Laser-induced Damage Properties Research Articles

Design, production, and characterization of a pair of positive and negative high dispersive mirrors for chirped pulse amplification systems.

We report a novel modified Gires-Tournois interferometer (MGTI) starting design for high-dispersive mirrors (HDMs). The MGTI structure combines multi-G-T and conjugate cavities and introduces a large amount of dispersion while covering a wide bandwidth. With this MGTI starting design, a pair of positive (PHDM) and negative highly dispersive mirrors (NHDM) providing group delay dispersions of +1000 fs2 and -1000 fs2 in the spectral range of 750 nm to 850 nm is developed. The pulse stretching and compression capabilities of both HDMs are studied theoretically by simulating the pulse envelopes reflected from the HDMs. A near Fourier Transform Limited pulse is obtained after 50 bounces on each positive and negative HDM, which verifies the excellent matching between the PHDM and NHDM. Moreover, the laser-induced damage properties of the HDMs are studied using laser pulses of 800 nm and 40 fs. The damage thresholds of the PHDM and NHDM are approximately 0.22 J/cm2 and 0.11 J/cm2, respectively. The laser-induced blister structure of the HDMs is observed, the formation and evolution processes of the blister are evaluated.

High-repetition rate picosecond laser-induced damage properties of Ta2O5:SiO2 coatings

High-repetition rate laser-induced damage of Ta2O5:SiO2 coatings was investigated at 355 nm wavelength and a repetition rate of 30 kHz. Laser-induced damage thresholds of coatings with different mixture ratios were measured. The relationships between laser-induced damage threshold and the material band gap and defect absorption were analyzed. Laser-induced damage threshold decreased with increase in number of laser pulses owing to enhancement of the absorption. Enhancement of absorption is attributed to the increase in density of mid-state defects induced by the picosecond laser pulses. The relationship between mid-state defects and the material mixture ratio was also analyzed.

Study on laser-induced damage of TbBiIG crystal at 1064 nm.

With the development of miniaturization of high-energy laser systems, a new Faraday rotator material must be studied to realize the miniaturization and integration of optical isolators. In this paper, high-quality (TbBi)3Fe5O12 (TbBiIG) and Ca-doped (TbBi)3Fe5O12 (Ca: TbBiIG) single crystal films with hundreds of microns thickness were grown by liquid phase epitaxy method on (111) oriented garnet substrate. The crystal structure, magneto-optical (MO), optical and laser induced damage properties were investigated in detail. We found that the (TbBi)3Fe5O12 film has outstanding magneto-optical and laser-induced damage properties. Optical and MO properties indicate that TbBiIG films have a high specific faraday rotation angle of 1452 deg/cm at 1310 nm, and 2812 deg/cm at 1064 nm, absorption coefficient (α) is 5.63 cm-1 and 15.7 cm-1 at 1310 nm and 1064 nm, respectively. The laser-induced damage threshold (LIDT) of TbBiIG irradiated by a multi-frequency laser is 8.91 J/cm2. The light absorption has a significant impact on LIDT value. Rare-earth ion doped iron garnet (RIG) material is a very potential MO material, which can greatly reduce the size and weight of optical isolators in the 1064 nm band.

The investigation of the antireflection method and laser induced damage properties for perfluoroalkoxy copolymer film as short pulse laser debris shields

Perfluoroalkoxy copolymer (PFA) film is a promising material for mitigating target debris in high-power laser system. However, the PFA film has a high reflectivity and the inert surface is difficult to achieve antireflection, which restrain the application for debris shield. In this paper, we experimentally demonstrate that broadband antireflection of PFA film can be achieved through combining oxygen plasma treatment and sol–gel coating techniques. In this case, transmittance over 99% with wide wave bands ranging from 600 to 1200 nm is achieved. For the plasma-treated PFA film, the withdrawal rate of 80 mm/min is an optimal withdrawal rate for broadband antireflection. The damage tests of bare and coated PFA films are investigated by a laser beam operating at 800 nm.

Laser-induced damage of 1064 nm multilayer antireflection coatings after exposure to gamma rays

Laser coatings designed for space applications not only encounter harsh space environments, but also suffer from laser irradiation. High-energy radiation in space, such as Gamma rays, can cause defects and other damage to materials, which could contribute to laser damage induced by defect absorption. In this work, we studied the optical properties and structural composition of three groups of 1064 nm multilayer antireflection (AR) coatings irradiated by Gamma rays (345 Gy), and the effect of Gamma ray radiation on the laser-induced damage properties of thin films. Experimental results revealed that after exposure to Gamma ray, the absorption and surface roughness of the AR coating increased while the transmittance decreased. X-ray photoelectron spectroscopy (XPS) analysis confirmed that SiO2 is more fragile under Gamma radiation compared to Ta2O5 and HfO2. It was also demonstrated that the Gamma ray damage of AR coatings mainly occurred in the SiO2 layers, and consist of generation of oxygen vacancies and charging defects. The defects generated by Gamma rays increased the absorption of the laser power by the film, hence increasing the probability of laser-induced damage and reducing the laser-induced damage threshold of the film. The coatings prepared by sputtering deposition technique showed lower probability of damage by Gamma ray radiation compared to electron-beam evaporated coatings.

