AgGaS2 Crystal Research Articles

Advances in the development of few-cycle gigawatt-peak-power mid-IR optical parametric amplifiers pumped by Cr:Forsterite laser using non-oxide nonlinear crystals

We demonstrate an experimental and theoretical comparison of non-oxide LiGaS2, HgGa2S4, and AgGaS2 crystals performance for wavelength conversion into the near and mid-IR range 1.5–8 μm in optical parametric amplifier pumped by Cr:Forsterite laser, delivering 100 fs pulses at 1.24 μm. It is shown that exceptionally high total energy conversion efficiency into the idler (4–5 μm) and signal (1.65–1.8 μm) waves up to 18% can be achieved using the HGS crystal, providing high nonlinearity, while the LGS crystal is more preferable for generating few-cycle mid-IR pulses due its unique dispersive properties. Our source features high peak power in gigawatt regime (0.4–2.4 GW) with pulse duration below 80 fs and optical synchronization with high harmonic generation (HHG) and THz beamlines, which is ideal for pump-probe experiments of nonlinear and strong-field physics.

Broadly tunable femtosecond OPA pumped by 1030 nm Yb: KGW laser with a range of non-linear crystals tested

We present a carrier-envelope phase-stable laser pulse source continuously tunable in the 2–4 µm wavelength range. The source relies on two-stage optical-parametric amplification, with the first stage pumped with the second harmonic of the 200-fs ytterbium pump laser. In contrast, the fundamental 1030 nm beam pumps the second stage directly. AgGaS2 (AGS), KTiOAsO4 (KTA), GaSe, LiGaS2 (LGS), and LiIO3 (LIO3) non-linear crystals were tested and the KTA crystal proved to be the most robust. We demonstrate operation without crystal damage at higher than previously reported peak intensities for AGS (290 GW/cm2) and LGS (214 GW/cm2) and report new values of damage threshold for GaSe (85 GW/cm2) and LIO3 (159 GW/cm2).

Adding a second AgGaS2 stage to Ti:sapphire/BBO/AgGaS2 setups increases mid-infrared power twofold.

We present a method for increasing the power of mid-infrared laser pulses generated by a conventional beta-barium borate (BBO) optical parametric amplifier (OPA) and AgGaS2 difference frequency generation (DFG) pumped by a Ti:sapphire amplifier. The method involves an additional stage of parametric amplification with a second AgGaS2 crystal pumped by selected outputs of the conventional DFG stage. This method does not require additional pump power from the Ti:sapphire laser source and improves the overall photon conversion efficiency for generating mid-infrared light. It merely requires an additional AgGaS2 crystal and dichroic mirrors. Following difference frequency generation, the method reuses near-infrared light (∼1.9 µm), typically discarded, to pump the additional AgGaS2 stage and amplifies the mid-infrared light twofold. We demonstrate and characterize the power, spectrum, duration, and noise of the mid-IR pulses before and after the second AgGaS2 stage. We observe small changes in center frequencies, bandwidth, and pulse duration for ∼150-fs pulses between 4 and 5 µm.

Synchronous upconversion of quantum cascade lasers in AgGaS2.

We investigate synchronous upconversion of a pulsed, tunable quantum cascade laser (QCL) in the important 5.4-10.2 µm range, with a 30 kHz, Q-switched, 1064 nm laser. The possibility to accurately control the repetition rate and pulse duration of the QCL results in a good temporal overlap with the Q-switched laser, leading to an upconversion quantum efficiency of 16% in a 10 mm-long AgGaS2 crystal. We investigate the noise properties of the upconversion process in terms of pulse-to-pulse energy stability and timing jitter. For QCL pulses in the 30-70 ns range the upconverted pulse-to-pulse stability is approximately 1.75%. The demonstrated combination of broad tunability and high signal to noise in the system is well-suited for mid-IR spectral analysis of highly absorbing samples.

