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Based on the microscale 3D point cloud projection with a digital micromirror device (DMD) and a microlens array (MLA) developed recently, we explore the capabilities of this specific type of 3D projection in 3D lithography with femtosecond light in this study. Unlike 3D point cloud projection with UV continuous light demonstrated before, high accuracy positioning between the DMD and the MLA is required to have rays simultaneously arrive at the designed voxel positions to induce two-photon absorption with femtosecond light. Because of this additional requirement, a new positioning method through direct microscope inspection of the relative positions of the DMD and the MLA is developed in this study. Because of the usage of a rectangular MLA, around four rays can arrive at each projecting voxel at the same time. Thus, to the best of our knowledge, a new algorithm for determining the pixel map on the DMD to the 3D point cloud projection with a femtosecond laser is also developed. It is observed that a very long exposure time is required to generate 3D patterns with the new 3D projection scheme because of the very limited number of rays used for projecting each voxel with the new algorithm. It is also found that 3D structures with desired shapes should be projected far away from the MLA ( ∼ 15 f to 30 f , with f being the focal distance of the MLA) in the 3D lithography with this femtosecond 3D point cloud projection. For patterns projected closer than 10 f , shapes are distorted because of unwanted voxels cured with the 3D projection technique using a DMD and MLA.

By integrating wave-type analysis and fluctuation-dissipation theorem, the enhancement of photon tunneling distance in near field thermal radiation through metallic nanopatterns with/without dielectric structures is theoretically studied. When metallic patterns are in the immediate proximity of the conductive emitter, substantial thermal electric enhancement at surface plasmon frequency is observed between the metallic patterns and the emitter when the periodicity of the thermal electric field along the emitter surface is around integer times of the period of the metallic patterns. The mechanism of field amplification is similar to Fabry–Perot type resonance between two reflecting surfaces. The strong thermal electric field from resonance allows long-distance photon tunneling observed in near field radiation at a ∼5 μm separation distance when the same metallic patterns are placed on the collector surfaces. This value is nearly 50 times longer than that with bared emitter surfaces. This long-distance photon tunneling can also happen at a broader range of parallel wavenumbers (i.e., not determined by the period of the metallic patterns) at the surface plasmon frequency when the periodic metallic patterns' sizes are different each period. However, increasing the range of parallel wavenumbers in long-distance photon tunneling with this approach can reduce the strength of photon tunneling. The reduced tunneling strength can be brought up by attaching high refractive index dielectric resonators on top of the metallic patterns. The dielectric resonators on top of the metallic patterns show additional Mie-type resonance when displacement current is induced at the interface between the metallic patterns and the high refractive index dielectric. The higher intensity long-distance photon tunneling with a broad range of parallel wavenumbers can be valuable in harvesting the high intensity and high quality near field radiative energy with engineering feasible micron level vacuum gaps.

Through years of development, we have successfully demonstrated 3D light field lithography with UV continuous light. We recently combined this approach with femtosecond laser sources as two-photon femtosecond 3D light lithography. It is found that consistent results can happen under limited conditions with this direct combination. Our theoretical analysis reported last year shows that the experimental difficulty can be attributed to digital micro-mirror devices (DMD) and microlens arrays (MLA) used in the current 3D light field projection. Though they can control the propagation directions and interact at designed 3D locations, rays from such a system diverge with respect to the propagation distance. As a result, 3D voxel intensity in the 3D projection changes as a function of the separation distance with respect to the MLA in the 3D projection. To solve this problem, we replace the combination of DMD and MLA with a phase-controlled spatial light modulator. With a lab-developed algorithm, a single femtosecond laser pulse can generate up to a million sub-rays through the phase-controlled spatial light modulator. These sub-rays with a precisely controlled propagation direction can intersect at designed 3D locations as voxels for 3D virtual object constructions. Moreover, these sub-rays have minimum divergence angles to ensure that the voxel intensities are maintained consistently at each 3D location. We also demonstrated that versatile 3D patterns could be generated with two-photon femtosecond 3D light field lithography based on this innovative approach.

