RESUMO
We report on a femtosecond thulium laser operating on the 3H4 â 3H5 transition with upconversion pumping around 1â µm and passively mode-locked by a GaSb-based SEmiconductor Saturable Absorber Mirror (SESAM). This laser employs a 6 at.% Tm:LiYF4 laser crystal and a polarization maintaining Yb-fiber master oscillator power amplifier at 1043â nm as a pump source addressing the 3F4 â 3F2,3 excited-state absorption transition of Tm3+ ions. In the continuous-wave regime, the Tm-laser generates 616â mW at â¼2313â nm with a slope efficiency of 10.0% (vs. the incident pump power) and a linear polarization (π). By implementing a type-I SESAM with a single ternary strained In0.33Ga0.67Sb quantum well embedded in GaSb for sustaining and stabilizing the soliton pulse shaping, the self-starting mode-locked Tm-laser generated pulses as short as 870 fs at a central wavelength of 2309.4â nm corresponding to an average output power of 208â mW at a pulse repetition rate of 105.08â MHz and excellent mode-locking stability. The output power was scaled to 450â mW at the expense of a longer pulse duration of 1.93 ps. The nonlinear parameters of the SESAM are also reported.
RESUMO
A GaSb-based SEmiconductor Saturable Absorber Mirror (SESAM) enables continuous-wave picosecond mode-locked operation with excellent stability of a polarization-maintaining mid-infrared Er:ZBLAN fiber laser. The GaSb-based SESAM mode-locked fiber laser delivers an average output power of 190â mW at 2.76 µm at a repetition rate of 32.07â MHz (corresponding to a pulse energy of â¼6 nJ) and exhibits a high signal-to-noise ratio of â¼80â dB. The polarization extinction ratio is more than 23â dB. By employing an intracavity diffraction grating, the laser wavelength is continuously tunable across 2.706-2.816 µm. Passively Q-switched operation of this laser is also demonstrated.
RESUMO
A Tm:LiYF4 laser operating on the 3H4 â 3H5 transition is embedded in a high-power diode-pumped Nd:ASL laser for intracavity upconversion pumping at 1.05â µm. This leads to a record-high output power at 2.3â µm for any bulk thulium laser pumped by an upconversion process. The continuous-wave Tm:LiYF4 laser delivers 1.81â W at 2.3â µm for 32â W of laser-diode pump power, making this kind of pumping competitive with direct diode pumping. The intracavity pumping process allows for counteracting the low absorption inherent to upconversion pumping and to dispatch the thermal loads on two separate laser crystals. The proposed laser architecture also features a relatively weak heating of the Tm:LiYF4 crystal and an increased tolerance to Tm3+ absorption. This laser design opens a new paradigm that holds great promise for high-power 2.3-µm solid-state lasers based on thulium ions.
RESUMO
We study a cascade laser scheme involving the 3H4 â 3H5 and 3F4 â 3H6 consecutive transitions in Tm3+-doped materials as a promising technique to favor laser emission at 2.3 µm. We examine the conditions in terms of the Tm3+ doping levels for which the cascade laser is beneficial or not. For this, Tm:LiYF4 lasers based on crystals with several doping levels in the range of 2.5 - 6 at.% with and without cascade laser are studied. For low doping of 2.5 at.% Tm3+, adding the laser emission at 1.9 µm allows to double the output power at 2.3 µm, whereas for high doping of 6 at.%, allowing the laser to operate at 1.9 µm totally suppresses the laser emission at 2.3 µm. An analytical model is developed and confronted with experimental results to predict this doping-dependent phenomenon and forecast the potential benefits. This study of cascade laser emission on the 3H4â 3H5 and 3F4â 3H6 transitions versus the Tm3+ doping level is finally extended to other well-known Tm3+-doped laser materials.
