This PDF file contains the front matter associated with SPIE Proceedings Volume 8786, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

We present a consistent model supported by experimental data of damage of dielectric films by femtosecond to nanosecond pulses. Special emphasis is given to the role of defects and transient processes in the material. New imaging and diagnostic techniques are discussed to characterize the film performance.

We investigated optical damage (surface and bulk) in wide band-gap (absorption edge below 532 nm) sulphide and selenide nonlinear crystals that can be used in 1064-nm pumped optical parametric oscillators (OPOs) for generation of idler pulses above 4 μm without two-photon absorption losses at the pump wavelength. The optical damage has been characterized at the pump wavelength for different repetition rates. Surface damage has been studied for uncoated and antireflection-coated (mainly with a single layer for pump and signal wavelengths) samples. Optical damage inside the OPO has a lower threshold and represents at present the principal limitation for the achievable output. It is related to peak and not to average intensities and in many of the studied crystals bulk damage in the form of scattering centers occurs before surface damage. Such bulk damage formation is faster at higher repetition rate. Lower repetition rates increase the lifetime of the crystal but do not solve the problem. In the most successful nonlinear crystal (both in terms of output energy and average power), orange-phase HgGa₂S₄, the safe pump intensity in extracavity measurements is below 100 MW/cm² which corresponds to less than 1 J/cm² for the 8 ns pulse duration (both values peak on-axis). In the OPO, however, peak on-axis fluence should not exceed 0.3 J/cm² limited by the formation of bulk scattering centers. The damage resistivity of yellow-phase HgGa₂S₄ or Cd-doped HgGa₂S₄ is higher and of the almost colorless CdGa₂S₄ it is roughly two times higher but the latter has no sufficient birefringence for phase-matching.

A novel oxyfluoride glass (OFG) was prepared. The laser induced damage threshold (LIDT) of the novel OFG is 24.9% higher than fused silica under 355nm nanosecond laser irradiation by R-on-1 procedure. Characterization by optical microscope and scanning electron microscope shows that the initial damage morphologies of two kind of materials are significantly different. Experiment results indicate that the novel OFG can be a good candidate component material for high energy laser applications.

The metrology of laser damage is essential for the development of intense laser chains and their applications, especially in micromachining. We first present a test bench able to accurately measure the damage and ablation behaviour of optical materials and components irradiated by femtosecond lasers (< 15 fs - 5 ps). We further illustrate the interest of our measurements through examples related to laser technology and engineering, and also fundamental knowledge of laser-matter interaction.

Potassium Dihydrogen Phosphate (KDP) is a non-linear optical material for the Pockelscells and laser frequency conversion used in inertial confinement fusion (ICF).But the performances are decreased by the presence of defects or impurities from the growth process. Furthermore, it is difficult to identify them due to their small size and sparse distribution. Laser conditioning provides an increase for the material damage resistance due to an unknown physical mechanism resulting from the interaction of sub-damage laser pulses with KDP defects. In this paper, the crystals first were laser conditioned by raster scanning using Nd:YAG laser at 355nm with pulse durations of approximately 7 ns. Then we investigated the KDP crystals with different non-destructive optical diagnostics. We measured in the same time the fluorescence, the photothermal absorption, Raman and FTIR spectroscopy of the material. We concentrated on the differences of conventionally grown KDP crystals before and after the laser conditioning. We obtained the different spectra information of KDP crystals.

To reduce manufacturing costs and to improve electrical efficiency of solar cells are top priorities of the whole photovoltaic (PV) industry. The success of laser processing techniques in the integrated circuits industry indicates that such techniques could also be adapted in the PV industry. In this paper, we presented an automated laser processing system which was specially designed and developed for manufacturing of high efficiency solar cells. This system is modulized and can be easily modified for different laser applications for solar cells, such as laser doping, laser drilling, laser ablation and laser scribing.