With chemical stability under high temperatures, dielectric materials can be idealized thermal emitters for different energy applications. However, dielectric materials do not support surface waves at near-infrared ranges for longer-distance thermal photon tunneling, which limits their applications in near-field thermal radiation. It is demonstrated in this study that thermal field amplification at near-infrared wavelengths at dielectric surfaces could be achieved through asymmetric Fabry–Perot resonance with anti-reflection coatings or 1D photonic crystal type structures. ⩾100 nm near-infrared thermal photon tunneling can be achieved when these thin film structures are added to the emitter and the collector surfaces. Among these two thin film structures, 1D photonic crystal type periodic structures constructed with the same high refractive index material as the emitter/collector material allow near-field thermal photon tunneling at large parallel wavenumbers. Moreover, the field amplification can be increased by adding more 1D photonic crystal layers to achieve even longer distances near field thermal photon tunneling.

An integrated analysis of laser induced breakdown (LIB) and the associated micro-cavitation in a water-like bio-tissue is developed in this study. With this integrated analysis using minimum experimentally fitted parameters, threshold energies of LIB in bio-tissue under different numerical apertures of the focusing lenses can be determined, which provides similar values as the corresponding experimental measurements. The integrated analysis can also determine the electron temperature and number density when LIB is triggered, which also fall in the same order as the corresponding experimental measurements. In addition, the rapid size increment of plasma plume through laser supported detonation wave during a LIB can be observed with the integrated analysis. The developed integrated analysis becomes unstable when strong pressure wave presents due to strong heating and the following rapid expansion of the bio-tissue under higher input laser energy (compared with the threshold energy of LIB). Therefore, for simulating high energy LIB and the following micro-cavitation in a bio-tissue, a more advanced numerical scheme that can better capture the propagation of pressure wave will be required in the future.

Based on the successful single-photon 3D light field photolithography we demonstrated in the last year, we extend the methodology to femtosecond 3D light field lithography. Compared with our previous single-photon work with UV LED light, using femtosecond light and the associated two-photon light absorption in 3D light field lithography can cure photoresist only around designed voxel locations in a 3D space. Such a two-photon scheme can prevent the unwilling curing of photoresists along the optical paths of rays before arriving at designed voxel locations, which is observed in our previous UV LED-based single-photon 3D light field lithography. The experimental scheme of femtosecond two-photon 3D light field lithography starts from delivering uniform femtosecond laser pulses to a spatial light modulator. The designed pixel map is presented on the spatial light modulator and then delivered to a microlens array to construct a 3D virtual image in the free space. By compressing the 3D virtual image in a photoresist layer with a microscope system, we can successfully generate different microscale 3D patterns without relying on scanning processes as in traditional 3D lithography. In this study, we present preliminary results of (a) algorithms developed to generated 3D patterns with femtosecond light, which should satisfy additional constraints when femtosecond light is used, and (b) 3D patterns generated in photoresists with femtosecond two-photon 3D light field lithography.

A simple analytical calculation scheme to determine near field radiation through decomposing an emission domain into lots of thin thermal current sheets is presented. Through finding the orthogonal modes of thermal current of each thin layer, the thin current sheets can be treated as radiation sources of electromagnetic waves with determined analytical solutions. The outgoing electromagnetic waves from each thin current sheets can be either in transverse electric (TE) or transverse magnetic (TM) modes depending on the orientations of the current in the thin current sheets with respect to the directions of amplitude modulations of the orthogonal modes. Electromagnetic waves arriving to a collection domain are related to the electromagnetic waves leaving from each thin current thermal sheet with transfer coefficients. Transfer coefficient for TE and TM waves can be determined analytically with transfer matrix method or scattering matrix methods. Compared with existing dyadic Green's function method, the new calculation scheme allows material and temperature variations along one direction of the emission domain based on determined analytical expressions of TE and TM waves leaving from each thin current sheets. The simple calculation scheme is especially useful in near field radiation of layered structures with different material such as hyperbolic material with negative refractive indices. With this new approach, we recovered analytical solutions of near field radiation between two semi-infinite domains with uniform temperature and derived closed form solution of near field radiation between two semi-infinite domains with temperature profiles with/without laminated structures.

3D light field camera has been provided as a valid method to capture 3D surface topography with a microlens array. Through inverting the propagation direction, 3D virtual image projection can also be achieved with conventional optics and a microlens array. By compressing the 3D virtual image from the microlens array with an additional lens, microscale 3D virtual image can be achieved. We propose that microscale 3D virtual image can be valuable in microscale 3D fabrication. In this study, we provide a theoretical basis to combine femtosecond laser with the above mentioned 3D virtual image reconstruction scheme to cure photopolymers. With multiphoton effects induced by femtosecond laser, we expect 3D patterning of regions inside the photopolymer can be possible. Compared with the demonstration of 3D patterning with continuous near UV light and the proposed 3D light field projection scheme, curing of photopolymer can be limited to focal points (i.e., voxel) of the projected microscale 3D surface with two photon absorption effect when femtosecond light with high enough intensity is applied. The required femtosecond light intensity is also determined in this study. We expect this new 3D photolithography method can be valuable in fast and high precision patterning of micro to macro structures in materials that are photoactive.

