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K9 glass is a classical transparent material widely used in high-power optical systems due to its high-temperature resistance. However, the precision machining of K9 glass is difficult. The laser processing method, characterized by being non-contact, having a small heat-affected zone, and having high processing precision, is commonly employed for processing intricate structures. In this study, the vector diffraction model is employed to simulate the internal electric field inside the material when focused by objective lenses with varying numerical apertures. Furthermore, the temperature field is simulated. The simulation considered the nonlinear absorption of the material, the stretching of the focal dot due to spherical aberration, and the energy loss of the laser during the focusing process. The experiment indicated that the ablated area consists of numerous small, ablated dots and that multiple ablated areas emerged under an NA of 0.6. This study can provide valuable references for the research of the interaction between lasers and glass materials. [ABSTRACT FROM AUTHOR]

K9 glass is a classical transparent material widely used in high-power optical systems due to its high-temperature resistance. However, the precision machining of K9 glass is difficult. The laser processing method, characterized by being non-contact, having a small heat-affected zone, and having high processing precision, is commonly employed for processing intricate structures. In this study, the vector diffraction model is employed to simulate the internal electric field inside the material when focused by objective lenses with varying numerical apertures. Furthermore, the temperature field is simulated. The simulation considered the nonlinear absorption of the material, the stretching of the focal dot due to spherical aberration, and the energy loss of the laser during the focusing process. The experiment indicated that the ablated area consists of numerous small, ablated dots and that multiple ablated areas emerged under an NA of 0.6. This study can provide valuable references for the research of the interaction between lasers and glass materials.

This work reports on the fabrication and characterization of a K9 glass planar waveguide structure. The helium ion implantation was employed to form the waveguide on the K9 glass. The choices of the energy of 0.4 MeV and the dose of 6. 0 × 1 0 1 6 ions/cm2 were conducted by the SRIM 2013. The m -line spectroscopy and the modal profile of the He + -irradiated K9 glass waveguide were performed by the prism-coupling system and the end-face coupling technique at 0.6328 μ m, which suggests the capability of light propagation. The He + -implanted K9 glass waveguides can serve as potential candidates for advanced integrated optoelectronic devices. [ABSTRACT FROM AUTHOR]

The k9 glass emerges as the promising host for the waveguide formation, owing to its unique optical properties. Ion implantation is a powerful technique for the fabrication of optical waveguides. In this work, the 400-keV proton implantation at a dose of 8. 0 × 1 0 1 6   ions/cm 2 was performed on the k9 glass to manufacture optical waveguide. Continuous annealing treatment at intervals of 5 0 ∘ C was used to enhance the guiding performances of the waveguide. The dark-mode spectrum and the refractive index profile of the waveguide were obtained by a prism coupling system and a reflectivity calculation method, respectively. The near-filed intensity distribution was measured by an end-face coupling equipment. The results suggest that the light field can be confined within the waveguide layer. [ABSTRACT FROM AUTHOR]

This work use the SPH method to study the relationship between grinding depth and grinding force of K9 glass in ultra-precision grinding, and the effect of grain shape on material removal. The relationship between the force and the depth in the stable scratching stage is FR = 0.55078ap1.15356, which provides a basis for controlling the grinding depth by force. The material removal modes at different grinding depths were obtained, that is, plastic removal occurs below 0.2 μm, brittle transition occurs between 0.2 and 0.4 μm, and brittle removal occurs at more than 0.5 μm. It is found that the cutting resultant force of sharp grains is smaller and the normal force is smaller than the tangential force. By analyzing the plastic deformation depth and residual stress depth, it is found that the material removal mode with small deformation and little removal has the lowest cutting force fluctuation and the highest grinding quality. It provides a reference for the choosing of grain shape in rough grinding and ultra-precision grinding. The correctness and reliability of the simulation results were verified by the comparison of the simulation findings with the results obtained from varied-depth scratching experiments and the multi-shape indenter scratch experiments. [ABSTRACT FROM AUTHOR]

Under the excitation of femtosecond laser pulses, the time-resolved observation of the nonequilibrium heat transfer process of the hot electrons in Pt films is studied using the femtosecond transient thermal reflection technique. The nonequilibrium heat transfer phenomenon plays a positive role in solving the problem that the devices are damaged in the processing of the laser heating the metals. The thickness of the Pt metal films on K9 glass and a monocrystalline Si silicon substrate is 20 and 40 nm, respectively, and the Pt films are deposited by the magnetron sputtering technique. The nonequilibrium heat transfer time of the electrons in the Pt films is measured by detecting the transient reflectivity of the probe beam on the Pt films. The results show that by the heating of the two femtosecond pump beams, the nonequilibrium heat transfer time of electrons in the 20 nm thick Pt film on a K9 glass substrate is as long as 130 ps, much more than tens of picoseconds. [ABSTRACT FROM AUTHOR]

