**13** Publications

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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 Âµm. 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 Âµm. 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.397981 | DOI Listing |

July 2020

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 Âµm radiation.

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http://dx.doi.org/10.1364/OL.388373 | DOI Listing |

April 2020

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 Âµm 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.58.009709 | DOI Listing |

December 2019

Appl Opt 2018 Sep;57(26):7440-7443

We present new experimental results for the phase-matching properties of the recently discovered BaGaGeSe crystal for harmonic generation of a Nd:YAG laser-pumped KTP OPO and a CO laser in the 0.778-10.5910Â Î¼m spectral range. In addition, we present new Sellmeier equations that provide a good reproduction of the present experimental results as well as the published data points for SHG of a CO laser at 10.5910Â Î¼m and a 1.85Â Î¼m-pumped OPO in the 2.156-3.220Â Î¼m and 4.348-13.035Â Î¼m spectral ranges.

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http://dx.doi.org/10.1364/AO.57.007440 | DOI Listing |

September 2018

Appl Opt 2018 Apr;57(11):2935-2938

This paper reports on the thermo-optic dispersion formula for BaGaSe that provides a good reproduction of the temperature-dependent phase-matching conditions for type-1 and type-2 second-harmonic generation of a Nd:YAG laser-pumped AgGaS optical parametric oscillator (OPO) and a CO laser in the 0.901-10.5910Â Î¼m spectral range, as well as the published data points for a Nd:YAG laser-pumped OPO at Î»=3.9040â€‰â€‰Î¼m when combined with the Sellmeier equations of the present authors [Appl. Opt.56, 2978 (2017)APOPAI0003-693510.1364/AO.56.002978].

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http://dx.doi.org/10.1364/AO.57.002935 | DOI Listing |

April 2018

Appl Opt 2017 Apr;56(10):2783-2786

An overall quantum conversion efficiency of 7.8% is achieved by intracavity mixing the signal and idler of a 1.064 Î¼m pumped Rb:PPKTP optical parametric oscillator in BaGa_{4}Se_{7}. In this way, a pulse energy of âˆ¼0.71â€‰â€‰mJ is generated at âˆ¼7â€‰ Î¼m for a repetition rate of 100 Hz. Tuning of the mid-IR radiation is demonstrated by heating of the Rb:PPKTP crystal.

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http://dx.doi.org/10.1364/AO.56.002783 | DOI Listing |

April 2017

Opt Lett 2016 Aug;41(15):3667-70

A BaGa_{4}Se_{7} nanosecond optical parametric oscillator (OPO) shows extremely wide idler tunability in the mid-IR (2.7-17Â Î¼m) under 1.064Â Î¼m pumping. The âˆ¼10â€‰â€‰ns pulses at âˆ¼7.2â€‰â€‰Î¼m have an energy of 3.7Â mJ at 10Â Hz. The pump-to-idler conversion efficiency for this wavelength reaches 5.9% with a slope of 6.5% corresponding to a quantum conversion efficiency or pump depletion of 40%.

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http://dx.doi.org/10.1364/OL.41.003667 | DOI Listing |

August 2016

Opt Lett 2016 Jun;41(12):2731-4

We directly measured the phase-matching directions of second-harmonic and difference frequency generation in the principal planes of the biaxial BaGa_{4}Se_{7} (BGSe) crystal using the sphere method. The simultaneous fit of the data allowed us to refine the Sellmeier equations of the three principal refractive indices of BGSe, and to calculate the tuning curves for infrared optical parametric generation.

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http://dx.doi.org/10.1364/OL.41.002731 | DOI Listing |

June 2016

Opt Lett 2015 Oct;40(20):4591-4

We performed a complete study of angle noncritical phase-matched second-harmonic generation in BaGa4Se7 in the mid-infrared region. We measured the dielectric frame orientation and showed that it does not rotate as a function of wavelength. We determined the phase-matching wavelengths and the associated spectral and angular acceptances along the x and y axes of the dielectric frame. We also estimated the magnitude of the nonlinear coefficients involved.

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http://dx.doi.org/10.1364/OL.40.004591 | DOI Listing |

October 2015

Opt Express 2015 Feb;23(3):2730-6

We employ AgGaSe(2) for difference-frequency generation between signal and idler of synchronously-pumped picosecond / femtosecond OPOs at 80 / 53 MHz. Continuous tuning in the picosecond regime is achieved from 5 to 18 Âµm with average power of 140 mW at 6 Âµm. In the femtosecond regime the tunability extends from 5 to 17 Âµm with average power of 69 mW at 6 Âµm. Maximum single pulse energies of >1 nJ in both cases represent the highest values at such high repetition rates.

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http://dx.doi.org/10.1364/OE.23.002730 | DOI Listing |

February 2015

Appl Opt 2014 Nov;53(33):7951-62

We compare linear, planar ring, and rotated image singly resonant twisted rectangle (RISTRA) type nanosecond optical parametric oscillator cavities using HgGa_{2}S_{4} nonlinear crystal pumped by 8Â ns pulses at 1064Â nm from a low beam quality pump source. The input-output characteristics and the output idler beam quality at 6300Â nm are compared for two values of the pump beam diameter presenting different cavity Fresnel numbers and magnitudes of the spatial walk-off effect due to birefringence. The RISTRA cavity ensures in all cases a circular output beam profile but is advantageous in terms of beam quality with respect to the planar ring only at a large pump beam diameter.

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http://dx.doi.org/10.1364/AO.53.007951 | DOI Listing |

November 2014

Opt Lett 2014 Aug;39(16):4895-8

We report on optical parametric generation in a mercury thiogallate (HgGa2S4) crystal pumped by 16 ps, 1064 nm pulses at 250 kHz. A broad tuning range extending from 1.19 to 1.47 Î¼m (signal) and from 3.85 to 10 Î¼m (idler) is achieved. Narrow bandwidth, quasi-Fourier limited operation with high beam quality for the signal/idler pulses and >14% pump depletion is obtained by continuous wave seed injection at 1.29 Î¼m.

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http://dx.doi.org/10.1364/OL.39.004895 | DOI Listing |

August 2014

Opt Lett 2012 Oct;37(19):4146-8

Max-Born-Institute for Nonlinear Optics and Ultrafast Spectroscopy, 2A Max-Born-Strasse, D-12489 Berlin, Germany.

The orthorhombic biaxial crystal BaGa(4)S(7) has been employed in a 1064 nm pumped optical parametric oscillator generating <6 ns long idler pulses with energies as high as 0.5 mJ at 6.217 Î¼m and average power of ~50 mW at 100 Hz. Notwithstanding the relatively low nonlinearity, ~3 times above threshold operation has been achieved at pump intensities more than 5 times below the crystal surface damage limit.

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http://dx.doi.org/10.1364/OL.37.004146 | DOI Listing |

October 2012