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1.
Opt Express ; 29(24): 40323-40332, 2021 Nov 22.
Artigo em Inglês | MEDLINE | ID: mdl-34809376

##### RESUMO

Sub-100 fs pulse generation from a passively mode-locked Tm,Ho-codoped cubic multicomponent disordered garnet laser at â¼2 µm is demonstrated. A single-walled carbon nanotube saturable absorber is implemented to initiate and stabilize the soliton mode-locking. The Tm,Ho:LCLNGG (lanthanum calcium lithium niobium gallium garnet) laser generated pulses as short as 63 fs at a central wavelength of 2072.7 nm with an average output power of 63 mW at a pulse repetition rate of â¼102.5 MHz. Higher average output power of 121 mW was obtained at the expense of longer pulse duration (96 fs) at 2067.6 nm using higher output coupling. To the best of our knowledge, this is the first report on mode-locked operation of the Tm,Ho:LCLNGG crystal.

2.
Appl Opt ; 60(22): 6600-6603, 2021 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-34612903

##### RESUMO

This paper reports refined Sellmeier equations for the biaxial nonlinear crystal BaGa4S7 that provide a good reproduction of the phase-matching angles for second-harmonic generation (SHG) and sum-frequency generation (SFG) of the mid-IR outputs of Nd:YAG and Ho:YLF laser-pumped optical parametric oscillators (OPOs) and a frequency-doubled CO2 laser in the 0.7584-8.018 µm range. The theoretical results are found to agree with the recent experimental data for 1-µm-pumped optical parametric processes based on BaGa4S7 beyond 8 µm.

3.
Opt Express ; 29(20): 31137-31144, 2021 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-34615213

##### RESUMO

We report on the first sub-100 fs mode-locked laser operation of a Tm3+-doped disordered calcium lithium tantalum gallium garnet (Tm:CLTGG) crystal. Soliton mode-locking was initiated and stabilized by a transmission-type single-walled carbon nanotube saturable absorber. Pulses as short as 69 fs were achieved at a central wavelength of 2010.4 nm with an average power of 28 mW at a pulse repetition rate of â¼87.7 MHz. In the sub-100 fs regime, the maximum average output power amounted to 103 mW.

4.
Opt Lett ; 46(18): 4454-4457, 2021 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-34525020

##### RESUMO

In this Letter, to the best of our knowledge, we present the first thulium (Tm) single-crystal fiber (SCF) laser with free-space propagation of the laser beam only. The SCF is equipped with diffusion-bonded end caps of undoped YAG for better thermal management and enhancement of pump guiding. By utilizing mode matching and pump guiding in different SCF parts, an output power of 9.1 W is achieved at â¼2.02µm with a slope efficiency of 49.4%. This straightforward approach, which is also simple to realize and is based on combining the advantages of fiber-geometry structure and crystalline properties of Tm:YAG, is expected to be useful for 2 µm amplification stages in different time formats as well.

5.
Opt Lett ; 46(14): 3428-3431, 2021 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-34264230

##### RESUMO

Kerr-lens mode-locked solid-state laser operation at â¼2µm is investigated. Using a Tm3+-doped (Lu,Sc)2O3 "mixed" sesquioxide ceramic as a gain medium, pulses as short as 58 fs are generated at â¼2081nm via soft-aperture Kerr-lens mode locking. The average output power amounts to 220 mW at a pulse repetition rate of 84.8 MHz. The emitted spectrum at the long-wavelength wing extends to >2.2µm which is attributed to vibronic transitions of the Tm3+ ions. The latter is found to be essential for generating pulses with durations in the 50 fs range.

6.
Opt Lett ; 46(11): 2642-2645, 2021 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-34061077

##### RESUMO

We report on sub-50 fs pulse generation from a passively mode-locked (ML) Tm,Ho-codoped crystalline laser operating in a 2 µm spectral region. A ${\rm Tm},{\rm Ho}{:}{\rm Ca}({\rm Gd},{\rm Lu}){{\rm AlO}_4}$ laser delivers pulses as short as 46 fs at 2033 nm with an average power of 121 mW at a pulse repetition rate of ${\sim}{78}\;{\rm MHz}$ employing a semiconductor saturable absorber mirror as a saturable absorber. To the best of our knowledge, this result represents the shortest pulses ever generated from a Tm- and/or Ho-based solid-state laser. Polarization switching in the anisotropic gain material is observed in the ML regime without any polarization selection elements which is essential for the shortest pulses.

