Laser-induced Damage Research Articles

Birefringent Glass-Engraved Tilted Pillar Metasurfaces for High Power Laser Applications.

Birefringent materials-which are highly needed in high power laser systems-may be limited in usage due to the laser-induced damage threshold of traditional birefringent materials. This work reports here on all-glass metasurfaces, fabricated by angled etching through sacrificial metal nanoparticle (NP) etching masks, for generation of effective birefringence in the formed layer. As a result, a fused silica metasurface, monolithic to the underlying substrate, is demonstrated to exhibit a birefringence of 6.57° under 375nm illumination. Full-wave analysis shows a good agreement with the measurement and presents potential paths forward to increasing the effective metasurface birefringence. This is the first demonstration, to the best of knowledge, of an etching technique to obtain the resulting tilted pillar-like nanofeatures. The anisotropy of the metasurface nanoelements along the two window in-plane major axes presents different effective paths for the two polarizations and thus generates birefringence in a nonbirefringent material. Additionally, the imparted anisotropy lends itself to manipulation of physical properties of the surface as well, with metasurface feature orientation suppressing water flow along one principal axis and giving rise to water flow steering capabilities.

Formation mechanism of DKDP surface in single point diamond fly-cutting process and the resulting degradation of laser-induced damage performance.

Laser damage performance of DKDP (KD2xH2(1-x)PO4) crystal is largely determined by the surface microstructures generated in the manufacturing process, more specifically, single point diamond fly-cutting process. However, because of the lack of knowledge about the formation mechanism and damage performance of the microstructures, laser induced damage of DKDP crystal remains a key issue limiting the output energy of the high power laser systems. In this paper, the influence of fly-cutting parameters on the generation of DKDP surface and the underlying material deformation mechanism have been investigated. Except for cracks, two kinds of new microstructures, namely micro grains and ripples, have been found on the processed DKDP surfaces. GIXRD, nano-indentation and nano-scratch test results prove that the micro grains are generated by the slip motion of the crystal, while the simulation results show that the cracks are induced by the tensile stress formed behind the cutting edge. Moreover, the formation of micro grains can facilitate the plastic chip flow through the mechanism of grain boundary sliding, which will further lead to a periodic fluctuation of the chip separation point and the formation of micro ripples. Finally, laser damage test results demonstrate that cracks will degrade the damage performance of DKDP surface significantly, while the formation of micro grains and micro ripples has little impact. The results of this study can deepen the understanding of the formation mechanism of the DKDP surface during the cutting process and provide guidance to improve the laser-induced damage performance of the crystal.

Dissection of DNA damage and repair pathways in live cells by femtosecond laser microirradiation and free-electron modeling

Understanding and predicting the outcome of the interaction of light with DNA has a significant impact on the study of DNA repair and radiotherapy. We report on a combination of femtosecond pulsed laser microirradiation at different wavelengths, quantitative imaging, and numerical modeling that yields a comprehensive picture of photon-mediated and free-electron-mediated DNA damage pathways in live cells. Laser irradiation was performed under highly standardized conditions at four wavelengths between 515 nm and 1,030 nm, enabling to study two-photon photochemical and free-electron-mediated DNA damage in situ. We quantitatively assessed cyclobutane pyrimidine dimer (CPD) and γH2AX-specific immunofluorescence signals to calibrate the damage threshold dose at these wavelengths and performed a comparative analysis of the recruitment of DNA repair factors xeroderma pigmentosum complementation group C (XPC) and Nijmegen breakage syndrome 1 (Nbs1). Our results show that two-photon-induced photochemical CPD generation dominates at 515 nm, while electron-mediated damage dominates at wavelengths ≥620 nm. The recruitment analysis revealed a cross talk between nucleotide excision and homologous recombination DNA repair pathways at 515 nm. Numerical simulations predicted electron densities and electron energy spectra, which govern the yield functions of a variety of direct electron-mediated DNA damage pathways and of indirect damage by •OH radicals resulting from laser and electron interactions with water. Combining these data with information on free electron-DNA interactions gained in artificial systems, we provide a conceptual framework for the interpretation of the wavelength dependence of laser-induced DNA damage that may guide the selection of irradiation parameters in studies and applications that require the selective induction of DNA lesions.

