Infrared light absorption of silver film coated on the surface of femtosecond laser microstructured silicon in SF6

Absorptive properties of 100 nm thick silver (Ag) films coated on the surface of microstructured silicon prepared by femtosecond laser pulses irradiation in SF₆ were measured in a wavelength range of 1.33–16.7 µm. Greatly enhanced light absorption of Ag films was observed in the entire measured wavelength range. For sample with 6–8 µm spikes, the absorptance is approximately 0.9 and essentially unchanged in the wavelength region of 1.33–10 µm, and decreases slightly when λ > 10 µm, but keeps higher than 0.75 over the whole measured wavelength range. The infrared absorption is strongly related to the height and density of the spikes. While for the samples without Ag coating, the absorption is much lower than that of the Ag films. Multiple reflection of light between spikes and surface plasmon excitation of nano-particles on the spikes surface may lead to the strongly enhanced infrared absorption in such a wide wavelength range.     

Enhanced light absorption of Ag films deposited onto femtosecond laser microstructured silicon

Absorptive properties of silver (Ag) films with the thickness varied from 160 nm to 340 nm deposited onto the surface of femtosecond laser microstructured silicon by vacuum thermal evaporation were measured in a wavelength range of 0.3-16.7 μm. Greatly enhanced light absorption of Ag films has been observed in the whole measured wavelength range. For the same Ag film thickness (268 nm), the light absorption was strongly depended on the height and spacing of the spikes, especially in the region of 1-16.7 μm. The relation between light absorption and thickness of Ag films has also been investigated, it was shown that the light absorption decreases with the increasing thickness of Ag films. The strongly enhanced light absorption in such a wide wavelength range is mainly ascribed to the multiple reflection of light between spikes and surface plasmon excitation of noble metal nano-particles on the spikes surface.     

Greatly enhanced infrared normal spectral emissivity of microstructured silicon using a femtosecond laser

The infrared normal spectral emissivity of microstructured silicon prepared by femtosecond laser irradiation in SF₆ was measured for the wavelength range 2.5 μm to 25 μm. Greatly enhanced emissivity compared to that of flat silicon was observed over the entire wavelength range. For a sample with 13-14 μm high spikes, the emissivity at a temperature of 100 °C is approximately 0.96. The emissivity decreases slightly in the wavelength region above 8 μm, but remains higher than 0.9 over most of the measured wavelength range. Also the average emissivity is less than Nextel- Velvet-811-21 Coating, it can be used stably at more wide temperatures from 100 °C to 400 °C. These results show the potential for microstructured silicon to be used as a flat blackbody source or silicon-based pyroelectric and microbolometer devices.     

Preparation and characterization of sol–gel processed GeO2/methyltrimethoxysilane hybrid thin films

We report on preparation and characterization of GeO₂/methyltrimethoxysilane hybrid thin films processed by the sol–gel spin coating technique. Acid catalyzed solutions of methyltrimethoxysilane mixed with germanium isopropoxide have been used as precursors for the hybrid materials. The optical properties of the thin films, including refractive index, thickness, and transparency as well as structural characterization, have been studied by using a prism coupling technique, atomic force microscopy, thermal gravimetric analysis, UV–visible spectroscopy, and Fourier transform infrared spectroscopy. The results indicate that a crack-free, low absorption, and high transparency in the visible range optical films with a thickness of about 1.3 μm could be obtained by a single spin-coating process and at low heat treatment temperature. A strong UV absorption region at short wavelength ∼200 nm, accompanied with a shoulder peaked at ∼240 nm, due to the neutral oxygen monovacancies defects, has also been identified.     

Multiscale transparent electrode architecture for efficient light management and carrier collection in solar cells

The challenge for all photovoltaic technologies is to maximize light absorption, to convert photons with minimal losses into electric charges, and to efficiently extract them to the electrical circuit. For thin-film solar cells, all these tasks rely heavily on the transparent front electrode. Here we present a multiscale electrode architecture that allows us to achieve efficiencies as high as 14.1% with a thin-film silicon tandem solar cell employing only 3 μm of silicon. Our approach combines the versatility of nanoimprint lithography, the unusually high carrier mobility of hydrogenated indium oxide (over 100 cm(2)/V/s), and the unequaled light-scattering properties of self-textured zinc oxide. A multiscale texture provides light trapping over a broad wavelength range while ensuring an optimum morphology for the growth of high-quality silicon layers. A conductive bilayer stack guarantees carrier extraction while minimizing parasitic absorption losses. The tunability accessible through such multiscale electrode architecture offers unprecedented possibilities to address the trade-off between cell optical and electrical performance.     