7.
Opt Express ; 29(9): 13496-13503, 2021 Apr 26.
Artigo em Inglês | MEDLINE | ID: mdl-33985081

##### RESUMO

We present a sub-50-fs diode-pumped Kerr-lens mode-locked laser employing a novel "mixed" monoclinic Yb:Ca4(Gd,Y)O(BO3)3 (Yb:GdYCOB) crystal as a gain medium. Nearly Fourier-limited pulses as short as 43 fs at 1036.7 nm are generated with an average power of 84 mW corresponding to a pulse repetition rate of â¼70.8 MHz. A higher average power of 300 mW was achieved at the expense of the pulse duration (113 fs) corresponding to an optical-to-optical efficiency of 35.8% representing a record-high value for any Yb-doped borate crystal. Non-phase-matched self-frequency doubling is observed in the mode-locked regime with pronounced strong spectral fringes which originate from two delayed green replicas of the fundamental femtosecond pulses in the time domain.

8.
Appl Opt ; 60(4): 805-808, 2021 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-33690386

##### RESUMO

We present refined Sellmeier equations for AgGaSe2 that provide good reproduction of the phase-matching angles for frequency upconversion of CO2 laser radiation in the 1.7652-10.5910 µm range and for frequency downconversion in the 1.85-18 µm range thus far reported in the literature.

9.
Opt Lett ; 46(2): 332-335, 2021 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-33449021

##### RESUMO

We report on efficient midinfrared difference-frequency generation (DFG) in orientation-patterned GaAs by intracavity mixing the signal and idler pulses of a narrowband nanosecond optical parametric oscillator based on periodically poled LiNbO3. The maximum average DFG output power reached 215 mW at 8.15 µm for a repetition rate of 35 kHz. The temperature tuning range spanned over 8026-8710 nm. The maximum overall conversion efficiency from 1 to 8 µm amounted to â¼1.3%.

10.
Opt Lett ; 46(1): 122-125, 2021 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-33362031

##### RESUMO

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 â¼1942nm(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.

11.
Appl Opt ; 59(33): 10493-10497, 2020 Nov 20.
Artigo em Inglês | MEDLINE | ID: mdl-33361983

##### RESUMO

Mode-locked laser operation near 2.05 µm based on a mixed sesquioxide Tm:LuYO3 ceramic is demonstrated. Continuous-wave and wavelength-tunable operation is also investigated. Employing a GaSb-based semiconductor saturable absorber mirror as a saturable absorber, a maximum average output power of 133 mW is obtained for a pulse duration of 59 fs. Pulses as short as 54 fs, i.e., eight optical cycles are generated at a repetition rate of â¼78MHz with an average output power of 51 mW. To the best of our knowledge, this result represents the shortest pulse duration ever achieved from Tm-based solid-state mode-locked lasers.

12.
Opt Lett ; 45(22): 6142-6145, 2020 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-33186935

##### RESUMO

We demonstrate sub-100-fs Kerr-lens mode-locking of a Tm:MgWO4 laser emitting at â¼2µm assisted by a single-walled carbon-nanotube saturable absorber. A maximum average output power of 100 mW is achieved with pulse duration of 89 fs at a pulse repetition rate of â¼86MHz. The shortest pulse duration derived from frequency-resolved optical gating amounts to 76 fs at 2037 nm, corresponding to nearly bandwidth-limited pulses. To the best of our knowledge, these are the shortest pulses generated from any Tm-doped tungstate crystal and the first report on saturable absorber assisted Kerr-lens mode-locking of a Tm laser at â¼2µm.