Graphical abstract K9 glass material is 20% higher luminous transmission than the crystal resin materials. Highlights • Two different homogeniser materials were characterised using spectrometer. • K9 glass homogeniser module performs higher electrical power than the crystal resin. • Homogeniser made of K9 glass experiences higher temperature than the crystal resin. Abstract In concentrating photovoltaic (CPV), increasing the incoming sunlight to the solar cell influences the performance of the solar cells. The optical efficiency of the CPV components is a key factor to improve the electrical efficiency. Two types of homogeniser materials (K9 glass and crystal resin) were investigated in the CPV application. The results show a higher power generation of the CPV module when using K9 glass homogeniser compared to the crystal resin homogeniser by 27% due to the high transmittance value of the K9 glass material. In addition, the K9 glass material shows an excellent resistance to the heat produced by the concentrated sunlight compared to the crystal resin material. [ABSTRACT FROM AUTHOR]

K9 optical glass has superb material properties used for various industrial applications. However, the high hardness and low fracture toughness greatly fluctuate the cutting force generated during the grinding process, which are the main factors affecting machining accuracy and surface integrity. With a view to further understand the grinding mechanism of K9 glass and improve the machining quality, a new arithmetical force model and parameter optimization for grinding the K9 glass are introduced in this study. Originally, the grinding force components and the grinding path were analyzed according to the critical depth of plowing, rubbing, and brittle tear. Thereafter, the arithmetical model of grinding force was established based on the geometrical model of a single abrasive grain, taking into account the random distribution of grinding grains, and this fact was considered when establishing the number of active grains participating in cutting Nd-Tot. It should be noted that the tool diameter changed with machining, therefore this change was taking into account when building the arithmetical force model during processing as well as the variable value of the maximum chip thickness amax accordingly. Besides, the force analysis recommends how to control the processing parameters to achieve high surface and subsurface quality. Finally, the force model was evaluated by comparing theoretical results with experimental ones. The experimental values of surface grinding forces are in good conformity with the predicted results with changes in the grinding parameters, which proves that the mathematical model is reliable.

K9 glass is an important optical element of the high energy laser system. In an attempt to investigate the variation of optical properties of K9 glass before and after laser induced damage, based on the transmission terahertz time-domain spectral system, the undamaged and the damaged K9 glasses induced by laser were tested to obtain the terahertz time-domain and frequency-domain spectra and the refractive index and absorption coefficient of the samples were calculated in terahertz band for further analysis. Results show that with the increase of laser energy, from the undamaged to the damaged K9 glasses to different extent, the peak to peak value in time domain and the amplitude value in frequency domain present a decreasing trend in varying degrees, and in the 0.4 ∼ 0.5 THz band, the absorption coefficient increases continuously with a slight change of refractive index, which indicates that K9 glass not only appears the melting and fracture in the macroscopic morphology after laser-induced damage, but also forms non-bridged oxygen atoms in its microstructure with more ion bonds and free electrons and the change of ion polarization. In this regard, this paper provides a technical basis for exploring the micro characteristics of K9 glass after laser-induced damage, and lays a good foundation for the application of terahertz time-domain spectroscopy to laser-induced damage analysis.

Laser cleaning is an environmentally friendly, stable and reliable cleaning method and has no mechanical contact. Laser cleaning also has high efficiency, low cost and other unique advantages, so can be used widely in many engineering applications of accurate positioning and online cleaning. The laser direct cleaning and laser-induced plasma shockwave (LIPS) cleaning were utilized to remove the dust particles on the surface of K9 glass. The laser cleaning effect was studied by using optical microscopy, spectrophotometer, and image analysis. The results showed that the particles on K9 glass surface were cleaned effectively, except some of the tiny particles. Under high laser fluency irradiation, laser-induced damage was found on the K9 glass surface. The LIPS cleaning achieved better cleaning effect and has no substrate damage. When the distance between the laser-induced plasma and the sample surface was about 1 mm, the contaminated K9 glass surface was cleaned by the LIPS cleaning with 10 pulses irradiation at laser wavelength of 1 064 nm, and laser energy of 70.7 mj. After the LIPS cleaning, the 355 nm laser-induced damage threshold of the K9 glass surface was improved from 5. 8 J/cm2 to 8. 0 J/cm2, and was similar to that of the substrate threshold ( 8. 5 J/cm2 @ 50% damage probability). This study is helpful to make clear the laser cleaning mechanism and to develop the laser cleaning application, as well as to increase the innovation and exploration in the experimental teaching. [ABSTRACT FROM AUTHOR]

Ablation rates of K9 glass were studied as a function of femtosecond laser fluences. The central wavelength was 800 nm, and pulse durations of 35 fs and 500 fs in air and vacuum were employed. Ablation thresholds of 0.42 J/cm 2 and 2.1 J/cm 2 were obtained at 35 fs and 500 fs, respectively, which were independent with the ambient conditions and depend on the incident pulse numbers due to incubation effects. The ablation rate of 35 fs pulse laser increased with the increasing of laser fluence in vacuum, while in air condition, it slowly increased to a plateau at high fluence. The ablation rate of 500 fs pulse laser showed an increase at low fluence and a slow drop of ablation rate was observed at high fluence in air and vacuum, which may due to the strong defocusing effects associated with the non-equilibrium ionization of air, and/or the shielding effects of conduction band electrons (CBEs) produced by multi-photon ionization and impact ionization in K9 glass surface. The typical ablation morphologies, e.g. smooth zone and laser-induced periodic surface structures (LIPSS) were also presented and illustrated. [ABSTRACT FROM AUTHOR]

The theoretical model of K9 glass irradiated by a 248-nm KrF excimer laser was established, and a numerical simulation was performed to calculate temperature and thermal stress fields in the K9 glass sample using the finite element method. The laser-induced damage thresholds were defined and calculated, and the effect of repetition frequency and the number of pulses on the damage threshold were also studied. Furthermore, the experiment research was carried out to confirm the numerical simulation. The damage threshold and damage morphology were analyzed by means of a metallurgical microscope and scanning electron microscopy. The simulation and experimental results indicated that the damage mechanism of K9 glass irradiated by a KrF excimer laser was melting damage and stress damage, and the stress damage first appeared inside the K9 glass sample. The tensile stress damage threshold, the compressive stress damage threshold, and the melting damage threshold were 0.64, 0.76, and 1.05 J/cm², respectively. The damage threshold decreased with increasing repetition frequency and number of laser pulses. The experimental results indicated that the damage threshold of K9 glass was 2.8 J/cm². [ABSTRACT FROM AUTHOR]

Surface roughness is one of the most important parameters of surface quality and a difficult technical issue in glass polishing, especially for traditional polishing. In this paper, the coupled algorithm of FEM/SPH has been used to simulate the deformation of brittle K9 glass in traditional polishing. The influences of polishing particle size and insert depth on surface roughness are analyzed in detail. Then, experiment is carried out on a ∅100 mm flat K9 mirror with three sorts of particle, ceria abrasive particle with 1.2, 1.6 and 2 μm. Simulation and experiment results show that surface roughness of brittle glass has direct relationship with particle size during traditional polishing process. The surface roughness is better as the particle size is smaller. [ABSTRACT FROM AUTHOR]

Highlights: [•] Transient absorption and luminescence spectra at sub-damage site of K9 glass by laser irradiation at 355nm are presented. [•] As the energy density increases to 2.54J/cm2, the absorption intensity reaches to about 0.2. [•] The mechanism of two-photon ionization mainly plays a critical role at sub-damage site. [•] Intensity of Raman spectra is very high at low energy density and decreased with respect to high energy density. [ABSTRACT FROM AUTHOR]

Abstract: In order to explore the damage mechanisms of K9 glass irradiated by high energy density ultraviolet laser, laser-induced fluorescence and Raman spectra were investigated. Compared the fluorescence spectra of damaged area, undamaged area and sub-damaged area, it can be conclude that the fluorescence spectrum of sub-damaged area is different from the structure of the other two areas. Especially, the main peak of the spectra at 415nm reveals the unique characteristics of K9 glass. The structure at the sub-damaged area enhances intensity of the Raman scattering spectra. Three peaks of the spectra at about 500nm and two characteristic peaks at about 550nm exhibit the characterization of damaged area. A peak of the Raman scattering spectra at 350nm which related to water can be observed. The relationship between intensity of Raman scattering and laser intensity at 355nm is investigated by confocal Raman microscopy. At sub-damage area, signal of Raman scattering is rather high and decreased dramatically with respect to energy density. The major band at about 1470cm−1 sharpened and moved to higher frequency with densification. These phenomena demonstrate that the structure of sub-damaged area has some characterization compared with the damaged area. The investigation of defect induced fluorescence and Raman spectra on surface of K9 glass is important to explore the damage mechanisms of optical materials irradiated by ultraviolet laser irradiation at 355nm. [Copyright &y& Elsevier]