Nonlinear optical response of polycrystalline GeSe films

GeSe exhibits in-plane optical anisotropy similar to black phosphorus and other two-dimensional materials, so it is believed to have remarkable nonlinear optical (NLO) properties. In this work, amorphous GeSe films were prepared by vacuum thermal evaporation. After annealing at 450 °C, GeSe films exhibited a polycrystalline phase. The NLO properties of these GeSe films were investigated by the Z-scan technique. The results indicated that GeSe films exhibited typical reverse saturable absorption (RSA) and self-focusing phenomenon. It was also found that the nonlinear optical parameters and laser-induced damage threshold of annealed recrystallized GeSe films were significantly improved. The nonlinear absorption and refractive coefficients were β = (2.90 ± 0.06)×10−7 m/W and n2= (1.06 ± 0.07)×10−13 m2/W at the incident laser intensity of 0.4 GW/cm2, respectively. The polycrystalline GeSe film showed remarkable RSA-induced optical limiting properties, which exhibited an optical limiting starting threshold of 0.018 GW/cm2 and an optical limiting threshold of 0.98 GW/cm2. These results strongly indicate that GeSe films have potential applications in solid-state optical limiting devices and laser protection.

Laser Ablation and Intravital Microscopy to Study Intestinal Remodeling.

Investigating intestinal recovery in vivo is an exquisite technical challenge. A lack of longitudinal imaging protocols has prevented deeper insights into the cell and tissue scale dynamics that orchestrate intestinal regeneration. Here, we describe an intravital microscopy method that locally induces tissue damage at the single crypt scale and follows the regenerative response of the intestinal epithelium in living mice. Single crypts or larger intestinal fields were ablated by a high-intensity multiphoton infrared laser in a time- and space-controlled manner. Subsequent long-term repetitive intravital imaging enabled the tracking of the damaged areas over time and allowed for the monitoring of crypt dynamics during tissue recovery over a period of multiple weeks. Crypt remodeling events such as crypt fission, fusion, and disappearance were observed in the neighboring tissue upon laser-induced damage. This protocol enables the study of crypt dynamics both in homeostatic and pathophysiological settings, such as aging and tumor initiation.

In Vivo Laser-Induced Vasoactive Microenvironmental Setting via a Stimuli-Responsive Microstructured Depot.

A stimuli-responsive polymeric three-dimensional microstructured film (PTMF) is a 3D structure with an array of sealed chambers on its external surface. In this work, we demonstrate the use of PTMF as a laser-triggered stimulus-response system for local in vivo targeted blood vessels stimulation by vasoactive substances. The native vascular networks of the mouse mesentery were used as model tissues. Epinephrine and KCl were used as vasoactive agents that were sealed into individual chambers upon precipitation in the amount of pictograms. We demonstrated the method for non-damaged one-by-one chamber activation using a focused 532 nm laser light passed through biological tissues. To avoid laser-induced photothermal damage to biological tissues, the PTMF was functionalized with Nile Red dye, which effectively absorbs laser light. Chemically stimulated blood vessel fluctuations were analyzed using digital image processing methods. Hemodynamics changes were measured and visualized using the particle image velocimetry approach.

