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We report on the first sub-100 fs mode-locked laser operation of a Tm(3+)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 similar to 87.7 MHz. In the sub-100 fs regime, the maximum average output power amounted to 103 mW. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Structured ultrashort-pulse laser beams, and in particular eigenmodes of the paraxial Helmholtz equation, are currently extensively studied for novel potential applications in various fields, e.g., laser plasma acceleration, attosecond science, and fine micromachining. To extend these prospects further, in the present work we push forward the advancement of such femtosecond structured laser sources into the 2-mu m spectral region. Ultrashortpulse Hermite- and Laguerre-Gaussian laser modes both with a pulse duration around 100 fs are successfully produced from a compact solid-state laser in combination with a simple single-cylindrical-lens converter. The negligible beam astigmatism, the broad optical spectra, and the almost chirp-free pulses emphasize the high reliability of this laser source. This work, as a proof of principle study, paves the way toward few-cycle pulse generation of optical vortices at 2 mu m. The presented light source can enable new research in the fields of interaction with organic materials, next generation optical detection, and optical vortex infrared supercontinuum. (C) 2021 Chinese Laser Press

A transparent "mixed" 7 at.% Er:(Lu,Sc)(2)O-3 sesquioxide ceramic was fabricated by hot isostatic pressing of commercial sesquioxide powders at 1750 degrees C/200 MPa in argon atmosphere. It exhibited a cubic bixbyite-type structure (a = 10.198 angstrom), a mean grain size of 5.7 um and high low-signal transmission of 79.1 % in the near- IR. The spectroscopic properties of Er3+ ions were studied. For the I-4(11/2) -> I-4(13/2) transition, the stimulated-emission cross-section sigma(SE) is 1.30 x 10(-20) cm(2) at 2719 nm, the corresponding luminescence branching ratio B (JJ') is 19.9 % and the radiative lifetime of the I-4(11/2) state is 4.80 ms, as determined using a Judd-Ofelt theory accounting for intermediate configuration interaction. The crystal-field splitting of Er3+ multiplets was studied at 12 K. The ceramic exhibits a significant inhomogeneous broadening of spectral bands. An Er:(Lu,Sc)(2)O-3 ceramic laser generated 342 mW at 2.71 and 2.85 mu m with a high slope efficiency of 41.7 % (exceeding the Stokes limit) and a laser threshold of 125 mW.

We report on the development of a novel laser crystal with broadband emission properties at similar to 2 mu m - a Tm3+, Li+-codoped calcium tantalum gallium garnet (Tm:CLTGG). The crystal is grown by the Czochralski method. Its structure (cubic, sp. gr . la (3) over bard, a = 12.5158(0) angstrom) is refined by the Rietveld method. Tm:CLTGG exhibits a relatively high thermal conductivity of 4.33 Wm(-1) K-1. Raman spectroscopy confirms a weak concentration of vacancies due to the charge compensation provided by Li+ codoping. The transition probabilities of Tm3+ ions are determined using the modified Judd-Ofelt theory yielding the intensity parameters Omega(2) = 5.185, Omega(4) = 0.650, Omega(6) = 1.068 [10(-20) cm(2)] and alpha = 0.171 [10(-4) cm]. The crystal-field splitting of the Tm3+ multiplets is revealed at 10 K. The first diode-pumped Tm:CLTGG laser generates 1.08 W at similar to 2 mu m with a slope efficiency of 23.8%. The Tm3+ ions in CLTGG exhibit significant inhomogeneous spectral broadening due to the structure disorder (a random distribution of Ta5+ and Ga3+ cations over octahedral and tetrahedral lattice sites) leading to smooth and broad gain profiles (bandwidth: 130 nm) extending well above 2 mu m and rendering Tm:CLTGG suitable for femtosecond pulse generation. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Highly-doped "mixed" transparent sesquioxide ceramics, 10 at.% Yb:(Lu2/3Sc1/3)(2)O-3, are fabricated by vacuum sintering at 1700 degrees C followed by hot isostatic pressing (HIPing) at 1680 degrees C and 200 MPa. The ceramics are of single-phase nature with a cubic (C-type, a = 10.191 A) structure and a mean grain size of 0.66 mu m. They feature high low-signal transmission of 79.0% at 1.20 mu m. The Yb3+ ions in "mixed" ceramics exhibit strong inhomogeneous broadening of the absorption and emission bands, with sSE of 0.43 x 10(-20) cm(2) at 1079.4 nm and an emission bandwidth of 25.7 nm. The crystal-field splitting for Yb3+ ions is revealed at 12 K. The Yb ceramic laser generated a maximum peak output power of 250 mW at similar to 1.04 and 1.08 mu m with a slope efficiency of 40.3%. The ceramics are promising for mode-locked lasers at similar to 1.08 mu m, including thin-disk geometry.

Sub-100 fs pulse generation from a passively mode-locked Tm,Ho-codoped cubic multicomponent disordered garnet laser at similar to 2 mu m 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 similar to 102.5 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. (C) 2021 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

We present a comparative study of two Lu-based oxide ceramics doped with Yb3+ ions, namely Yb:Lu3Al5O12 (garnet) and Yb:Lu2O3 (sesquioxide), promising for thin-disk lasers. The ceramics are fabricated using nano-powders of 3.6 at.% Yb:Lu2O3 and Al2O3 produced by laser ablation: Yb:Lu3Al5O12 - by vacuum sintering at 1800 degrees C for 5 h with the addition of 1 wt% TEOS as a sintering aid, and Yb:Lu2O3 - by vacuum pre-sintering at 1250 degrees C for 2 h followed by Hot Isostatic Pressing at 1400 degrees C for 2 h under Ar gas pressure of 207 MPa. The comparison includes the structure, Raman spectra, transmission, optical spectroscopy and laser operation. The crystal-field splitting of Yb3+ multiplets is revealed for Lu3Al5O12. A continuous-wave (CW) Yb:Lu3Al5O12 ceramic microchip laser generates 5.65 W at 1031.1 nm with a slope efficiency of 67.2%. In the quasi-CW regime, the peak power is scaled up to 8.83 W. The power scaling for the Yb:Lu2O3 ceramic laser is limited by losses originating from residual coloration and inferior thermal behavior.

A transparent Tm:Lu3Al5O12 ceramic is fabricated by solid-state reactive sintering at 1830 degrees C for 30 h using commercial alpha-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 mu m). The in-line transmission at similar to 1 mu m 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 2.37x10(-21) cm(2) at 1749nm and the radiative lifetime of the F-3(4) state is about 10 ms. The modified Judd-Ofelt theory accounting for configuration interaction is applied to determine the transition probabilities of Tm3+, yielding the intensity parameters Omega(2) =2.507, Omega(4) = 1.236, Omega(6) = 1.340 [10(-20) cm(2)] and alpha = 0.196x10(-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 792 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 mu m. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement