High Reflective Film Research Articles

Enhancement of laser-induced damage threshold of optical coatings by ion-beam etching in vacuum environment

Ion-beam sputtering (IBS) method was used to etch the different thickness of the outer layer overcoat for high reflection film. Laser resistance improvements enabling to exceed 1.5× have been observed on high reflection coatings. The smoothing process of surface and subsurface convex defect induced by ion-beam etching caused the decreasing electric field intensity. A process model was presented to understand the smoothing process of surface and subsurface convex defect. The decreasing electric field intensity, accompanying with small surface roughness value, low defect density and organic contamination adsorption concentration of sample surface, was attributed to the high laser-induced damage threshold in vacuum environment.

Experimental study of the thermal protection performance of the high reflectivity-phase change material (PCM) roof in summer

In order to reduce the building heat gain through the roof, a new kind of high reflectivity-PCM roof was proposed. That is to lay a layer of PCM outside the common roof, then a layer of high reflectivity film was laid outside the PCM layer. To compare the thermal protection performance of the high reflectivity-PCM roof with PCM roof, high reflectivity roof and common roof, three real size rooms were built. The three rooms were first installed with PCM roof, reflectivity roof and common roof. The thermal protection performance of the three roofs was compared for eight days (July 23rd to July 30th). Then the PCM roof and the high reflectivity roof were combined to form the high reflectivity-PCM roof, and the thermal protection performance of the high reflectivity-PCM roof was also compared to that of common roof for another eight days (Aug. 17th to Aug. 24th). Results showed that the high reflectivity-PCM roof performed more excellent in decreasing indoor air temperature, inner surface temperature and inner surface heat flux. Thermal balance results showed that the new type of roof can significantly reduce the solar radiation heat gain and storage most part of the heat passing through the high reflectivity film. The high reflectivity-PCM roof had better thermal protection performance than the other three roofs.

Research on a Dual-Mode Infrared Liquid-Crystal Device for Simultaneous Electrically Adjusted Filtering and Zooming.

A new dual-mode liquid-crystal (LC) micro-device constructed by incorporating a Fabry–Perot (FP) cavity and an arrayed LC micro-lens for performing simultaneous electrically adjusted filtering and zooming in infrared wavelength range is presented in this paper. The main micro-structure is a micro-cavity consisting of two parallel zinc selenide (ZnSe) substrates that are pre-coated with ~20-nm aluminum (Al) layers which served as their high-reflection films and electrodes. In particular, the top electrode of the device is patterned by 44 × 38 circular micro-holes of 120 μm diameter, which also means a 44 × 38 micro-lens array. The micro-cavity with a typical depth of ~12 μm is fully filled by LC materials. The experimental results show that the spectral component with needed frequency or wavelength can be selected effectively from incident micro-beams, and both the transmission spectrum and the point spread function can be adjusted simultaneously by simply varying the root-mean-square value of the signal voltage applied, so as to demonstrate a closely correlated feature of filtering and zooming. In addition, the maximum transmittance is already up to ~20% according the peak-to-valley value of the spectral transmittance curves, which exhibits nearly twice the increment compared with that of the ordinary LC-FP filtering without micro-lenses.

Design and numerical analysis of high-reflective film used in F-P sapphire optical fiber high-temperature sensor

PurposeThe Fabry-Perot sapphire optical fiber sensor is an excellent choice for high-temperature sensing in civil and military fields, such as oil exploitation, engine and turbine. The purpose of this paper is to study the high-reflective film system withstanding high temperature in Fabry-Perot sapphire optical fiber high-temperature sensor. To improve the performance of the sensor and reduce the difficulty of signal acquisition, one of the key ways is to enhance the normalized light intensity of F-P sensor, which can be achieved by coating the high-reflective film system on the fiber end.Design/methodology/approachThe high-reflective film system can be achieved by a multilayer film with alternating ZrO2 and Al2O3 film layers whose refractive indexes are different. In addition, the optimum film alternating sequences and the influence of the number of film layers, incident angle and temperature should be obtained by numerical analysis.FindingsWith the increase of the number of film layers, the reflectivity rises gradually and the change trend is more and more gentle. A minimum of the spectral reflectivity will occur at a certain incident angle depending on the design of the periodic multilayer system. Temperature affects the reflectivity of high-reflective film system. The normalized light intensity of the F-P sensor coated with high-reflective film system enhances greatly which is helpful to the signal demodulation. The temperature response of the F-P sensor is mainly determined by the characteristics of the F-P cavity.Originality/valueHigher reflectivity, lower cost and easy signal acquisition are the most important features of the introduced high-reflective film system for the Fabry-Perot sapphire optical fiber high-temperature sensor.