Investigation on nano-absorbing precursors in the picosecond regime via the comparative study of HfO2/SiO2 and Ta2O5/SiO2 high-reflectivity coating damage

Laser-induced damage to the final reflective and diffractive optics limits the total output energy of petawatt laser systems with pulse durations ranging from a few hundred femtoseconds (fs) up to a few tens of picoseconds (ps). In this study, the laser damage to HfO2/SiO2 and Ta2O5/SiO2 multilayer dielectric high-reflectivity (HR) coatings induced by a 1053 nm laser with a pulse width of 8.6 ps was studied to investigate the nano-absorbing precursors in ps regimes. The HfO2/SiO2 HR coating exhibited stronger laser resistance than the Ta2O5/SiO2 HR coating. Flat-bottom pits, pinpoints, and funnel pits were the three typical damage morphologies for the experimental HR coatings. The damage to the HfO2/SiO2 HR coating was primarily dominated by flat-bottom pits, whereas dense pinpoints were the most significant damage for the Ta2O5/SiO2 HR coating. The nano-absorbing precursors introduced by the ion-assisted deposition process were proved to be the damage precursors that trigger pinpoints under a strong electric field intensity (EFI). The nano-absorbing precursors located in the second EFI peak of the SiO2 top layer induced the funnel pits. The funnel pits were expected to be the previous stage of the flat-bottom pits. After they grew along the upward-sloping crack and separated from the interface, the flat-bottom pits were formed. In addition, poor-binding interfaces promoted the formation of flat-bottom pits.

Effect of annealing on the properties of plasma-enhanced atomic layer deposition grown HfO2 coatings for ultraviolet laser applications

HfO2 monolayer coatings are grown by plasma-enhanced atomic layer deposition (PEALD), and the effects of the thermal annealing atmosphere and temperature on the surface morphology, crystal structure, chemical composition, optical absorption, and laser-induced damage threshold (LIDT) of the HfO2 monolayer coatings are investigated. The experimental results show that annealing in an oxygen atmosphere is more beneficial to the decomposition of impurity compounds (carbonates and amines) and the elimination of oxygen deficiency in HfO2 coating than in a nitrogen atmosphere. Compared to the as-deposited coating, the HfO2 coating annealed under an oxygen atmosphere and specific temperature has lower C and N impurity contents, a better stoichiometric ratio, and thus lower absorption and higher LIDT. The highest LIDT (at 355 nm) of 6.3 J/cm2 is obtained at an annealing temperature of 700 ℃, which is approximately three times that of the as-deposited coating. We believe that this experimental result can help improve the LIDT of PEALD-grown oxide coatings or other oxide coatings containing similar impurities.

Cd2 Nb2 Te4 O15 : A Novel Pseudo-Aurivillius-Type Tellurite with Unprecedented Nonlinear Optical Properties and Excellent Stability.

Oxides are emerging candidates for mid-infrared (mid-IR) nonlinear optical (NLO) materials. However, their intrinsically weak second harmonic generation (SHG) effects hinder their further development. A major design challenge is to increase the nonlinear coefficient while maintaining the broad mid-IR transmission and high laser-induced damage threshold (LIDT) of the oxides. In this study, it is reported on a polar NLO tellurite, Cd2 Nb2 Te4 O15 (CNTO), featuring a pseudo-Aurivillius-type perovskite layered structure composed of three types of NLO active groups, including CdO6 octahedra, NbO6 octahedra, and TeO4 seesaws. The uniform orientation of the distorted units induces a giant SHG response that is ≈31 times larger than that of KH2 PO4 , the largest value among all reported metal tellurites. Additionally, CNTO exhibits a large band gap (3.75eV), a wide optical transparency window (0.33-14.5µm), superior birefringence (0.12@ 546nm), high LIDT (23×AgGaS2 ), and strong acid and alkali resistance, indicating its potential as a promising mid-IR NLO material.

The Optical Properties of V2O5 Films Deposited on Single Crystal Diamond Under Homogenizing Preparation Technology

In this article, the V2O5 films’ temperature stratification theoretical model was built, and then the films were deposited on single crystal diamond substrates using homogenizing preparation technology. The results show that the films prepared under homogenizing preparation technology have higher optical-mutation properties than normal preparation technology. More interestingly, the optical phase-transition time was 1.5 ms under homogenizing preparation technology compared to 1.9 ms under normal preparation technology, showing a dramatic decline. In addition, the transmittance before and after phase change under homogenizing preparation technology were 78% and 11% respectively, much better than normal preparation technology of 74% and 17%. Furthermore, the laser-induced damage threshold was from 60 W/mm2 under normal technology up to 70.8 W/mm2 under homogenizing preparation technology.