In high power laser system, laser-induced damage threshold (LIDT) in optical coating is very important for obtaining high performances. The dependence of LIDT on the pulse duration and the repetition rate are well known phenomena. But recently, LIDT was found to have strong temperature dependences in the bulk, surface of substrates, and in coatings. This temperature dependence of LIDT was carefully measured, and the damage formation model was constructed regarding to this temperature dependence. This paper introduces LFEX laser system for First Ignition scheme in the laser fusion. A large-scale pulse compression chamber was designed and constructed, and segmented grating system has been employed for large-scale pulse compressor. This compressor provided good pulse compression performances, but we observed a heavy oil-contamination of optics in this chamber. We have analyzed contaminants and evaluated the effects of the contamination. We also developed new cleaning methods to remove contamination from the coating, and the quantitative analysis of contamination on LIDT was made. We have investigated the characteristics of LIDT in dielectric coatings under the controlled contamination. LIDT of coating drops to 1/2 in the saturated toluene vapor at room temperature.

We report on controllable production of nanostructures embedded in a porous glass by femtosecond laser direct writing. We show that a hollow nano-void with a lateral size of ~40 nm and an axial size of ~1500 nm can be achieved by manipulating the peak intensity and polarization of the writing laser beam. The single nano-voids can be smoothly connected into a continuous nanochannel by water-assisted femtosecond laser direct writing. With this technique, integrated micro-nanofluidic systems have been achieved by simultaneously writing micro- and nanofluidic channels arranged into various 3D configurations in glass substrates. The fabricated micro- and nanofluidic systems have been applied to demonstrate DNA analysis, e. g., stretching of DNA molecules. Our technique offers new opportunities to develop novel 3D micro-nanofluidic systems for a variety of lab-on-a-chip applications.

In this work we present the results on volumetric fused silica modifications using femtosecond Gaussian and Gaussian-Bessel laser beams. We show that for specific photonic device, like volume Bragg grating, fabrication, Bessel beams are more superior to Gaussian, as the recording process is much faster and fabricated devices have better efficiencies. Also Gaussian beam tend to be more efficient in formation of nanogratings that causes the appearance of birefringence in modified zones. This reduces optical quality of fabricated device and limits overall recording velocity. We have successfully fabricated volume Bragg gratings in the bulk of fused silica that had absolute diffraction efficiencies reaching ∼90% using femtosecond Gaussian-Bessel beam, while gratings made with Gaussian beam reached only 60%.

Glass panel substrates have been widely used in consumer electronics such as in flat panel TVs, laptops, and cell phones. With the advancement in the industry, the glass substrates are becoming thinner and stronger for reduced weight and volume, which brings great challenges for traditional mechanical processes in terms of cut quality, yield, and throughput. Laser glass cutting provides a non-contact process with minimum impact and superior quality compared to the mechanical counterparts. In this paper, we presented recent progresses in advanced laser processing of ultra-thin glass substrates, especially laser-cutting of ultra-thin glasses by a high power laser through a nonlinear interaction effect. Our results indicate that this technique has great potential of application for mass production of ultra-thin glass substrates.

In order to mitigate the dopant concentration gradient by post-growth diffusion method, high optical quality Cr²⁺:ZnSe ceramics had been prepared by hot-pressing method with powders being diffusion doped in a previous step, which reduced the concentration gradient down to a grain size level. A optimal combination of sintering parameters, including temperature, pressure, dwell time, have been determined (1050°C/150MPa/2h) according to background absorption intensity. Comparison with diffusion doped CVD-grown ZnSe showed a stronger background absorption and blueshifted emission peak, both indicating scattering sources inside material. Micro-structure observation proved the inference above as being residual pores and inclusions, which could be eliminated or reduced by, as suggested here, preliminary treatment of powders and enhancement of densification pressure and dwell time.

High–purity fused silica irradiated by UV laser in vacuum with different laser pulse parameters were studied experimentally. The defects induced by UV laser are investigated by UV absorption, fluorescence spectra and the structural modifications in the glass matrix are characterized by Raman spectra. Results show that, for laser fluence below the laser–induced damage threshold (LIDT), irradiation results in the formation of an absorption band and four defect–related fluorescence (FL) bands, and the intensities of absorption band and FL bands were increased with laser power and/or number of laser pulses. The optical properties of these point defects were discussed in detail. Analyzed these spectra, it indicates that the presence of different centers whose spectral features are modulated by structural disorder typical of the glass matrix.

