Polycrystalline Zinc Selenide Research Articles

Generation mechanism of optical surface in ultra-precision cutting polycrystalline zinc selenide

Despite having an excellent infrared optical property, efficient material removal of zinc selenide (ZnSe) is yet to be realized and its defect generation mechanisms during ultra-precision cutting are not fully elucidated. In this study, ultra-precision cutting experiments on polycrystalline ZnSe were conducted by considering various cutting parameters and utilising surface topography, chip morphology, cutting force, and X-ray diffraction data to investigate its surface generation mechanisms, which were further augmented by molecular dynamics simulations to analyse the generation and suppression of surface defects. The results revealed the presence of irregular microstructures on the surface of polycrystalline ZnSe, arising from variations in material rebound owing to differing grain orientations, as well as micron-sized craters located at grain boundaries and submicron-sized pits within individual grains. Increasing the cutting speed facilitated instantaneous grain fractures, thus preventing grain peeling and effectively suppressing the generation of micron-sized craters and material rebound. Although the use of a negative rake angle on the tool suppressed the generation of micron-sized craters, it introduced a proliferation of burrs that was detrimental to the surface finish. These findings provide valuable insights for optimising the ultra-precision machining process and enhancing the surface quality of brittle polycrystalline ZnSe.

Investigation of the Nonlinear Refractive Index of Polycrystalline Zinc Selenide by Single-Beam Z-Scan

Investigation of the Nonlinear Refractive Index of Polycrystalline Zinc Selenide by Single-Beam Z-Scan

Investigation on the machinability of polycrystalline ZnSe by elliptical vibration diamond cutting.

Polycrystalline zinc selenide is widely used in advanced optical systems due to its superior optical properties. However, the soft and brittle properties bring a challenge for high-quality surface processing. In recent years, elliptical vibration cutting has been proven as a promising method for machining brittle materials. In the present research, a series of grooving and planning experiments were carried out to investigate the machinability of zinc selenide with elliptical vibration cutting. The removal mechanism was analyzed from fracture characteristics, chip morphology, and phase transformation. The results show that elliptical vibration cutting is effective in suppressing cleavage-induced craters. Reducing the nominal cutting speed is beneficial to inhibit the spring back-induced tearing of grains. A 94-time increase in the critical depth of cut was achieved by vibration trajectory optimization compared to ordinary cutting. Moreover, the influence mechanism of feed on the evolution of surface morphology was revealed. Finally, a zinc selenide microlens array was successfully fabricated. The performance was evaluated by geometric parameter measurements and a multiple imaging test. The findings provide a prospective method for ductile regime machining of zinc selenide.

Вивчення взаємодії інфрачервонопрозорих матеріалів ZnSe, ZnS, Si, Ge з розплавами металів

Wetting of infrared-transparent materials — selenide and sulfide zinc, germanium, and silicon by metal melts in a vacuum in a wide temperature range was studied by the sessile drop method using the method of capillary purification of the drop melt during the experiment. Pure metals In, Sn, Pb, Al, Fe, Ni, binary Al—Si, Ge—Si, In—Cu and multicomponent In—Sn—Cu—Ti alloys were used. When zinc chalcogenides are wetted with In—Sn—Cu—Ti melts, zinc selenide is wetted better than zinc sulfide. This is due to the lower thermodynamic stability of selenide. In systems where copper is present in melts, wetting is affected not only by the interaction of selenium or sulfur with titanium, but also by the interaction of copper and zinc (in the copper-zinc system, solid solutions of copper and zinc are formed and copper dissolves in solid zinc). This conclusion also confirms the wetting of the substrate by the In—Cu melt. The values of the contact angle at 650 C are equal to 32, which is less than for the In—Sn—Ti melt at the same temperature. It can be said that for such a system, the interaction of zinc with copper is very important, which is not inferior to the wetting effect of the interaction of chalcogens with titanium. The wetting of single crystals of germanium and silicon by metal melts improves with increasing temperature. Iron and nickel wet silicon (contact angles close to zero) at temperatures lower than their melting point. Contact melting also occurs when silicon substrates are wetted with aluminum melts (the eutectic in the Al—Si system has a temperature of 577 °C). Germanium is better wetted by tin than by indium and lead. Technological processes of soldering infrared transparent materials with metals were developed and soldered joints were obtained. Keywords: infrared transparent materials, polycrystalline zinc selenide and sulfide, single crystals of germanium and silicon, wetting, soldering.

