Publications by authors named "Andrius Zukauskas"

18 Publications

  • Page 1 of 1

µJ-level multi-cycle terahertz generation in a periodically poled Rb:KTP crystal.

Opt Lett 2021 Feb;46(4):741-744

We demonstrate multi-cycle terahertz (MC-THz) generation in a 15.5 mm long periodically poled rubidium (Rb)-doped potassium titanyl phosphate (Rb:PPKTP) crystal with a poling period of 300 µm. By cryogenically cooling the crystal to 77 K, up to 0.72 µJ terahertz energy is obtained at a frequency of 0.5 THz with a 3 GHz bandwidth. A maximum internal optical-to-terahertz conversion efficiency of 0.16% is achieved, which is comparable with results achieved using periodically poled lithium niobate crystal. Neither photorefractive effects nor damage was observed with up to 900/, showing the great potential of Rb:PPKTP for multi-millijoule-level MC-THz generation.
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http://dx.doi.org/10.1364/OL.413410DOI Listing
February 2021

Ion-exchanged waveguides in periodically poled Rb-doped KTiOPO for efficient second harmonic generation.

Opt Express 2020 Dec;28(26):38822-38830

An ion-exchange process has been developed for periodically poled Rb-doped KTiOPO (RKTP) which warrants high efficiency and low loss channel waveguides. The domain stability was investigated, and it was found that domain gratings with uncharged walls could stand the ion-exchange process without deterioration. 3.1 mW of blue second harmonic light was generated from 74 mW of radiation at 940.2 nm coupled into an 8 µm wide and 7 mm long waveguide, corresponding to a normalized conversion efficiency of 115%/Wcm. Waveguides in PPRKTP open the possibility for stable operation at high optical powers, as well as generating entangled photons at low optical powers, and enable the investigation of novel nonlinear processes such as counter-propagating interactions in a waveguide format.
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http://dx.doi.org/10.1364/OE.410773DOI Listing
December 2020

Development and experimental demonstration of negative first-order quasi-phase matching in a periodically poled Rb-doped KTiOPO crystal.

Opt Lett 2020 Nov;45(21):6026-6029

We worked on a new scheme of quasi-phase matching (QPM) based on the negative first order of the spatial modulation of the sign of the second-order nonlinearity. Applying this scheme in the case of angular-QPM (AQPM) in a biaxial crystal reveals new directions of propagation for efficient parametric frequency conversion as well as "giant" spectral acceptances. The experimental validation is performed in a periodically poled rubidium-doped biaxial crystal. This new approach naturally extends to other periodically poled uniaxial crystals such as periodically poled .
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http://dx.doi.org/10.1364/OL.408839DOI Listing
November 2020

Coherent phase transfer and pulse compression at 1.4  μm in a backward-wave OPO.

Opt Lett 2019 Jun;44(12):3066-3069

The frequency modulation transfer property of a backward-wave optical parametric oscillator (BWOPO) is investigated in the context of near-IR pulse compression. The maximum transferrable bandwidth from the pump to the forward wave in a BWOPO is determined by the group dispersion mismatch. In comparison, the third-order phase introduced in a single-grating compressor setup is more detrimental to achieve optimum compression of the BWOPO forward wave. Nevertheless, we demonstrate a 220 GHz bandwidth transfer from 800 nm to 1.4 μm, with a compression factor of 115, leading to near-IR pulses as short as 1.3 ps with μJ energy.
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http://dx.doi.org/10.1364/OL.44.003066DOI Listing
June 2019

Narrowband, tunable, infrared radiation by parametric amplification of a chirped backward-wave OPO signal.