A series of fused silica surface have been created by reaction ion etching to determine the effect of the contamination level on surface state and optical performance of the optics. The results show that both impurity elements contamination and scratches of fused silica surface can be removed dramatically during RIE process. The laser induced damage threshold is raised by 37.6% when the polishing layer is removed for a thickness of 6μm, and the laser weak absorption doesn’t increase obviously. The results can provide technique support for improving laser induced damage performance of fused silica.

Fabrication-induced metal contaminations and subsurface damage are generally identified as the laser damage initiators that are responsible for the laser induced damage in fused silica. In this paper, the removal of those two initiators are realized by two methods: wet chemical surface cleaning and optimized HF-based etch process. Two kinds of chemical leaching are used to removing the Ce and other metal impurities respectively. In order prevent the redeposition of the reactive byproducts during HF etch process, we optimized the traditional HF etch process in two ways: absence of NH₄F in etch solution and presence of megasonic and ultrasonic agitation during and after etch respectively. And laser damage tests show that these two treatments greatly improve the laser damage resistance of fused silica.

The high-precision aspheric surface is hard to be achieved due to the mid-spatial frequency error in the finishing step. The influence of mid-spatial frequency error is studied through the simulations and experiments. In this paper, a new polishing process based on magnetorheological finishing (MRF), smooth polishing (SP) and ion beam figuring (IBF) is proposed. A 400mm aperture parabolic surface is polished with this new process. The smooth polishing (SP) is applied after rough machining to control the MSF error. In the middle finishing step, most of low-spatial frequency error is removed by MRF rapidly, then the mid-spatial frequency error is restricted by SP, finally ion beam figuring is used to finish the surface. The surface accuracy is improved from the initial 37.691nm (rms, 95% aperture) to the final 4.195nm. The results show that the new polishing process is effective to manufacture large-aperture and high-precision aspheric surface.

Light scattering is one of the loss mechanisms of optical components. It is caused by intrinsic and extrinsic imperfections such as roughness, index fluctuations, and bulk or surface defects that can all play critical roles for the laser stability of optical components. Light scattering metrology has proven to be a versatile non-destructive technique to characterize imperfections. Information can be retrieved with high sensitivity even over large areas. The total scatter levels or scattering coefficients provide information about scatter losses whereas the angle resolved scattering provides detailed information about the sources of scattering. An overview of the instruments developed at Fraunhofer IOF will be given and a variety of examples of application will be discussed comprising roughness and defect maps of lithography optics, investigations of bulk scattering of optical materials, and enhanced scattering through thickness errors of interference coatings.

Transverse stimulated Raman scattering (TSRS) gain coefficient of a KDP sample is measured by improved methods. The improvements include color separation of TSRS, noise light management and acquisition of valid TSRS temporal pulse. After extracting TSRS temporal pulse and data analysis, we obtained a TSRS gain coefficient of 0.28±0.03cm/GW for the KDP sample. Our improvements of measurement method include the following three aspects: First, the separation of TSRS irradiation (362.2nm) from Rayleigh irradiation (351.15nm) is realized by first-order diffraction of grating for TSRS and Rayleigh. Second, to improve the ratio of TSRS signal and noise light owing to spurious reflection of pump radiation, we remove noise light by using band-pass filter and absorption traps. Third, by analyzing the time delay between pump signal and noise signal, we demonstrates the valid TSRS temporal pulse can be extracted from the noise signal and used to calculate the TSRS gain coefficient of KDP.

Blue laser based on Neodymium doped strontium lanthanum magnesium aluminoxide (Sr_1-xLa_x-yNd_yMg_xAl_12-xO₁₉) single crystal were constructed by second harmonic generation. Output power of 1.72 W at 900nm was obtained under 792nm laser diode pump. Intra cavity second harmonic generation were performed with non linear crystal LBO leading to output power of 76.6 mW at 450nm with absorbed power of 13.7 W and average absorption efficiency of 61% in Nd:ASL crystal.

The development of 355 nm high reflection (HR) coatings with high laser-induced damage threshold (LIDT) is one of the continuing challenges for the high power laser field. To increase the LIDT, many efforts have been done concerning the coating material, coating design and deposition process. By optimization of the coating design and deposition parameters, the 355 nm HR coating with LIDT higher than 18J/cm² has been prepared. The development of the measuring technique has promoted the investigation of laser damage precursors, enabling a better understanding of laser damage mechanism.

