This PDF file contains the front matter associated with SPIE Proceedings Volume PLD, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Modeling of laser-induced optics damage has been introduced to benchmark existing optic usage at the National Ignition Facility (NIF) which includes the number of optics exchanged for damage repair. NIF has pioneered an optics recycle strategy to allow it to run the laser at capacity since fully commissioned in 2009 while keeping the cost of optics usage manageable. We will show how the damage model is being used to evaluate strategies to streamline our optics loop efficiency, as we strive to increase the laser shot rate without increasing operating costs.

Thin-film polarizers are essential components of large laser systems, switching the beam out of the primary laser cavity and/or protecting the system from back-reflected light. The requirements for a polarizer include specific spectral performance, high laser-induced damage resistance and low surface figure deformation. Generally speaking, a polarizer coating has a thicker thickness than a mirror coating, and a narrower bandwidth that fulfills the specific spectral specification, which makes the design and fabrication of polarizer coating challenging. Large aperture (up to ~900 mm in diameter) polarizer coating deposited on both BK7 and fused silica substrates with p-polarized transmittance higher than 98%, s-polarized reflectance higher than 99% at 1053 nm, and can tolerance a fluence higher than 17 J/cm² (9 ns) at 1053 nm has been achieved.

We have fabricated a 410 x 468 mm size deformable mirror with 100 Bimorph piezoceramic actuators for the LFEX laser system at Osaka University. In the case of Bimorph-type deformable mirrors, the mirror surface had to be polished and coated after bonding the piezoceramic actuators to the rear side of the thin mirror substrate. This provides a good surface figure, but the coating temperature for the high-reflection mirror was strictly limited because of the thermal fragility of piezoceramic actuators. The mirror substrate with the actuators was polished, and an ion-assisted multilayer dielectric coating was produced at 60 degrees Celsius with our 80-inch coating chamber. The flatness of the mirror just after coating was 7 μm, and reduced by aging to 3.2 μm when the mirror was assembled. The surface figure of the assembled mirror with 20 piezostack bonded actuators is demonstrated and a laser-induced damage threshold tested with a witness sample is also reported.

Ultrashort laser pulse has been widely used in various applications. Its parameters, such as the pulse duration and the spectral bandwidth, should be controlled accurately in order to achieve high spatial and temporal resolution, as well as high local field intensity. In this paper, we have proposed a method to trace the propagation of ultrashort pulses through optical systems, especially the complex optics. The approach, in which both the material’s dispersion and optical aberrations are taken into consideration, is developed based on the geometrical ray-tracing combined with wave theories. This method is validated by simulating the propagation of a femtosecond pulse through a specific practical imaging system. As the numerical result shows that the spatial-temporal performances of pulses are influenced greatly by optical elements, the calibration arrangement is employed to compensate for those undesired distortions. The negative dispersion of the optical grisms (the combination of gratings and prisms) is utilized in the calibration process to offset the positive dispersion introduced by lenses. The final result shows effectiveness of the correction.

Some silica plates of high power nanosecond lasers may be a few centimeter thick for instance because they should sustain vacuum. Measuring laser-induced damage thresholds at the output surface of these thick silica plates is a complex task because non-linear laser propagation effects may occur inside the plate which prevents knowing accurately the fluence at the output. Two non-linear effects have to be considered: stimulated Brillouin scattering (SBS) and Kerr effect. SBS is mainly driven by the spectral power density of the pulses: if the spectral power density is below a threshold, SBS is negligible. Thus, spectral broadening is required. Kerr effect depends on the instantaneous intensity. Hence, a smooth temporal shape without overshoots is required. However, both conditions (wide spectrum and no overshoots) are impossible to fulfill with standard lasers. As a matter of fact, an injected laser has a smooth temporal profile but is spectrally narrow. Without injection, the laser is multimode yielding a wide spectrum but a chaotic temporal profile. We solved the problem by phase-modulating a continuous-wave seeder of our laser (patent pending). The phasemodulation frequency is adjusted to a multiple of the inverse of the round-trip time of the laser cavity. The laser pulses have a wide spectrum to suppress SBS and do not exhibit temporal overshoots to reduce Kerr effects. During the presentation, we will show the features of the laser pulses and laser-induced damage measurements of thick silica plates using this scheme.

For pulse laser materials processing often optical step index and gradient index multimode fibers with core diameters ranging from 100 to 600 μm are used. The design of a high power fiber transmission system must take into account limitations resulting from both surface and volume damage effects. Especially, breakdown at the fiber end faces and selffocusing in the fiber volume critically influence the fiber performance. At least operation charts are desirable to select the appropriate fiber type for given laser parameters. In industry-relevant studies the influence of fiber core diameter and end face preparation on laser-induced (surface) damage thresholds (LIDT) was investigated for frequently used all-silica fiber types (manufacturer LEONI). Experiments on preform material (initial fiber material) and compact specimens (models of the cladding and coating material) accompanied the tests performed in accordance with the relevant LIDT standards ISO 21254-1 and ISO 21254-2 for 1-on-1 and S-on-1 irradiation conditions, respectively. The relation beam diameter vs. LIDT was investigated for fused silica fibers. Additionally, laser-induced (bulk) damage thresholds of fused silica preform material F300 (manufacturer Heraeus) in dependence on external mechanical stress simulating fiber bending were measured. All experiments were performed with 10-ns laser pulses at 1064 and 532 nm wavelength with a Gaussian beam profile.