The Kurtz-Perry powder technique revisited: A case study on the importance of reference quality and broadband nonlinear optical measurements using LiInSe2

The Kurtz-Perry powder technique (KPPT) is widely utilized for the rapid characterization of newly grown nonlinear optical (NLO) materials available in pristine powder form. It assesses the effective nonlinear susceptibility of randomly oriented powder in comparison with a reference material. This technique becomes especially versatile when equipped with a broad wavelength range and intensity tunability because it provides key NLO properties of the materials under investigation, such as the frequency dispersion of the NLO susceptibility, phase-matching (PM) range, and laser-induced damage threshold (LIDT) as a guideline. In this study, wavelength-dependent NLO experiments (λ= 1100 – 3700 nm) were conducted on polycrystalline LiInSe2, prepared by high-temperature, solid-state synthesis. Our LiInSe2 was found to be phase-matchable for λ> 2500 nm and the effective NLO susceptibility was estimated as 20.0 ± 1.9 pm/V, assessed at the static limit using commercial-grade single crystals of AgGaS2 and AgGaSe2 that were ground to powders. Alternatively, the effective NLO susceptibility was determined to be twice as large, ~40 pm/V, when utilizing a homemade, microcrystalline AgGaSe2 reference at the static limit. This severe overestimation of the NLO susceptibility that can occur while working with a homemade standard underscores the importance of using a commercial-grade reference with the KPPT. Furthermore, this study also discusses the LIDT of LiInSe2 based on intensity-dependent SHG at 1064 nm with picosecond pulses, and compares with those of the commercial-grade AgGaS2 and AgGaSe2, determined under identical conditions. As defect levels can cause widely varying apparent color, thus optical bandgap, in LiInSe2, this study stresses the importance of using a high-quality standard when exploiting the KPPT for NLO materials characterization. The role of defects is discussed in terms of χ2, phase matching onset and LIDT, parameters that predominantly affect the evaluation of new NLO materials.

Ultra-broadband long-wave-infrared pulse production using a chirped-pulse difference-frequency generation.

We present a broadband light source based on near-infrared chirped-pulse difference-frequency mixing that is suitable for seeding long-wave-infrared (LWIR) optical parametric chirped-pulse amplification (OPCPA). A nitrocellulose pellicle is used in a Ti:sapphire regenerative amplifier to generate dual-frequency output pulses, which are subsequently mixed in a 0.4-mm thick AgGaS2 crystal. LWIR pulses with ∼1 µm full width at half maximum (FWHM) bandwidth centered at 10.5 µm are generated by mixing transform-limited pulses. Assisted by genetic algorithm optimization, the bandwidth is broadened to ∼3 µm FWHM within the 8-12 µm atmospheric transmission window. The seed source paves the path towards tabletop ultrafast terawatt-class passively carrier-envelope-phase stabilized OPCPA in the LWIR region.

Electronic Structure, Optical, and Elastic Properties of AgGaS2 Crystal: Theoretical Study

AbstractA comprehensive theoretical study of the structure, electronic, optical, and elastic properties of ternary semiconductor silver thiogallate crystal AgGaS2 is carried out based on the density functional theory and dipole electron shifting model (DES) for finding a structure–properties relationship. The deformation and displacement parameters, describing the deviation of the structural parameters of AgGaS2 from ideal chalcopyrite structure, are determined. It is noticed that the significant discrepancies concerning peculiarities of the band structure between initial results of the DFT‐based calculation and the experiment for the titled crystal have been efficiently eliminated by choosing the proper DFT + U approach. By utilizing the calculated dielectric function for two principal directions, the refractive indices and extinction coefficients dispersions are determined. For the first time, the linear electro‐optic properties, electrogyration coefficients, and second‐order nonlinear optical coefficients of AgGaS2 crystals are calculated in the frame of the DES model. The elastic properties of the AgGaS crystal are analyzed in the frame of the calculated full matrix of elastic coefficients. A number of parameters, such as Young's modulus E, Poisson's ratio ν, bulk B, and shear G moduli are predicted for the crystal. The calculated anisotropy coefficients for the moduli show very good agreement with ones available from experiment.

Optical and generation characteristics of new nonlinear Ba2Ga8GeS16 and Ba2Ga8(GeSe2)S14 crystals for the mid-IR range

Ba2Ga8GeS16 and Ba2Ga8(GeSe2)S14 single crystals of large size and good optical quality have been grown for the first time. Their linear optical characteristics – transmission spectra in the range of 0.3 – 25 μm, dispersion of principal refractive indices, and birefringence – have been measured. Irradiation of the crystals by 100-fs laser pulses with a wavelength of 8.3 μm initiated second-harmonic generation with an efficiency comparable with that obtained for the AgGaS2 crystal.