Opt Express 2019 Apr;27(8):10602-10610

The strict momentum conservation constraints for backward-wave optical parametric oscillators (BWOPOs) gives an inherently narrowband backward-generated wave, even with broadband pumping. Unfortunately, the limited tuning range of this wave restricts potential applications. Here we demonstrate a method to circumvent this restriction and increase the tuning range by more than one order of magnitude. A linearly chirped pump modulation is transferred to the forward-generated BWOPO wave, which is then mixed with an identically chirped pump in a conventional optical parametric amplifier to obtain narrowband (38 GHz), broadly tunable, infrared radiation around 1.86 µm, with an output energy of 19 µJ.
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http://dx.doi.org/10.1364/OE.27.010602DOI Listing
April 2019

Validation of the angular quasi-phase-matching theory for the biaxial optical class using PPRKTP.

Opt Lett 2018 Sep;43(17):4276-4279

We report the first experimental validation of angular quasi-phase-matching (AQPM) theory in a biaxial crystal by performing second-harmonic generation (SHG) in the periodically-poled Rb-doped KTiOPO (PPRKTP) crystal cut as a sphere. Both AQPM and birefringence phase-matching (BPM) angles were measured thanks to a Kappa circle.
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http://dx.doi.org/10.1364/OL.43.004276DOI Listing
September 2018

Counter-propagating parametric interaction with phonon-polaritons in periodically poled KTiOPO4.

Opt Express 2017 Feb;25(3):2677-2686

Strongly enhanced backward stimulated polariton scattering (BSPS) is demonstrated in periodically-poled KTiOPO4 (KTP) crystals with a high power-conversion efficiency up to 70%. We study the physical mechanism of such counter-propagating parametric interaction with phonon-polaritons in χ(2) modulated structures. BSPS is a three-wave mixing that is distinguished from backward stimulated Raman scattering (BSRS), while a strong absorption at large polariton wave-vectors can still make BSPS display certain characteristics of BSRS such as self-compression of the Stokes pulse. We also compare BSPS with counter-propagating parametric oscillation in the near- and mid-infrared range, providing an estimation of the fabrication error margin to expect the outcome of their competition in the same device.
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http://dx.doi.org/10.1364/OE.25.002677DOI Listing
February 2017

Highly efficient mirrorless optical parametric oscillator pumped by nanosecond pulses.

Opt Lett 2017 Jul;42(13):2435-2438

A highly efficient mirrorless optical parametric oscillator (MOPO), pumped by narrowband nanosecond pulses at 1064 nm, is demonstrated. The MOPO is based on quasi-phase-matched parametric interaction of counter-propagating photons in 1-mm-thick periodically poled Rb-doped KTiOPO crystal with a period of 755 nm. It generates a co-propagating signal at 1740 nm and a counter-propagating idler at 2741 nm, achieving mJ-level output with a total signal-and-idler conversion efficiency of 47%. Both generated waves present narrow spectral bandwidths, thanks to the unique properties of the counter-propagating nonlinear interaction. The high conversion efficiency, inherently narrow spectral width, and simplicity of the optical setup make the MOPO an attractive alternative to conventional co-propagating optical parametric oscillators.
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http://dx.doi.org/10.1364/OL.42.002435DOI Listing
July 2017

Cascaded counter-propagating nonlinear interactions in highly-efficient sub-µm periodically poled crystals.

Sci Rep 2017 Aug 14;7(1):8037. Epub 2017 Aug 14.

Department of Applied Physics, Royal Institute of Technology, Roslagstullsbacken 21, 10691, Stockholm, Sweden.

Mirrorless optical parametric oscillators (MOPOs) are very attractive parametric devices that rely on the nonlinear interaction of counter-propagating photons to inherently establish distributed feedback, without the use of external mirrors or surface coatings. These devices offer unique spectral and coherence properties that will benefit a large variety of applications ranging from spectroscopy to quantum communications. The major obstacle in exploiting their full potential is ascribed to the difficulty in engineering a nonlinear material in which the generation of counter-propagating waves can be phase matched. Here we present a reliable and consistent technique for fabrication of highly-efficient sub-micrometer periodically poled Rb-doped KTiOPO. We experimentally demonstrate the first cascaded counter-propagating interactions in which the generated forward signal serves as a pump for a secondary MOPO process, reaching pump depletion larger than 60%. The cascaded process exemplifies the high efficiency of our nonlinear photonic structures. Our domain-engineering technique paves the way to realize counter-propagating schemes and devices that have been deemed unfeasible until now.
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http://dx.doi.org/10.1038/s41598-017-07016-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5556100PMC
August 2017

Intracavity difference-frequency mixing of optical parametric oscillator signal and idler pulses in BaGa4Se7.

