Tm,Ho:LiYF4 planar waveguide laser at 2.05 μm

Growth, spectroscopy and laser operation of Tm,Ho:GdScO3 perovskite crystal

We report on the growth, polarized spectroscopy and first laser operation of an orthorhombic (space group Pnma) Tm3+,Ho3+-codoped gadolinium orthoscandate (GdScO3) perovskite-type crystal. A single crystal of 3.76 at.% Tm, 0.35 at.% Ho:GdScO3 was grown by the Czochralski method. Its polarized absorption and fluorescence properties were studied revealing a broadband emission around 2 µm. The parameters of the Tm3+ ↔ Ho3+ energy transfer was quantified, P28 = 1.30 × 10-22 cm3µs-1, and P71 = 0.99 × 10-23 cm3µs-1, and the thermal equilibrium lifetime was measured to be 3.5 ms. The crystal-field splitting of Tm3+ and Ho3+ multiplets in Cs symmetry sites of the perovskite structure was determined by low-temperature spectroscopy and the mechanism of spectral line broadening is discussed. The continuous-wave Tm,Ho:GdScO3 laser generated 1.16 W at ∼2.1 µm with a slope efficiency of 50.5%, a laser threshold of 184 mW, a linear laser polarization (E || c) and a spatially single-mode output. The Tm,Ho:GdScO3 crystal is promising for broadly tunable and femtosecond mode-locked lasers emitting above 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.

Tm3+ and Ho3+ colasing in in-band pumped waveguides fabricated by femtosecond laser writing

We report on the first, to the best of our knowledge, in-band pumped Tm³⁺,Ho³⁺ codoped waveguide (WG) laser. A depressed-index surface channel WG (type III) with a 50 µm half-ring cladding is fabricated in a 5 at. % Tm³⁺, 0.5 at. % Ho³⁺:KLu(WO₄)₂ crystal by femtosecond pulse direct laser writing. Under in-band pumping by a 1679 nm Er Raman fiber laser, Tm³⁺ and Ho³⁺ colasing is observed in the WG and explained by bidirectional energy transfer. The maximum total output power at ∼1942nm(Tm³⁺) and 2059 nm (Ho³⁺) is 448 mW with a slope efficiencyM of 40.6%, which is a record high for this type of WG lasers. The maximum output power of the Ho laser reaches 144 mW.

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.