RESUMO
We report on a bulk thulium laser operating on the 3H4 â 3H5 transition with pure upconversion pumping at 1064â nm by an ytterbium fiber laser (addressing the 3F4 â 3F2,3 excited-state absorption (ESA) transition of Tm3+ ions) generating 433â mW at 2291â nm with a slope efficiency of 7.4% / 33.2% vs. the incident / absorbed pump power, respectively, and linear laser polarization representing the highest output power ever extracted from any bulk 2.3â µm thulium laser with upconversion pumping. As a gain material, a Tm3+-doped potassium lutetium double tungstate crystal is employed. The polarized ESA spectra of this material in the near-infrared are measured by the pump-probe method. The possible benefits of dual-wavelength pumping at 0.79 and 1.06â µm are also explored, indicating a positive effect of co-pumping at 0.79â µm on reducing the threshold pump power for upconversion pumping.
RESUMO
We report on the first laser operation of a disordered Tm:CaGdAlO4 crystal on the 3H4 â 3H5 transition. Under direct pumping at 0.79 µm, it generates 264â mW at 2.32â µm with a slope efficiency of 13.9% and 22.5% vs. incident and absorbed pump power, respectively, and a linear polarization (σ). Two strategies to overcome the bottleneck effect of the metastable 3F4 Tm3+ state leading to the ground-state bleaching are exploited: cascade lasing on the 3H4 â 3H5 and 3F4 â 3H6 transitions and dual-wavelength pumping at 0.79 and 1.05 µm combining the direct and upconversion pumping schemes. The cascade Tm-laser generates a maximum output power of 585â mW at 1.77â µm (3F4 â 3H6) and 2.32â µm (3H4 â 3H5) with a higher slope efficiency of 28.3% and a lower laser threshold of 1.43 W, out of which 332â mW are achieved at 2.32â µm. Under dual-wavelength pumping, further power scaling to 357â mW at at 2.32â µm is observed at the expense of increased laser threshold. To support the upconversion pumping experiment, excited-state absorption spectra of Tm3+ ions for the 3F4 â 3F2,3 and 3F4 â 3H4 transitions are measured for polarized light. Tm3+ ions in CaGdAlO4 exhibit broadband emission at 2.3 - 2.5 µm making this crystal promising for ultrashort pulse generation.
RESUMO
Excited-state absorption (ESA) is a key process for upconversion pumping schemes of thulium (Tm3+) doped laser materials. We have systematically studied two ESA transitions in the near-infrared spectral range, namely 3F4 â 3F2,3 (at â¼1â µm) and 3F4 â 3H4 (at â¼1.5â µm), in various Tm3+-doped fluoride (ZBLAN glass, cubic KY3F10 and CaF2, tetragonal LiYF4 and LiLuF4, monoclinic BaY2F8 crystals) and oxide (cubic Y3Al5O12, orthorhombic YAlO3 crystals) laser materials, using a pump-probe method with a polarized light. An approach to calculate the constants of energy-transfer upconversion (ETU) is also presented.
RESUMO
Upconversion pumping of thulium lasers emitting around 2.3 µm (the 3H4 â 3H5 transition) has recently attracted a lot of attention as it is compatible with the mature Yb-laser technology. To explore this possibility, we built a mid-infrared Tm:LiYF4 laser pumped by an Yb:CaF2 laser at 1.05 µm delivering an output power of 110 mW at 2.31 µm for a maximum incident pump power of 2.0 W. A strong absorption issue appeared in the Tm laser: the slope efficiency vs. the incident pump power was 7.6% while that vs. the absorbed pump power reached 29%. To overcome this issue, a dual-wavelength pumping at 0.78 µm and 1.05 µm was explored (combining both the direct and upconversion pumping schemes). The reciprocal interplay between the two pumps was studied to evaluate their benefits in terms of the pump absorption and laser efficiency. We observed an interesting decrease of the laser threshold for upconversion pumping when adding a small fraction of the direct pump revealing a seeding effect for the excited-state absorption from the metastable 3F4 level. A recycling process of this manifold by excited-state absorption in the 3F4 â 3F2,3 loop was also observed. The pump absorption seeding is a viable route for the development of low-threshold upconversion pumped thulium lasers.