Effect of annealing on the damage threshold and optical properties of HfO2/Ta2O5/SiO2 high-reflection film

The effect of thermal annealing on the optical properties, microstructure, and laser-induced damage threshold (LIDT) of HfO2/Ta2O5/SiO2 HR films has been investigated. The transmission spectra shift to a short wavelength and the X-ray diffraction peaks of monoclinic structure HfO2 are enhanced after thermal annealing. The calculated results of the m(−111) diffraction peak show that the HfO2 grain size is increased, which is conducive to increasing the thermal conductivity. Thermal annealing also reduces the laser absorption of high-reflection films. The improvement of thermal conductivity and the decrease of laser absorption both contribute to the improvement of LIDT. The experimental results show that the highest LIDT of 22.4 J/cm2 is obtained at 300°C annealing temperature. With the further increase of annealing temperature, the damage changes from thermal stress damage to thermal explosion damage, resulting in the decrease of LIDT.

Development of broad-band high-reflectivity multilayer film for positron emission tomography system

The use of non-ideal reflective materials and low-precision manual manufacturing technologies is a fundamental technical obstacle blocking the positron emission tomography (PET) systems from achieving better performances. We propose to address that long-standing obstacle with advanced multilayer dielectric coating technologies. We designed an broad-band multilayer high-reflectivity (HR) film that can be coated directly on the surface of ultra-precision polished lutetium-yttrium oxyorthosilicate (LYSO) scintillators. The film consists of 48 layers of TiO2/SiO2/HfO2 which are deposited on LYSO scintillator crystal alternately using the electron beam evaporation method. The overall thickness of the HR film is about 3μm. The HR film combines 3 quarter wavelength reflective films, with the central wavelengths of 365 nm, 430 nm and 570 nm respectively, to match the emission spectrum of the LYSO scintillator. The optical experimental results show that the HR film achieved an excellent average reflectivity of 99.50% at 8̂ incident angle for incident lights with wavelengths between 360 to 620 nm. The average reflectivity at 60̂ incident angle is higher than 90%. The results of the hardness experiments and the adhesive strength experiments show that the HR film has an excellent mechanical strength. The HR coating technology developed in this study is very attractive because it allows to “print” high-performance reflectors on a scintillator directly with high-precision, instead of manually gluing reflective films on the scintillator. Thus, we conclude that the HR film provides a viable solution to the long standing technical bottleneck that limits the development of high-performance detectors for advanced PET imaging.

Research on Application of a Three Dimensional Solar Power

Traditional transmission lines on-line monitoring device solar power supply usually adopts flat-panel structure, which has low energy use efficiency of solar power and easy to be destroyed by wind and rain. Therefore, a three-dimensional solar power is proposed in this paper. This structure includes the cube of solar power, hollow high transparency cylindrical shell, reflective films and bracket, and has carried on the hardware design. Then, the output power of three-dimensional and flat-panel structure solar power is discussed respectively under the condition of sunny, cloudy, overcast and rainy days. The results show that the efficiency of the three-dimensional solar power is higher. Finally, taking the South China power grid for transmission lines online monitoring device power consumption as an example, the application scheme of three-dimensional solar power supply in transmission lines on-line monitoring device is completed.

Improvement of Aluminium Film Adhesion on PMMA Using Pre-Layer and Specific Annealing

During the electron beam evaporation for deposition of an aluminium film, high-speed electrons decelerate when they bombard the material and part of the electron energy contributes to radiation. Due to the high sensitivity of polymethyl methacrylate (PMMA) to such radiation (in UV), the PMMA surface is degraded. This results in a weak surface of PMMA layer and decreases film adhesion. Based on the film interface adhesion mechanism and the relationship between film structure and stress, this research proposed and investigated a method for producing high quality Al reflective thin film on a PMMA surface with good adhesion. This was done by depositing a pre-layer of 20 nm Al using resistant evaporation to protect the PMMA surface from radiation damage, followed by the deposition of 80 nm Al using e-beam evaporation with ion assisted deposition. Using this method, an average reflectance of 88.6% was achieved in the wavelength range of 400–800 nm. The elastic modulus and hardness were tested by nanoindentation for the calculation of the thermal stress of the film. Adhesion was tested using the pressure strip peeling test and meets the military national standard.

高反射光学薄膜激光损伤研究进展

高反射光学薄膜激光损伤研究进展

Prototyping hexagonal light concentrators using high-reflectance specular films for the Large-Sized Telescopes of the Cherenkov Telescope Array

We have developed a prototype hexagonal light concentrator for the Large-Sized Telescopes of the Cherenkov Telescope Array. To maximize the photodetection efficiency of the focal-plane camera pixels for atmospheric Cherenkov photons and to lower the energy threshold, a specular film with a very high reflectance of 92–99% has been developed to cover the inner surfaces of the light concentrators. The prototype has a relative anode sensitivity (which can be roughly regarded as collection efficiency) of about 95 to 105% at the most important angles of incidence. The design, simulation, production procedure, and performance measurements of the light-concentrator prototype are reported.