Challenges in the development of a reliable cw-LIDT measurement routine

The characterization of continuous-wave (cw) laser-induced damage threshold (LIDT) requires a suitable measurement routine to obtain reliable results. In this study, we show that the existing measurement protocols are of limited use for cw-LIDT measurements. On the basis of testing several mirrors with varied distance and number of spots on the samples an adapted protocol for the damage behavior under cw laser irradiation is proposed. We observed a significant effect governed by debris and induced stress of induced damages on the damage behavior of subsequent irradiation spots. Finally, we performed a parametric study on the optical properties of mirror designs consisting of a metal and a dielectric multilayer film and demonstrated the LIDT dependence on the thermal conductivity of the substrate and the absorption of the components.

Calcination-Enhanced Laser-Induced Damage Threshold of 3D Micro-Optics Made with Laser Multi-Photon Lithography

Laser Direct Writing (LDW), also known as 3D multi-photon laser lithography of resins, is a promising technique for fabricating complex free-form elements, including micro-optical functional components. Regular organic or hybrid (organic–inorganic) resins are often used, with the latter exhibiting better optical characteristics, as well as having the option to be heat-treated into inorganic glass-like structures particularly useful for resilient micro-optics. This work is a continuation of our SZ2080™ calcination development of micro-optics, specifically studying the Laser-Induced Damage Threshold (LIDT). Such sol–gel-derived glass 3D micro-structures, particularly those that undergo heat treatment, have not been well-characterized in this respect. In this pilot study, we investigated the LIDT using the Series-on-One (S-on-1) protocol of functional micro-lenses produced via LDW and subsequently calcinated. Our results demonstrate that the LIDT can be significantly increased, even multiple times, by this approach, thus enhancing the resilience and usefulness of these free-form micro-optics. This work represents the first investigation in terms of LIDT into the impact of calcination on LDW-produced, sol–gel-derived glass micro-structures and provides important insights for the development of robust micro-optical devices.

Comparative analysis of thermal damage to laser-irradiated breast tumor based on Fourier conduction and non-Fourier heat conduction models: A numerical study

In recent decades, laser technology has been widely used in surgeries and thermal therapies. To ensure patient safety and enhance therapeutic effectiveness in laser applications, it is crucial to accurately analyze burn injuries during the treatment process. In this study, a bioheat transfer model that includes the effects of metabolic heat generation, capillary blood vessels, and relaxation times of heat flux and temperature gradient was developed to study the non-Fourier heat conduction behavior in 2-D spherical breast tumor during the laser hyperthermia process. By employing different heat conduction models and the Arrhenius burn integration, the temperature distribution and laser-induced thermal damage to tumors were obtained. The progression of burn injury in time and the effect of various parameters on it were investigated. It was observed that the DPL model provides more reliable results in comparison with the CV model in predicting thermal damage to bio-tissue when non-Fourier effects are taken into consideration. The results showed that increasing heat flux phase lag leads to severe thermal damage, earlier onset of empyrosis, and wider and deeper burn injury. However, a greater phase lag of temperature gradient results in lower and superficial thermal damage, milder burn, later onset of empyrosis, and smaller burned area. The effect of laser power density on the onset time of different degrees of burn and their sensitivity to input power were investigated, and the results were represented graphically. Finally, investigation of wave propagation in various tissues revealed that the wave propagation speed is not constant and reduces as time increases.

Nonlinear Optical Sulfides LiMGa8 S14 (M=Rb/Ba, Cs/Ba) Created by Li+ Driven 2D Centrosymmetric to 3D Noncentrosymmetric Transformation.

