Publications by authors named "Valentin Petrov"

163 Publications

Kerr-lens mode-locked Tm-doped sesquioxide ceramic laser.

Opt Lett 2021 Jul;46(14):3428-3431

Kerr-lens mode-locked solid-state laser operation at ∼2µ is investigated. Using a -doped (,) "mixed" sesquioxide ceramic as a gain medium, pulses as short as 58 fs are generated at ∼2081 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 >2.2µ which is attributed to vibronic transitions of the ions. The latter is found to be essential for generating pulses with durations in the 50 fs range.
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http://dx.doi.org/10.1364/OL.431067DOI Listing
July 2021

Sub-50  fs pulse generation from a SESAM mode-locked Tm,Ho-codoped calcium aluminate laser.

Opt Lett 2021 Jun;46(11):2642-2645

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.
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http://dx.doi.org/10.1364/OL.426113DOI Listing
June 2021

Diode-pumped sub-50-fs Kerr-lens mode-locked Yb:GdYCOB laser.

Opt Express 2021 Apr;29(9):13496-13503

We present a sub-50-fs diode-pumped Kerr-lens mode-locked laser employing a novel "mixed" monoclinic Yb:Ca(Gd,Y)O(BO) (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 ∼70.8 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.
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http://dx.doi.org/10.1364/OE.424769DOI Listing
April 2021

Refined Sellmeier equations for AgGaSe up to 18  µm.

Appl Opt 2021 Feb;60(4):805-808

We present refined Sellmeier equations for that provide good reproduction of the phase-matching angles for frequency upconversion of 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.
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http://dx.doi.org/10.1364/AO.401828DOI Listing
February 2021

Nanosecond optical parametric oscillator with midinfrared intracavity difference-frequency mixing in orientation-patterned GaAs.

Opt Lett 2021 Jan;46(2):332-335

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 . 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 ∼1.3.
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http://dx.doi.org/10.1364/OL.413583DOI Listing
January 2021

Tm and Ho colasing in in-band pumped waveguides fabricated by femtosecond laser writing.

Opt Lett 2021 Jan;46(1):122-125

We report on the first, to the best of our knowledge, in-band pumped , 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. % , 0.5 at. % :() crystal by femtosecond pulse direct laser writing. Under in-band pumping by a 1679 nm Er Raman fiber laser, and colasing is observed in the WG and explained by bidirectional energy transfer. The maximum total output power at ∼1942() and 2059 nm () 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.
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http://dx.doi.org/10.1364/OL.399546DOI Listing
January 2021

SESAM mode-locked Tm:LuYO ceramic laser generating 54-fs pulses at 2048  nm.

Appl Opt 2020 Nov;59(33):10493-10497

Mode-locked laser operation near 2.05 µm based on a mixed sesquioxide : 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 ∼78 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.
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http://dx.doi.org/10.1364/AO.408650DOI Listing
November 2020

Single-walled carbon-nanotube saturable absorber assisted Kerr-lens mode-locked Tm:MgWO laser.

Opt Lett 2020 Nov;45(22):6142-6145

We demonstrate sub-100-fs Kerr-lens mode-locking of a : laser emitting at ∼2µ 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 ∼86. 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 ∼2µ.
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http://dx.doi.org/10.1364/OL.411288DOI Listing
November 2020

Efficient, sub-4-cycle, 1-µm-pumped optical parametric amplifier at 10  µm based on BaGaS.

Opt Lett 2020 Oct;45(20):5692-5695

We report on a microjoule-scale mid-infrared optical parametric amplifier (OPA) based on the recently developed wide-bandgap orthorhombic crystal, (BGS) and directly compare its performance to that of (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.
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http://dx.doi.org/10.1364/OL.403856DOI Listing
October 2020

Spectroscopy and diode-pumped laser operation of transparent Tm:LuAlO ceramics produced by solid-state sintering.