Compact Two-Color Pr3+-Doped ZBLAN Fiber Lasers

ABSTRACTTwo-color laser simultaneous oscillation in compact trivalent praseodymium ion (Pr3+)-doped ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber lasers is investigated. Fiber pigtails by coating high-reflective visible dielectric films are utilized as fiber mirrors (FMs) to construct compact all-fiber laser cavity. Reflectance/transmittance of FMs is intentionally designed to balance net gains and reduce gain competition of different lasable wavelengths in the constructed fiber lasers. By using two selected FMs with high reflectivity at green-light and low reflectivity at red-light, simultaneous green and red laser emission in all-fiber Pr3+-doped ZBLAN fiber laser is obtained. Moreover, simultaneous orange and red laser emission is also achieved with another selected FM of high reflectivity at orange-light and low reflectivity at red-light. Our work will provide an effective and easy method to construct compact special fiber (e.g.,ZBLAN fiber, chalcogenide fiber) lasers.

A self-correction method for deformable mirror with thermal deformation

In high-power laser systems, temperature gradient distribution arises in optical components irradiated by a high-power continuous wave (CW) laser, leading to the thermal deformation of the optical components and further the degradation of the beam quality. The deformable mirrors (DMs) are commonly used to improve the beam quality, but the thermal deformation of the DM irradiated by the high-power CW laser also exist and is more complex than that of conventional reflecting mirrors, resulting in high-frequency distortion of the corrected wavefront. In this paper, a finite element model for the DM with high reflectivity films is built up, and then the thermal deformation of the DM is simulated and analyzed. According to the deformable feature of the DM, a self-correction method is proposed, i.e., the DM corrects its thermal deformation by itself, and a self-correction function is established to control the actuators of the DM. Finally, effects of the self-correction method on beam quality are discussed quantitatively. Results show that the self-correction method can compensate the thermal deformation distribution of the DM and even constrain the generation of high-frequency distortion. Consequently, the self-correction method is feasible to compensate the thermal deformation of the DM, and further improves the beam quality.

Two‐dimensional spectrum detection based on the imperfect virtually imaged phased array

AbstractVirtually imaged phased array (VIPA) is typically consists of a thin plate of glass coated with high reflection film coated on both sides. The effects of plate defects on virtually imaged phased array are investigated in this article. We mainly analyze the parallelism and surface roughness of the glass plate by simulation. A 2D disperser is established by a virtually imaged phased array and a diffraction grating. Results show that the degree of plate parallelism will affect the spot size of the beam output, wavelength of the maximum power and 3‐dB bandwidth, and the surface roughness will lead to scattering and loss. The simulation results are validated by experiment.

Improving the Performance of a Semitransparent BIPV by Using High-Reflectivity Heat Insulation Film

Currently, standard semitransparent photovoltaic (PV) modules can largely replace architectural glass installed in the windows, skylights, and facade of a building. Their main features are power generation and transparency, as well as possessing a heat insulating effect. Through heat insulation solar glass (HISG) encapsulation technology, this study improved the structure of a typical semitransparent PV module and explored the use of three types of high-reflectivity heat insulation films to form the HISG building-integrated photovoltaics (BIPV) systems. Subsequently, the authors analyzed the influence of HISG structures on the optical, thermal, and power generation performance of the original semitransparent PV module and the degree to which enhanced performance is possible. The experimental results indicated that the heat insulation performance and power generation of HISGs were both improved. Selecting an appropriate heat insulation film so that a larger amount of reflective solar radiation is absorbed by the back side of the HISG can yield greater enhancement of power generation. The numerical results conducted in this study also indicated that HISG BIPV system not only provides the passive energy needed for power loading in a building, but also decreases the energy consumption of the HVAC system in subtropical and temperate regions.

Low-threshold-current yellow BeZnCdSe quantum-well ridge-waveguide laser diodes under continuous-wave room-temperature operation

Low-threshold-current yellow BeZnCdSe single-quantum-well (SQW) laser diodes (LDs) have been developed by using a ridge-waveguide structure. The top p-cladding layer was etched to suppress the leakage current that flowed laterally outside of the electrode. Ridge waveguides were covered with a SiO2 layer and planarized by chemical–mechanical polishing and reactive ion etching. Room-temperature lasing under continuous-wave condition was achieved with the laser cavity formed by cleaved waveguide facets coated with high-reflectivity dielectric films. Two types of LDs with different SQW thicknesses and Cd contents were developed and compared at various waveguide widths and lengths. Yellow LDs with sub-10 mA threshold current were obtained.