Laser shock micro-forming is a non-thermal laser forming method that use laser-induced shockwave to modify surface properties and to adjust shapes and geometry of work pieces. In this paper, we present an adaptive optical technique to engineer spatial profiles of the laser beam to exert precision control on the laser shock forming process for free-standing MEMS structures. Using a spatial light modulator, on-target laser energy profiles are engineered to control shape, size, and deformation magnitude, which has led to significant improvement of the laser shock processing outcome at micrometer scales. The results presented in this paper show that the adaptive-optics laser beam forming is an effective method to improve both quality and throughput of the laser forming process at micrometer scales.

Tightly focused femtosecond laser pulses can be used to alter the refractive index of virtually all optical glasses. As the laser-induced modification is spatially limited to the focal volume of the writing beam, this technique enables the fabrication of fully three-dimensional photonic structures and devices that are automatically embedded within the host material. While it is well understood that the laser-material interaction process is initiated by nonlinear, typically multiphoton absorption, the actual mechanism that results in an increase or sometimes decrease of the refractive index of the glass strongly depends on the composition of the material and the process parameters and is still subject to scientific studies. In this paper, we present an overview of our recent work aimed at uncovering the physical and chemical processes that contribute to the observed material modification. Raman microscopy and electron microprobe analysis was used to study the induced modifications that occur within the glass matrix and the influence of atomic species migration forced by the femtosecond laser writing beam. In particular, we concentrate on borosilicate, heavy metal fluoride and phosphate glasses. We believe that our results represent an important step towards the development of engineered glass types that are ideally suited for the fabrication of photonic devices via the femtosecond laser direct write technique.

A new method is proposed to inspect the subsurface damage (SSD) that plays a key role on improving the laser induced damage threshold (LIDT) of optics applied in high power laser system. This method is based on total internal reflection microscopy (TIRM) and digital image processing technique. Because of relatively small depth of focus of a microscope at large magnification, a series of TIRM images can be obtained while the microscope focuses into different depths of sample by micro-focusing control. Definition of each image is calculated through wavelet transform. The relation between definition of TIRM images and the depth of SSD is established. According to the definition curve, the position and size along the depth direction can be acquired simultaneously. The measurement accuracy is dependent on the depth of field of microscope. This proposed method has been applied to measure the SSD information of finished K9 glass, fused silica glass and Nd-doped glass.

As one of the key elements of high-power laser systems, the pulse compression multilayer dielectric grating is required for broader band, higher diffraction efficiency and higher damage threshold. In this paper, the multilayer dielectric film and the multilayer dielectric gratings(MDG) were designed by eigen matrix and optimized with the help of generic algorithm and rigorous coupled wave method. The reflectivity was close to 100% and the bandwith were over 250nm, twice compared to the unoptimized film structure. The simulation software of standing wave field distribution within MDG was developed and the electric field of the MDG was calculated. And the key parameters which affected the electric field distribution were also studied.

Preventing contamination is vital to achieving high laser-induced damage thresholds in optical coatings. The importance of removing contamination from optical substrates has led to the development of many specialized cleaning processes, including the application of solvents, acids, mild detergents, and abrasives. To further enhance contamination removal, the substrate may be treated with ion cleaning just prior to depositing the optical coating. Ion cleaning is attractive thanks to the convenience of providing in-situ treatment to optical substrates, and also avoiding the hassle of managing hazardous chemicals or applying mechanical force to scrub off detergents and other cleaning agents. In this study, we compare the effectiveness of ion cleaning for increasing the laser-induced damage thresholds of high reflection (527 nm and 1054 nm) and antireflection (527 nm) coatings. Ion cleaning was performed using a radio frequency ion source with argon and oxygen. The coatings investigated were deposited with layers of HfO₂ and SiO₂ in an e-beam evaporation system, and are designed to withstand nanosecond pulses from a kJ-class laser.

The EUSO (Extreme Universe Space Observatory) project is developing a new mission concept for the scientific research of Ultra High Energy Cosmic Rays (UHECRs) from space. The EUSO wide-field telescope will look down from space onto the Earth night sky to detect UV photons emitted from air showers generated by UHECRs in our atmosphere. In this article we concentrate on the mitigation strategies agreed so far, and in particular on the implementation of a careful early selection and testing of subsystem materials (including optics), design and interfaces of the subsystem and an optimization of the instrument operational concept.