The laser-induced damage threshold (LIDT) of optical thin film is influenced by certain preconditioning processes. HfO₂/SiO₂ 532nm high reflective multi-layers were prepared by electron beam evaporation and were preconditioned by 532nm laser. The 532nm LIDT, surface condition, and damage morphology of the sample were characterized and compared before and after laser conditioning process. Results are presented that the LIDT of e-beam deposited multilayer HfO₂/SiO₂ thin films can be increased after laser conditioning. Possible reasons for such enhancement have been analyzed.

Metal multilayer dielectric gratings (MMDGs) for pulse compressors used in high-energy laser systems should enable high efficiency, as well as provide broad bandwidths and high laser-induced damage thresholds. The non-uniform optical near-field distribution of MMDGs is an important factor that limits damage resistance capabilities. The efficiency and electric field distributions of MMDGs with a corrugated SiO2 layer and operated at 800 nm are analyzed by rigorous coupled-wave analysis. The maximum electric field in the grating ridge, match layer, and metal layer decreases with increasing grating diffraction efficiency. High efficiency and a low electric field are obtained with a 90° slope angle in the grating ridge. The bandwidth and maximum electric field in the metal layer decrease with increasing high- and low-index material pairs, and the maximum electric fields in the grating ridge and match layer initially decrease and then increase. The peak electric field in the grating is optimized with a merit function; the optimization covers the enhancement of diffraction efficiency, bandwidth, and reduction of electric field. The bandwidth of the optimized MMDGs is 160 nm with a diffraction efficiency exceeding 90%. The largest electric field is modulated in air to obtain a low electric field and high laser-induced damage threshold.

In this work we present an overview of the best 2μm laser results obtained in Tm-doped fluoride hosts LiYF₄(YLF), LiLuF₄ (LLF) and BaY₂F₈ (BYF) and we report on the growth, spectroscopy and first laser test emission of a novel mixed material BaYLuF₈ (BYLF), interesting as a variant of BYF material with a partial substitution of Y³⁺ ions by Lu³⁺. The novel host is interesting mainly because indications are that the mixed crystal would be sturdier than BYF. The addition of Lutetium would improve the thermo-mechanical properties going into the direction of high power applications, as suggest from works on YLF and its isomorph LLF. A detailed description of Czochralski growth of fluoride laser materials is provided, focusing on the growth parameters of the novel BYLF:Tm³⁺12% material grown. With regard of spectroscopy analysis, we report on the results obtained with BYLF host. Detailed absorption, fluorescence and lifetime measurements have been performed focusing on the ³H₄ and ³F₄ manifolds, the pumping and upper laser level. Moreover diode pumped CW laser emission at 2 μm has been achieved in BYLF: Tm³⁺12% sample obtaining a slope efficiency of about 28% with respect to the absorbed power.

We demonstrate passive Q-switching (PQS) of the Tm-doped BaY₂F₈ (Tm:BYF) laser for the first time. The Tm:BYF laser is diode-pumped using an L-shaped hemispherical resonator. In the cw regime, the maximum output power with an 18% Tm-doped BYF crystal reached 1.12 W at ~1920 nm for an absorbed pump power of 3.06 W. In the PQS regime, maximum pulse energy (720 μJ) and peak power (17.1 kW) were obtained with an 8% Tm-doped BYF crystal and a Cr:ZnS saturable absorber with 92% low-signal transmission, again near 1920 nm, for a pulse width of ~40 ns and a repetition rate of 50 Hz.

LIDT specification of optical components is now widely required to perform laser systems where high power and/or long term life are the critical points. Depending on the application, the system has to resist to single shot with the highest possible intensity as in the NIF and Megajoule projects. Otherwise a compromise on LIDT value is necessary to permit a great shot number (10⁹ shots) for example for spatial applications. In order to characterize the LIDT and long term life of components, specific laser induced damage setups are used. The test configuration is close to the final application (wavelength, pulse duration, beam shape), but most often, parameters as spatial and temporal beam profiles are different. Otherwise, different test procedures as raster scan method or statistic procedure are used to determine the behavior of material, which induces additional differences between the obtained LIDT values. For practical reasons (cost and size of sample) the beam size is most often smaller than in the final application. Because of these parameters misfit, differences are highlighted between the setups of different laboratories even using the same ISO norm. In this context differences with the final system has to be expected in terms of LIDT. A good knowledge of the influence of the different parameters on the final result is required to reduce the LIDT uncertainty. In this paper, to illustrate the purpose, we will present examples of significant influence induced by test sampling, beam diameter, spatial and temporal profile applied to non-linear crystal and silica.