13.
Opt Lett ; 45(20): 5692-5695, 2020 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-33057261

##### RESUMO

We report on a microjoule-scale mid-infrared optical parametric amplifier (OPA) based on the recently developed wide-bandgap orthorhombic crystal, BaGa4S7 (BGS) and directly compare its performance to that of LiGaS2 (LGS) in the same OPA setup. The source is based on a single OPA stage amplifying supercontinuum seed pulses with a quantum efficiency of 29% at an idler wavelength of 10 µm, featuring nominally carrier-envelope phase-stable pulses. As a result of pumping the OPA directly at 1 µm, the overall conversion efficiency far exceeds that of traditional schemes based on OPAs followed by difference frequency generation. Chirp compensation using bulk germanium resulted in 126 fs pulses covering the 7.6-11.5 µm spectral range. BGS holds great promise for power scaling due to its availability in larger single-crystal sizes than LGS.

14.
Opt Express ; 28(19): 28399-28413, 2020 Sep 14.
Artigo em Inglês | MEDLINE | ID: mdl-32988111

##### RESUMO

A transparent Tm:Lu3Al5O12 ceramic is fabricated by solid-state reactive sintering at 1830 °C for 30âh using commercial α-Al2O3 and Lu2O3/Tm2O3 powders and sintering aids - MgO and TEOS. The ceramic belongs to the cubic system and exhibits a close-packed structure (mean grain size: 21 µm). The in-line transmission at â¼1 µm is 82.6%, close to the theoretical limit. The spectroscopic properties of the ceramic are studied in detail. The maximum stimulated-emission cross-section is 2.37×10-21 cm2 at 1749nm and the radiative lifetime of the 3F4 state is about 10âms. The modified Judd-Ofelt theory accounting for configuration interaction is applied to determine the transition probabilities of Tm3+, yielding the intensity parameters Ω2 = 2.507, Ω4 = 1.236, Ω6 = 1.340 [10-20 cm2] and α = 0.196×10-4 cm. The effect of excited configurations on lower-lying interconnected states with the same J quantum number is discussed. First laser operation is achieved under diode-pumping at 792ânm. A 4 at.% Tm:Lu3Al5O12 ceramic laser generated 3.12 W at 2022-2035nm with a slope efficiency of 60.2%. The ceramic is promising for multi-watt lasers at >2 µm.

15.
Opt Lett ; 45(13): 3813-3815, 2020 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-32630961

##### RESUMO

BaGa2GeSe6 (BGGSe) is a newly developed nonlinear material that is attractive for ultrabroad frequency mixing and ultrashort pulse generation due to its comparably low dispersion and high damage threshold. A numerical study shows the material's capacity for octave-spanning mid-infrared pulse generation up to 18 µm. In a first experiment, we show that a long crystal length of 2.6 mm yields a pulse energy of 21 pJ at 100 MHz with a spectral bandwidth covering 5.8 to 8.5 µm. The electric field of the carrier-envelope-phase stable pulse is directly measured with electro-optical sampling and reveals a pulse duration of 91 fs, which corresponds to sub-four optical cycles, thus confirming some of the prospects of the material for ultrashort pulse generation and mid-infrared spectroscopy.

16.
Opt Lett ; 45(14): 4060-4063, 2020 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-32667354

##### RESUMO

Surface channel waveguides (WGs) based on a half-ring (40-60-µm-diameter) depressed-index cladding (type III) geometry are fabricated in monoclinic Tm3+:MgWO4 by femtosecond (fs) laser writing at a repetition rate of 1 kHz. The WGs are characterized by confocal laser microscopy and µ-Raman spectroscopy. A Tm3+:MgWO4 WG laser generates 320 mW at â¼2.02µm with a slope efficiency of 64.4%. The WG emits a transverse single-mode and linear polarization (E||Nm). A remarkable low loss of <0.1dB/cm is measured for the WG. Vibronic laser emission at â¼2.08µm is also achieved.