Non-stoichiometry and point native defects in non-oxide non-linear optical large single crystals: advantages and problems

Advances and limitations in the field of growing large, high optical quality single crystals of AgGaS2(AGS), AgGaGeS4(AGGS), ZnGeP2(ZGP), LiInS2(LIS), LiGaS2(LGS), LiInSe2(LISe), LiGaSe2(LGSe) and LiGaTe2(LGT) are considered in this article.

Mid-infrared photon pair generation in AgGaS2

We demonstrate nondegenerate photon pair generation by spontaneous parametric downconversion in a silver gallium sulfide AgGaS2 crystal. By tuning the pump wavelength, we achieve phase matching over a large spectral range. This allows to generate idler photons in the mid-infrared spectral range above a 6 μm wavelength with corresponding signal photons in the visible. Also, we show photon pair generation with broad spectral bandwidth. These results are a valuable step toward the development of quantum imaging and sensing techniques in the mid-infrared.

Temperature-dependent optical properties of AgGaS2 in the terahertz range

The temperature-dependent optical properties of the AgGaS2 crystal were characterized in the 0.2–2 THz range by terahertz time-domain spectroscopy (TDS). The refractive indices and the absorption coefficients along and orthogonal to the optical axis (c axis) were measured, and the temperature-dependent Sellmeier equations were fitted for various applications of linear and nonlinear optical devices. An E mode vibrating orthogonal to the c axis centering at 1.03 THz (34 cm−1) and a B2 mode along the c axis centering at 1.86 THz (62 cm−1), were observed for the first time. The phonon softening during the temperature rise was discussed and analyzed with the help of Raman spectroscopy. According to the measured absorption spectrum of AgGaS2, we also fitted the parameters of the low-frequency phonon modes at room temperature with the Lorentz dispersion model, which is helpful in predicting the lattice dynamics and optical behaviors of the crystal.

Investigation of intermediate impurities on high quality AgGaS2 single crystal grown by vertical gradient freezing method

In this study, intermediate impurities on synthesized AgGaS2 polycrystal and grown AgGaS2 single crystal were studied by X-ray photoelectron spectroscopy (XPS) which was recommended as workable method to characterize intermediate impurities on AgGaS2 while the content of those impurity components were too low to be detected using common X-ray diffraction (XRD) measurement. Meanwhile, XRD, Energy Dispersive Spectrometer (EDS) and Fourier-transform infrared spectrophotometry (FTIR) were employed to characterize the quality of AgGaS2 crystals. The results manifest that AgGaS2 crystal with high infrared transmittance and good uniformity were successfully obtained. However, XPS results indicate that intermediate impurities with different content and varieties exist on both AgGaS2 polycrystal and AgGaS2 single crystal respectively and decrease of intermediates may lead to improvement of its optical property.

Investigation of the Thermal Properties and Crystal Growth of the Nonlinear Optical Crystals AgGaS2 and AgGaGeS4

The thermal properties of orthorhombic AgGaGeS4 and chalcopyrite AgGaS2 crystals, including thermal expansion, specific heat, and thermal conductivity, have been investigated. For the AgGaS2 crysta...

Acousto-optic interaction between circularly polarized optical eigenwaves: example of AgGaS2 crystals

We analyze acousto-optic (AO) diffraction occurring at the light wavelength of a so-called "isotropic point" in AgGaS2 crystals. It is shown that a natural optical activity, which manifests itself as circular birefringence at the isotropic point, can lead to two different types of AO Bragg diffraction, isotropic and anisotropic. The first type concerns the interaction of circularly polarized optical eigenwaves with the same sign of rotations of their electric-field vectors. In the case of the second diffraction type, the AO interaction takes place between the circularly polarized waves having opposite signs of electric-field rotations. Relations for effective elasto-optic (EO) coefficients are derived for different types of AO diffraction, including a collinear one. The main peculiarities of the latter diffraction type are revealed. The modules of all the EO coefficients are determined experimentally for the AgGaS2 crystals, using a Dixon-Cohen method. Finally, we evaluate AO figures of merit referring to the AO interactions of circularly polarized optical eigenwaves at the optical wavelength of the isotropic point.