Electron beam modification of glasses containing Ag and Au nanoparticles

The goal of our work was the investigation of the processes of interaction electrons (5-30 keV) with metal nanoparticles in glasses. The objects of our research were the silicate glasses containing Au and Ag nanoparticles. The experiments have shown that electron irradiation with electron energy 5-10 keV of glass containing Au nanoparticles results in the formation of high reflective gold film about 50 nm thick on a glass surface. Electron irradiation (5-30 keV) of glass containing Ag nanoparticles results in the increase of optical density in the irradiated areas and formation of silver clusters (Agx, x<5) in a form of a ring at periphery. Thus, electron beam can be used to produce photonic and plasmonic devices without etching mask.

BeZnCdSe quantum-well ridge-waveguide laser diodes under low threshold room-temperature continuous-wave operation

Low threshold current ridge-waveguide BeZnCdSe quantum-well laser diodes (LDs) have been developed by completely etching away the top p-type BeMgZnSe/ZnSe:N short-period superlattice cladding layer, which can suppress the leakage current that flows laterally outside of the electrode. The waveguide LDs are covered with a thick SiO2 layer and planarized with chemical-mechanical polishing and a reactive ion etching process. Room-temperature lasing under continuous-wave condition is achieved with the laser cavity formed by the cleaved waveguide facets coated with high-reflectivity dielectric films. For a 4 μm-wide green LD lasing around a wavelength of 535 nm, threshold current and voltage of 7.07 mA and 7.89 V are achieved for a cavity length of 300 μm, and the internal differential quantum efficiency, internal absorption loss, gain constant, and nominal transparency current density are estimated to be 27%, 4.09 cm−1, 29.92 (cm × μm)/kA and 6.35 kA/(cm2 × μm), respectively. This compact device can realize a significantly improved performance with much lower threshold power consumption, which would benefit the potential application for ZnSe-based green LDs as light sources in full-color display and projector devices installed in consumer products such as pocket projectors.

Temperature field analysis of high reflection film induced by long-pulse and short-pulse lasers under different irradiation angles

Modeling laser beam as a tapered wave with a Gaussian spectrum, The temperature fields in HfO2/SiO2 high-reflection (HR) film, induced by 1ms long-pulse and 10ns short-pulse lasers, under different incident angles are calculated. The damage differences between long-pulse and short-pulse-induced damage in the HR film are analyzed. The results show for long-pulse laser, the temperature distribution is much less affected by the laser field effect than short-pulse case. Furthermore, as the irradiation angles increase from 0 to 35° for 1ms and 10ns lasers, the peak temperature rises in the HR film increase for s polarized laser. Other than long-pulse laser, for short-pulse laser, the positions of the peak temperature shift gradually toward the air–film interface as the incident angle increases, which may have a great influence on the position of thermal stress coupling and damage probability.

Degradation mechanism of laser-induced damage of porous ZrO2/SiO2 high reflective films in vacuum

Degradation mechanism of laser-induced damage of porous ZrO2/SiO2 high reflective films was discussed in vacuum. The experimental results show that the laser-induced damage (LIDT) in vacuum dropped to 57% of its atmospheric value and 65% of the value filled with air after vacuum pumping for the high reflective films. Typical damage micrographs of the films in air and in vacuum were obtained, showing the distinct damage morphologies. Such a degradation mechanism of laser-induced damage was found to originate from the water desorption on the surface and internally in porous films, which could cause a decrease of the thermal conductivity. A theoretical and kinetic model was used to illustrate the occurrence of the damage and corresponding damage morphologies.

Design of new multipass gas cells with circular and elliptical cross‐section

ABSTRACTTwo new types of multipass gas cells with circular and elliptical cross‐sections were developed. As for a cylindrical cell, the reflected rays in the circle would be an irregular trace without superposition and termination, if its central angle is a bit more than 2π/3 for an example. Each two adjacent reflected points have the same optical path difference and optical light passes through different optical distances before different reflection points. As for a cylindroidal cell, if the optical ray passes through one focus point of the ellipse, it must also pass through the other. The light will exit finally from the termination point of an axis. The optical distance depends on the eccentricity of the ellipse and the size of the emergent window. In this article, the detailed mathematical derivations of the optical multireflection traces for the two structures are presented. The unified formula is developed. It is found that these designs have small volumes and adjustable long optical paths. For example, the optical distances in the two structures are about 625 mm for a circle with 50 mm radius. The performance of the system can be enhanced by coating high total reflection film, increasing the processing and positioning precisions, and using highly collimating laser beam. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:3003–3009, 2014