concept is applicable to a variety of laser crystals with different rare-earth dopants.

In-band pumping of Tm:LiYF4 channel waveguide: a power scaling strategy for ∼2 µm waveguide lasers.

We report on a novel power scaling strategy for thulium waveguide (WG) lasers relying on in-band pumping by high-brightness Raman fiber lasers (RFLs) and the use of liquid-phase-epitaxy-grown fluoride crystalline thin films for better thermal management. Thulium channel WGs are produced by microstructuring the Tm3+:LiYF4/LiYF4 epitaxies via diamond-saw dicing. They are pumped by a RFL based on an erbium master oscillator power amplifier and a GeO2-doped silica fiber and emit polarized output at 1679 nm. A CW in-band-pumped (H63→F43) Tm3+:LiYF4 WG laser generates up to 2.05 W of a linearly polarized single-transverse-mode output at 1881 nm with a slope efficiency of 78.3% and a laser threshold of only 12 mW (versus the absorbed pump power).

Laser operation of highly-doped Tm:LiYF4 epitaxies: towards thin-disk lasers.

Quasi-continuous-wave laser operation of 20 at.% Tm:LiYF4 thin films (84-240 µm) grown by Liquid Phase Epitaxy (LPE) on undoped LiYF4 substrates is achieved. The 240 µm-thick Tm:LiYF4 active layer pumped at 793 nm with a simple double-pass scheme generated 152 mW (average power) at 1.91 µm with a slope efficiency of 34.4% with respect to the absorbed pump power. A model of highly-doped Tm:LiYF4 lasers accounting for cross-relaxation, energy-transfer upconversion and energy migration is developed showing good agreement with the experiment. The pump quantum efficiency for Tm3+ ions is discussed and the energy-transfer parameters are derived. These results show that LPE-grown Tm:LiYF4 thin films are promising for ~1.9 µm thin-disk lasers.

Ytterbium calcium fluoride waveguide laser.

Calcium fluoride is a well-known material for optical components. It is also suited for doping with rare-earth ions, e.g., ytterbium ones. Yb:CaF2 is an efficient gain medium for high-power and ultrashort-pulse bulk lasers around 1 µm. We report on the first Yb:CaF2 planar waveguide laser. High-optical-quality single-crystalline waveguiding Yb:CaF2 thin films are grown on bulk CaF2 substrates by Liquid Phase Epitaxy. The spectroscopic study indicates the predominant coordination of isolated Yb3+ ions in trigonal oxygen-assisted sites, C3v(T2). The optical gain in Yb:CaF2 waveguide is demonstrated. A 1.4 at.% Yb:CaF2 planar waveguide laser generated 114 mW at 1037 nm with a slope efficiency of 12.9%. Yb:CaF2 films are promising for power-scalable waveguide mode-locked lasers and amplifiers.

Watt-level Tm:LiYF4 channel waveguide laser produced by diamond saw dicing.

Low-loss surface channel waveguides with a cross-section of 30 × 30 µm2 are produced by diamond saw dicing of 6.2 at.% Tm3+, 3.5 at.% Gd3+:LiYF4 films grown by liquid phase epitaxy (LPE) on (001)-oriented bulk undoped LiYF4 substrates. Pumped by a Ti:Sapphire laser at 783 nm, a continuous-wave Tm:LiYF4 waveguide laser generated 1.30 W at 1880 nm (for π-polarization) with a slope efficiency of 80% with respect to the absorbed pump power. The laser threshold was at 80 mW. The waveguide morphology was studied revealing low roughness (3 ± 2 µm) as expressed by the propagation losses of <0.3 dB/cm. A combination of LPE and diamond saw dicing is a promising technology for multi-watt single-mode channel waveguide lasers and amplifiers.

Tm,Ho:LiYF4 planar waveguide laser at 2.05 µm.

The first holmium fluoride waveguide laser, to the best of our knowledge, is reported using a 25-µm-thick Gd3+-ion-modified 4.5 at. % Tm3+, 0.5 at. % Ho3+-codoped LiYF4 active layer grown by liquid phase epitaxy on (001)-oriented LiYF4 substrate. Pumped by a Ti:sapphire laser at 797.2 nm, the planar waveguide laser generates 81 mW of continuous-wave (CW) output at ∼2051 nm with a slope efficiency of 24%. Power scaling up to 186 mW at 2051 nm and 2065 nm in quasi-CW regime is demonstrated. The parameters of the Tm3+↔Ho3+ energy transfer are determined. Tm,Ho:LiYF4/LiYF4 epitaxies are promising for waveguide lasers and amplifiers at above 2 µm.

Green, orange, and red Pr(3+)∶YLiF(4) epitaxial waveguide lasers.

Efficient guided laser oscillation in the visible spectral region is demonstrated with praseodymium-doped YLiF(4) layers grown by liquid phase epitaxy. By exciting Pr(3+) ions at 479.2 nm with an optically pumped semiconductor laser, maximum slope efficiencies of 40% at 639 nm and 32% at 604 nm are obtained in a cw regime. Green laser oscillation at 522.5 nm, in a quasi-cw regime, with an average output power of 66 mW, is demonstrated for the first time, to our knowledge, in a crystalline fluoride epitaxial waveguide. Furthermore, a record efficiency of 60% at 639 nm in the quasi-cw regime is reported.

Red and orange Pr3+:LiYF4 planar waveguide laser.

In this Letter we report on room temperature continuous wave laser operation in the red (639 nm, (3)P(0)→(3)F(2)) and orange (604 nm, (3)P(0)→(3)H(6)) spectral regions of Pr(3+)-doped LiYF(4) planar waveguides fabricated by liquid phase epitaxy. Output powers of 25 and 12 mW and slope efficiencies of 5% and 6% were achieved at 639 and 604 nm, respectively, by pumping with an optically pumped semiconductor laser operating at 479.2 nm.

Tm:LiYF4 planar waveguide laser at 1.9 µm.

Continuous wave laser operation at 1.87 µm of liquid-phase epitaxially (LPE) grown Tm(3+)-doped YLiF(4) (Tm:YLF) layers is demonstrated. The waveguide laser delivers 560 mW by pumping with a Ti:Sapphire laser at 780 nm leading to an efficiency of 76% with respect to the absorbed pump power. This constitutes the first Tm(3+)-doped crystalline fluoride waveguide laser ever demonstrated as well as a record in efficiency and output power for an LPE grown waveguide laser operating in the 2 µm spectral range.