Effects of beam focusing on the efficiency of planar waveguide grating couplers

Results of a theoretical and experimental study into the variation of coupling efficiency with a grating angle are presented for various beam focusing conditions for an integrated optical grating coupler. The study shows that the acceptance angle of the grating coupler can be broadened within a relatively large range and with a relatively small loss of coupling efficiency, by focusing the incident laser beam

Systems and Methods of Laser Texturing of Material Surfaces and Their Applications

The surface of a material is textured and by exposing the surface to pulses from an ultrafast laser. The laser treatment causes pillars to form on the treated surface. These pillars provide for greater light absorption. Texturing and crystallization can be carried out as a single step process. The crystallization of the material provides for higher electric conductivity and changes in optical and electronic properties of the material. The method may be performed in vacuum or a gaseous environment. The gaseous environment may aid in texturing and/or modifying physical and chemical properties of the surfaces. This method may be used on various material surfaces, such as semiconductors, metals and their alloys, ceramics, polymers, glasses, composites, as well as crystalline, nanocrystalline, polycrystalline, microcrystalline, and amorphous phases

Plume and Nanoparticle Formation During Laser Ablation

The processes that lead to material ejection when a solid sample is irradiated near and above the pulsed laser ablation threshold are discussed. Emphasis is placed on the thermal and mechanical mechanisms that occur during pulsed laser irradiation of metals and semiconductors. Distinctions are drawn between ultrafast-pulsed irradiation, which occurs under stress confinement, and shortpulsed irradiation, in which stress is released during the laser pulse. Similarly, the distinctions between the spallation and phase explosion regimes are discussed. Spallation is only possible when the time of the laser heating is shorter than the time needed for mechanical equilibration of the heated volume, while phase explosion can occur for pulses shorter than tens of ns. Nanoparticle formation can occur directly in the plume as the result of the decomposition of ejected liquid layers or a porous foam created by the phase explosion, as well as through condensation of vaporized atoms (enhanced by the presence of an ambient gas)

121.6 nm Radiation Source for Advanced Lithography

A vacuum ultraviolet (VUV) light source based on a high-pressure cylindrical dielectric barrier discharge (DBD) has been developed. Intense and spectrally clean Lyman-α line at 121.6 nm was obtained by operating a DBD discharge in neon with a small admixture of hydrogen. The spectrum, optical power, stability, and efficiency of the source were measured. The influence of the gas mixture and total gas pressure on the VUV intensity has been investigated. Maximum optical power of 3.2 W and spectral width 0.03 nm was achieved. Power stability of 2% for 100 h of operation has also been obtained. The newly developed Lyman- line source at 121.6 nm appears very promising for advanced lithography and other applications

Solar powered micrometeorite sensors using indoor ambient light for the International Space Station

Sensors for detecting micrometeorite impact locations and magnitudes as well as pressure vessel leaks have been under investigation for some time by the NASA Langley Research Center and other related entities. NASA has been investigating the use of the Distribution Impact Detection System (DIDS) for use on the International Space Station (ISS). However, the DIDS currently requires thionyl chloride lithium batteries which pose explosion and toxicity hazards, and replacing batteries is tedious and utilizes scarce man-hours. Carrying replacement batteries into space is also expensive. To hardwire new sensing devices into the ISS while in orbit would be time consuming. To overcome this problem, high efficiency GaAs solar cells have been studied under low light conditions comparable to those found inside the ISS. The cells were also studied for temperature dependence. Solar concentrators were investigated for possible use with ambient lighting. The power generated by the cells was stored in a large 300 F supercapacitor. A DC to DC boost regulator was modified to produce an output voltage of 3.55 V that is required by the DIDS. The successful operation of the DIDS with ambient light power, supercapacitor energy storage, and boost regulation was demonstrated

Conducting nanotubes or nanostructures based composites, method of making them and applications

An electromagnetic interference (EMI) shielding material includes a matrix of a dielectric or partially conducting polymer, such as foamed polystyrene, with carbon nanotubes or other nanostructures dispersed therein in sufficient concentration to make the material electrically conducting. The composite is formed by dispersing the nanotube material in a solvent in which the dielectric or partially conducting polymer is soluble and mixing the resulting suspension with the dielectric or partially conducting polymer. A foaming agent can be added to produce a lightweight foamed material. An organometallic compound can be added to enhance the conductivity further by decomposition into a metal phase

Multiple-crystal X-ray topographic characterization of periodically domain-inverted KTiOPO4 crystal

A periodically domain-inverted KTiOPO4 crystal has been characterized for the first time by multiple-crystal multiple-reflection x-ray topography. The striation contrast within the domain- inverted regions has been revealed in high strain-sensitivity reflection topographs. The origin of formation of the striation contrast and the mechanism of domain inversion in KTiOPO4 are discussed in terms of the structural characteristics of KTiOPO4

Room Temperature Processing of TiOx Electron Transporting Layer for Perovskite Solar Cells

In order to realize high-throughput roll-to-roll manufacturing of flexible perovskite solar cells, low temperature processing of all device component must be realized. However, the most commonly used electron transporting layer is based on TiO2 thin films processed at high temperature (>450C). Here, we demonstrate room temperature solution processing of TiOx layer that performs as well as the high temperature TiO2 layer in perovskite solar cells, as evidenced by a champion solar cell efficiency of 16.3%. Using optical spectroscopy, electrical measurements and X-ray diffraction, we show that the room temperature processed TiOx is amorphous with organic residues and yet their optical and electrical properties are on par with the high temperature TiO2. Flexible perovskite solar cells, that employ the room temperature TiOx layer, with power conversion efficiency of 14.3% are demonstrated

A Digital, Constant-Frequency Pulsed Phase-Locked-Loop Instrument for Real-Time, Absolute Ultrasonic Phase Measurements

A digitally controlled instrument for conducting single-frequency and swept-frequency ultrasonic phase measurements has been developed based on a constant-frequency pulsed phase-locked-loop (CFPPLL) design. This instrument uses a pair of direct digital synthesizers to generate an ultrasonically transceived tone-burst and an internal reference wave for phase comparison. Real-time, constant-frequency phase tracking in an interrogated specimen is possible with a resolution of 0.000 38 rad (0.022), and swept-frequency phase measurements can be obtained. Using phase measurements, an absolute thickness in borosilicate glass is presented to show the instruments efficacy, and these results are compared to conventional ultrasonic pulse-echo time-of-flight (ToF) measurements. The newly developed instrument predicted the thickness with a mean error of 0.04 m and a standard deviation of error of 1.35 m. Additionally, the CFPPLL instrument shows a lower measured phase error in the absence of changing temperature and couplant thickness than high-resolution cross-correlation ToF measurements at a similar signal-to-noise ratio. By showing higher accuracy and precision than conventional pulse-echo ToF measurements and lower phase errors than cross-correlation ToF measurements, the new digitally controlled CFPPLL instrument provides high-resolution absolute ultrasonic velocity or path-length measurements in solids or liquids, as well as tracking of material property changes with high sensitivity. The ability to obtain absolute phase measurements allows for many new applications than possible with previous ultrasonic pulsed phase-locked loop instruments. In addition to improved resolution, swept-frequency phase measurements add useful capability in measuring properties of layered structures, such as bonded joints, or materials which exhibit non-linear frequency-dependent behavior, such as dispersive media