Anisotropy of acousto-optic figure of merit for the collinear diffraction of circularly polarized optical waves at the wavelength of isotropic point in AgGaS2 crystals

Anisotropy of acousto-optic figure of merit for the collinear diffraction of circularly polarized optical waves at the wavelength of isotropic point in AgGaS2 crystals

Pressure-Assisted Method for the Preparations of High-Quality AaGaS2 and AgGaGeS4 Crystals for Mid-Infrared Laser Applications.

Recently developed chalcogenides nonlinear optical crystals have potential application in mid- to far-infrared laser fields. However, high-quality single crystals are hard to be prepared because of high vapor pressure of sulfur component and decomposition of chalcogenides during the polycrystalline synthesis and single-crystal growth. A pressure-assisted technique was performed to prepare stoichiometric AgGaS2 and AgGaGeS4 polycrystalline materials. On the basis of the synthesized polycrystalline materials, high-quality AgGaS2 and AgGaGeS4 single crystals were successfully obtained using the seed directional Bridgman method with a well-designed crucible-capsule technique. These single crystals possess high homogeneity and low absorption coefficient, making it can be applied in nonlinear optical experiments. The pressure-assisted method can also be suitable to prepare other chalcogenide and phosphide compounds. The method of polycrystalline synthesis and single crystals growth described in this work will be helpful for preparing other chalcogenides nonlinear optical crystals.

Determination of the Subpicosecond Laser Pulse Chirp in the Middle IR Range Based on the Fourth Harmonic Noncollinear Generation

A new method is proposed to determine the subpicosecond laser pulse chirp in the middle IR range at the central wavelength of 10 μm, based on the generation of the second-harmonic pulses both by the bandwidth-limited and frequency-modulated subpicosecond pulses and the subsequent noncollinear generation of the fourth-harmonic radiation by the corresponding second-harmonic pulses. The time dependences are given of the instantaneous frequency of the frequency-modulated second-harmonic pulse at the central wavelength of 5 μm, generated in the field of the frequency-modulated subpicosecond IR pulse, propagating in the negative uniaxial AgGaS2 crystal along the direction of 61°36′ relative to the optical axis. These results can be used in designing a nonlinear optical phase correlator to determine the phase and time profile of the subpicosecond laser pulse in the middle IR range.

Pressure-tuning the nonlinear-optical properties of AgGaS_2 crystal: a first-principle study

A specialized genetic algorithm approach in combination with first-principles calculations is employed to predict the stable structures of AgGaS2 crystal at different pressures. The results show that the chalcopyrite structure first transforms to the monoclinic Cc phase, and then to a centrosymmetric structure that the second-harmonic generation (SHG) response of AgGaS2 is disappeared. The effects of external pressures, up to 7 GPa, on the linear and second-order nonlinear optical properties of AgGaS2 are explored systematically. Our work reveals that the resistance to laser-induced damage, the transparency range, and the phase matchability can be improved by the pressure-induced deformation of AgGaS2 crystal. Moreover, the feature of the strong SHG response of AgGaS2 crystal is still preserved in the whole IR region even under pressure up to 7 GPa.

A modified method to simulate the dispersion properties of infrared nonlinear optical crystals

This paper presents a modified method to study the dispersion properties of infrared nonlinear optical crystals, which takes advantage of the first principles calculations and oscillator model. The phonon effects play an important role in the dispersion properties, and obvious discrepancies between calculated and experimental results are found due to the lack of such effects in first principles optical property calculations. In order to compensate for such deficiency, the oscillator model was introduced. Phonon oscillator terms are added to the calculated dispersion equations, and the phonon oscillator coefficients can be obtained from first principles infrared dielectric property calculations. With the modified method, the simulated dispersion curves of GaAs, CdSiP2, AgGaS2, and ZnGeP2 crystals show excellent agreement with the experimental results.

Calculation of refraction indices of triple chalcogenide crystals

We use Harrison’s bond-orbital method to calculate high frequency refraction indices of AgGaS2, CdGa2S4, and CdGa2Se4 crystals. We demonstrate a satisfactory agreement between obtained results and experimental data.