High Laser Damage Threshold Research Articles

MgSiP2: An Infrared Nonlinear Optical Crystal with a Large Non‐Resonant Phase‐Matchable Second Harmonic Coefficient and High Laser Damage Threshold

AbstractSuperior infrared nonlinear optical (NLO) crystals are in urgent demand in the development of lasers and optical technologies for communications and computing. The critical challenge is to find a crystal with large non‐resonant phase‐matchable NLO coefficients and high laser damage threshold (LDTs) simultaneously, which however scale inversely. This work reports such a material, MgSiP2, that exhibits a large second harmonic generation (SHG) coefficient of d14≈d36 = 89 ± 5 pm V−1 at 1550 nm fundamental wavelength, surpassing the commercial NLO crystals AgGaS2, AgGaSe2, and ZnGeP2. First principles theory reveals the polarizability and geometric arrangement of the [SiP4] tetrahedral units as the origin of this large nonlinear response. Remarkably, it also exhibits a high LDT value of 684 GW cm−2, which is six times larger than ZnGeP2 and three times larger than CdSiP2. It has a wide transparency window of 0.53–10.35 µm, allowing broadband tunability. Further, it is Type I and Type II phase‐matchable with large effective SHG coefficients of deff,I ≈80.2 pm V−1 and deff,II ≈73.4 pm V−1. The outstanding properties of MgSiP2 make it a highly attractive candidate for optical frequency conversion in the infrared.

Three-in-One Strategy Constructing the First High-Performance Nonlinear Optical Sulfide Crystallizing with the P43 Space Group.

The balance between large nonlinear optical (NLO) effect and wide bandgap is the key scientific issue for the exploration of infrared NLO materials. Targeting this issue, two new pentanary chalcogenides KGaGe1.37 Sn0.63 S6 (1) and KGaGe1.37 Sn0.63 Se6 (2) are obtained by the three-in-one strategy, viz. three types of fourfold-coordinated metal elements co-occupying the same site. They crystallize in the tetragonal P43 (1) and monoclinic Cc (2) space group. Their structures can be evolved from benchmark AgGaS2 (AGS) by suitable substitution. Remarkably, 1 is the first NLO sulfide crystallizing with the P43 space group, representing a new structure-type NLO material. The structural relationship between 1 and 2 and the evolution from 1, 2 to AGS are also analyzed. Both 1 and 2 show balanced NLO properties. Specifically, 1 exhibits phase-matchable SHG response of 0.6 × AGS, a wide bandgap of 3.50eV, and a high laser damage threshold of 6.24 × AGS. Theoretical calculation results suggest that the Ga/Ge/Sn element ratios of the co-occupied sites of 1 and 2 are the most appropriate for stabilizing the structures. The strategy adopted here will provide some inspiration for exploring new high-performance NLO materials.

Tailoring of the femtosecond-laser-induced damage properties and hydrolysis resistance of fluoroaluminate glass

In this study, we investigated and compared the hydrolysis resistance properties of three different types of fluoride glasses and their damage characteristics induced by an 800 nm fs (fs) laser. The results show that the hydrolysis resistance of the fluoroaluminate (AYF) glass is significantly higher than that of the fluorozirconate (ZBLAN) and the fluoroindate (IZBS) glass. After soaking in distilled water for 7 days, the average transmittance of the fluoroaluminate glass (AYF) remains around 80% in the range of 2–6 μm, while that of the other two glasses decrease to zero at the hydroxyl group absorption wavelength of ∼2.96 μm. After 24 h of immersion, the mass loss rate of AYF glass is less than one-eleventh of ZBLAN glass and one-eighth of IZBS glass, respectively. Under the irradiation of fs laser (800 nm, 91 fs, 1 kHz), the “1-on-1″ mode laser-induced damage threshold of the AYF glass is as high as 5164.9 mJ/cm2, which is 80.3% higher than that of the IZBS glass (2863.3 mJ/cm2) and 16.8% higher than that of the ZBLAN glass (4420.1 mJ/cm2). The higher laser damage threshold is attributed to the relative larger optical bandgap and higher Al–F energies of the AYF glass. Using this mechanism, we further tailored the fluoroaluminate glass's optical bandgap increased and the accumulation rate of electrons decreased by introducing up to 20 mol % TeO2 into the AYF glass, finally the fs laser-induced damage threshold of the corresponding sample with 20 mol % TeO2 increased by about 79.5% to the maximum 9272.2 mJ/cm2, compared with the TeO2-free AYF sample.

