Laser-induced structural modification in calcium aluminosilicate glasses using molecular dynamic simulations.

Glass structures of multicomponent oxide systems (CaO-Al2O3-SiO2) are studied using a simulated pulsed laser with molecular dynamics. The short- and intermediate-range order structures revealed a direct correlation between the transformation of Al(IV) to Al(V), regions of increased density following laser processing, inherent reduction in the average T-O-T (T = Al, Si) angle, and associated elongation of the T-O bonding distance. Variable laser pulse energies were simulated across calcium aluminosilicate glasses with high silica content (50-80%) to identify densification trends attributed to composition and laser energy. High-intensity pulsed laser effects on fictive temperature and shockwave promotion are discussed in detail for their role in glass densification. Laser-induced structural changes are found to be highly dependent on pulse energy and glass chemistry.

Using phase-corrected Bessel beams to cut glass substrates with a chamfered edge.

Ultrafast laser cutting of a glass substrate at an oblique angle is demonstrated using a phase-corrected Bessel beam. Simulations are used to predetermine the ideal phase of the incident Bessel beam such that an unaberrated Bessel beam is formed inside the tilted substrate. Additional corrections to the beam such as shortening, moving the intensity of the beam within the substrate, and the formation of an elliptical focal spot were necessary to ensure consistent chamfering of the substrate and are discussed herein. Three cuts are combined to create a damage tract in the glass substrate in the shape of a chamfer, and then the glass is separated using a CO2 laser resulting in a chamfered edge.

Design of emitter structures based on resonant perfect absorption for thermophotovoltaic applications.

We report a class of thermophotovoltaic emitter structures built upon planar films that support resonant modes, known as perfectly-absorbing modes, that facilitate an exceptional optical response for selective emission. These planar structures have several key advantages over previously-proposed designs for TPV applications: they are simple to fabricate, are stable across a range of temperatures and conditions, and are capable of achieving some of the highest spectral efficiencies reported of any class of emitter structure. Utilization of these emitters leads to exceptionally high device efficiencies under low operating temperature conditions, which should open new opportunities for waste heat management. We present a theoretical framework for understanding this performance, and show that this framework can be leveraged as a search algorithm for promising candidate structures. In addition to providing an efficient theoretical methodology for identifying high-performance emitter structures, our methodology provides new insight into underlying design principles and should pave way for future design of structures that are simple to fabricate, temperature stable, and possess exceptional optical properties.

Solar thermophotovoltaic system using nanostructures.

This paper presents results on a highly efficient experimental solar thermophotovoltaic (STPV) system using simulated solar energy. An overall power conversion efficiency of 6.2% was recorded under solar simulation. This was matched with a thermodynamic model, and the losses within the system, as well as a path forward to mitigate these losses, have been investigated. The system consists of a planar, tungsten absorbing/emitting structure with an anti-reflection layer coated laser-microtextured absorbing surface and single-layer dielectric coated emitting surface. A GaSb PV cell was used to capture the emitted radiation and convert it into electrical energy. This simple structure is both easy to fabricate and temperature stable, and contains no moving parts or heat exchange fluids.

Optical and infrared properties of glancing angle-deposited nanostructured tungsten films.

Nanotextured tungsten thin films were obtained on a stainless steel (SS) substrate using the glancing-angle-deposition (GLAD) method. It was found that the optical absorption and thermal emittance of the SS substrate can be controlled by varying the parameters used during deposition. Finite-difference time-domain (FDTD) simulations were used to predict the optical absorption and infrared (IR) reflectance spectra of the fabricated samples, and good agreement was found between simulated and measured data. FDTD simulations were also used to predict the effect of changes in the height and periodicity of the nanotextures. These simulations show that good control over the absorption can be achieved by altering the height and periodicity of the nanostructure. These nanostructures were shown to be temperature stable up to 500°C with the addition of a protective HfO2 layer. Applications for this structure are explored, including a promising application for solar thermal energy systems.

Graded-index structures for high-efficiency solar thermophotovoltaic emitting surfaces.

This Letter presents a highly efficient emitter structure for solar thermophotovoltaic systems. The structure consists of a graded index on tungsten, shows a spectral efficiency of 59%, or 70% with the use of a back reflector, and is compared to other state-of-the-art emitter structures. The effects of different structures and periodicities on the efficiency of the emitter are explored, as well as the effect of a protective oxide coating. The causes of the antireflection properties of these structures are also explored.