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.
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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.
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We report on a polarization-resolved study of mid-infrared emission properties of Er3+-doped orthorhombic yttrium aluminum perovskite YAlO3 single crystal. For the 4I11/2 â 4I13/2 Er3+ transition, the stimulated emission cross section is 0.20 × 10-20â cm2 at 2919â nm for light polarization E â c. Pumped by an Yb-fiber laser at 976â nm, the 10â at.% Er:YAlO3 laser delivered 1.36â W at 2919â nm with a slope efficiency of 31.4%, very close to the Stokes limit, a laser threshold as low as 33â mW and a linear polarization. Pump-induced polarization switching between E || b and E || c eigen states was observed and explained by excited-state absorption from the terminal laser level.
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The generation of terahertz radiation via laser-induced plasma from two-color femtosecond pulses in air has been extensively studied due to its broad emission spectrum and significant pulse energy. However, precise control over the temporal properties of these ultra-broadband terahertz pulses, as well as the measurement of their polarization state, remain challenging. In this study, we review our latest findings on these topics and present additional results not previously reported in our earlier works. First, we investigate the impact of chirping on the fundamental wave and the effect of manipulating the phase difference between the fundamental wave and the second-harmonic wave on the properties of generated terahertz pulses. We demonstrate that we can tune the time shape of terahertz pulses, causing them to reverse polarity or become bipolar by carefully selecting the correct combination of chirp and phase. Additionally, we introduce a novel technique for polarization characterization, termed terahertz unipolar polarimetry, which utilizes a weak probe beam and avoids the systematic errors associated with traditional methods. This technique is effective for detecting polarization-structured terahertz beams and the longitudinal component of focused terahertz beams. Our findings contribute to the improved control and characterization of terahertz radiation, enhancing its application in fields such as nonlinear optics, spectroscopy, and microscopy.
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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
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.
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We report on the first, to our knowledge, mid-infrared laser operation of two Er3+-doped barium-containing fluorite-type crystals, BaF2 and (Sr,Ba)F2, featuring a low-phonon energy behavior. A continuous wave 4.9 at.% Er:(Sr,Ba)F2 laser generated 519â mW at 2.79â µm with a slope efficiency of 25.0% and a laser threshold of 27â mW. The vibronic and spectroscopic properties of these crystals are determined. The phonon energy of (Sr,Ba)F2 is as low as 267â cm-1. The Er3+ ions in this crystal feature a broadband emission owing to the 4I11/2 â 4I13/2 transition and a long luminescence lifetime of the 4I11/2 level (10.6â ms) making this compound promising for low-threshold, broadly tunable, and pulsed 2.8-µm lasers.
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We report on mid-infrared optical parametric generation in the 4-5 µm and 9-12 µm bands by pumping custom-designed orientation-patterned gallium arsenide (OP-GaAs) rib waveguides with an ultrafast femtosecond fiber laser system. This pump source is seeded by a mode-locked fluoride fiber laser with 59 MHz repetition rate and can be tuned between 2.8 and 3.2 µm using a soliton self-frequency shifting stage. The single TE and TM modes OP-GaAs crystals feature quasi-phase-matched grating periods of 85 and 90 µm and different transverse sizes thus allowing a wide spectral tunability.
RESUMO
We present a compact passively mode-locked fiber laser emitting near 910 nm with an all-polarization-maintaining fiber laser architecture. The ring-cavity laser configuration includes a core-pumped neodymium-doped fiber as a gain medium and a semiconductor saturable absorber mirror as a passive mode-locking element. A bandpass filter is used to suppress parasitic emission near 1.06 µm and allows wavelength tuning between 903 and 912 nm. The laser operates in a highly stable and self-starting all-normal-dispersion regime with a minimum pulse duration of 8 ps at 28.2 MHz pulse repetition rate and 0.2 nJ maximum pulse energy. A single-pass amplifier stage increases the pulse energy up to 1.5 nJ, and pulse compression with a pair of gratings is demonstrated with nearly Fourier transform limited pulses.
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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.
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We demonstrate a fiber optical parametric chirped-pulse oscillator (FOPCPO) pumped in the normal-dispersion regime by chirped pulses at 1.036 µm. Highly chirped idler pulses tunable from 1210 nm to 1270 nm with energies higher than 250 nJ are generated from our system, along with signal pulses tunable from 870 nm to 910 nm. Numerical simulations demonstrate that further energy scaling is possible and paves the way for the use of such FOPCPOs for applications requiring high-energy, compact, and low-noise sources, such as in biophotonics or spectroscopy.
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
This Letter presents the efficient laser operation of a Tm:CaF2 crystal in-band pumped at 1610 nm by an Er-Yb-codoped fiber laser system. A laser slope efficiency of 55% (versus incident pump power) was achieved in a continuous-wave regime, with a maximum output power of 1.25 W at â¼1.88µm in a nearly diffraction-limited beam (M2=1.14). We also demonstrated a continuous tuning range of 180 nm, which extends to short wavelengths down to 1773 nm.
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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
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
We demonstrate for the first time, to our knowledge, an all-polarization-maintaining double-clad neodymium fiber laser operating in the dissipative soliton resonance (DSR) regime where stable mode-locking is achieved using a nonlinear amplifying loop mirror (NALM) with large normal dispersion in a figure-8 cavity design. The laser thereby generates square-shaped nanosecond pulses whose duration linearly scales with pump power from 0.5 up to 6 ns, with a maximum energy of 20 nJ. In addition, output pulses feature a remarkably narrow bandwidth of 60 pm along with a signal-to-noise ratio higher than 80 dB. This study then paves the way toward using such DSR-based sources for efficient frequency doubling in the blue spectral range.
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).
RESUMO
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.
RESUMO
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 â¼2051 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+âHo3+ energy transfer are determined. Tm,Ho:LiYF4/LiYF4 epitaxies are promising for waveguide lasers and amplifiers at above 2 µm.