Optimizing sub-nanosecond laser conditioning of DKDP crystals by varying the temporal shape of the pulse.

We propose a strategy to optimize the laser conditioning of DKDP crystals by varying the temporal shape of sub-nanosecond pulses. Four sub-ns temporally shaped pulses with nearly the same full width at half maxima of ∼600 ps but different rising-falling statuses were designed to conduct laser-induced damage (LID) and laser conditioning experiments on DKDP crystals. The shape of the pulse substantially influences the damage pinpoints size and LID threshold (LIDT) of the crystals in the sub-nanosecond range. After sub-nanosecond laser conditioning, the ns R-on-1 LIDT showed that slow-rising fast-falling pulse (R400-F200 and High-foot pulses) conditioning achieved a 14%-20% LIDT enhancement than the traditional Gaussian pulse (R300-F300 pulse). The 8-ns laser damage morphologies after slow-rising fast-falling pulse conditioning showed cracks, whereas those after fast-rising slow-falling pulse (R200-F400 pulse) conditioning were pinpoint core, as usual. These results suggest that the rising front plays an important role in the LID and laser conditioning of the DKDP crystals. A pulse with a slower rising front is beneficial for thermal modification, thereby leading to better LID properties. This strategy greatly expands and enriches the manipulation methods to improve the LIDT of DKDP crystals, and sheds light on understanding the laser damage mechanisms.

Study on defect-induced damage behaviors of ADP crystals by 355 nm pulsed laser.

High-quality ammonium dihydrogen phosphate (NH4H2PO4, ADP) crystals were grown in Z direction and in defined crystallographic direction (θ=90°, φ=45°) by the rapid growth method, respectively. Defect-induced damage behavior in 355 nm of three types of ADP samples cutting in type-II matching and third harmonic generation direction from the as-grown crystals were investigated, including the initial laser induced damage (LID) characteristics and the physical and chemical properties of defects which serve as the damage precursors. The evaluations of damage behaviors include the "sampling" laser induced damage threshold (LIDT) by 1-on-1 and R-on-1 methods, bulk damage growth and bulk damage morphology. UV-visible transmittance spectrum, ultraviolet absorption spectrum, fluorescence spectrum, positron annihilation spectrum and the online light scattering measurements were carried out to investigate the defect-induced damage behavior in ADP crystals. The study will provide a reference for the investigations on laser induced damage properties of ADP crystals in short wavelength.

Effects of ion beam etching of fused silica substrates on the laser-induced damage properties of antireflection coatings at 355 nm

Antireflection (AR) coatings are deposited on UV grade fused silica substrates, which are cleaned in the dual ion beam sputtering device. Compared to ultrasonic and acid etching cleaning progress, ion beam etching improves the laser-induced damage threshold (LIDT) of substrates and AR coatings significantly at 355 nm. Ion beam etching declines the low LIDT defects drastically and removes lots of the impurity elements (Ce, Fe, K, and Na). Roughness test shows that the AR coatings and substrates with ion beam etching are very flat and of low roughness. Ion beam etching reduces the density of deep defect from substrates greatly. Damage morphologies show double layers delamination, which is explained via calculation of layer stress. This study will be helpful for preparation of high LIDT optical coatings.

Effects of depositing temperature on structural, optical and laser-induced damage properties of Ga2O3 films deposited by electronic beam evaporation

Ga2O3 thin films were prepared by electron-beam evaporation from a starting material of high-purity Ga2O3 granules. The relations between depositing temperature and properties including structural and optical aspects of the film were investigated. When the depositing temperatures were 50, 100, 150 and 200 °C, the corresponding refractive indexes were 1.790, 1.799, 1.816 and 1.830 at a wavelength of 532 nm. With the rise of depositing temperature, transparency of the thin films presented a decreasing trend in the ultraviolet as well as visible regions, and the edges of absorption showed red-shifted characteristic simultaneously. During the testing process, a 532 nm laser with variable energy from 5 to 200 mJ was loaded on film for 10 ns. The laser-induced damage threshold (LIDT) of the Ga2O3 samples rose up from 1.89, 3.28, and 4.13 to 4.49 J/cm2 against the increasing of depositing temperature. It demonstrated that optical properties of Ga2O3 film relied heavily on the depositing temperature.