Opt Express 2020 Sep;28(19):28399-28413

A transparent Tm:LuAlO ceramic is fabricated by solid-state reactive sintering at 1830 °C for 30 h using commercial α-AlO and LuO/TmO 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 ∼1 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 cm at 1749nm and the radiative lifetime of the F state is about 10 ms. The modified Judd-Ofelt theory accounting for configuration interaction is applied to determine the transition probabilities of Tm, yielding the intensity parameters Ω = 2.507, Ω = 1.236, Ω = 1.340 [10 cm] and α = 0.196×10 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:LuAlO 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.
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http://dx.doi.org/10.1364/OE.400802DOI Listing
September 2020

Low-loss fs-laser-written surface waveguide lasers at >2  µm in monoclinic Tm:MgWO.

Opt Lett 2020 Jul;45(14):4060-4063

Surface channel waveguides (WGs) based on a half-ring (40-60-µm-diameter) depressed-index cladding (type III) geometry are fabricated in monoclinic Tm:MgWO by femtosecond (fs) laser writing at a repetition rate of 1 kHz. The WGs are characterized by confocal laser microscopy and -Raman spectroscopy. A Tm:MgWO WG laser generates 320 mW at ∼2.02µm with a slope efficiency of 64.4%. The WG emits a transverse single-mode and linear polarization (||). A remarkable low loss of <0.1dB/cm is measured for the WG. Vibronic laser emission at ∼2.08µm is also achieved.
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http://dx.doi.org/10.1364/OL.395811DOI Listing
July 2020

Few-cycle mid-infrared pulses from BaGaGeSe.

Opt Lett 2020 Jul;45(13):3813-3815

(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.
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http://dx.doi.org/10.1364/OL.397981DOI Listing
July 2020

Effective nonlinearity of the new quaternary chalcogenide crystal BaGaGeSe.

Opt Lett 2020 Apr;45(8):2136-2139

The unknown magnitude and relative signs of the trigonal crystal ${\rm BaGa}_{2}{\rm GeSe}_{6}$BaGaGeSe nonlinear coefficients have hindered defining an optimum orientation for maximum frequency conversion efficiency. This issue is resolved in the present work, obtaining ${d_{11}}= + {23.6}$d=+23.6, ${d_{22}}= - {18.5}$d=-18.5, and ${d_{31}}= + {18.3}\;{\rm pm/V}$d=+18.3pm/V for frequency doubling of the 10.591 µm radiation.
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http://dx.doi.org/10.1364/OL.388373DOI Listing
April 2020

Spectroscopy and high-power laser operation of a monoclinic Yb:MgWO crystal.

Opt Lett 2020 Apr;45(7):1770-1773

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 ${{\rm Yb}^{3 + }}{:}\,{{\rm MgWO}_4}$Yb:MgWO crystal featuring high stimulated emission cross section (${\sigma _{\rm SE}}\; = \;{6}.{2}\; \times \;{{10}^{ - 20}}\;{{\rm cm}^2}$σ=6.2×10cm at 1056.7 nm for light polarization ${\rm E}\;||\;{N_m}$E||N), large Stark splitting of the ground state (${765}\;{{\rm cm}^{ - 1}}$765cm), large gain bandwidth (26.1 nm for ${\rm E}\;||\;{N_g}$E||N), and strong Raman response (most intense mode at ${916}\;{{\rm cm}^{ - 1}}$916cm). A diode-pumped ${{\rm Yb}^{3 + }}{:}\,{{\rm MgWO}_4}$Yb:MgWO laser generated 18.2 W at ${\sim}{1056}\;{\rm nm}$∼1056nm with a slope efficiency of ${\sim}{89}\% $∼89% and a linearly polarized laser output.
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http://dx.doi.org/10.1364/OL.389627DOI Listing
April 2020

Laser operation of cleaved single-crystal plates and films of Tm:KY(MoO).

