Zinc Germanium Phosphide Research Articles

Enhanced near-infrared optical transmission in zinc germanium phosphide crystals via precise magnesium doping.

A zinc germanium phosphorus (ZnGeP2) crystal with a chalcopyrite structure is an efficient frequency converter in the mid-infrared region. However, point defect-induced optical absorption at the pumping wavelength (near infrared region) blocked the further application of ZnGeP2. To alleviate the absorption losses caused by point defects, in situ magnesium doping compensation was presented during the ZnGeP2 bulk crystal growth process via the vertical Bridgman method. Combined with theoretical calculations, the structural distortion of the magnesium-doped ZnGeP2 crystals in different orientations was illustrated. The thermodynamic and kinetic stability of the magnesium-doped ZnGeP2 structure were demonstrated. The transmission results indicated the improvement of transmittance within a wavelength range of 1.8-2.4 μm when doped with magnesium, which revealed the powerful ability of the appropriate dopant in optimizing near-infrared optical properties. Thus, the introduction of magnesium is a practical approach to improve the transmittance performance and extend the pumping source wavelengths of ZnGeP2 crystals.

Experimental Investigation of Laser Damage Limit for ZPG Infrared Single Crystal Using Deep Magnetorheological Polishing of Working Surfaces

Zinc germanium phosphide (ZGP) crystals have garnered significant attention for their nonlinear properties, making them good candidates for powerful mid-IR optical parametric oscillators and second-harmonic generators. A ZnGeP2 single crystal was treated by deep magnetorheological processing (MRP) until an Angstrom level of roughness. The studies presented in this article are devoted to the experimental evaluation of the influence of deep removal (up to 150 μm) from the surface of a ZnGeP2 single crystal by magnetorheological polishing on the parameters of optical breakdown. It was shown that the dependence of the ZnGeP2 laser-induced damage threshold on MRP depth is a smooth monotonically decreasing logarithmic function. The obtained logarithmic dependence indicates the thermal nature of optical breakdown and the dependence of the ZnGeP2 laser-induced damage threshold on the concentration of surface absorbing defects.

Longwave infrared (6.6-11.4 µm) dual-comb spectroscopy with 240,000 comb-mode-resolved data points at video rate.

Using sub-3-cycle pulses from mode-locked Cr:ZnS lasers at λ ≈ 2.4 µm as a driving source, we performed high-resolution dual-frequency-comb spectroscopy in the longwave infrared (LWIR) range. A duo of highly coherent broadband (6.6-11.4 µm) frequency combs were produced via intrapulse difference frequency generation in zinc germanium phosphide (ZGP) crystals. Fast (up to 0.1 s per spectrum) acquisition of 240,000 comb-mode-resolved data points, spaced by 80 MHz and referenced to a Rb clock, was demonstrated, resulting in metrology grade molecular spectra of N2O (nitrous oxide) and CH3OH (methane). The key to high-speed massive spectral data acquisition was low intensity and phase noise of the LWIR combs and high (7.5%) downconversion efficiency, resulting in a LWIR power of 300 mW for each comb.

Compact Radio Frequency Discharge-Pumped Slab CO Laser System with a Zinc Germanium Phosphide (ZnGeP2) Sum-Frequency Generator for Remote Sensing of the Atmosphere.

Based on our experimental study of spectral characteristics of an improved compact CO laser system, the prospects of using such a laser system for solving urgent problems of atmospheric sounding were demonstrated. An increase in the number of laser lines due to intracavity generation of the second harmonic and sum-frequencies in a nonlinear zinc germanium phosphide (ZnGeP2) crystal enriches capabilities of the laser. It was shown that such a CO laser system with frequency conversion in ZnGeP2 crystal can be used for detection and measuring concentration of at least 14 minor natural and pollution gases components of the atmosphere. The advantages and disadvantages of various laser operation modes, and the prospects for using its radiation for atmospheric remote sensing in various spectral ranges are discussed.

Long-wave infrared ZnGeP2 optical parametric oscillator with improved tunability by use of a cavity compensation technique

We present a cavity compensation technique based on a tunable long-wave infrared zinc germanium phosphide ZnGeP2 (ZGP) optical parametric oscillator (OPO). The slope efficiency increased from 3.6% to 7.0% at 9.15 μm after using the cavity compensation technique in the tuning range of 8.02 to 9.15 μm. We used a Q-switched 2.1 μm Ho:YAG laser pump source with a pulse repetition frequency of 10 kHz. Under the incident pump power of 23.03 W, the maximum average idler output power of 2.16 W at 8.02 μm was achieved with a pulse width of 21.5 ns and spectral bandwidth of 29.5 nm; the slope efficiency was 16.5%. To the best of our knowledge, this is the first application of the cavity compensation technique in tunable long-wave infrared ZGP OPO.