Nonlinear optical crystals KPb3(3-C5H4NCOO)2Br5 and KPb3(3-C5H4NCOO)2Cl3Br2 with new Pb-centered nitrogen-halide polyhedrons obtained by the halide anionic substitution

The rational synthesis of nonlinear optical (NLO) crystals with good performances remains a great challenge. Herein, the total/partial halide anionic substitution has been successfully expanded to discover two new NLO crystals, KPb3(3-C5H4NCOO)2Br5 and KPb3(3-C5H4NCOO)2Cl3Br2. Interestingly, KPb3(3-C5H4NCOO)2Br5 and KPb3(3-C5H4NCOO)2Cl3Br2 not only contain highly distorted [PbO2Br] and [PbO2Cl] trigonal pyramids, but also possess unique Pb-centered nitrogen-halide functional units, including [PbNBr4] square pyramid, as well as [PbNBr2Cl] four-coordinated polyhedron with mixed halogen anions. Remarkably, after the total halide anionic substitution, the net polarization of the Pb-centered nitrogen-halide functional units runs parallel to that of the π-conjugated nicotinate groups, resulting in the enhancement of macroscopic polarization. Therefore, KPb3(3-C5H4NCOO)2Br5 displays a strong phase-matching second-harmonic generation response of 2.9 × KDP. Furthermore, KPb3(3-C5H4NCOO)2Br5 has a high laser damage threshold of 149 MW/cm2, a wide transparent window of 0.39–5.5 µm, a suitable birefringence of 0.11 @ 1064 nm and good stability. Theoretical calculations have been performed to elucidate the origin of their optical properties.

Resonant Second Harmonic Generation in Proline Hybrid Lead Halide Perovskites

AbstractChiral hybrid organic−inorganic perovskites (HOIPs) with intrinsic noncentrosymmetry have shown great potentials for chiroptoelectronic applications including second‐order nonlinear optics (NLO). Ideal NLO materials should simultaneously feature a large NLO coefficient, wide optical transparency, high laser damage threshold, and physicochemical stability. However, the development of applicable second‐order NLO materials has been largely restricted due to their strict requirement on structural noncentrosymmetry. Here, chiral amino acids abundant in nature have been adopted to synthesize hybrid lead halide perovskites (D‐/L‐Pro)PbI3·H2O (Pro = Proline) with resonance enhanced second‐harmonic generation (SHG). Their crystals feature balanced NLO performances with a large NLO coefficient, wide transparent region, high laser damage threshold, and high polarization ratio. This work demonstrates the promise of naturally abundant amino acids for the construction of hybrid chiral metal halide perovskites for next generation optoelectronic materials.

Research on post-processing polishing technology of pulse compression gratings with high laser damage threshold

Research on post-processing polishing technology of pulse compression gratings with high laser damage threshold

Laser-based defect characterization and removal process for manufacturing fused silica optic with high ultraviolet laser damage threshold

Laser-based defect characterization and removal process for manufacturing fused silica optic with high ultraviolet laser damage threshold

D6versus d10, Which Is Better for Second Harmonic Generation Susceptibility? A Case Study of K2TGe3Ch8 (T = Fe, Cd; Ch = S, Se)

Two acentric chalcogenide compounds, K2CdGe3S8 and K2CdGe3Se8, were synthesized via conventional high-temperature solid-state reactions. The crystal structures of K2CdGe3S8 and K2CdGe3Se8 were accurately determined by single-crystal X-ray diffraction and crystallize in the K2FeGe3S8 structure type. K2CdGe3S8 is isostructural to K2FeGe3S8 with superior nonlinear optical properties. For the second harmonic generation (SHG) response, K2CdGe3S8 is 18× K2FeGe3S8 for samples of particle size of 38-55 μm. The superior nonlinear optical properties of K2CdGe3S8 over K2FeGe3S8 are mainly contributed by the chemical characteristics of Cd compared with Fe, which are elucidated by nonlinear optical property measurements, electronic structure calculations, and density functional theory calculations. The [CdS4] tetrahedra within K2CdGe3S8 exhibit a higher degree of distortion and larger volume compared to the [FeS4] tetrahedra in K2FeGe3S8. This study possesses a good platform to investigate how d-block elements contribute to the SHG response. The fully occupied d10-elements are better for SHG susceptibility than d6-elements in this study. K2CdGe3S8 is a good candidate as an infrared nonlinear optical material of high SHG response (2.1× AgGaS2, samples of particle size of 200-250 μm), type-I phase-matching capability, high laser damage threshold (6.2× AgGaS2), and good stability.