RESUMO
We report on Czochralski growth, detailed ground- and excited-state absorption and emission spectroscopy and highly-efficient mid-infrared (â¼2.3 µm) laser operation of a cubic potassium yttrium fluoride crystal, Tm:KY3F10. The peak stimulated-emission cross-section for the 3H4 â 3H5 transition is 0.34×10-20 cm2 at 2345 nm with an emission bandwidth exceeding 50 nm. The excited-state absorption spectra for the 3F4 â 3F2,3 and 3F4 â 3H4 transitions are measured and the cross-relaxation is quantified. A continuous-wave 5 at.% Tm:KY3F10 laser generated 0.84 W at 2331-2346 nm by pumping at 773 nm, with a record-high slope efficiency of 47.7% (versus the incident pump power) owing to the efficient action of energy-transfer upconversion leading to a pump quantum efficiency approaching 2. The first Tm:KY3F10 laser with ESA-assisted upconversion pumping (at 1048 nm) is also demonstrated. Due to its broadband emission properties, Tm:KY3F10 is promising for ultrashort pulse generation at â¼2.3-2.4 µm.
RESUMO
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 â¼815 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 â¼1.91 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.
RESUMO
We report on an efficient mid-infrared thulium (Tm) fiber laser operating on the 3H4â3H5 transition and featuring an upconversion pumping scheme. This laser comprises a heavily Tm3+-doped (2.50 mol. %) zirconium fluoride glass fiber pumped by a tunable Yb fiber laser around 1.05 µm corresponding to the 3F4â3F2,3 excited-state absorption transition. The laser generates 1.24 W at 2269-2282 nm with a slope efficiency of 37% in the quasi-continuous-wave regime. The Tm-glass fiber exhibits a broadband 3H4â3H5 emission with a bandwidth of 173 nm, making it very promising for femtosecond fiber oscillators at â¼2.3µm.
RESUMO
We report on efficient diode-pumped mid-infrared lasers based on Tm:LiYF4, Tm:Y3Al5O12, and Tm:YAlO3 crystals. These lasers operate in the continuous-wave (CW) regime and deliver watt-level output power at the wavelengths of 2.2-2.3 µm (the 3H4â3H5Tm3+ transition). In particular, a 1.8 at. % Tm:YAlO3 laser pumped at 789 nm generates a maximum CW output power of 1.32 W at 2272-2277 nm with a slope efficiency of 33.1% (with respect to the absorbed pump power), a linear laser polarization (Eâ¥b), and a fundamental transverse output mode (the measured Mx2=1.26, My2=1.68). In the quasi-CW regime, the output peak power is scaled up to 2.69 W. The pump quantum efficiency and the fractional heat loading are estimated and discussed.
RESUMO
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.
RESUMO
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.
RESUMO
We report on novel upconversion (UC) pumping schemes for 2.3 µm thulium (Tm) lasers (the H43âH53 transition) based on a photon avalanche mechanism populating the intermediate metastable level (F43) acting as an effective ground state. The proposed pump wavelengths are â¼1 and â¼1.5 µm, each one corresponding to a resonant excited-state absorption transition F43âF2,33 and F43âH43, respectively. UC pumping at 1040, 1055, and 1451 nm of 2.3 µm Tm:LiYF4 lasers is demonstrated. In the former case, the laser generates 102 mW at 2302 nm with a slope efficiency of 14.6% (versus the incident pump power). The laser dynamics is studied. UC pumping is promising for reaching high efficiencies in 2.3 µm Tm lasers.
RESUMO
The orthorhombic Tm3+:YAlO3 crystal is promising for laser operation at the H43âF43 (1.5 µm) and H43âH53 (2.3 µm) transitions. Stimulated-emission cross-sections for these transitions are determined with polarized light. Peak values of 0.59×10-20 cm2 and 0.80×10-20 cm2 are found at 1438 nm and 2275 nm, respectively, both for Eâ¥b. The cross-relaxation defining the upper-laser level lifetime is quantified. Continuous-wave lasing at the H43âH53 transition is achieved with an a-cut 1.5 at.% Tm:YAlO3 crystal. The laser generated 254 mW at 2273 nm with a slope efficiency of 17.8% and linear polarization (Eâ¥b).
RESUMO
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 (H63âF43) 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).