Photothermal response is a process in which the absorption of optical wave in a sample will induce a temperature rise, hence a modification of the refractive index of the sample. By detecting the change of the refractive index, the absorption property of the sample can be obtained. In this paper, an ellipsometric study of the photothermal response is presented. By analyzing the polarization change of the probe beam caused by the pump beam through photothermal response, we can obtain the surface absorption property of the samples we are interested in. Our results indicate that this technique is very promising for the analysis of weak absorption in thin film coatings.

The under-construction SG-III laser facility is a huge high power solid laser driver, which contains 48 beams and is designed to deliver 180kJ energy at 3ns pulse duration. The testing ending up at September 2012 validated that the first bundle lasers of SG-III facility had achieved all the designed requirements. And shortly later in December 2012, the first round of running-in physics experiment provided a preliminary X-ray diagnostic result. In the testing experiment, detailed analysis of the laser energy, the temporal characteristics, the spatial distribution and the focusing performance was made by using the Beam Integrated Diagnostic System. The 25kJ 3ω energy produced by the first bundle lasers created the new domestic record in China. These great progresses in the laser performance and the physics experiment have already demonstrated that the facility is in excellent accordance with the designs, which establish a solid foundation for completing all the construction goals.

Theoretical models of laser-induced damage mechanisms in optical materials are reviewed: inclusion-initiated thermal explosion (extrinsic mechanism) and impact ionization and photoionization (intrinsic mechanisms). Different approaches to impact ionization theory based on quantum kinetic equation, Boltzman equations, and rate equations are briefly described. A relative contribution of impact ionization and photoionization predicted by these models at different laser pulse durations, including fs-range, are discussed and compared with available experimental data. Basing on an analysis of published theoretical and experimental results, a today’s state of understanding fundamental laser damage mechanisms is concluded.

Studies for temperature dependences of laser-induced damage thresholds for optical devise is introduced in this paper. Additionally, the temperature dependence of the laser-induced damage threshold of single-layer optical coatings as resent progress was clarified using Nd:YAG and Ti:sapphire lasers. The wavelengths of the lasers were 1064 nm and 800 nm and the pulse widths were 4 ns, 200 ps, 2 ps, and 100 fs. For pulses longer than a few picoseconds, the laser-induced damage threshold of coated substrates increased with decreasing temperature. This temperature dependence was reversed for pulses shorter than a few picoseconds. A flowchart was presented including the several mechanisms for laser damage mechanism. The differences in the temperature dependence are explained by the flowchart. As one of results in theoretical analysis, the electron resistivity i. e. electron mobility is key point to elucidate the temperature dependence of laser-induced damage threshold.

Photothermal techniques have been widely used for the measurement and analysis of optical absorption, especially the weak absorption of optical components used for high-power laser applications. In this paper we present the progress in the development of a “turn-key” system for weak absorption measurement and analysis. The system provides userfriendly operations of the whole absorption measurement process. There is no need of manual realignment when changing different samples. Compared with those bench-top systems built in various research laboratories, this system is more reliable and more stable. Different measuring geometries, such as transmission measuring and reflection measuring can be selected depending on application need. Two dimensional defect mapping and three dimensional defect imaging are also made possible, and the experimental results show that non-uniformity is an important issue for both thin film coatings and bulk materials.

We report laser-induced damage threshold (LIDT) measurements of periodically poled lithium niobate (PPLN) and magnesium-oxide-doped PPLN (MgO:PPLN) in the femtosecond pulse duration regime at 1030 nm with 100 kHz and 75 MHz repetition rate. PPLN and MgO:PPLN crystals with broadband Nb₂O₅/SiO₂ AR coatings for 1.4 - 1.8 um spectral range were used. S-on-1 test for LIDT measurements were performed. S was equal to 10⁶ and 4.56*10¹⁰ pulses for 100 kHz CPA laser system and 75 MHz oscillator, respectively. Evaluated LIDT was 20 mJ/cm² for 290 fs pulses at 100 kHz repetition rate and 0.63 mJ/cm² for 105 fs pulses at 76 MHz repetition rate.