An integrated analysis considering radiative energy transport among each component and carrier generation in the photovoltaic (PV) material is established for solar thermophotovoltaic (STPV) devices. STPV has been estimated with previous thermodynamics analysis to provide up to ∼85% solar energy conversion efficiency (ECE) because of its capability to convert broadband solar radiation to narrowband thermal radiation that can be fully used with PV materials. However, in previous demonstrations, the ECE of STPVs is less than 10%, even with ∼200 solar radiation concentrations. Based on our analysis, the maximum ECE of STPV without any radiation heat loss control is nearly zero when the solar concentration ratio is 1 and is ∼18.78% when the solar concentration ratio is 1000. Maximum ECE of STPV with spectral selected absorber optimized for 1000 K level temperature, which has been proposed in recent STPV studies, can be ∼9.56% when the solar concentration is 1 and can be ∼31.72% when the solar concentration ratio is 1000. Maximum ECE of STPV with our proposed multi-layered radiation shield to prevent radiative heat loss from the STPV to the ambient can provide ECE up to ∼9.53% and ∼57.02%, when the solar concentration ratio is 1 and 1000, respectively. When we combine both the spectral selected absorber and our designed radiation shield, the ECE value of STPV can be up to ∼20.65% and ∼59.23% when the solar concentration ratio is 1 and 1000, respectively. It is also observed that a ∼1 µm level bandwidth of photonic crystal (PhC), a device that can control the emission bandwidth, is required for STPV to achieve high ECE under each solar concentration ratio with difference radiative heat loss control.

A Tayler series expansion based high accuracy meshfree method (TS-HAMM) is developed to calculate first and second derivatives of property values stored in dispersed particle clouds. Compared with other meshfree methods such as smoothed particle hydrodynamics (SPH), TS-HAMM can (a) systematically increase accuracies in gradient, derivative and Laplacian calculations with similar computational cost; (b) provide boundary conditions directly from conservation equations at the fluid/solid interfaces with guaranteed order of accuracy; (c) simulate fluid dynamics and heat transfer of low viscous weakly compressible fluid (e.g. water) directly without making incompressible assumptions. Through numerical verifications with water-like low viscous low compressible fluid in Couette flow, lid-driven flow inside a cavity, and natural convection inside an enclosure, we justify the validity of TS-HAMM in simulating fluid dynamics and heat transfer of water-like low viscous weakly compressible fluid, which are challenging with other meshfree methods such as smoothed particle hydrodynamics (SPH).

A three-dimensional (3D) system is developed with a microlens array (MLA) and a digital micromirror device (DMD) type spatial light modulator (SLM) to perform light field projection. In order to get 3D projections, a pixel value map, i.e. elemental images, is required to be loaded into SLM. Algorithm to render elemental images is developed in this study using ray tracing. The reconstructed 3D projection, which is the 3D output of the system, is examined by cameras at different focal positions. The result shows that the intended projection patterns are correctly reconstructed. The light field projection method can be extended to photolithography when photoresist is exposed to reveal the 3D structures of the intended projection. Compared with current 3D lithography, the proposed MLA based projection/lithography can reconstruct micro-structure with 3D curved structures in a single projection, which can significantly improve the 3D fabrication speed and quality. With the future implementation of optical compression and femtosecond laser, the proposed technique has the capability of conduct large area microfabrication with resolutions better than diffraction limit at a very high speed.

A high numerical aperture (NA) scanning digital oil immersion lithography scheme is proposed and demonstrated in this study. To successfully conduct the scanning digital oil immersion lithography, immersion oil should be removed from the photoresist layer before the development process. Also, uniformity of the projected light patterns becomes crucial in the quality of this high NA photolithography. To solve these issues, we developed a cleaning procedure for the immersion oil and an intensity calibration scheme to achieve a highly uniform intensity distribution of the projected patterns. With these preparations, we were able to achieve 400 nm resolution large area patterning with the developed scanning digital oil immersion lithography system and a better than 200 nm resolution in the single line patterning. Also, with a double layered photoresist scheme and our lab-prepared photoresist, we successfully achieved large area lift-off patterns of 400 nm metallic dot arrays through the scanning digital oil immersion lithography system.