Effect of doped niobium pentoxide on structure and properties of hafnium oxide films deposited by ion beam assisted deposition

Hafnium oxide is widely used in optical coating materials because of its high refractive index, broad band gap, high laser damage threshold and its high transparency in the wavelength range from ultraviolet to middle infrared (0.20–12 μm). However, hafnium oxide has some defects such as strong crystallinity and poor surface quality, which results in enhanced absorption and reflection of light wave and limits its application in optical field. As a pentoxide with high transparency and excellent optical properties in the wavelength range from ultraviolet to mid-infrared(0.35–9 μm), the doping of niobium pentoxide can effectively improve the surface quality and optical properties of the films. Mixed films with different chemical compositions were prepared by ion beam assisted deposition, and the microstructure, crystallinity, surface quality, optical properties and mechanical properties of the mixed films with different chemical compositions were investigated. The doping of niobium pentoxide inhibits the crystallization of hafnium oxide, optimizes the surface quality of the films, and improves the refractive index and mechanical properties of mixed films, effectively broadens the application of hafnium oxide in the field of optical films.

Achieving Large Second Harmonic Generation Effects via Optimal Planar Alignment of Triangular Units

AbstractTrigonal planar units with large polarizability anisotropy and high physicochemical stability are ideal structural units for exploring nonlinear optical (NLO) materials. Integrating the merits of two types of triangular‐like moieties, a family of second‐order NLO‐active hybrid halides, MATX (X = Cl (1), Br (2), and I (3)), are achieved. MATX crystallizes in a nonpolar space group of 2c but exhibits the optimal spatial arrangement and superior NLO performance. The low coordination planar trigonal AgX3 units enable segregation in layers of the three‐winged propeller‐like Me3TPA units. All of the layers are packed in a perfect parallel fashion, making the functional materials exhibit superior NLO performances, including the phase matchable behavior with strong SHG responses (6.2/1, 6.5/2, and 7.6/3 times that of potassium dihydrogen phosphate), large birefringence (0.232/1, 0.252/2 and 0.260/3 at 1064 nm), high laser damage threshold, wide transparent window, and easiness of crystal growth. The first‐principles calculations reveal that the coexistence of strong linear and nonlinear optical properties are ascribed to the synergistic effect of the trigonal moieties. This study points out a useful path for the rational design of excellent NLO materials.

Novel structural transformation in K3ReP2S8 thiophosphates originating from the rare-earth (Re) cation sizes induced local coordination asymmetry

Noncentrosymmetric (NCS) structure is a prerequisite condition for nonlinear optical (NLO) crystals and searching for feasible design strategy on the discovery of new NCS compounds has become extremely important. For that reason, new series of rare-earth (Re) based NCS K3ReP2S8 (Re = Y, Ho, Er; P21 space group) and CS K3ReP2S8 (Re = Pr, Sm, Gd; P21/c) thiophosphates were successfully prepared and this interesting CS to NCS structural remodeling shows the interior relationship with cation-size effect of Re metals. Systematic structural analysis indicates that several of varying influence factors including Re's ionic radii, average Re–S bond lengths and distortion degrees of ReS8 units induce the born of local coordination asymmetry between ReS8 and PS4 units, which facilitates the transformation from CS to NCS structures in K3ReP2S8 system. Moreover, excellent performances including strong NLO responses (1.1–1.4 times that of commercial AgGaS2) and required phase-matching behavior in P21–K3ReP2S8 were determined. Note that P21–K3ReP2S8 can be viewed as first NLO examples in the quaternary rare-earth thiophosphates. Moreover, NCS K3ReP2S8 also satisfy the well-balance between large NLO effects (1.1–1.4 × AgGaS2) and high laser damage thresholds (2.5–7.0 × AgGaS2). Theoretical study demonstrates that synergetic contributions of ReS8 and PS4 units guarantee the intrinsic origin of NLO response and ReS8 units provide the major NLO contribution. Therefore, this work not only affords one effective pathway to design new NCS materials through breaking the local symmetry in CS structures based on the size-directing effect of Re cations, but also verifies that bridging ReSn units into thiophosphates is beneficial to the huge enhancement of intrinsic NLO performances.

Temporal Contrast Enhancement Based on the Self-Diffraction Process with Different Kerr Media

In this study, the self-diffraction (SD) process proved to be a competitive method to achieve a seed pulse with high temporal contrast in ultra-intense lasers. Several different nonlinear, transparent Kerr media including BK7 glasses, AL2O3 and CVD diamonds were compared experimentally to obtain SD signals with high energy and high conversion efficiency. AL2O3, with a high third-order nonlinear coefficient and high laser damage threshold, was found to be the best medium to improve the conversion efficiency of SD signals. The highest first-order SD signal of 401.7 μJ was achieved, with the conversion efficiency at approximately 9.1%, when the incident pulse energy was 4.40 mJ. The temporal contrast of the obtained first-order SD signal was improved by 7 orders of magnitude to 1012. As a result, this cleaning pulse will facilitate research involving ultra-intense laser systems and high-intensity laser–matter interactions.