Opt Express 2020 Mar;28(7):9039-9048

We report on the crystal growth, spectroscopy and first laser operation of a novel double molybdate compound - Tm:KY(MoO). 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 F → H transition is 2.70×10 cm at 1856nm with a bandwidth of >110 nm (for E || b). The lifetime of the F state is 2.29 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 ∼1.9 µm with a slope efficiency of 65.8% and a linearly polarized laser output. Vibronic lasing is demonstrated at ∼2.06 µm. Tm:KY(MoO) is promising for microchip and thin-disk lasers.
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http://dx.doi.org/10.1364/OE.384260DOI Listing
March 2020

Ultrafast laser inscribed waveguide lasers in Tm:CALGO with depressed-index cladding.

Opt Express 2020 Feb;28(3):3528-3540

Depressed-index buried and surface channel waveguides (type III) are produced in a bulk 3.5 at.% Tm: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 (H → F 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 200 mW. The waveguide propagation losses were as low as 0.3 ± 0.2 dB/cm. The laser performance under in-band pumping was superior compared pumping at ∼800 nm (H → H 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 Tm:CALGO waveguides for mode-locked laser operation at ∼2 µm.
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http://dx.doi.org/10.1364/OE.384258DOI Listing
February 2020

Upconversion pumping of a 2.3  µm Tm:KYF laser with a 1064  nm ytterbium fiber laser.

Opt Lett 2020 Feb;45(4):931-934

We report efficient lasing of the isotropic ${{\rm Tm}^{3 + }}\!:\!{{\rm KY}_3}{{\rm F}_{10}}$Tm:KYF crystal near 2.3 µm via upconversion pumping with a 1064 nm ytterbium fiber laser as the pump source. When pumped at 1064 nm, an x-cavity ${{\rm Tm}^{3 + }}\!:\!{{\rm KY}_3}{{\rm F}_{10}}$Tm:KYF laser operated at the free-running wavelength of 2344 nm. Lasing was obtained with output couplers having transmissions in the range of 1-3%, and as high as 124 mW of continuous-wave (cw) output power was generated with 604 mW of absorbed pump power by using the 3% output coupler. Broadly tunable cw lasing could be obtained in the 2268-2373 nm wavelength range. An analysis of the experimental power efficiency data shows that nearly all of the absorbed pump photons were converted to 2.3 µm laser output after accounting for the quantum defect of the laser transition and resonator losses. We expect that higher lasing efficiency should be possible by using longer crystals to increase the pump absorption.
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http://dx.doi.org/10.1364/OL.384284DOI Listing
February 2020

High-energy 2  µm pulsed vortex beam excitation from a Q-switched Tm:LuYAG laser.

Opt Lett 2020 Feb;45(3):722-725

We report on the first, to the best of our knowledge, direct generation of pulsed vortex beams at 2 µm from a ${ Q}$Q-switched Tm:LuYAG laser. High-energy Laguerre-Gaussian (${{\rm LG}_{0,l}}$LG) pulsed laser beams with well-defined handedness are selectively excited through spatially matched pump gain distribution and asymmetric cavity loss without using any intracavity handedness-selective optical elements. Pulse energies of 1.48 mJ for the ${{\rm LG}_{0, + 1}}$LG mode and 1.51 mJ for the ${{\rm LG}_{0, - 1}}$LG mode, respectively, are achieved at a repetition rate of 500 Hz. The pulsed laser beams with helical wavefronts are potentially useful for studying orbital angular momentum transformation dynamics, generation of mid-IR vortex beams, and nanostructuring of organic materials.
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http://dx.doi.org/10.1364/OL.384201DOI Listing
February 2020

Graphene mode-locked operation of Tm:YLiF and Tm:KYF lasers near 2.3  µm.