The growth of laser induced damage on the surface of fused silica plays a major role in determining the operation fluence and optics lifetime in high power laser system. In this paper, the damage growth characteristic of fused silica and possible growth mechanisms were investigated. The morphology of damage site was measured by scanning electron microscopy (SEM) and optical microscopy (OM). The finite difference time domain (FDTD) method was used to calculate the electric field distribution around the damage site. Furthermore, energy dispersive spectrometers (EDS) micro-analysis technique, x-ray photoelectron spectrometer (XPS) and Raman spectroscopy were applied to detect the chemical composition, point defect and microstructure of damage site in order to explore the growth mechanism. It’s found that the growth threshold is greatly affected by the size of damage site, and the growth threshold of damage site is much lower than that of undamaged area. Theoretical calculation demonstrated that the rough damage site can strong modulate the distribution of electric field and result in the enhancement of local light field around the damage site. Results also showed that the oxygen defect was generated and the structure was changed after initial laser damage. Based on the above analysis, a mechanism of laser-induced damage growth on fused silica surface was proposed.

It is important for testing the process of crystal growing and crystal quality. This paper built a mathematical model based on principle of photothermal common-path interferometry, the index change induced in the crystal by the heating pump beam and the phase distortion of probe beam in the heated area are presented，then obtain the intensity distribution of the interference in the near filed. Optical geometry of focusing pump beam and intersecting pump and probe beams at waist position of the pump beam is used. This optical instruction can be adjusted easily and stabilized. Now CRYSTECH have the largest NLO crystals product line in the world, especially KTP crystals. With absorption measurements in nonlinear laser crystal KTP as an example to investigate the experimental parameters affecting the photothermal interference signal and high measuring precision. The analysis of experimental data showed this kind of instruction can reach the measurement accuracy of 0.1ppm.

Large-aperture Nd-doped metaphosphate glasses are used in high-power/high-energy laser facilities. High transmission wave front accuracy of Nd-doped metaphosphate glasses is required to decrease beam distortion, which affects the focus ability and damages optical components. Elliptical shape astigmatism of the transmission wave front easily occurs when Nd-doped metaphosphate glasses are detected and utilized at Brewster incident angle compared with zero angle. The astigmatism is difficult to decrease for precision annular polishing because the surface profile adjustment of the polishing pitch plane has low accuracy. Non-uniform removal at different velocity rates between the pitch plane and Nd-doped metaphosphate glasses can be used to eliminate horizontal elliptical-shaped astigmatism. The improved process contributes to the production of high-efficiency Nd-doped metaphosphate glasses.

Laser ablation is a powerful tool to clean the radioactively contaminated surface in nuclear industry. A prototype was set up to test the decontamination of the radioactively contaminated surface using simulated sample. A laser induced breakdown spectroscopy was used to monitor the progress of the contaminated surface layer removal. More than 80% of the contamination was removed after 100 shots KrF laser irradiation with the intensity of 1J/cm2.

On the basis of theoretical analysis of biaxial birefringent thin films, this study investigates the optical properties of phase shift on reflection and/or transmission through slanted columnar TiO₂ sculptured anisotropic thin film (ATF) deposited with glancing angle deposition (GLAD) technique via reactive electron-beam evaporation. The tilted nanocolumn microstructures of thin film induce the optical anisotropy. The optical constants dispersion equations of TiO₂ ATF are determined from fitting the transmittance spectra for s- and p-polarized waves measured at normal and oblique incidence within 400-1200nm. With the extracted structure parameters, the phase shifts of polarized light are analyzed with the characteristic matrix and then measured with spectroscopic ellipsometry in the deposition plane. A reasonably good agreement between the theoretical studies and experimental measurements is obtained. In addition, the dependence of the phase shift on oblique incidence angle is also discussed. The results show a greater generality and superiority of the characteristic matrix method. Birefringence of the biaxial ATF performed a sophisticated phase modulation with varied incidence angles over a broad range to have a wide-angle phase shift.

