It has recently been experimentally demonstrated that reproducible and controllable all-optical magnetization reversal in
GdFeCo films can be achieved with a single ultrafast (from 40fs to 3ps) femtosecond laser pulse. While the microscopic
origin of the effect is still unclear, we suggest that the effect is caused by a combination of light-induced quasi-static
magnetic field, with dynamic thermal effects due to laser heating, as well as magnetic fields generated by thermoelectric
effect-caused electrical currents. This finding reveals great potential for ultrafast data storage through magnetic
switching without the aid of an external magnetic field. It was further recently predicted that utilization of plasmonic
nanostructures may provide the way to achieve fast all-optical magnetization switching with smaller/cheaper laser
sources with longer pulse durations. We will present the simulations of temporal dynamics of magnetization reversal
around plasmonic nanostructures with the combination of Landau Lifshitz Bloch and finite element modeling. Our
modeling results predict that plasmonic nanostructures can significantly alter all-optical magnetization switching process
and may help achieve a number of technologically important effects that cannot be achieved otherwise. Results of
experimental studies of optical magnetization reversal in GdFeCo films around plasmonic nanostructures are also
At present, the light conversion efficiencies achievable with organic photovoltaic (OPV) technology are significantly
below those seen in inorganic materials. The efficiency of OPV devices is limited by material properties; the high energy
and narrow-band absorption of organic semiconductors results in inefficient harvesting of solar radiation, while the low
charge carrier mobility in organic semiconductors limits the possible active layer thickness. Utilization of plasmonic
structures in or around the OPV active layer has been suggested as a way to achieve a higher conversion efficiency in
thin film photovoltaic devices. Our theoretical and experimental results indicate that aluminum-based plasmonic
nanostructures hold significant promise for conversion efficiency enhancement in OPV devices. The high plasma
frequency of aluminum permits a nanoparticle concentration close to the percolation threshold, which results in a
broader band of plasmonically enhanced absorbance in OPV material and better overlap between the natural absorption
bands of OPV materials and the plasmonic band of the metal nanostructure than what is achievable with gold or silver
plasmonic structures. This is demonstrated experimentally by embedding aluminum nanoparticles in P3HT:PCBM
layers, which leads to a significantly enhanced absorption over a broad range of wavelengths. While aluminum
nanoparticles are prone to oxidation, our results also indicate the path to stabilization of these particles via proper surface
Ultrafast all optical magnetization switching in GdFeCo layers on the basis of Inverse Faraday Effect (IFE) was
demonstrated recently and suggested as a possible path toward next generation magnetic data storage medium with much
faster writing time. However, to date, the demonstrations of ultrafast all-optical magnetization switching were performed
with powerful femtosecond lasers, hardly useful for practical applications in data storage and data processing. Here we
show that utilization of IFE enhancement in plasmonic nanostructures enables fast all-optical magnetization switching
with smaller/cheaper laser sources with longer pulse durations. Our modeling results predict significant enhancement of
IFE around all major types of plasmonic nanostructures for a circularly polarized incident light. Unlike the IFE in
uniform bulk materials, nonzero value of IFE is predicted in plasmonic nanostructures even with a linearly polarized
excitation. Experimentally, all-optical magnetization switching at 20 times lower laser fluence and roughly 100 times
lower value of laser fluence/pulse duration ratio is demonstrated in plasmonic samples to verify the model predictions.
The path to achieve higher levels of enhancement experimentally is discussed.
Structural Health Monitoring (SHM) is required for early detection of damage in structural components to improve the
safety, reduce the cost, and increase the performance and efficiency of aircrafts. Currently available techniques have a
number of deficiencies prohibiting wide spread of SHM in aerospace applications. In this contribution we will present
the initial results of development at Luna Innovations of an all-fiber optic ultrasonic airframe SHM system that will be
able to address the deficiencies of solutions suggested/developed to date. In this contribution we will present the details
on design, development and testing of the prototype fiber optic SHM system.
The development of both “soft” and “hard” fabrication techniques for the patterning of nonlinear photonic devices in ionically self-assembled monolayer (ISAM) films is reported. A combination of electron beam lithography and reactive ion etching was used to pattern two-dimensional holes with a lattice of 710 nm and diameters ranging from 550 to 650 nm. A soft alternative to this fabrication was also demonstrated. Nanoimprint lithography was successfully employed to pattern similar photonic structures with average hole diameters of 490 nm and a lattice spacing of 750 nm, as well as Bragg gratings with a period of 620 nm. Potential impact of this fabrication process on the chemical composition and nonlinear properties of the ISAM films was assessed using Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, and second harmonic generation. The spectroscopy techniques confirmed that the chemical composition and bonding of the ISAM films was not adversely affected by the thermal cycles required for nanoimprinting. Second harmonic generation analysis also confirmed that the nanoimprinting process did not affect the nonlinear properties of the material, PCBS/PAH ISAM films, further indicating the suitability of such materials for the nanoimprinting of nonlinear optical photonic structures.