Extreme nonlinear optics in a long pulse regime: High harmonic generation of picosecond mid-IR pulses in polycrystalline zinc selenide.

High harmonic generation (HHG) in semiconductors has been extensively studied recently in the high-intensity limit using middle infrared (mid-IR) femtosecond laser pulses resulting in emission spectra of self-phase modulated harmonics resting on top of a broadband continuum. In this report, a different approach to HHG in polycrystalline zinc selenide (poly-ZnSe) was explored utilizing a relatively low power regime (1-40 GW/cm2) and much longer (30 ps) mid-IR laser pulses. Through a combination of low power, picosecond excitation, and narrowband (<10 nm full width at half maximum) mid-IR excitation, the nonlinear optical effects in poly-ZnSe could be isolated and studied independently. From the clearly distinguishable HHG peaks, harmonic conversion efficiencies of 10-4-10-12 for second to ninth harmonic in poly-ZnSe were measured, and the relationship between the Nth harmonic intensity and excitation intensity (I0) was found to follow a power law, I0x with x ≤ N/2, as a result of the random quasi-phase matching process.

Random quasi-phase-matching for pulse characterization from the near to the long wavelength infrared.

Experiments requiring ultrafast laser pulses require a full characterization of the electric field to glean meaning from the experimental data. Such characterization typically requires a separate parametric optical process. As the central wavelength range of new sources continues to increase so too does the need for nonlinear crystals suited for characterizing these wavelengths. Here we report on the use of poly-crystalline zinc selenide as a universal nonlinear crystal in the frequency resolved optical gating characterization technique from the near to long-wavelength infrared. Due to its property of random quasi-phase-matching it's capable of phase matching second-harmonic and sum-frequency generation of ultra-broadband pulses in the near and long wavelength infrared, while being crystal orientation independent. With the majority of ultra-fast laser sources being in this span of wavelengths, this work demonstrates a greatly simplified approach towards ultra-fast pulse characterization spanning from the near to the long-wavelength infrared. To our knowledge there is no single optical technique capable of such flexible capabilities.

Near infrared performance of a pile-of-plates polariser based on poly-crystalline Zinc Selenide

Zinc Selenide (ZnSe) has wide transparency from 0.6 μm–18 μm making it a desirable substrate for infrared (IR) optical applications. We present experimental results on the NIR transmission of a pile-of-plates polariser at 780 nm and 1.06 μm based on polycrystalline ZnSe plates tilted at Brewster's angle. Due to the high refractive index of ZnSe, n ∼2.5, the degree of polarisation (DOP, V) at λ = 780 nm and 1.06 μm reached V = 0.98 and 0.97 respectively with 4 plates and an extinction ratio E < 10−2 at 780 nm. The calculated DOP for 1–4 plates agree well with theory when allowance is made for internal surface reflections, as in the Airy expressions. While the DOP achieved with 4, 1 mm thick plates is relatively high, the absolute transmission for the P component (TP = 0.83, 0.84 respectively) is much lower than expected, based on the NIR extinction coefficients k < 10−6 (780 nm) and k ∼10−7 (1.06 μm), inferring TP > 0.96. The source of this absolute loss has been considered, including residual surface scatter, diffuse scatter from grain boundaries in the polycrystalline micro-structure and the likely effect of residual birefringence. This loss, we believe is primarily due to residual surface scatter in thin crystal lattice damage layers created during the polishing process and observed when using a hand-held near infrared (NIR) camera. This scatter is polarisation dependent as expected but much higher than scatter theory predicts, consistent with crystalline surface damage. A 6-plate assembly demonstrated an extinction ratio of 1/600 and transmission Tp ∼0.72 at 1.06 μm. The very low absorption and dispersion in ZnSe, particularly at longer wavelengths infer that this polariser would work well in the important MIR region.