Opt Lett 2020 Feb;45(3):656-659

We report experimental demonstration of graphene mode-locked operation of ${{\rm Tm}^{3 + }}\!:\!{{\rm YLiF}_4}$Tm:YLiF (YLF) and ${{\rm Tm}^{3 + }}\!:\!{{\rm KY}_3}{{\rm F}_{10}}$Tm:KYF (KYF) lasers near 2.3 µm. To scale up the intracavity pulse energy, the cavity was extended, and double-end pumping was employed with a continuous-wave, tunable ${{\rm Ti}^{3 + }}\!:\!{\rm sapphire}$Ti:sapphire laser delivering up to 1 W near 780 nm. The extended ${{\rm Tm}^{3 + }}\!:\!{\rm KYF}$Tm:KYF laser cavity was purged with dry nitrogen to eliminate pulsing instabilities due to atmospheric absorption lines, but this was not needed in the case of the ${{\rm Tm}^{3 + }}\!:\!{\rm YLF}$Tm:YLF laser. Once initiated by graphene, stable uninterrupted mode-locked operation could be maintained with both lasers. With the extended cavity ${{\rm Tm}^{3 + }}\!:\!{\rm YLF}$Tm:YLF laser, 921 fs pulses were generated at a repetition rate of 17.2 MHz at 2304 nm. 739 fs pulses were obtained at the repetition rate of 54 MHz from the ${{\rm Tm}^{3 + }}\!:\!{\rm KYF}$Tm:KYF laser at 2340 nm. The corresponding pulse energy and peak power were 2.4 nJ and 2.6 kW for the ${{\rm Tm}^{3 + }}\!:\!{\rm YLF}$Tm:YLF laser, and 1.2 nJ and 1.6 kW for the ${{\rm Tm}^{3 + }}\!:\!{\rm KYF}$Tm:KYF laser. We foresee that it should be possible to generate shorter pulses at higher pump levels.
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http://dx.doi.org/10.1364/OL.385629DOI Listing
February 2020

Thermo-optic dispersion formula for BaGaGeSe.

Appl Opt 2019 Dec;58(35):9709-9711

A thermo-optic dispersion formula for ${{\rm BaGa}_2}{{\rm GeSe}_6}$BaGaGeSe nonlinear crystal is reported. The experimentally determined temperature-dependent phase-matching conditions for second-harmonic and sum-frequency generation of Nd:YAG laser-pumped ${{\rm KTiOPO}_4}$KTiOPO (KTP) and ${{\rm RbTiOAsO}_4}$RbTiOAsO (RTA) optical parametric oscillators as well as a ${{\rm CO}_2}$CO laser and its harmonics in the 0.805-10.5910 µm range are precisely reproduced by the formula when combined with the Sellmeier equations previously reported by the present authors [Appl. Opt.57, 7440 (2018)APOPAI0003-693510.1364/AO.57.007440].
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http://dx.doi.org/10.1364/AO.58.009709DOI Listing
December 2019

Narrow-band periodically poled lithium niobate nonresonant optical parametric oscillator.

Opt Lett 2019 Dec;44(23):5659-5662

We report on a narrowband, nonresonant periodically poled lithium niobate (PPLN) optical parametric oscillator using a volume Bragg grating (VBG) as the spectral narrowing element. Pumping by a Nd:YVO laser at 1.06 μm, a maximum output power of 4.75 W is achieved at a repetition rate of 20 kHz for a conversion efficiency of 47.5%. Both signal and idler spectra are narrowed to less than 2 nm, at good beam quality and stability.
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http://dx.doi.org/10.1364/OL.44.005659DOI Listing
December 2019

2.7  μm optical vortex beam directly generated from an Er:YO ceramic laser.

Opt Lett 2019 Oct;44(20):4973-4976

We demonstrate, to the best of our knowledge, the first direct vortex beam generation in the 3 μm spectral region by employing an Er:YO ceramic laser. Controllable handedness with high purity is achieved by introducing asymmetric cavity loss and reducing the number of longitudinal modes. The average orbital angular momentum of the produced scalar vortex beam is quantitatively evaluated to be 0.95ħ for the LG mode and -0.94ħ for the LG mode. The corresponding optical spectrum is centered at 2710.8 and 2710.5 nm, respectively.
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http://dx.doi.org/10.1364/OL.44.004973DOI Listing
October 2019

Continuous-wave mid-infrared laser operation of Tm:KYF at 2.3  μm.