Contamination of optics observed in LFEX compression chamber was a critical problem for maintaining high damage threshold and high optical performance for mirrors and gratings in the vacuum environments. We conducted a study for understanding this problem, and we found important knowledge on the nature of contamination, namely materials of contaminants, source of contamination, the invasion mechanism, and removal method of contamination. We also found the samples for the damage test is easily contaminated in the storage environment. This means the optical coating accumulate contaminations even in the air. So we tested in-situ damage test in a gas flowing chamber with controlled contaminants. The degradation was time-dependent phenomena, and proportional to the vapor pressure of contaminants. Several materials were tested, and even in water vapor, the damage threshold was decreased about 10%. We also found out two methods for removing contaminations from the coatings. According to these studies, our conclusion is special treatments should be used for knowing the intrinsic damage threshold of the coatings.

Aluminum alloy containing zeolite was analyzed by using nanosecond and femtosecond laser-induced breakdown spectroscopy (ns and fs-LIBS). The results reveal that Laser parameters, target physical properties, and ambient conditions affect the laser ablation process. The aluminum silicate minerals present in the alloy under investigation enable material volume expansion under compression. In laser interaction with this alloy, it has been observed that the crater depth decreases with the increase of the surface hardness. In ns –LIBS, it is noted that the ablation speed decreases with time and suddenly decreases with less sharp slope and after that the ablation speed increases slightly. In additional the results show the vanishing and reform of the crater rim with the increase of ablation time. Furthermore, a comparison between ns and fs-LIBS analysis has been done. Ns-LIBS analysis reveals that both spectra intensity and lines detection are significantly influenced by the ambient conditions. However in fs-LIBS, the ambient conditions affect the presented lines amplitude and width with the same effect on all lines.

Meanwhile, by the convention wire-saw technique, it is difficult to slice off a thin wafer from bulk SiC crystal without the reserving space for cutting. In this study, we have achieved exfoliation of 4H-SiC single crystal by femtosecond laser induced slicing method. By using this, the exfoliated surface with the root-mean-square roughness of 3 μm and the cutting-loss thickness smaller than 30 μm was successfully demonstrated. We have also observed the nanostructure on the exfoliated surface in SiC crystal.

Fluorescent Carbon nanoparticles (CNPs) with tunable emission are successfully synthesized from the water suspension of graphene oxide by the femtosecond laser irradiation. The luminescence properties were controllable by doping nitrogen into CNPs in the presence of an ammonia molecule. We have also confirmed that CNPs with diamond structure were directly precipitated from the solvent molecules such as cyclohexane.

In high-power laser facilities for the inertial confinement fusion, there are many large-radius optical elements, which inevitably have some flaws on the surface. The flaws can cause optical intensity intensification and therefore damage the optical elements in the downstream, especially for the beam sampling grating (BSG), which is an important element in the final optics assembly. In this paper, several physical models are established to study the optical field enhancement in the BSG position modulated by upstream flaw. Firstly, when only the linear transportation is considered, it is found that there is a peak or valley of the maximum intensity after the focus lens compared with the ideal wave front. Meanwhile the influence of flaw has an effective range. Secondly, when the nonlinear effect of the focus lens is also considered, the peak maximum downstream is much bigger than the one for the linear consideration and the damage risk of the BSG there is much higher too. From the simulation, we can see that it is important to place the BSG in a properly selected position to mitigate the laser induced damage. The results could give some references to the mitigation of BSG damage caused by upstream flaws and the layout of the final optics assembly.

EOIS (electro-optical imaging system) is vulnerable to laser beam because EOIS focuses the incident laser beam onto the image sensor via lens module. Accordingly, the laser-induced damage of EOIS is necessary to be identified for the counter-measure against the laser attack. In this study, the damage of CMOS EOIS and image sensor induced by CW (continuous wave) NIR (near infrared) laser was experimentally investigated. When the laser was emitted to CMOS EOIS, a temporary damage was occurred first such as flickering or dazzling and then a permanent damage was followed as the increase of laser irradiance and irradiation time. If the EIOS is composed of the optical equipment made of heatresistant material, laser beam can penetrate the lens module of EOIS without melting the lens and lens guide. Thus, it is necessary to investigate the damage of CMOS image sensor by the CW laser and we performed experimentally investigation of damage on the CMOS image sensor similar with case of CMOS EOIS. And we analyzed the experiment results by using OM (optical microscopy) and check the image quality through tomography. As the increase of laser irradiance and irradiation time, the permanent damage such as discoloration and breakdown were sequentially appeared.

Due to the unique imaging approach for ground-based radar, identification and classification in observation area is very difficult. In order to improve the accuracy of the calculation and application combine with other data resource. it is necessary to implement data matching of radar images and 3D laser point cloud. First, the 3D cloud should to be transformed to orthographic maps, and then the horizontal rotation and orbit attitude angle parameters would be estimated for similarity transformation according to the characteristics such as common points and lines. Finally, the same reference point of the ground-based SAR data and cloud data is employed to accomplished in a two-dimensional coordinate system (called local common coordinate system).