Obtaining High-Quality Optical Surfaces of Elements Based on Polycrystalline Zinc Selenide (CVD-ZnSe) that is Doped by Transition Metals in the Process of Mechanical, Chemical Mechanical, and Magnetorheological Treatment

Obtaining High-Quality Optical Surfaces of Elements Based on Polycrystalline Zinc Selenide (CVD-ZnSe) that is Doped by Transition Metals in the Process of Mechanical, Chemical Mechanical, and Magnetorheological Treatment

Effects of the Processing Technology of CVD-ZnSe, Cr2+:ZnSe, and Fe2+:ZnSe Polycrystalline Optical Elements on the Damage Threshold Induced by a Repetitively Pulsed Laser at 2.1 µm

Polycrystalline zinc selenide (ZnSe) and Cr2+ or Fe2+ doped ZnSe are key optical elements in mid-infrared laser systems. The laser-induced damage of the optical elements is the limiting factor for increasing the power and pulse energy of the lasers. In the present work, the optical damage of the ZnSe, Cr2+:ZnSe, and Fe2+:ZnSe samples induced by a repetitively pulsed Ho3+:YAG laser at 2091 nm was studied. The probability of the optical damage and the laser-induced damage threshold (LIDT) were determined for the samples manufactured using different processing techniques. The highest LIDT was found in ZnSe samples annealed in an argon atmosphere. It was also found that the samples annealed in a zinc atmosphere or with hot isostatic pressing resulted in a decrease in the LIDT. The Cr2+-doped ZnSe had the lowest LIDT at 2.1 µm compared to Fe2+-doped or undoped ZnSe. The LIDT fluence of all tested ZnSe samples decreased with the increase in the pulse repetition rate and the exposure duration. The results obtained may be used to improve the treatment procedures of ZnSe, Cr2+:ZnSe, and Fe2+:ZnSe polycrystals to further increase their LIDT.

Laser properties of active media based on ZnSe doped with Fe and In from spray pyrolysis deposited films

A technique was presented for obtaining laser media based on polycrystalline zinc selenide doped with iron from spray pyrolysis deposited films in the solid-phase diffusion process. The effect of the ligature film composition and the high-temperature treatment conditions on the lasing characteristics of Fe:(In):ZnSe active elements was investigated. Lasing with an energy of 100 mJ at a differential absorbed energy efficiency of 42% was obtained on 20 mm disk Fe:ZnSe element pumped by a pulsed electric-discharge HF laser.

Two-photon absorption and stimulated emission in poly-crystalline Zinc Selenide with femtosecond laser excitation

The optical nonlinearity in polycrystalline zinc selenide (ZnSe), excited with 775 nm, 1 kHz femtosecond laser pulses was investigated via the nonlinear transmission with material thickness and the Z scan technique. The measured two photon absorption coefficient <em>β</em> was intensity dependent, inferring that reverse saturated absorption (RSA) is also relevant during high intensity excitation in ZnSe. At low peak intensity <em>I</em> &lt; 5 GW cm^–2, we find <em>β</em> = 3.5 cm GW^–1 at 775 nm. The spectral properties of the broad blueish two-photon induced fluorescence (460 nm-500 nm) was studied, displaying self-absorption near the band edge while the upper state lifetime was measured to be τ_e ~ 3.3 ns. Stimulated emission was observed when pumping a 0.5 mm thick polycrystalline ZnSe sample within an optical cavity, confirmed by significant line narrowing from Δ<em>λ</em> = 11 nm (cavity blocked) to Δ<em>λ</em> = 2.8 nm at peak wavelength <em>λ</em>_p = 475 nm while the upper state lifetime also decreased. These results suggest that with more optimum pumping conditions and crystal cooling, polycrystalline ZnSe might reach lasing threshold via two-photon pumping at <em>λ</em> = 775 nm.

High-aspect-ratio ZnSe microstructure generated by spatially shaped femtosecond laser writing assisted with wet chemical etching

A high-aspect-ratio microstructure in polycrystalline Zinc selenide (ZnSe) is important for waveguides and photonic crystals application. In this work, we demonstrated a successful approach for fabricating microstructure with Bessel beam inscription and etching using a mixed solution of hydrogen peroxide (H2O2) and ammonia hydroxide (NH4OH). The microstructure inscribed using the femtosecond laser back-side fabrication and selective etching, has a longitudinal length of 140 μm and a width of 12 μm. The aspect ratio of microstructures is ∼ 11.2. To showcase the potential of this technique, a rib waveguide with a longitudinal length and width of 60 μm was prepared and the rib waveguides supported a well confined mode at 1.55 μm. This process makes it possible to produce three-dimensional microstructures inside polycrystalline ZnSe, and thus offers a pathway for expanding the photonic crystal structure to the mid-to-far infrared field.