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 μm pumped Rb:PPKTP optical parametric oscillator in BaGa4Se7. In this way, a pulse energy of ∼0.71  mJ is generated at ∼7  μm 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.56.002783DOI Listing
April 2017

Fully-resonant, tunable, monolithic frequency conversion as a coherent UVA source.

Opt Express 2017 Jan;25(2):1142-1150

We demonstrate a monolithic frequency converter incorporating up to four tuning degrees of freedom, three temperature and one strain, allowing resonance of pump and generated wavelengths simultaneous with optimal phase-matching. With a Rb-doped periodically-poled potassium titanyl phosphate (KTP) implementation, we demonstrate efficient continuous-wave second harmonic generation from 795 to 397, with low-power efficiency of 72% and high-power slope efficiency of 4.5%. The measured performance shows good agreement with theoretical modeling of the device. We measure optical bistability effects, and show how they can be used to improve the stability of the output against pump frequency and amplitude variations.
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http://dx.doi.org/10.1364/OE.25.001142DOI Listing
January 2017

Terahertz parametric generation and amplification from potassium titanyl phosphate in comparison with lithium niobate and lithium tantalate.

Opt Express 2016 Nov;24(23):25964-25973

We report superior terahertz parametric generation from potassium titanyl phosphate (KTP) over congruent-grown lithium niobate (CLN) and lithium tantalate (CLT) in terms of parametric gain and laser damage resistance. Under the same pump and crystal configurations, the signal emerged first from KTP, 5% Mg-doped CLN, CLN, and then finally from CLT. The signal growth rate in KTP was comparable to that in 5%-Mg-doped CLN, but the signal power from KTP reached a much higher value after all the other crystals were damaged by the pump laser. We further demonstrate seeded terahertz parametric amplification in an edge-cut KTP at 5.74 THz. The THz parametric amplifier (TPA) employs a 17-mm long KTP gain crystal, pumped by a passively Q-switched pump laser at 1064 nm and seeded by a continuous-wave diode laser tuned to the signal wavelength at 1086.2 nm. With 5.8-mJ energy in a 520-ps pump pulse and 100-mW seed signal power, we measured 5-W peak-power THz output from the KTP TPA with 22% pump depletion. In comparison, we measured no detectable THz output power from a similar edge-cut CLN TPA under the same pump power, detection scheme, and crystal configuration, when tuning the seed laser wavelength to 1072.2 nm and attempting to generate a radiation at 2.1 THz.
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http://dx.doi.org/10.1364/OE.24.025964DOI Listing
November 2016

Rb:PPKTP optical parametric oscillator with intracavity difference-frequency generation in AgGaSe2.

Opt Lett 2016 Jun;41(12):2791-4

A 1.064 μm pumped Rb:PPKTP optical parametric oscillator (OPO) generates mid-IR radiation by intracavity mixing the resonant signal and idler waves in AgGaSe2. The ∼6  ns pulses at ∼7  μm have an energy of 670 μJ at 100 Hz, equivalent to an average power of 67 mW. The overall quantum conversion efficiency from 1.064 μm amounts to 8%, and the power conversion efficiency is 1.2%.
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http://dx.doi.org/10.1364/OL.41.002791DOI Listing
June 2016

Intracavity-pumped, cascaded AgGaSe₂ optical parametric oscillator tunable from 5.8 to 18 µm.