The lifetime of optics in high power laser system is typically limited by both laser-initiated damage and the subsequent growth of laser-initiated damage sites. The single- and multiple-shot irradiations for HfO2 /SiO2 high-reflective coatings, deposited from hafnia and silica at 1064nm in nanosecond were investigated. It was found that when shot number increased, the possibility of damage growth increased as well. The relationship between field distribution and damage morphologies and inner structures was discussed to reveal mechanism of damage initiation. Additionally, the damage morphologies under different laser fluence and shot numbers were characterized to discuss the damage growth mechanism upon subsequent pulses. The tested results illustrated the absorbers which induced damages were random distribution, and the second highest peak of field intensity at the fourth interface was high enough to induce the micron-sized damage pits. It was found that defect density had a significant impact on the damage site whether growing or not upon subsequent laser pulses. Additionally, the growth resulted in delamination, and in turn delamination accelerated damage growth, finally the catastrophic damage happened.

The CeO₂ nanoparticles with modified surface and mean sizes distribution during 107.0 nm - 127.7 nm are used as abrasive in magnetorheological finishing (MRF) fluid. The slow rotation dispersion without shearing thinning is better than fast emulsification dispersion. Steady D-shaped finishing spots and high quality precise processing surface with PV=0.1λ, GRMS=0.002λ/cm, Rq=0.83 nm are obtained on a 435 mm x 435 mm BK7 glass under self-developed MRF apparatus.

Based on the finite element analysis method, establishment of a three dimensional fused silica lens model under the laser irradiation, and simulated the ideal fused silica surface temperature field and thermal stress field distribution situation, then the influences of subsurface deficiency on fused silica‘s laser damage threshold (LDT) were analyzed, which include scratch and impurity. It is found that the deficiencies in subsurface may affect the distribution of temperature field and thermal stress field of the fused silica surface, which makes the injected laser beams energy centralize on a small area around the deficiencies, thus leading to stress cracking of fused silica and LDT reduction.

AlF₃ thin films were prepared by thermal evaporation at different substrate temperatures and deposition rates. The relationships between optical properties, mechanical properties and laser-induced damage threshold (LIDT) at 355nm of AlF₃ films were discussed. Both absorption and stress increased with increasing substrate temperatures and deposition rates, which was a disadvantage to laser-induced damage resistance. Meanwhile, interfacial adhesion and hardness increased with substrate temperatures and deposition rates, which was an advantage to enhance the LIDT. The LIDT increased from room temperature to 200°C duo to increasing interfacial adhesion and hardness, and then decreased to 300°C duo to increasing absorption and stress. The LIDT decreased with deposition rates due to increasing absorption and stress.

A 10-mm-long cylindrical shell was written in neodymium doped phosphate glass by a femtosecond laser delivering pulses with a pulse repetition of 1 kHz, energies of 90 uJ and duration of 120 fs. The pulses were focused below the glass surface by an objective producing ablation filaments about 200 um in length. During processing, the sample was placed on a three-dimensional (3-D) translation stage, which moved along an enclosed pattern in the horizontal plane followed by a minor descent less than the filament length in the vertical direction. As this procedure continued, a cylinder, which demonstrated optical waveguiding, was fabricated with a rarified periphery and densified center region due to plasmonic expansion and outward shockwave upon laser ablation. The refractive-index contrast, propagation loss, near- and farfield mode distribution, and microscopic fluorescence micrograph of the waveguides were measured. 1-to-N splitters with adjustable splitting ratio were also fabricated using current approach indicating its 3-D processing flexibility. Compared with previous femtosecond laser fabrication methods, waveguides prepared in this approach exploit both depressed cladding and stress-induced refractive index increase in core region and show controllable mode conduction, strong field confinement, large numerical aperture, low propagation loss, acceptable thermal stability and intact core region.