Numerical simulation for growing Large-scale and High-quality Zinc germanium phosphide crystals

The mid-infrared nonlinear crystals have shown great promise for the usage in the fields of sum frequency generation, optical parametric amplifier and optical parametric oscillator. These motivations are empowered by high-quality ZnGeP2 optical devices with high second-order dielectric susceptibility, thermal conductivity and hardness. However, the rapid development of large-sized ZnGeP2 single crystals with high optical quality is limited by traditional time-consuming and unpredictable growth route. Herein, for the first time, a strategy of comprehensive unsteady computer modeling is implemented to stimulate the Vertical Bridgman growth process of large-sized ZnGeP2 single crystal by the Crystal Growth Simulator (CGSim) software. The accurate simulations of temperature field, crystal growth rate, crystallization interface shape and thermal stress evolution are achieved by using this established numerical model. The accuracy and feasibility have been confirmed by the agreement between stimulated and experimental results of the temperature field curves and crystallization interface shape. The optimal parameters for growing large-sized (Φ = 60 mm) ZnGeP2 single crystal are determined: pulling speed of 0.3 mm/h, temperature gradient of 5 K/cm and slow cooling regime. The large-sized (Φ = 60 mm) ZnGeP2 single crystal with better quality is thus successfully obtained in the crystal-growth experiment in our lab, further verifying the accuracy of the constructed numerical model. Our work provides a new way to predict and guide the growth of large ZnGeP2 single crystal and other similar single crystals.

Mid-infrared optical parametric oscillator pumped by a high-pulse-energy, Q-switched Ho3+:YAG laser.

A high-pulse-energy mid-infrared light source is presented, based on a zinc-germanium-phosphide optical parametric oscillator (ZGP OPO) pumped by an actively $Q$-switched high-pulse-energy ${{\rm Ho}^{3 +}}{:}{\rm YAG}$ laser. The ${{\rm Ho}^{3 +}}{:}{\rm YAG}$ pump laser source is capable of generating a pulse energy of 15 mJ from a single ${{\rm Ho}^{3 +}}{:}{\rm YAG}$ rod at room temperature at a pulse repetition frequency (PRF) of 700 Hz. A maximum power of 20.1 W at a central wavelength of 2090 nm can be obtained in continuous operation, with a slope efficiency of 45.1%. A good beam quality with an ${{\rm M}^2}$ better than 1.3 was achieved in $Q$-switched operation. The presented laser architecture was used as a suitable pump source for a ZGP-based OPO. Operated at a PRF of 2 kHz and pumped with a pulse energy of 8 mJ, a low conversion threshold of 1.5 W and a maximum total output power of 6.3 W could be obtained in a linear ZGP-based OPO. At maximum power, the peak power of the generated mid-infrared radiation exceeded 120 kW, while the beam quality was affected by the strong gain lens building inside the nonlinear material as a consequence of the high-energy pump pulses.

Dispersion management for optical parametric amplifiers in midinfrared

Midinfrared (MIR) is an attractive spectral region for many applications ranging from vibrational spectroscopy to attosecond physics. However, in this spectral region, the dispersion management techniques are not as mature as the ones in the near-infrared (NIR) or visible, which is a key ingredient of ultrafast laser technology. In this manuscript,thetransferofdispersionmanagementschemesforopticalparametric(chirpedpulse)amplifiers(OP(CP)As) from NIR to MIR is discussed. Among those, a scheme based on Martinez-type grating stretcher and a bulk compressor is proposed and numerically analyzed. As a case study, the proposed scheme is applied numerically to a 2-µm pumped two-stageopticalparametricamplifier(OPA)systemat4.06µm. InthemodelOPAsystem,theseedpulsesaregenerated by white-continuum in bulk crystal and then amplified via zinc germanium phosphide (ZGP)-based OPAs. Parametric gain bandwidth of the ZGP nonlinear crystal is numerically studied. According to the numerical simulations, 3-mm crystal supports pulses with 26.5 fs pulse duration (FWHM) at 4.06 µm. With the proposed dispersion management scheme, the seed pulses are first stretched inside a Martinez grating stretcher to 1.4-1.6 ps for efficient amplification in OPA stages and then compressed down to the transform-limit inside CaF2 bulk material.

Generation of High Power THz Radiation in ZnGeP2 upon Femtosecond Ti:Sapphire Laser Pumping

The possibility of generating high power terahertz radiation in a nonlinear crystal of zinc germanium phosphide (ZnGeP2) with pumping in a short-wavelength absorption shoulder of 0.67–2.5 μm is studied in detail. High power femtosecond Ti:Sapphire laser system operating at wavelengths of 800 and 950 nm are considered as a pump source. A peak terahertz radiation power of ~1 kW is obtained.