Deformation behaviour of soft-brittle polycrystalline materials determined by nanoscratching with a sharp indenter

Polycrystalline zinc selenide (p-ZnSe) is a typical soft brittle material with important optical applications. In this work, single and repeated nanoscratching tests were performed using a Berkovich indenter along the face-forward (FF) and edge-forward (EF) directions. The morphological features of the scratched grooves and the subsurface microstructural changes in the material were characterised by scanning electron microscopy, Raman spectroscopy, and electron backscatter diffraction (EBSD). Material removal in the ductile mode was obtained in the EF scratching direction; this was accompanied by the slip lines, and the radial cracks generated along grain boundaries. In contrast, brittle fractures occurred in the FF scratching direction, resulting in radial and lateral cracks which are responsible for generating the peeling of the material. The EBSD results demonstrated that the {111} planes are the primary slip plane and secondary cleavage plane, whereas the {110} planes are the primary cleavage plane and secondary slip planes. Tensile residual stress was detected in the subsurface region of the grooves scratched along the FF direction, whereas compressive residual stress was detected in the EF scratching direction. Fishbone-like patterns were observed in the scratched grooves under all conditions, while no phase transformation was detected. This study provides insights into the fundamental material removal mechanisms of soft brittle crystals in various abrasive machining processes, such as grinding, lapping, and polishing.

Spray pyrolysis deposited Cr and In doped CdS films for laser application

Abstract By using the spray pyrolysis technique, CdS films uniform in composition and structure with different contents of chromium and indium ions were deposited on quartz substrates. Their structure, optical properties, and surface morphology were investigated. Employing the films as dopant sources, a correlation has been revealed between the composition of the films and the content of optically active centers in bulk ZnSe samples after doping at the HIP treatment. The process of Cr2+ ions diffusion in polycrystalline zinc selenide was studied, concentration profiles were measured, and the diffusion coefficients of Cr2+ions in one-side doped CVD-ZnSe samples were determined.

Fundamental Investigation of Diamond Cutting of Micro V-Shaped Grooves on a Polycrystalline Soft-Brittle Material

Fabricating micro-structures on optical materials has received great interest in recent years. In this work, micro-grooving experiments were performed on polycrystalline zinc selenide (ZnSe) to investigate the feasibility of surface micro-structuring on polycrystalline soft-brittle material by diamond turning. A photosensitive resin was coated on the workpiece before cutting, and it was found that the coating was effective in suppressing brittle fractures at the edges of the grooves. The effect of tool feed rate in groove depth direction was examined. Results showed that the defect morphology on the groove surface was affected by the tool feed rate. The crystallographic orientation of grains around the groove was characterized by electron backscatter diffraction (EBSD), and it was found that the formation of defects was strongly dependent on the angle of groove surface with respect to the cleavage plane of grain. The stress distribution of the micro-grooving process was investigated by the finite element method. Results showed that the location of tensile stresses in the coated workpiece was farther from the edge of the groove compared with that in the uncoated workpiece, verifying the experimental result that brittle fractures were suppressed by the resin coating.

Establishment of the conditions to improve the luminescence properties of ZnSe for application as scintillating bolometer in the search for neutrinoless double beta decay

The improvement of luminescence/scintillation properties of zinc selenide is the key to reduce the detection background for its application as a scintillating bolometer in experiments that search for neutrinoless double beta decay. This rare event is predicted in extensions of the Standard Model and carries important information about the nature of neutrinos and their mass scale. If detected, new perspectives involving symmetry breaking may be explored in particle physics. In this work we investigate by photoluminescence and complementary techniques the luminescence properties of ultra-pure polycrystalline zinc selenide samples grown by the chemical vapor deposition (CVD) method and submitted to thermal treatments, gamma and particle irradiations, as well as doping processes with aluminum and gallium by diffusion and ion implantation. The results on this work demonstrate that the improvement of the luminescence of zinc selenide depends of the controlled introduction of shallow donor impurities into the material. Furthermore, pair defects involving shallow donor impurities and deep zinc acceptor vacancies (A-centers) – responsible for luminescence bands in the yellow to red spectral region according to the literature – are demonstrated to be the most efficient centers of radiative recombination in the material.