As a widely used engineering material, optical glass is very difficult to process because of its high hardness and brittleness. The material removal mechanism still needs further investigation. In this paper, a mesh-free simulation method—smooth particle hydrodynamics (SPH)—is introduced and an ultra-precision cutting model for K9 glass is provided. Compared with conventional finite element method, the SPH method can effectively avoid mesh distortion when dealing with large deformation problems such as cutting. Several numerical simulations were carried out to further investigate the critical value of transition. Simulation results indicate that when cutting depth is small enough, the K9 glass can be machined in ductile mode and a relatively smooth machined surface without crack can be obtained. The chip is always in irregular and discontinuous way no matter what the cutting mode is. Three cutting tools with different rake angle were used in simulation and the effect of rake angle is analyzed. [ABSTRACT FROM AUTHOR]

Abstract: In the high power laser facility, surface contaminations on the optics will worsen the laser beam quality and damage the optics. Particle and grease contaminations are two of the usual contaminations on the surface of optics. In this work, the 1064-nm laser induced plasma shockwave cleaning is utilized to remove SiO2 particle contaminations on the K9 glass surface. The results indicate the removal ratio can reach above 95%. The effects of parameters (particle position, laser gap distance and laser energy) on the cleaning efficiency have been studied in the case of single pulse laser cleaning. In addition, CO2 laser (10.6μm) is utilized to remove the dimethylsilicone oil contaminations on the gold-coated K9 glass surface. The results show that CO2 laser can effectively remove the dimethylsilicone oil by properly controlling the laser parameters. The cleaned area increases with the increased laser power or irradiation time when the other parameters are constant. [Copyright &y& Elsevier]

Supersmooth surfaces are often needed in high- and new-technology products. The traditional polishing method to obtain supersmooth surfaces is abrasive polishing. In this paper, a new kind of polishing method, non-abrasive polishing (NAP), is presented. The polishing wheel of NAP is made of ice that is frozen deionized water, so there is no abrasive in the polishing wheel. Compared with traditional polishing methods, NAP can obtain A˚ngstro¨m-order surface roughness values free from microscratches and subsurface cracks. Based on adhesion theory, the material removal mechanism of NAP is presented in the paper. The paper also analyzes the polishing equipment and processing technique of NAP. The best surface roughness, Ra=0.48 nm, of K9 glass is obtained using NAP. According to the relationship between surface roughness and adhesion, the surface roughness fluctuation phenomenon is explained in the paper. The surface roughness fluctuation phenomenon is expected to be avoided by measuring the fractal dimension of the polished surface. [Copyright &y& Elsevier]

K9 optical glass has superb material properties used for various industrial applications. However, the high hardness and low fracture toughness greatly fluctuate the cutting force generated during the grinding process, which are the main factors affecting machining accuracy and surface integrity. With a view to further understand the grinding mechanism of K9 glass and improve the machining quality, a new arithmetical force model and parameter optimization for grinding the K9 glass are introduced in this study. Originally, the grinding force components and the grinding path were analyzed according to the critical depth of plowing, rubbing, and brittle tear. Thereafter, the arithmetical model of grinding force was established based on the geometrical model of a single abrasive grain, taking into account the random distribution of grinding grains, and this fact was considered when establishing the number of active grains participating in cutting Nd-Tot. It should be noted that the tool diameter changed with machining, therefore this change was taking into account when building the arithmetical force model during processing as well as the variable value of the maximum chip thickness amax accordingly. Besides, the force analysis recommends how to control the processing parameters to achieve high surface and subsurface quality. Finally, the force model was evaluated by comparing theoretical results with experimental ones. The experimental values of surface grinding forces are in good conformity with the predicted results with changes in the grinding parameters, which proves that the mathematical model is reliable. [ABSTRACT FROM AUTHOR]

Micro-scratch tests have been carried out on borosilicate K9 glass using a Rockwell C diamond indenter with a spherical tip radius 105 μm in order to study deformation/damage regimes and microcracking patterns of K9 glass with increasing normal load. The abrupt changes of test data together with optical microscopy observation can be used to determine three transition loads corresponding to initiation of sub-surface median crack, onset of surface ring crack, and lateral cracks reaching the surface, respectively. Based on linear elastic fracture mechanics, fracture toughness obtained from scratch test under a low driving speed and a suitable fitting range of nominal size is found to be 0.85 MPa•m1/2 for K9 glass, which is close to 0.82 MPa•m1/2 obtained from Vickers hardness technique, making micro-scratch a powerful means to assess fracture toughness of material, and opening new application of scratch test as a quantitative method. [ABSTRACT FROM AUTHOR]