A methodology of 3D photolithography through light field projections with a microlens array (MLA) is proposed and demonstrated. With the MLA, light from a spatial light modulator (SLM) can be delivered to arbitrary positions, i.e., voxels, in a 3D space with a focusing scheme we developed. A mapping function between the voxel locations and the SLM pixel locations can be one-to-one determined by ray tracing. Based on a correct mapping function, computer-designed 3D virtual objects can be reconstructed in a 3D space through a SLM and a MLA. The projected 3D virtual object can then be optically compressed and delivered to a photoresist layer for 3D photolithography. With appropriate near-UV light, 3D microstructures can be constructed at different depths inside the photoresist layer. This 3D photolithography method can be useful in high-speed 3D patterning at arbitrary positions. We expect high-precision 3D patterning can also be achieved when a femtosecond light source and the associated multi-photon curing process is adopted in the proposed light field 3D projection/photolithography scheme. Multi-photon polymerization can prevent the unwilling patterning of regions along the optical path before arriving to the designed focal voxels as observed in our single photon demonstrations.

With high spatial but low temporal coherent nanosecond (ns) green light, ns pulsed illumination phase-contrast microscopy is successfully constructed. The pulsed illumination phase-contrast microscopy can provide ns time resolution to resolve transient dynamics of transparent targets with high contrast ratio that cannot be achieved with traditional bright-field or phase-contrast microscopies. Transient dynamics of laser-induced microcavitation is successfully recorded with this imaging technique to demonstrate its capabilities. In addition to tracing the evolutions of vapor bubbles and shockwaves during a laser-induced microcavitation, this imaging technique can sense the refractive index change of the transparent target during a pressure field variation.

A two-wavelength thermoreflectance (2WTR) imaging technique is developed to conduct steady-state temperature measurement of miniature electronic devices, such as micro-scale gold resistors. Compared with traditional single wavelength thermoreflectance (TR) imaging requiring comparison of TR signals from a target under heated and unheated conditions, 2WTR method obtains temperature information from heated target under operation directly. Therefore, 2WTR is not affected by movement of a heated target due to thermal expansion. Note that thermal expansion of targets between heated and unheated conditions is a main constraint of current TR imaging of miniature targets. In addition to the low sensitivity to the target movement, the new 2WTR can provide even higher temperature resolution than single wavelength TR by appropriately selecting the adopted two wavelength to have different signs of TR coefficients. With this new TR imaging technique, we successfully measure temperature distribution of a microscale gold resistor under steady-state operation, which are challenging to be obtained by traditional single wavelength TR method.

3D thermoreflectance (TR) imaging utilizing light field camera is proposed and developed in this study. With the capability of resolving light direction and intensity simultaneously, we are able to measure directional TR signal from tilted or curved surfaces through the light field camera. Once the directional TR coefficients of the target surface is collected, we can then estimate the temperature distributions of tilted or curved surfaces based on the measured directional TR signal. This new 3D TR imaging approach has the potential to measure temperature of surfaces with different configurations as long as the TR signal is strong enough. In this technical paper, we first present basic principles of 3D TR imaging techniques based on light field theory. The construction and calibration procedures of the resulting 3D TR imaging system are then presented. At the end of the technical paper we present steady-state surface temperature measurements of microscale electronic devices including an infrared laser diode and a gold wire with the current 3D TR imaging system. The obtained temperature distributions of the microscale samples showing high temperature and spatial resolutions in real-time temperature measurement on the 3D surfaces that cannot be achieved with traditional 2D TR imaging techniques.

Laser-induced microcavitation refers to the rapid formation and expansion of a vapor bubble inside the bio-tissue when it is exposed to intense, pulsed laser energy. With the associated microscale dissection occurring within the tissue, laserinduced microcavitation is a common approach for high precision bio-surgeries. For example, laser-induced microcavitation is used for laser in-situ keratomileusis (LASIK) to precisely reshape the midstromal corneal tissue through excimer laser beam. Multiple efforts over the last several years have observed unique characteristics of microcavitions in biotissues. For example, it was found that the threshold energy for microcavitation can be significantly reduced when the size of the biostructure is increased. Also, it was found that the dynamics of microcavitation are significantly affected by the elastic modules of the bio-tissue. However, these efforts have not focused on the early events during microcavitation development. In this study, a direct numerical simulation of the microcavitation process based on equation of state of the biotissue was established. With the direct numerical simulation, we were able to reproduce the dynamics of microcavitation in water-rich bio tissues. Additionally, an experimental setup in deionized water and 10% PAA gel was made to verify the results of the simulation for early micro-cavitation formation for 10% Polyacrylamide (PAA) gel in deionized water.