Alignment control of columnar liquid crystals with wavelength tunable CO2 laser irradiation

Infrared-induced alignment change with wavelength tunable CO₂ laser irradiation for columnar liquid crystal domains was investigated for a liquid crystalline triphenylene derivative. A uniformly aligned alignment change of domains was observed when a chopped linearly polarized infrared laser light corresponding to the wavelength of the aromatic C-O-C stretching vibration band (9.65 μm) was irradiated. The results strongly imply that the infrared irradiation is a possible technique for device fabrication by use of columnar mesophase as a liquid crystalline semiconductor.     

Silicon nitride films prepared by reactive plasma sputtering

Silicon nitride films were prepared by reactive plasma sputtering in nitrogen at a pressure of 2×10^-4 Torr. The residual gas in the reactor during film sputtering was analysed. The chemical composition of the films was determined from infrared absorption spectra in the wavelength region 2.0–15.0 μm and by the elastic scattering of ³He particles.The best quality silicon nitride films were obtained in pure nitrogen at the minimum residual gas pressures. An absorption minimum at 11.0 μm in the infrared spectra, corresponding to the Si-N chemical bond in the Si₃N₄ molecule, was observed in our films, indicating that their composition was close to stoichiometric.With a residual hydrogen pressure above 10% or a residual oxygen pressure above 2% the generation of new chemical bonds Si-H, N-H and Si-O respectively was observed in the silicon nitride films.     

Integrated all-optical infrared switchable plasmonic quantum cascade laser

We report a type of infrared switchable plasmonic quantum cascade laser, in which far field light in the midwave infrared (MWIR, 6.1 μm) is modulated by a near field interaction of light in the telecommunications wavelength (1.55 μm). To achieve this all-optical switch, we used cross-polarized bowtie antennas and a centrally located germanium nanoslab. The bowtie antenna squeezes the short wavelength light into the gap region, where the germanium is placed. The perturbation of refractive index of the germanium due to the free carrier absorption produced by short wavelength light changes the optical response of the antenna and the entire laser intensity at 6.1 μm significantly. This device shows a viable method to modulate the far field of a laser through a near field interaction.     

Optical,structural and photophysical properties of Ga2BiTaO7 compound

The Ga₂BiTaO₇ compound was synthesized by solid-state reaction method and characterized by powder X-ray diffraction method and the Rietveld structure refinement. This compound crystallizes in the pyrochlore-type structure, cubic system with space group Fd3m and the lattice parameter a = 10.4544(2) Angstrom. The band gap of the Ga₂BiTaO₇ compound was estimated to be about 2.47(1) eV. It shows strong optical absorption in the visible light region (λ > 420 nm). This indicates that the Ga₂BiTaO₇ compound has the ability to respond to wavelength of visible light region and has potential for splitting water into H₂ and O₂ under visible light irradiation. Photocatalytic degradation of methylene blue (MB) dye on the Ga₂BiTaO₇ compound was first investigated under ultraviolet light and visible light irradiation. MB was obviously degraded after visible light irradiation for 140 min with the photocatalyst at room temperature in air. The high activity has potential to be kept in a wide range of wavelength up to 505 nm.     

Metal nanoparticles generated by laser ablation

We study a new method for producing ultrafine metal particles (nanopartides) that employs Laser Ablation of Microparticles (LAM). Pulsed excimer laser radiation at 248 nm wavelength was used to ablate ~2 μm feedstock of silver, gold, andpermalloy (Ni₈₁%:Fe_19%) under both normal atmospheric conditions and in other gases and pressures. A model for nanoparticle formation by LAM is proposed that includes plasma breakdown and shock-wave propagation through the initial microparticle. Behind the shock a large fraction of the original microparticle mass is converted to nanoparticles that diffuse to silicon substrates and TEM grids for collection and analysis. Nanoparticle morphologies are spherical except for gold nanoparticles >100 nm that are generally cubes. Electron micrographs of the samples were analyzed by computer-aided image processing to determine the effect of irradiation conditions on the nanoparticle size distribution. The results showed that mean particle diameters were normally in the range from 10 to 100 nm and that the particle size distributions were generally log-normal, with dispersion (diameter/standard deviation) ranging from 0.2 to 0.5. For metallic microparticle feedstock, the mean size of the produced nanoparticles generally increased with increasing laser fluence and were smallest for fluences not too far above the breakdown threshold.     