X‐Ray Topography: X‐Ray Topography Characterization of the Bridgman‐Grown Crystals of Zinc Germanium Phosphide (Crystal Research and Technology 11/2018)

Crystal Research and TechnologyVolume 53, Issue 11 1870020 Cover PictureFree Access X-Ray Topography: X-Ray Topography Characterization of the Bridgman-Grown Crystals of Zinc Germanium Phosphide (Crystal Research and Technology 11/2018) First published: 08 November 2018 https://doi.org/10.1002/crat.201870020AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract X-ray image of the zinc germanium phosphide crystal obtained at the synchrotron radiation using the rocking topography technique. More details can be found in article number 1800154 by Alexander A. Kaloyan, Konstantin M. Podurets, and co-workers. Volume53, Issue11November 20181870020 RelatedInformation

Efficient middle-infrared ZGP-OPO pumped by a Q-switched Ho:LuAG laser with the orthogonally polarized pump recycling scheme

We describe an efficient middle-infrared laser source based on the Tm:YLF-Ho:LuAG-ZnGeP2 system in this paper. A new orthogonally polarized recycling pump scheme with a simple thin-film polarizer and a half-wave plate are used in a Ho:LuAG laser. Under an incident pump power of 63.8W, we achieve a maximum continuous wave output power of 35.7W in the Ho:LuAG laser, corresponding to a slope efficiency of 60.4% and an optical-to-optical efficiency of 56.0%. With the Q-switched mode, maximum average output powers of 34.1W, 34.9W, and 35.2W were achieved in the Ho:LuAG laser with pulse repetition frequencies of 10kHz, 15kHz, and 20kHz, respectively. With a Ho pump power of 34.1W, maximum average output powers of 16.7W, 15.3W, and 12.6W were achieved in a middle-infrared zinc germanium phosphide optical parametric oscillator (ZGP-OPO) under pulse repetition frequencies of 10kHz, 15kHz, and 20kHz, respectively. The evaluated beam quality factor M2 of the ZGP-OPO was 2.2 for the signal and 1.9 for the idler. To the authors' best knowledge, this is the best performance reported for a middle-infrared ZGP-OPO pumped by a Ho:LuAG laser.

Compact and efficient mid-IR OPO source pumped by a passively Q-switched Tm:YAP laser.

We describe a compact and efficient mid-infrared (mid-IR) source based on zinc germanium phosphide (ZGP) and cadmium silicon phosphide (CSP) optical parametric oscillators (OPOs), operating in near degenerate condition, directly pumped by a 1.94μm thulium (Tm)-doped yttrium-aluminum-perovskite (YAP) laser. The Tm:YAP laser is passively Q-switched by a chromium-doped zinc sulfide saturable absorber, and is operated to 4W average power with a peak power of 29kW. The laser emission was used to pump CSP and ZGP doubly resonant linear OPO cavities, generating a maximum 3.5-4.2μm mid-IR emission of 2.5W for CSP and 2.3W for ZGP, with maximum optical conversion efficiencies of 65% and 58%, respectively, achieved for the two OPO crystals.

Linear optical properties of ZnGeP_2 in the terahertz range

We investigated the optical properties of zinc germanium phosphide (ZnGeP2 or ZGP) crystals in a wide terahertz (THz) range from 0.2 THz to 6 THz, and made comparisons between crystals grown by both horizontal gradient freezing (HGF) and vertical gradient freezing (VGF) techniques. THz time-domain spectroscopy (TDS) and Fourier transform infrared spectroscopy (FTIR) systems were used to measure and analyze the transmittance, refractive indices and absorption coefficients. It was found that the HGF grown crystals have different birefringence and absorption in the THz range compared with the VGF grown crystals. The anisotropic absorption in the THz range was observed and the polar phonon modes at 3.6 THz and 4.26 THz were also discussed. The dispersion and absorption data of ZGP given in this report enabled us to know it better in the THz range and optimize its THz applications.

Towards Terawatt Sub-Cycle Long-Wave Infrared Pulses via Chirped Optical Parametric Amplification and Indirect Pulse Shaping

We present an approach for both efficient generation and amplification of 4–12 μm pulses by tailoring the phase matching of the nonlinear crystal Zinc Germanium Phosphide (ZGP) in a narrowband-pumped optical parametric chirped pulse amplifier (OPCPA) and a broadband-pumped dual-chirped optical parametric amplifier (DC-OPA), respectively. Preliminary experimental results are obtained for generating 1.8–4.2 μm super broadband spectra, which can be used to seed both the signal of the OPCPA and the pump of the DC-OPA. The theoretical pump-to-idler conversion efficiency reaches 27% in the DC-OPA pumped by a chirped broadband Cr2+:ZnSe/ZnS laser, enabling the generation of Terawatt-level 4–12 μm pulses with an available large-aperture ZGP. Furthermore, the 4–12 μm idler pulses can be compressed to sub-cycle pulses by compensating the tailored positive chirp of the idler pulses using the bulk compressor NaCl, and by indirectly controlling the higher-order idler phase through tuning the signal (2.4–4.0 μm) phase with a commercially available acousto-optic programmable dispersive filter (AOPDF). A similar approach is also described for generating high-energy 4–12 μm sub-cycle pulses via OPCPA pumped by a 2 μm Ho:YLF laser.