Effects of substrate on the femtosecond laser-induced damage properties of gold films

In this work, gold films on two different types of substrates were fabricated by electron beam (e-beam) evaporation, and the femtosecond laser-induced damage properties were evaluated. The first sample was gold film deposited on fused silica, whereas the second was gold deposited on photoresist. 1-on-1 damage tests were implemented by an 800 ± 30 nm laser with pulse duration of 30 fs. Different damage thresholds and morphologies were obtained for the two samples. The damage threshold of the gold film on fused silica was 0.64 J/cm2, with the typical damage morphology of thermal ablation and melting; the damage threshold of the gold film on photoresist was 0.30 J/cm2, with the typical damage morphology of blisters or peeling off. In order to better understand the impact of the substrate on the properties of the whole sample, the normalized electric field intensity, temperature, and thermal stress distributions were calculated. The adhesion between the gold film and substrate were measured and the experimental results well agreed with the theoretical analysis. The results indicate that gold films deposited onto grating-structured fused silica will have more powerful laser damage resistance performance.

Role of defects in laser-induced modifications of silica coatings and fused silica using picosecond pulses at 1053 nm: II. Scaling laws and the density of precursors.

We investigate the role of defects in laser-induced damage of fused silica and of silica coatings produced by e-beam and PIAD processes which are used in damage resistant, multi-layer dielectric, reflective optics. We perform experiments using 1053 nm, 1-60 ps laser pulses with varying beam size, number of shots, and pulse widths in order to understand the characteristics of defects leading to laser-induced damage. This pulse width range spans a transition in mechanisms from intrinsic material ablation for short pulses to defect-dominated damage for longer pulses. We show that for pulse widths as short as 10 ps, laser-induced damage properties of fused silica and silica films are dominated by isolated absorbers. The density of these precursors and their fluence dependence of damage initiation suggest a single photon process for initial energy absorption in these precursors. Higher density precursors that initiate close to the ablation threshold at shorter pulse widths are also observed in fused silica, whose fluence and pulse width scaling suggest a multiphoton initiation process. We also show that these initiated damage sites grow with subsequent laser pulses. We show that scaling laws obtained in more conventional ways depend on the beam size and on the definition of damage for ps pulses. For this reason, coupling scaling laws with the density of precursors are critical to understanding the damage limitations of optics in the ps regime.

Influence of Substrate Surface Properties on Laser-induced Damage Properties of TiO2 Thin Films

Various investigations have focused on the laser-induced damage of thin films. However, substrate surface properties have not been taken into account. TiO2 thin films with a one-quarter wavelength optical thickness were deposited by electron beam evaporation on two types of substrates with different surface properties. The surface morphologies of TiO2 thinfilms were captured by atomic force microscopy, and the laser-induced damage threshold of TiO2 thin films was measured. The relationship between the substrate surface properties and the laser-induced damage properties of TiO2 thin films was observed and analyzed.

The Transmittance, Transmittance Wavefront, and Laser Induced Damage Properties of Thin Fluoride Polymer Films May Be Used as Short Pulse Laser Debris Shields

Debris mitigation which pollutes and even damages the optical elements is a major challenge for all high-peak-power lasers system. In order to solve the problem, we employed some preliminary research. In this work, first, the film optical properties of fluorinated ethylene propylene (FEP), perfluoroalkoxy copolymer (PFA), and ethane-tetrafluoroethylene copolymer (ETFE) were investigated with respect to their possible application as laser debris shields. The results indicate that three of the polymer films have high transmittance at 355 nm, especially in FEP film, the transmittance of which at 355 nm is near to 94%. The transmittance wavefront and the laser that induce damage of FEP film were investigated further. The result indicates that the wavefront error of FEP film (with a diameter of 90 mm) is about 0.33λ. The damage test was performed by a 355 nm neodymium:yttrium aluminum garnet (Nd:YAG) laser with a 9.3 ns pulse duration, and it was found that the highest nondamage fluence for FEP film is 10.35 J/cm2. Through a demonstration experiment, it was testified that the FEP film can prevent large amount of metal fractions and the FEP film can be used as the debris shields indeed.

Effect of etching morphology of artificial defect on laser-induced damage properties under 355 nm laser irradiation.