17.
Opt Express ; 28(7): 9039-9048, 2020 Mar 30.
Artigo em Inglês | MEDLINE | ID: mdl-32225517

##### RESUMO

We report on the crystal growth, spectroscopy and first laser operation of a novel double molybdate compound - Tm:KY(MoO4)2. This orthorhombic (sp. gr. Pbna) crystal exhibits strong anisotropy of the spectroscopic properties due to its layered structure. The maximum stimulated emission cross-section for the 3F4 â 3H6 transition is 2.70×10-20 cm2 at 1856nm with a bandwidth of >110ânm (for E || b). The lifetime of the 3F4 state is 2.29âms. Crystalline films and plates (thickness down to 70 µm) of high optical quality are obtained by mechanical cleavage along the (100) plane. Continuous-wave diode-pumped laser operation is achieved in such thin films and plates yielding a maximum output power of 0.88 W at â¼1.9 µm with a slope efficiency of 65.8% and a linearly polarized laser output. Vibronic lasing is demonstrated at â¼2.06 µm. Tm:KY(MoO4)2 is promising for microchip and thin-disk lasers.

18.
Opt Lett ; 45(8): 2136-2139, 2020 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-32287175

##### RESUMO

The unknown magnitude and relative signs of the trigonal crystal ${\rm BaGa}_{2}{\rm GeSe}_{6}$BaGa2GeSe6 nonlinear coefficients have hindered defining an optimum orientation for maximum frequency conversion efficiency. This issue is resolved in the present work, obtaining ${d_{11}}= + {23.6}$d11=+23.6, ${d_{22}}= - {18.5}$d22=-18.5, and ${d_{31}}= + {18.3}\;{\rm pm/V}$d31=+18.3pm/V for frequency doubling of the 10.591 µm radiation.

19.
Opt Lett ; 45(7): 1770-1773, 2020 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-32235995

##### RESUMO

Monoclinic (wolframite-type) monotungstate crystals are promising for rare-earth doping. We report polarized room- and low-temperature spectroscopy and efficient high-power laser operation of such a ${{\rm Yb}^{3 + }}{:}\,{{\rm MgWO}_4}$Yb3+:MgWO4 crystal featuring high stimulated emission cross section (${\sigma _{\rm SE}}\; = \;{6}.{2}\; \times \;{{10}^{ - 20}}\;{{\rm cm}^2}$σSE=6.2×10-20cm2 at 1056.7 nm for light polarization ${\rm E}\;||\;{N_m}$E||Nm), large Stark splitting of the ground state (${765}\;{{\rm cm}^{ - 1}}$765cm-1), large gain bandwidth (26.1 nm for ${\rm E}\;||\;{N_g}$E||Ng), and strong Raman response (most intense mode at ${916}\;{{\rm cm}^{ - 1}}$916cm-1). A diode-pumped ${{\rm Yb}^{3 + }}{:}\,{{\rm MgWO}_4}$Yb3+:MgWO4 laser generated 18.2 W at ${\sim}{1056}\;{\rm nm}$â¼1056nm with a slope efficiency of ${\sim}{89}\%$â¼89% and a linearly polarized laser output.

20.
Opt Express ; 28(3): 3528-3540, 2020 Feb 03.
Artigo em Inglês | MEDLINE | ID: mdl-32122019

##### RESUMO

Depressed-index buried and surface channel waveguides (type III) are produced in a bulk 3.5 at.% Tm3+:CALGO crystal by femtosecond direct-laser-writing at kHz repetition rate. The waveguides are characterized by confocal microscopy and µ-Raman spectroscopy. Under in-band-pumping at 1679 nm (3H6 â 3F4 transition) by a Raman fiber laser, the buried channel waveguide laser with a circular cladding (diameter: 60 µm) generated a continuous-wave output power of 0.81 W at 1866-1947 nm with a slope efficiency of 71.2% (versus the absorbed pump power) and showed a laser threshold of 200âmW. The waveguide propagation losses were as low as 0.3 ± 0.2âdB/cm. The laser performance under in-band pumping was superior compared pumping at â¼800ânm (3H6 â 3H4 transition), i.e., the convetional pump wavelength. Vibronic laser emission from the WG laser above 2 µm is also achieved. The low-loss behavior, the broadband emission properties and good power scaling capabilities indicate the suitability of Tm3+:CALGO waveguides for mode-locked laser operation at â¼2 µm.

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