Opt Lett 2019 Jul;44(13):3242-3245

We report continuous-wave lasing demonstration of a Tm:KYF crystalline gain medium at 2343 nm. A narrow-linewidth, tunable, continuous-wave Ti:sapphire laser was used to end pump a Tm:KYF crystal with thulium doping of 8 at. %. With 1 W of pump power, the resonator with a 1% output coupler generated output powers of 31 and 122 mW in single-pumping and double-pumping configurations, respectively. Excitation efficiency of the laser was investigated for pump wavelengths in the 765-806 nm range. Four pump bands were identified in this wavelength range, with the two most efficient pump bands centered at 773 and 778 nm. The output of the laser could be tuned smoothly and continuously over a spectral width of 125 nm from 2260 to 2385 nm. The lifetime of the H3 level was further measured to be 16 μs, and the emission cross section was determined based on lasing threshold measurements.
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http://dx.doi.org/10.1364/OL.44.003242DOI Listing
July 2019

Broadband vibrational sum-frequency generation spectrometer at 100 kHz in the 950-1750 cm spectral range utilizing a LiGaS optical parametric amplifier.

Opt Express 2019 May;27(11):15289-15297

We present a 100 kHz broadband vibrational sum-frequency generation (VSFG) spectrometer operating in the 5.7-10.5 µm (950-1750 cm) wavelength range. The mid-infrared beam of the system is obtained from a collinear, type-I LiGaS-crystal-based optical parametric amplifier seeded by a supercontinuum and pumped directly by 180 fs, ~32 µJ, 1.03 µm pulses from an Yb:KGd(WO) laser system. Up to 0.5 µJ mid-infrared pulses with durations below 100 fs were obtained after dispersion compensation utilizing bulk materials. We demonstrate the utility of the spectrometer by recording high-resolution, low-noise vibrational spectra of Langmuir-Blodgett supported lipid monolayers on CaF. The presented VSFG spectrometer scheme offers superior signal-to-noise ratios and constitutes a high-efficiency, low-cost, easy-to-use alternative to traditional schemes relying on optical parametric amplification followed by difference frequency generation.
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http://dx.doi.org/10.1364/OE.27.015289DOI Listing
May 2019

Fs-laser-written thulium waveguide lasers Q-switched by graphene and MoS.

Opt Express 2019 Mar;27(6):8745-8755

We report the generation of mid-infrared (~2 µm) high repetition rate (MHz) sub-100 ns pulses in buried thulium-doped monoclinic double tungstate crystalline waveguide lasers using two-dimensional saturable absorber materials, graphene and MoS. The waveguide (propagation losses of ~1 dB/cm) was micro-fabricated by means of ultrafast femtosecond laser writing. In the continuous-wave regime, the waveguide laser generated 247 mW at 1849.6 nm with a slope efficiency of 48.7%. The laser operated at the fundamental transverse mode with a linearly polarized output. With graphene as a saturable absorber, the pulse characteristics were 88 ns / 18 nJ (duration / energy) at a repetition rate of 1.39 MHz. Even shorter pulses of 66 ns were achieved with MoS. Graphene and MoS are therefore promising for high repetition rate nanosecond Q-switched infrared waveguide lasers.
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http://dx.doi.org/10.1364/OE.27.008745DOI Listing
March 2019

"Mixed" Tm:Ca(Gd,Lu)AlO - a novel crystal for tunable and mode-locked 2 µm lasers.