Simultaneous recrystallization, phosphorous diffusion and antireflection coating of silicon films using laser treatment

Laser technique application to polycrystalline silicon thin-film solar cell fabrication on glass substrates has received appreciable attention. In this paper, a laser-doping technique is developed for plasma-deposited amorphous silicon film. A process involving recrystallization, phosphorous diffusion and antireflection coating can be achieved simultaneously using the laser annealing process. The doping precursor, a phosphorous-doped titanium dioxide (TiO₂) solution, is synthesized using a sol-gel method and spin-coated onto the sample. After laser irradiation, the polycrystalline silicon grain size was about 0.5∼1.0 μm with a carrier concentration of 2 × 10¹⁹ cm^− 3 and electron mobility of 92.6 cm²/V s. The average polycrystalline silicon reflectance can be reduced to a value of 4.65% at wavelengths between 400 and 700 nm, indicating the upper TiO₂ film of antireflection coating.     

Photothermal Characteristics of Novel Flexible Black Silicon for Solar Thermal Receiver

In this article, a novel type of flexible black silicon used for enhancing the absorption of a solar thermal receiver is reported. The optical absorption properties of this kind of flexible black silicon with three different sizes of conical microstructure are analyzed using the finite-difference time-domain (FDTD) method and the heat transfer properties are studied using the COMSOL multiphysics heat transfer solver. The results show that flexible black silicon with small-size microstructure has the highest optical absorptance and heat transfer speed. A commercial silicon-on-insulator wafer is irradiated by an auto-scanning femtosecond laser system and then split by etching out its middle layer in 52?% hydrofluoric acid to fabricate the flexible black silicon. The obtained flexible black silicon presents very good flexibility, and its photothermal characteristics are investigated. The optical absorption spectrum test results indicate that the absorptance of the flexible black silicon is as high as 97?% in the visible spectral region and is higher than that of anodized aluminum in a broad spectral range from 250?nm to 2500?nm. The light radiation heating experiment results show that the energy absorption efficiency of the water covered with flexible black silicon is improved 13?% compared with that of the water covered with anodized aluminum. It is confirmed that as a light-absorbing and heat-transferring layer the flexible black silicon has an important potential application in exploring solar energy.     

An investigation of spatial distribution of laser ablation products and their deposition on a substrate in the case of laser action with sharp focusing

Results are given of numerical simulation of the effect of laser radiation at a wavelength of 1.313 μm with sharp focusing on a silicon target. The behavior of the gasdynamic parameters is investigated, as well as the characteristic features of the modes of plasma formation, under such irradiation. The pattern is determined of the dependence of configuration and velocity of motion of the cloud boundary on the size of irradiation spot, angle of convergence of incident radiation, and its intensity. The time dependences are obtained for the temperature and density within the plasma cloud. The possibility of spraying the laser ablation products onto a substrate is assessed, and the configurations of deposited film are calculated for different modes of irradiation.     

Temperature and intensity dependence of Yb-fiber laser light absorption in water

Absorption of CW Yb-fiber laser light of 1.07 μm wavelength in water has been measured at different water temperatures and laser intensities. The absorption coefficient was estimated to be 0.135 cm(-1) at 25 °C water temperature, and this was found to decrease with temperature at a rate of 5.7 × 10(-4) cm(-1) °C(-1). The absorption coefficient increased significantly when the laser beam was focused in water, and the increase depended on the distance of the focal point from the water surface. This has been attributed to the absorption and scattering losses of laser radiation in a cavity formed in water by the focused beam at laser intensities in the megawatts per square centimeter and higher range.     