Opt Express 2015 Dec;23(26):33460-5

A AgGaSe2 nonlinear crystal placed in a coupled cavity is intracavity pumped by the ~1.85-µm signal pulses of a 1.064-µm pumped Rb:PPKTP doubly-resonant optical parametric oscillator (OPO) operating at a repetition rate of 100 Hz. Using two samples cut for type-I and II phase-matching, the overall idler tunability of the singly-resonant AgGeSe2 OPO covers an unprecedented spectral range from 5.8 to ~18 µm in the mid-IR.
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http://dx.doi.org/10.1364/OE.23.033460DOI Listing
December 2015

Studies of sub-millisecond domain dynamics in periodically poled Rb-doped KTiOPO(4), using online in situ second harmonic generation.

Opt Express 2015 Aug;23(16):20332-9

The temporal evolution of in situ second-harmonic generation was employed to study domain dynamics during periodic poling in Rb-doped KTP. With this method we investigated the influence of various poling parameters, including electric-field pulse shape, pulse magnitude, and number of pulses, on the quality of the QPM structure. It was found that the grating formation can be a sub-millisecond process and the benefits of using symmetric triangular electric-field pulse shape over square pulse shape in the single-pulse poling regime were demonstrated. Multiple-pulse poling with triangular pulses was shown to have a detrimental effect on the QPM structure quality, while multiple square pulses can provide additional flexibility to the structuring process.
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http://dx.doi.org/10.1364/OE.23.020332DOI Listing
August 2015

Contact poling of Rb:KTiOPO(4) using a micro-structured silicon electrode.

Opt Express 2015 Jan;23(2):636-41

A contact poling technique for domain engineering of ferroelectrics using a micro-structured silicon electrode is demonstrated on Rb:KTiOPO4. High quality QPM gratings were reproducibly fabricated. The silicon electrode is reusable and the technique potentially suitable when complex structures with sub-μm features are to be domain engineered, which otherwise is incompatible with conventional photolithography. A non-negligible domain broadening was seen and attributed to a low nucleation rate using this type of electrode. However, under the appropriate poling conditions, this could be exploited to obtain a QPM grating with a short pitch (2 μm), equal to half of the electrode period.
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http://dx.doi.org/10.1364/OE.23.000636DOI Listing
January 2015

High-power continuous-wave frequency-doubling in KTiOAsO4.

Opt Express 2013 Dec;21(25):30453-9

High-power continuous-wave generation at 533 nm is demonstrated in bulk periodically poled KTiOAsO(4) (KTA) by single-pass frequency doubling of a VBG-locked Yb-doped fiber laser. Absorption characteristic and second harmonic generation (SHG) performance of different KTA samples are studied and compared. The best performing sample catered for 25%-efficient SHG of 13.6 W green light with high spatial beam quality M(2) <1.2.
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http://dx.doi.org/10.1364/OE.21.030453DOI Listing
December 2013

Second-harmonic generation in periodically poled bulk Rb-doped KTiOPO₄ below 400 nm at high peak-intensities.

Opt Express 2013 Jan;21(2):1395-403

Department of Applied Physics, Royal Institute of Technology, Roslagstullsbacken 21, 10691 Stockholm, Sweden.

We demonstrate that bulk Rb-doped KTiOPO₄ (RKTP) shows improved susceptibility to gray-tracking compared to flux-grown KTiOPO₄ . We show high-fidelity periodic poling of 1 mm thick RKTP with a period of 3.18 µm for second harmonic generation at 398 nm with a normalized conversion efficiency of 1.79%/Wcm. The crystal is used to frequency-double 138 fs-long pulses with an efficiency of 20% and a peak intensity of 560 MW/cm² without visible gray-tracking signs. We demonstrate that two-photon absorption is the predominant mechanism limiting the SHG efficiency in this spectral range at high peak powers and high repetition rates.
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http://dx.doi.org/10.1364/OE.21.001395DOI Listing
January 2013
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