Characteristic of fixed abrasive polishing for KDP in an anhydrous environment.

High grade optical components are rapidly being employed in a wide range of applications due to their great performance. Among these, KDP (potassium dihydrogen phosphate) is the preferred choice for frequency doubling components because to its large non-linear optical technique and high laser damage threshold. In this research, KDP is treated employing fixed polishing in an anhydrous environment. Copper oxide is utilized as abrasive, and toner and phenolic resin are combined to form pellets for KDP polishing. Calculation of the temperature field on the surface of the workpiece based on the relationship of the movement. The ideal polishing parameters are also determined from the findings of the temperature field and the optimum process parameters are 5kPa pressure, 150rpm and 8mm eccentricity. A new material removal model is presented and based on this, a unique processing technique to increase the material removal depth is provided. Interestingly, with this form of polishing, the surface roughness of the workpiece remains about Ra 20nm after a quick shift and does not alter with re-pressing.

Optical limiter coatings towards reusable high irradiance shielding

Optical limiters (OLs) are systems designed to protect objects from high intensity irradiance above a set threshold. Often times, these OL systems are in the form of coatings and can be used to protect objects such as sensors, critical components, or human eyes. In this work, we report the successful development of a multilayer reflective OL coating system based on a non-linear Fabry-Perot resonator structure. The structure utilized distributed Bragg reflectors (DBRs) composed of silicon/silicon nitride and a boron nitride non-linear layer embedded in the resonant cavity. The coatings were fabricated via DC and RF magnetron sputtering and exhibited high reflectance (∼99%) over a 525 nm bandwidth with a single resonant transmission peak (∼7%). The optical limiters fabricated in this study exhibited a transmission drop-off when exposed to irradiances above ∼1000 kW/cm2 from a 1064 nm Nd:YAG laser, demonstrating an abrupt reduction in resonant transmission. Fabricated optical limiters also demonstrated multi-hit survivability, maintaining low transmittance (<0.4%) after numerous 3.6 ns laser pulse exposures. This multi-hit survivability and high reflectivity offers promising opportunities for improved protection against directed energy weapons. This study lays groundwork for future evaluation of the observed on/off mechanism, as well as further development of high laser damage threshold optical limiting thin films.

Spontaneous Raman spectra analysis and efficient nanosecond pulse Raman laser of a BaTeW2O9 crystal.

In this Letter, the spontaneous Raman spectra of a novel, to the best of our knowledge, crystal α-BaTeW2O9 (α-BTW) are characterized and analyzed. The relative Raman gain coefficient of the α-BTW crystal is calculated to be 0.84 times that of YVO4. With a 35-mm-long crystal, the first-order Raman laser of α-BTW operating at 1178 nm is realized. The simple external resonator setup is employed in the first-order Raman laser of α-BTW. The pump source is a lamp-pumped electric-optical Q switched Nd:YAG laser amplifier system operating at 1064 nm with a pulse width of 10 ns. The Raman laser exhibits a threshold of 14.7 MW/cm2. In our experiments, a maximum pulse energy of 21.5 mJ is obtained with an optical-to-optical conversion efficiency and slope efficiency of 43.6%, 57.9%, respectively. Due to its high laser damage threshold, relative high Raman gain coefficient, and excellent thermal properties, the α-BTW crystal is a potential Raman material.

Broadband BiOCl Nonlinear Saturable Absorber for Watt‐Level Passively Q‐Switched Yb:LuAG Single Crystal Fiber Laser

AbstractThe development of nonlinear optical (NLO) devices is limited to the mid‐infrared range due to the lack of broadband NLO response. As an indirect band gap semiconductor, BiOCl has a band gap of ≈3.3 eV. The special anisotropic lamellar structure makes it exhibit excellent electrical and optical properties; however, its NLO saturable absorption effect is rarely reported. In this study, the NLO response, optical properties, and applications of BiOCl crystals grown by chemical vapor phase transport method are studied in detail. The transmission spectrum indicates the BiOCl crystal has a broadband transparent region (0.4–11 µm). The saturable absorption of BiOCl is characterized by the Z‐scan method with 532 and 1030 nm pulsed lasers. With BiOCl as the saturable absorber (SA), watt‐level passively Q‐switched pulsed laser based on Yb:LuAG single crystal fiber (SCF) is realized. This is the first report of BiOCl as SA for passively Q‐switched all‐solid‐state pulsed laser, and the obtained average power is the highest value of passively Q‐switched SCF pulsed lasers reported so far. The high transmittance, high laser damage threshold, wideband NLO response, and environmental stability of BiOCl indicate that BiOCl crystal is a potential candidate for NLO applications.