Structural defects and absorptive impurities generated in the process of grinding and polishing optical substrates before coating significantly lower the resistance of optical elements to laser. Thus, artificial defects that contain indentations and absorptive particles are fabricated in this study. Chemical etching is used to examine the morphology and depth of artificial defects with different sizes and types under various etching times. Moreover, the transverse and longitudinal sizes, as well as the morphology, of defects are determined to analyze the damage properties of artificial defects under 355nm of laser irradiation. Finally, the differences in the artificial defects induced by various materials are discussed along with their influences on damage properties.

原子层沉积HfO2薄膜的激光损伤特性分析

原子层沉积HfO₂薄膜的激光损伤特性分析

Laser-induced damage properties of subwavelength antireflective grating on fused silica

We describe the design, fabrication and performance of an optimized one-dimensional subwavelength grating for use in 1064nm wavelength laser systems. The laser-induced damage threshold (LIDT) under the irradiation of 12ns 1064nm pulses on the grating was performed, and a higher LIDT was obtained compared with LIDT of traditional antireflective coatings. Laser irradiation produces some morphological modifications on grating. Light interferometric surface profiler, scanning electron microscope and atomic force microscope were used to study these modifications, and these studies indicate the significant ablation and resolidification have occurred. To understand possible damage mechanisms, the role of electric field distribution inside the grating during the laser radiation process was investigated by a three-dimensional finite difference time-domain method, and the simulation result indicates the temperature distribution resulting from the internal electric field may be the main factor behind the damage.

Effect of etching on the laser-induced damage properties of artificial defects under 1064-nm laser irradiation

The cracks and scratches inevitably generated by previous grinding and polishing significantly lower the ability of laser resistance of optical substrates. In this study, the artificial indentations, scratches, and structural defects imbedded with metal nanoparticles are fabricated. The laser-induced damage characteristics of such defects in different types and sizes are investigated qualitatively and quantitatively under 1064-nm laser irradiation. Moreover, the etching effect on improving the laser-induced damage threshold (LIDT) of artificial defects under different etching conditions is analyzed. LIDT is then evaluated according to the etching depth and the morphologies of artificial defects.

Spectroscopic and laser-induced damage properties of Fe2+-doped fluorophosphate glass, a new color-separation material

Fe2+-doped fluorophosphate glass (FEFG), a new color-separation material, is prepared by a melt-quenching method. The spectroscopic and laser-induced damage (LID) properties of FEFG are investigated by transmittance spectroscopy, LID tests, scanning electron microscopy, and Raman spectroscopy. Results show that the sample has intensive absorption (>85 %) at 1,053 nm and high transmittance (~86.5 %) at 351 nm after introducing 0.3 wt% Fe2O3. The LID thresholds of 0.3 wt% Fe2O3-doped FEFG sample irradiated by 351- and 1,053-nm lasers with 8 ns pulse width are 4.5 and 36.0 J/cm2, respectively. Thus, FEFG has laser-separation ability and can resist nanosecond laser irradiation, indicating that FEFG is a potential color-separation material for high-power lasers.

Effect of Advanced Plasma Source bias voltage on properties of HfO2 films prepared by plasma ion assisted electron evaporation from metal hafnium

HfO2 films, using metal hafnium as starting material, are deposited by plasma-ion assisted electron evaporation with different Advanced Plasma Source (APS) bias voltages. The refractive index and extinction coefficient are calculated, the chemical state and composition, as well as the stress and aging behavior is investigated. Laser induced damage threshold (LIDT) and damage mechanism are also evaluated and discussed. Optical, structural, mechanical and laser induced damage properties of HfO2 films are found to be sensitive to APS bias voltage. The film stress can be tuned by varying the APS bias voltage. Damage morphologies indicate the LIDT of the HfO2 films at 1064nm and 532nm are dominated by the nodular-defect density in coatings, while the 355nm LIDT is dominated by the film absorption. HfO2 films with higher 1064nm LIDT than samples evaporated from hafnia are achieved with bias voltage of 100V.

Influence of Laser-Conditioning on Laser-Induced Damage Properties of ZnSe Thin Films

With the development of high power laser systems, laser protection of optical components becomes more and more important. In order to enhance the laser-induced damage capability of optical films components, besides advanced methods and processes, post-treatment has significant influence on the laser-induced damage threshold (LIDT) of thin films. Q switch Nd:YAG laser of the working wave length at 1064nm, was used to post process on ZnSe single layer films with thickness of /2 (=1064nm) deposited by thermal evaporation, and the laser-induced damage and optical properties were investigated. By changing the energy density and pulse number under the spot size remained a fixed value, their effects on thin films damage threshold were studied respectively, the optimal processing parameters were obtained: energy density is 3.0 J/cm2 and pulse number is 1.The LIDT of post processed ZnSe films was improved from 5.0J/cm2 to 8.2J/cm2.