Opt Express 2019 Apr;27(7):9987-9995

We report on the crystal growth, spectroscopy characterization and first laser operation of a new tetragonal disordered "mixed" calcium aluminate crystal, Tm:Ca(Gd,Lu)AlO. The introduction of Lu leads to an additional inhomogeneous broadening of Tm absorption and emission spectra compared to the well-known Tm:CaGdAlO. The maximum stimulated-emission cross-section for the F → H Tm transition is 0.91 × 10 cm at 1813 nm for σ-polarization, and the emission bandwidth is more than 200 nm. A continuous-wave diode-pumped Tm:Ca(Gd,Lu)AlO laser generates 1.82 W at 1945 nm with a slope efficiency of 29%. Under Ti:Sapphire laser pumping, a continuous tuning of the laser wavelength from 1836 to 2083 nm (tuning range: 247 nm) is demonstrated. The Tm:Ca(Gd,Lu)AlO crystal is promising for tunable/femtosecond lasers at ~2 μm.
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http://dx.doi.org/10.1364/OE.27.009987DOI Listing
April 2019

Femtosecond-laser-written Ho:KGd(WO) waveguide laser at 2.1  μm.

Opt Lett 2019 Apr;44(7):1738-1741

We report on efficient laser operation of the first holmium monoclinic double tungstate waveguide laser fabricated by femtosecond direct laser writing. A depressed-index buried channel waveguide with a 60 μm diameter circular cladding was inscribed in 5 at.% Ho:KGd(WO). It was characterized by confocal microscopy and μ-Raman and μ-luminescence spectroscopy, indicating well-preserved crystallinity of its core. Pumped by a thulium bulk laser, the holmium waveguide laser generated 212 mW at 2055 nm with a slope efficiency of 67.2%. The waveguide propagation losses were 0.94±0.2  dB/cm.
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http://dx.doi.org/10.1364/OL.44.001738DOI Listing
April 2019

Diamond saw dicing of thulium channel waveguide lasers in monoclinic crystalline films.

Opt Lett 2019 Apr;44(7):1596-1599

A surface channel waveguide (WG) laser is produced by diamond saw dicing of a 15 μm thick 10 at. % Tm:KYGdLu(WO) monoclinic double tungstate thin film grown by liquid phase epitaxy on an undoped KY(WO) substrate. The WG propagation losses are 1.1±0.5  dB/cm. When pumped at 802 nm, laser operation is achieved with a maximum output power of 262 mW at 1833 nm with a record slope efficiency of 82.6% (versus the absorbed pump power) in a TE spatial mode (linear laser polarization, E‖N). Diamond saw dicing of double tungstate epitaxies is a promising technology for manufacturing WGs for sensing applications.
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http://dx.doi.org/10.1364/OL.44.001596DOI Listing
April 2019

Thermo-optic dispersion formula for LiGaS.

Appl Opt 2019 Feb;58(6):1519-1521

This paper reports on new experimental results on the temperature-dependent phase-matching properties of LiGaS for second-harmonic generation and sum-frequency generation in the 0.820-10.5910 μm spectral range. In addition, we present a thermo-optic dispersion formula that provides a good reproduction of the present experimental results when combined with the Sellmeier equations presented in our previous paper, Kato et al. [Opt. Lett.42, 4363 (2017)OPLEDP0146-959210.1364/OL.42.004363].
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http://dx.doi.org/10.1364/AO.58.001519DOI Listing
February 2019

67-fs pulse generation from a mode-locked Tm,Ho:CLNGG laser at 2083 nm.

Opt Express 2019 Feb;27(3):1922-1928

We report on a mode-locked Tm,Ho:CLNGG laser emitting in the 2 µm spectral range using single-walled carbon nanotubes (SWCNTs) as a saturable absorber (SA). Pulses with duration of 98 fs are generated at 99.28 MHz repetition rate with an average output power of 123 mW, yielding a pulse energy of 1.24 nJ. Using a 0.5% output coupling, pulses as short as 67 fs, i.e., 10 optical cycles, are produced after extracavity compression with a 3-mm-thick ZnS plate.
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http://dx.doi.org/10.1364/OE.27.001922DOI Listing
February 2019
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