An excellent deep-ultraviolet birefringent material based on [BO2]∞ infinite chains

Birefringent materials play indispensable roles in modulating the polarization of light and are vital in the laser science and technology. Currently, the design of birefringent materials operating in the deep-ultraviolet region (DUV, λ ≤200 nm) is still a great challenge. In this work, we developed a new DUV birefringent crystal LiBO2 based on [BO2]∞ infinite chains in the Li-B-O system, which simultaneously achieves the shortest UV cutoff edge (164 nm) and the largest birefringence (≥0.168 at 266 nm) among all the reported borate-based DUV birefringent materials. Single crystals of LiBO2 with dimensions up to Ø55 × 34 mm3 were grown by the Czochralski method, providing access to large-sized single crystal with low cost. Moreover, it has a high laser damage threshold and stable physicochemical properties. These outstanding characters unambiguously support that LiBO2 can be an excellent birefringent material for DUV application.

Plate laser beam splitter with mixture-based quarter-wave coating design

Plate laser beam splitter (PLBS) coatings for intensity-splitting in high-power laser applications face increasing requirements, where the challenge is to simultaneously satisfy a given transmittance (T)/reflectivity (R) intensity-splitting ratio with a certain bandwidth, and a high laser damage threshold (LIDT). Traditionally, a given T/R ratio is achieved by using a non-quarter-wave design. We propose a quarter-wave design strategy for arbitrary T/R ratios by using mixture layers with tunable refractive index (n) and optical bandgap as high-n layers. Two quarter-wave PLBS coatings based on HfO2–Al2O3 mixture with a designed T/R ratio of 50:50 are experimentally demonstrated and compared with the traditional PLBS coating. The mixture-based PLBS coating shows good spectral performance, low surface roughness, and high LIDT. For an s-polarized 8 ns pulse laser at a wavelength of 1064 nm, a mixture-based PLBS coating design can improve LIDT by a factor of ∼ 2 with a slightly wider bandwidth. This tunable mixture-based PLBS coating design strategy provides support for the increasingly high output power of high-power laser systems.

Design of a High-Efficiency Multilayer Dielectric Diffraction Grating with Enhanced Laser Damage Threshold.

Diffraction gratings are becoming increasingly widespread in optical applications, notably in lasers. This study presents the work on the characterization and evaluation of Multilayer Dielectric Diffraction Gratings (MDG) based on the finite element method using Comsol MultiPhysics software. The optimal multilayer dielectric diffraction grating structure using a rectangular three-layer structure consisting of an aluminum oxide Al2O3 layer sandwiched between two silicon dioxide SiO2 layers on a multilayer dielectric mirror is simulated. Results show that this MDG for non-polarized lasers at 1064 nm with a significantly enhanced −1st diffraction efficiency of 97.4%, reaching 98.3% for transverse-electric (TE) polarization and 96.3% for transverse-magnetic (TM) polarization. This design is also preferable in terms of the laser damage threshold (LDT) because most of the maximum electric field is spread across the high LDT material SiO2 for TE polarization and scattered outside the grating for TM polarization. This function allows the system to perform better and be more stable than normal diffraction grating under a high-intensity laser.

Sr3[SnOSe3][CO3]: A Heteroanionic Nonlinear Optical Material Containing Planar π‐conjugated [CO3] and Heteroleptic [SnOSe3] Anionic Groups

AbstractInorganic heteroanionic materials are attracting increasing attention for exploring new nonlinear optical (NLO) materials because they could better satisfy the necessary but conflicting properties of NLO crystals, e.g. large SHG response and wide band‐gap. Up to now, the reports on heteroanionic NLO materials have mainly focused on ultraviolet or visible oxide‐based fluoroborates, fluorophosphates, borate‐phosphates and borate‐iodates. However, chalcogenides containing different kinds of anionic groups have barely been reported. Herein, we have synthesized the first oxychalcogenide‐carbonate, Sr3[SnOSe3][CO3] that contains two different kinds of anionic groups, [SnOSe3] and [CO3]. It crystallizes in a noncentrosymmetric space group and exhibits fascinating NLO properties, including a large SHG response (≈1×AGS), sufficient birefringence (0.12 @1064 nm), wide band‐gap (3.46 eV) and high laser damage threshold (240 MW cm−2). These make Sr3[SnOSe3][CO3] a promising NLO crystal.