Chip-free surface patterning of toxic brittle polycrystalline materials through micro/nanoscale burnishing

Brittle crystalline materials have important applications in optics and optoelectronics. However, their powders are highly toxic; thus, the chips generated in material removal processes such as cutting, grinding, and polishing are harmful to human health and the environment. In this study, micro/nanoscale burnishing tests were conducted on polycrystalline zinc selenide (p-ZnSe) to explore the feasibility of high-precision surface patterning of a toxic material by local plastic deformation without chip generation. The local deformation behaviours and subsurface damage formation mechanisms were investigated under dry and oil-lubricated conditions. Two types of cracks occurred when the force exceeded a critical value: cracks along the slip planes at the groove bottom and cracks along the cleavage planes at the groove edge. Below the critical force value, however, a crack-free surface was obtained with lower surface roughness than those for diamond-turned surfaces. No phase transformation was detected after burnishing, but lattice distortion appeared in the subsurface layer. A model was developed to predict the activated slip planes by calculating the maximum Schmid factors of the slip systems, and the distribution of subsurface defects was clarified by cross-sectional direct observations. It was also found that the use of a lubricating oil could greatly reduce material pile-ups around the tool. As test pieces, microgrid patterns were fabricated by crossing and overlapping the grooves, and smooth surfaces with surface roughness of 1.85 nm Sa and 4.5 nm Sa, respectively, were achieved. The findings from this study demonstrate the feasibility of chip-free surface patterning on toxic brittle polycrystalline materials by micro/nanoscale burnishing, which is an effective alternative to cutting and grinding for the fabrication of micro structured optical elements and microfluidics.

Post-processing ZnSe optical fibers with a micro-chemical vapor transport technique

Polycrystalline zinc selenide optical fibers and fiber lasers are expected to provide powerful capabilities for infrared waveguiding and laser technology. High pressure chemical vapor deposition, which is the only technique currently capable of producing zinc selenide optical fibers, leaves a geometric imperfection in the form of a central pore which is detrimental to mode quality. Chemical vapor transport with large temperature and pressure gradients not only fills this central pore but also encourages polycrystalline grain growth. Increased grain size and a reduction in defects such as twinning are demonstrated with transmission electron microscopy, Raman spectroscopy, and X-ray diffraction, supporting that high-quality material is produced from this method. Finally, the mode structure of the waveguide is improved allowing most of the guided optical intensity to be centrally positioned in the fiber core. Loss as low as 0.22 dB/cm at 1908nm is demonstrated as a result of the material improvement.

Impurity- and defect-related luminescence of ZnSe:Fe at Low Temperatures

Polycrystalline zinc selenide is doped with an iron impurity to a concentration of ~1019 cm−3 in a zinc vapor atmosphere by the thermal diffusion method, and the distribution profile of optically active iron Fe2+ is obtained. The effect of the Fe2+ concentration on impurity-and defect-related ZnSe luminescence spectra at low temperatures is determined. In the range of 1.28—1.31 eV, a luminescence line with a decay time of ~0.341 ms is detected, with its intensity increasing in regions with Fe2+ concentration close to the maximum one. The line is attributed to the luminescence center arising due to the Fe2+ interaction with a background impurity or defect in ZnSe.

Spatial Distribution of Impurity Defect Centers in Fe-Doped Polycrystalline Zinc Selenide

The spatial distribution of impurity defect centers in Fe-doped chemical vapor deposited (CVD) ZnSe has been studied by two-photon confocal microscopy and scanning Fourier transform spectroscopy using an IR microscope. It has been shown that, as a result of doping with Fe, CVD ZnSe contains regions hundreds of microns in size that are parallel to the doping plane and differ in luminescence characteristics. The characteristics of these regions have been shown to correlate with the concentration of optically active Fe. Our results can be interpreted in terms of a model that assumes codiffusion of Fe and two types of impurity defect centers. We have pointed out that the data obtained in this study should be taken into account in interpreting results on the photoluminescence of semiconductors doped via thermal diffusion.