Bandwidth control in 5 μm pulse generation by dual-chirped optical parametric amplification

We extend the technique of difference-frequency mixing of broadband chirped near-infrared (IR) pulses to longer wavelengths, thereby generating high-energy, bandwidth-tunable laser pulses in the mid-IR spectral region. Numerical modeling has been performed to examine the influence of pump and seed chirp on the generated idler bandwidth and pulse duration. The amplifier is realized using zinc-germanium phosphide crystals pumped by a 2 μm ultrafast parametric source. Idler pulses at a center wavelength of 5 μm with adjustable bandwidth are produced by equally chirping the pump and seed pulses using material dispersion. Using this simple approach, efficient generation of narrowband, short, mid-IR laser pulses is achieved without the use of high-loss dispersive gratings or prism pairs.

Mid-infrared Laser System Development for Dielectric Laser Accelerators

Abstract Laser-driven particle accelerators based on dielectric laser acceleration are under development and exhibit unique and challenging pump requirements. Operation in the mid-infrared (5 μm) range with short pulses ( 500 μJ) and good beam quality is required. We present our progress on the design and development of a novel two- stage source of mid-infrared pulses for this application, which is based on optical parametric amplification. Beta barium borate and zinc germanium phosphide crystals are used, and are pumped by a Ti:sapphire ultrashort laser and seeded by self-phase modulation and parametric generation-based sources.

Electronic, elastic and optical properties of ZnGeP2 semiconductor under hydrostatic pressures

Abstract The electronic, elastic and optical properties of zinc germanium phosphide, ZnGeP2, semiconductor have been studied using local density approximation (LDA) method within the density functional theory (DFT). The lattice constants (a and c), band structure, density of states (DOS), bulk modulus (B) and pressure derivative of bulk modulus (B′) have been discussed. The value of pseudo-direct band gap (Eg) at Г point has been calculated. The pressure dependences of elastic stiffness coefficients (Cij), Zener anisotropy factor (A), Poisson's ratio (ν), Young modulus (Y) and shear modulus (G) have also been calculated. The ratio of B/G shows that that ZnGeP2 is ductile in nature. The optical properties have been discussed in detail under three different pressures in the energy range 0–22 eV. The calculated values of all parameters are compared with the available experimental values and the values reported by different workers. Reasonably good agreement has been obtained between them.

99 W mid-IR operation of a ZGP OPO at 25% duty cycle

We have demonstrated the highest reported output power from a mid-IR ZGP OPO. The laser is a cascaded hybrid system consisting of a thulium fibre laser, Ho:YAG solid state laser and a Zinc Germanium Phosphide parametric oscillator. The system produces 27 W of output power in the 3-5 μm wavelength range with an M(2) = 4.0 when operating in a repetitively q-switched mode, and a modulated peak output power of 99 W at a reduced duty cycle of 25%.

High power 4.65 μm single-wavelength laser by second-harmonic generation of pulsed TEA CO2 laser in AgGaSe2 and ZnGeP2

A high power 4.65 μm single-wavelength laser by second-harmonic generation (SHG) of TEA CO2 laser pulses in silver gallium selenide (AgGaSe2) and zinc germanium phosphide (ZnGeP2) crystals is reported. Experimental results show that the average output power of SHG laser is not only restricted by the damage threshold of the nonlinear crystals, but also limited by the irradiated power of fundamental-wave laser depending on the operating repetition-rate. It is found that ZnGeP2 can withstand higher 9.3 μm laser irradiation intensity than AgGaSe2. As a result, using a parallel array stacked by seven ZnGeP2 crystals, an average power of 20.3 W 4.65 μm laser is obtained at 250 Hz. To the best of our knowledge, it is the highest output power for SHG of CO2 laser by far.

A high power hybrid mid-IR laser source

An efficient hybrid mid-IR laser system comprising a thulium fibre laser, Ho:YAG solid state laser and a zinc germanium phosphide optical parametric oscillator is presented. A 790 nm diode pumped 1908 nm thulium fibre laser operating at 30 W pumps an RTP q-switched Ho:YAG laser emitting 17 W at 40 kHz and 2090 nm. The zinc germanium phosphide optical parametric oscillator efficiently converts this into the 3–5 μm region producing 10.1 W with 59% optical conversion efficiency and an M 2 = 1.5.