Combined theoretical studies of the optical characteristics of II-IV-V2 semiconductor thin films

The optical absorbance of four ternary thin films, i.e. MgSiP₂, MgGeP₂, MgSiAs₂, MgGeAs₂ have been theoretically examined over a wide range of wavelength from 300 nm to 800 nm. The combination of first-principle electronic structure calculations and the optical matrix approach for modeling the multilayer assembly have been employed for theoretical studies. The analysis of the calculated absorbance spectra at room temperature with unpolarized light and normal incidence, revealed that MgGeAs₂ with a direct energy band gap of 1.6 eV exhibit a considerable high optical absorption, where a thickness of 3.2 μm of this thin film is sufficient to absorb 90% of the incident light and generates a maximum photocurrent of ∼23 mA/cm².     

SnO2 films prepared by activated reactive evaporation

Transparent conducting films of SnO₂ doped with antimony were prepared on glass substrates by activated reactive evaporation for the first time. The sheet resistance and optical transmittance in the wavelength range 0.4–1.6 μm were studied as functions of various deposition parameters such as the ambient pressure of an 85%Ar15%O₂ mixture, the substrate temperature and the antimony doping concentration in the SnSb alloys. The sheet resistance and optical transmittance showed a strong dependence on the above-mentioned deposition parameters. The best results were obtained for a 90at.%Sn10at.%Sb alloy evaporated in 85%Ar15%O₂ at a partial pressure of about 5 × 10^?4 Torr with a substrate temperature about 350°C. These films, with a sheet resistance of 10 μ/□ had an average transmittance of 95% over the wavelength range 0.4–1.8 μm. The film thickness was about 0.25 μm. Thicker films (about 0.5 μm) had a sheet resistance as low as 1.5 ω/□ with an average transmittance 85% in the wavelength range 0.4–1.6 μm.     

Enhancing efficiency of crystalline silicon solar cells by the mixture of downshifting CaAlSiN3:Eu2+ and Y2O3:Eu3+ phosphors

Y₂O₃:Eu³⁺ (YO) phosphors which have high quantum yield in the range 200–280 nm are mixed with downshifting CaAlSiN₃:Eu²⁺ (CASN) phosphors to improve CASN’s low quantum yield in the wavelength range below 280 nm. The luminescence downshifting ethyl vinyl acetate films with the mixture of YO and CASN phosphors are fabricated and then used to package crystalline silicon solar cells. Experimental results show that the introduction of YO phosphors not only improves the external quantum efficiency of the solar cells in the range below 280 nm but also leads to the better absorption of the light in the range 280–500 nm due to the scattering by YO phosphors. The conversion efficiency of the solar cells with the mixed phosphors can be enhanced from 19.60 to 19.98% after packaging.

     

Methane detection with a narrow-band source at 3.4 µm based on a Nd:YAG pump laser and a combination of stimulated Raman scattering and difference frequency mixing

We report the characterization of a 10-Hz pulsed, narrow-band source that is coincident with a fundamental ν(3) rovibrational absorption of methane at 3.43 μm. To generate this midinfrared wavelength, an injection-seeded 1.06-μm Nd:YAG laser is difference frequency mixed with first Stokes light generated in a high-pressure methane cell (1.06 ? 1.54 μm) to result in light at a wavelength of 3.43 μm, that is, the ν(1) Raman active frequency of methane (~2916.2 cm(-1)). With a modest-energy Nd:YAG laser (200 mJ), a few millijoules of this midinfrared energy can be generated with a pulse width of ~7 ns (FWHM). The methane ν(1) frequency can be pressure tuned over 8-32 atm (corresponding to ~13 GHz) and scanned across part of the ν(3)P(10) rovibrational level of methane, resulting in a peak measured methane absorption coefficient of 4.2 cm(-1) atm(-1).     

一种燃烧型干扰剂的设计及其多频谱消光性能研究

为实现一剂化可见光、红外、激光的多频谱遮蔽干扰,基于铝热燃烧反应设计了一种新型燃烧型多频谱干扰剂,结合理论计算与实验获得了优选配方,并在烟箱内进行了干扰性能测试。结果表明:烟幕对可见光、近红外光（1~3 μm波段）、中红外光（ 3~5 μm波段）和波长为1.06 μm的激光可基本实现完全遮蔽;对远红外光（8~14 μm波段）的消光系数可达0.967 m²/g,对波长为10.60 μm激光的消光系数为0.655 m²/g。设计的干扰剂配方可基本实现一剂化多频谱干扰的目的,有望应用于燃烧型烟幕干扰弹。