Photovoltaic technology will have a substantial impact on the nation's wealth and economy in 21<sup>st</sup> century. The main
obstacle for widespread use of PV energy at present is the higher cost of PV energy generation equipment compared to
that of fossil fuels. Improved in-line diagnostics can reduce the cost and increase the productivity by significantly
improving the yield of the process. Here we present the first results of development of a high-throughput PV
(Photovoltaic) characterization system, which can provide fast and accurate data on the spatial uniformity of thickness,
refractive indices, and birefringence of the thin films comprising the solar cell in a single scan over the entire solar cell
area. The unmatched throughput, the amount of retrieved information, and the unique capability of characterization of
both plane and structured surfaces and interfaces of such a system will provide the opportunity to use this system and
develop in-situ, real time process diagnostics/prognostics capabilities that would result in improved yield and reduced
cost of solar cell manufacturing. Here we provide the modeling results, demonstrate applicability of the technique for
characterization of organic solar cells and discussing the modifications of the system that would permit characterization
of structured solar cell surfaces.
We report the development of novel porous silicon IR filters. The key component of the filter technology is a porous silicon multilayer obtained by the electrochemical etching of single-crystal silicon wafers. The unique property of such a material is the extremely wide transparency range. It will be shown that the transparency range of porous silicon extends from the visible to the far IR region (up to 100μm and above). Good control over the porosity obtained with the electrochemical fabrication method permits the fabrication of the narrow band-pass, band-pass, long wave pass or band-blocking types of filters with pass bands centered anywhere within the transparency range of the material. Such filters have a number of important advantages over multilayer interference filters. Since the filters are made from a single material (rather than through the deposition of multilayers of dissimilar materials), these filters do not exhibit delamination problems and are well suited for operation at cryogenic temperatures. Further, several hundreds of micrometer thick multilayers can be obtained on 4- or 6-inch diameter wafers in a single process run with high lateral uniformity of the transmission spectrum. Methods of enhancement of the environmental and mechanical stability of these filters have been developed as well. The results of experimental testing of such filters are presented.
We present in this paper the development of novel mid-to-far IR filters that are based on porous silicon structures. The diameters of the pores in such filters are by orders of magnitude less than the central wavelength of the transmission band, leading to effective averaging of the porous structure by the light waves. Such filters have a number of important advantages over multilayer interference filters. Since the filters are made from a single material by means of an electrochemical etching process (rather than through deposition), these filters do not exhibit delamination problems and are well suited for operation at extreme temperatures (for example, in the environment of space). Our fabrication technique permits the fabrication of filters up to 200 mm (8 inches) in diameter, suitable for any wavelength from below 1.1 μm to more than 45 μm. The results of experimental testing of such filters are shown to prove the main predictions.
Currently used optical filters exhibit strong limitations in the deep UV and shorter wavelength ranges. We propose an entirely different type of UV filter to solve many of the problems due to inadequate materials and fabrication techniques. These filters consist of three-dimensionally ordered Macroporous Silicon (MPSi), with the pores used as waveguide cores separated by the reflective silicon host. Ordered pores serve as a two-dimensional array of optical waveguides. Multilayer coating of the pore walls results in the band-pass, short-pass, or band-blocking transmittance spectra of MPSi filters. Such filters have a number of advantages. They do not exhibit spectral shifts of the passed or blocked spectral bands with the angle of incidence, permitting operation in tilted and divergent light beams to simplify optical system design and fabrication. Due to their structures (fewer and thinner layers on the pore walls required to gain the same level of rejection), the filters do not exhibit delamination problems and are well suited for operation at extreme temperatures (for space as well as for terrestrial environments). The fabrication process is different from that used for multilayer interference filters. This process permits the fabrication of filters up to 200mm in diameter that are suitable for wavelengths from longer than 400 nm to shorter than 100 nm. Far-UV filters can be manufactured as simply and economically as the near UV ones. The theory of light propagation through the MPSi layers is developed, the main predictions of the theory are experimentally validated, and the fabrication procedure for MPSi UV filters is reported.
Currently used transmission-type polarizers exhibit strong limitations in the deep UV and shorter wavelength. We propose an entirely different type of polarizer to solve many of the problems caused by the absence of adequate materials in this spectral range. The new polarizers consist of three-dimensionally ordered Macroporous Silicon (MPSi), with the pores used as waveguide cores separated by the reflective silicon host. Ordered pores serve as a two-dimensional array of optical waveguides. Multilayer coating of the pore walls, together with the rectangular shape of the pores (with the length along one axis being several times greater than that of the second axis) results in polarized transmission. Calculations demonstrate potentially very high extinction. In addition, the extinction achieved by such polarization components does not exhibit degradation with the angle of incidence, permitting operation in tilted and divergent light beams to simplify optical system design and fabrication. The fabrication process is different from that used in the fabrication of multilayer interference filters. It permits the fabrication of deep UV polarizers up to 200mm in diameter, suitable for wavelengths from above 600nm to less than 50nm. Far-UV polarizers can be manufactured as simply and economically as the near UV ones. The theory of light propagation through such MPSi layers is developed, the main predictions of the theory are experimentally validated, and the fabrication procedure for MPSi UV polarizers is described.