Cations that can regulate the configuration of anion group are greatly important but regularly unheeded. Herein, the structural transformation from 2D CS to 3D noncentrosymmetric (NCS, which is the prerequisite for second-order NLO effect) is rationally designed to newly afford two sulfides LiMGa8 S14 (M = Rb/Ba, 1; Cs/Ba, 2) by introducing the smallest alkali metal Li+ cation into the interlamination of 2D centrosymmetric (CS) RbGaS2 . The unusual frameworks of 1 and 2 are constructed from C2 -type [Ga4 S11 ] supertetrahedrons in a highly parallel arrangement. 1 and 2 display distinguished NLO performances, including strong phase-matchable second-harmonic generation (SHG) intensities (0.8 and 0.9 × AgGaS2 at 1910 nm), wide optical band gaps (3.24 and 3.32 eV), and low coefficient of thermal expansion for favorable laser-induced damage thresholds (LIDTs, 4.7, and 7.6 × AgGaS2 at 1064nm), which fulfill the criteria of superior NLO candidates (SHG intensity >0.5 × AGS and band gap >3.0 eV). Remarkably, 1 and 2 melt congruently at 873.8 and 870.5°C, respectively, which endows them with the potential of growing bulk crystals by the Bridgeman-Stockbarge method. This investigated system provides a new avenue for the structural evolution from layered CS to 3D NCS of NLO materials.

Mechanisms of the sharp decrease of the LIDT from the plastic surface defect to the brittle surface defect on optical surface

Micro-nano surface defects are inevitably introduced on mechanically processed fused silica surfaces and even almost all the optical glasses, severely decreasing their laser-induced damage thresholds (LIDTs). There are two types of defects: brittle surface defects and plastic surface defects, whose diverse structural characteristics could affect their influence on the LIDTs. Due to their tiny dimensions, brittle and plastic defects are difficult to be distinguished and identified clearly in industrial production. However, there is a sharp decrease (even to 10%) of LIDT from plastic to brittle surface defect, whose mechanisms have not been revealed. Herein, a reciprocal relationship between the highest photoluminescence intensity (HPI) and LIDT of the surface-defect zone is constructed for the first time. The increase of HPI is found to cause a sharp decrease of the LIDT when HPI is low, which is the first cause of the sharp decrease of LIDT. E’-Center and STE point defects would substantially increase from plastic to brittle surface defect, causing a sharp increase of HPI, which is the second cause. This work fundamentally reveals the mechanisms of the sharp decrease of the LIDT from plastic to brittle surface defect, which is beneficial to characterize and mitigate the hazardous brittle surface defects.

Effect of residual impurities on the behavior and laser-induced damage of oxide coatings exposed to deep space radiation

Atomic layer deposition (ALD) is an emerging coating deposition technique filled with potential that is expected to deposit coatings with high laser-induced damage threshold (LIDT). As lasers play an important role in space exploration which are gradually moving to higher orbits and longer lifetimes, a higher demand for space laser coatings has been raising. At the current state of the art, the reliability of ALD-deposited laser coatings for space applications is unclear. This work presents investigations on the stability of three ALD-deposited oxide coatings under space proton and UV radiation at values typical for space environment. Changes in the coatings containing low and high amounts of impurities under space radiation were analyzed through optical parse and composition analysis respectively. Both SiO2 and Al2O3 coatings with few impurities generated color centers after irradiation, which resulted in increased absorption loss and reduced transmittance and optical band gap, and increased probability of damage under laser irradiation. However, the changes in the ZrO2 coating were surprising, when the ZrO2 coating with a large amount of impurities was exposed to radiation, the impurity atoms bound to Zr were displaced first, and the released Zr combined with the oxygen vacancies in the coating, which reduced the number of defects, reduced the absorption loss of the coating, and led to a higher transmittance and an increased optical band-gap. This work provided a novel insight on the impact of the impurities on the stability of the ALD-manufactured oxide coatings against laser-induced damage in effect with space proton and UV radiation. Additionally, we show that high initial LIDT in ALD-prepared oxides may be compromised by the space radiation, while fine tuning of the impurities may result a mitigation approach leading to enhanced laser coatings for space applications.