The effect of oxygen vacancy on the laser-induced damage behaviors of HfO₂/SiO₂ high reflective coating was investigated by single 355nm-8ns laser. The oxygen vacancy was tuned by controlling the oxygenation of the outmost HfO₂ layer during the deposition procedure. The reflectivity of the coating with higher oxygen vacancy drops by 0.2% and the damage threshold drops by 60%, compared with the normal coating. Damage morphologies of samples were obtained by optical microscope, AFM, SEM and FIB technology. Typical morphologies of these coatings show little difference. Average oxygen vacancy of single HfO₂ layer prepared on the BK7 substrate measured by XPS is about 43%. Theoretical analysis with a nonlinear thermodynamics model shows that the damage can be attributed to nonlinear thermal process. Moreover, the size of damage crater can be interpreted by a mechanics model.

The optical crystal α-Al₂O₃ has been widely used as the matrix of ruby and blue sapphire for its wide transparency, high thermal conductivity, big scale and low cost. α-Al₂O₃ is so hard that cutter is easily abraded. Micromachining of α-Al₂O₃ by ultrashort pulsed laser is superior to the traditional mechanical approach as its non-contact and cold machining features. However, unexpected cracks on the surface of α-Al₂O₃ are observed after femtosecond laser machining. In order to hinder the crack source from stretching, we optimize the laser parameters accompanied with annealing. The crack-free machining can be achieved. Three-dimensional α-Al₂O₃ microstructures free from fracture, such as cylinder, barrel and sphere are demonstrated.

Infrared spectra of optical fiber cladding materials have been investigated by the irradiating treatment, and the quenching and annealing process with different temperature. The results show that, with the method of quenching firstly, the 1100 cm^-1 peak in the IR spectrum of cladding materials changes dramatically, which may attribute to the quenching process, corrected the fictive temperature and induced structural disorder. And then, the irradiation process induces defects. Finally annealing process can make the material become more stable, but the intensity and shape of 1100 cm^-1 peak no change remarkably. This result shows that annealing process repaired the structural disorder induced by quenching process and the defects induced by irradiated.

This article deals with designing broadband and high efficiency metal multi-layer dielectric grating (MMDG) used to compress and stretch ultra-short laser pulse. The diffraction characteristics of MMDG are analyzed with the method of rigorous coupled-wave analysis (RCWA). Taking the diffraction efficiency of the -1 order as the value of merit function, the parameters such as groove depth, residual thickness, duty cycle are optimized to obtain broadband and high diffraction efficiency. The optimized MMDG shows an ultra-broadband working spectrum with the average efficiency exceeding 97% over 135nm wavelength centered at 800nm and TE polarization. The optimized MMDG should be useful for chirped pulse amplification.

In this paper, we report the optical and thermal properties of a new Nd-doped phosphate laser glass. Glass samples with 0.5-3.7 wt% Nd-doping concentrations were prepared, annealed, cut and polished for different measurements, including glass density and refractive index, absorption spectra and emission cross section, as well as laser properties. A Mach- Zehnder interferometer was used to measure the temperature coefficient of refractive index (dn/dT) and optical path length (dS/dT) in the temperature range of 30-100 °C. Moreover, by increasing the glass temperature up to 500 °C, the thermal expansion of this new glass was also measured. On the basis of these optical, thermal and thermo-optic parameters, we calculated and analyzed some of glass parameters, such as the electronic polarizability of oxygen ions, the optical basicity of this phosphate-based glass, and especially discussed their thermal shock resistance properties. It is suggested that this new Nd-doped phosphate laser glass is an excellent candidate for high energy and high repetition rate laser applications.

In:Er:LiTaO₃ single crystals with 1.0mol.% Er³⁺ and various In³⁺ ions were grown by the Czochralski method from a congruent melt (C_Li/C_Ta=0.946). Defect structure of the crystals was determined by their infrared absorption spectra. Threshold concentration of In³⁺ ion is 3.0mol.%. The optical damage resistance of In:Er:LiTaO₃ crystals was characterized by the change of light-induced birefringence as well as distortion of transmitted beam pattern. Optical damage resistance of In:Er:LiTaO₃ crystals significantly increases when the concentration of In³⁺ ion exceeds its threshold concentration. The optical damage resistance magnitude of In(3.0mol.%):Er:LiTaO₃ crystal is two orders higher than that of Er:LiTaO₃ crystal. The change of light-induced birefringence decreases with the increasing In³⁺ ion concentration. The optical damage resistance could be well understood in view of defect structure.