Importance of crystal length on the stability of a picosecond supercontinuum generated in undoped YAG

In this paper, we present the stability characteristics of a supercontinuum (SC) generated in a 60 mm, 100 mm, and 130 mm long undoped yttrium aluminum garnet (YAG) crystal pumped by a Yb thin-disk regenerative amplifier. The 1.2 ps pulses with a central wavelength of 1030 nm and repetition rate of 89 kHz are loosely focused (NA = 0.0031) into the crystal in order to prevent laser-induced damage and to increase the energy stability of the generated SC. Out of the tested crystal lengths, the optimal is experimentally determined to be 130 mm. The energy contained in the blueshifted side, which has a 530 nm spectral cutoff, is 71 nJ and exhibits average power stability of 0.4% RMS, which is 2.5× better than the stability of the pump beam.

{[In2S7]8–}∞ Chain and Isolated HgS4 Planar Unit Constructed One-Dimensional Pentanary Sulfide K2Ba7HgIn4S16 Exhibiting Nonlinear-Optical Activity

Hg-based chalcogenides possess diverse structures, large nonlinear-optical (NLO) responses, and suitable birefringences, making them potentially suitable for numerous crucial criteria of practical application as infrared (IR) NLO crystals. Here, a new pentanary Hg-based sulfide K2Ba7HgIn4S16 has been discovered by a high-temperature solid-state method. It crystallizes in the orthorhombic P21212 space group, and its one-dimensional structure is constructed by {[In2S7]8-}∞ chains and isolated [HgS4]6- planar quadrilateral units located bewteeen the chains, representing a novel type of chalcogenide. K2Ba7HgIn4S16 exhibits a moderate NLO effect of 0.5 × AGS at 2.1 μm and a high laser-induced damage threshold of ∼5.8 × AGS, as well as a band gap of 2.98 eV, demonstrating that K2Ba7HgIn4S16 is a potential IR NLO material. This work enriches the structural chemistry of chalcogenides and the family of Hg-based IR NLO chalcogenides.

Optical and femtosecond laser-induced damage-related properties of Ta2O5-based oxide mixtures

In this study, four Ta2O5-based mixture coatings, including Ta2O5-TiO2, Ta2O5-HfO2, Ta2O5-Al2O3, and Ta2O5-SiO2, are deposited via plasma-ion-assisted electron-beam co-evaporation and compared with a Ta2O5 monolayer coating. The chemical compositions, microstructures, and optical and femtosecond laser-induced damage threshold (LIDT) properties of the coatings are investigated. For different doping materials, when the refractive indices of the mixture coatings are close, the femtosecond LIDTs exhibit a considerable difference. The experimental results indicate that the Ta2O5-HfO2 mixture coating exhibits a larger optical bandgap and higher femtosecond LIDT than other coatings. The 1-on-1 LIDT of the Ta2O5-HfO2 mixture coating is approximately 1032.3 mJ/cm2 (170 fs), which is 25% higher than that of the Ta2O5 monolayer coating. We believe the Ta2O5-HfO2 mixture will be useful for various multilayer coatings such as chirped mirrors and other mirrors in femtosecond laser applications.

Temporal-spatial dynamics of electronic plasma in a femtosecond laser-induced sapphire microstructure.

In this study, the time-spatial evolution of single-pulse femtosecond laser-induced plasma in sapphire is studied by using femtosecond time-resolved pump-probe shadowgraphy. Laser-induced sapphire damage occurred when the pump light energy was increased to 20µJ. Based on its shadowgraphy image, the threshold electron density can be estimated to be about 2.48×1020 c m -3. The evolution law of the transient peak electron density and its spatial position as femtosecond laser propagation in sapphire were researched. The transitions from single-focus to multi-focus as the laser focus shifted from the surface to a deeper part were observed from the transient shadowgraphy images. The focal point distance in multi-focus increased as the focal depth increased. The distributions of femtosecond laser-induced free electron plasma and the final microstructure were consistent with each other.