A numerical analysis capable of describing the early stage of a thermal microcavitation process in a water-rich biotissue without avalanche breakdown was developed. The analysis successfully reproduced the laser-induced heating, vapor bubble formation, bubble expansion, and shockwave propagation inside a water-rich biotissue during a thermal microcavitation process. Based on the analysis, it was determined that the evolution of the temperature, pressure, and laser-induced shockwave is dependent on the incident laser energy and laser pulse width. On the other hand, the early stage dynamics of the microcavitation process showed little dependence on the elastic modulus of the biotissue for the laser and tissue conditions studied.

A methodology of thermoreflectance (TR) imaging using two different optical wavelengths for nonintrusive surface temperature measurement is developed. Compared with the existing single wavelength TR imaging, two-wavelength thermoreflectance (2WTR) imaging collects the required TR signals for temperature measurement solely from the heated target. Therefore, target movement between heated and unheated conditions due to thermal expansion, which is a main obstacle for current single wavelength TR imaging, is properly handled. As a result, a steady state temperature distribution of a heated target can now be determined by the 2WTR imaging method, which is especially useful in determining the operating temperature of microelectronic devices which are sensitive to physical contacts during a measurement. With the 2WTR method, the surface temperature of a microscale gold resistor under different input currents is measured and compared with the results from the corresponding single wavelength TR and heat transfer simulations. The experimental results indicate that 2WTR not only provides temperature measurement with no nonphysical temperature values caused by the target movement, but also has potential for providing a higher signal-to-noise ratio than single wavelength TR when a high bit-depth spatial light modulator and the two optical wavelengths adopted are appropriately selected.

A scanning digital lithography system using computer controlled digital spatial light modulator, spatial filter, infinity correct optical microscope and high precision translation stage is proposed and examined. Through utilizing the spatial filter to limit orders of diffraction modes for light delivered from the spatial light modulator, we are able to achieve diffraction limited deep submicron spatial resolution with the scanning digital lithography system by using standard one inch level optical components with reasonable prices. Raster scanning of this scanning digital lithography system using a high speed high precision x-y translation stage and piezo mount to real time adjust the focal position of objective lens allows us to achieve large area sub-micron resolved patterning with high speed (compared with e-beam lithography). It is determined in this study that to achieve high quality stitching of lithography patterns with raster scanning, a high-resolution rotation stage will be required to ensure the x and y directions of the projected pattern are in the same x and y translation directions of the nanometer precision x-y translation stage.

The structure and evolution of the laser-induced vapor plume and shockwave were measured from femtosecond time resolved shadowgraph images. By changing the wavelength of the probe beam (400 and 800 nm), differences in the opacity of the vapor plume were measured as a function of delay time from the ablation laser pulse. The evolution of the temperature and electron number density during and after the ablation laser pulse were determined and compared for ablation in argon and helium background gases. A laser supported detonation wave (LSD) observed for ablation in argon, blocks the incoming laser energy and generates a high-pressure region above the vapor plume.

To study the expansion and cooling process of the laser induced plasma generated by nanosecond pulsed laser ablation, experiments have been conducted which measure the position of the external shockwaves and the temperature of the vapor plumes. The positions of external shockwaves were determined by a femtosecond laser time-resolved imaging system. Vapor plume temperature was determined from spectroscopic measurements of the plasma emission lines. A model which considers the mass, momentum, and energy conservation of the region affected by the laser energy was developed. It shows good agreement to the experimental data.

A systematic measurement of plasma properties (temperature, electron number density, pressure) was performed during LIBS of silicon with two nanosecond pulsed lasers operating at 1064 nm. The spectral characteristics of the plasmas were measured to determine the plasma properties as delay time between the laser pulses was changed from 0 to 10 ms. The plasma properties and crater dimensions increased abruptly from 100 to 200 ns. The crater depth increased from 2 to 10 μm (volume increased about 5 times) per pair of double pulses. Enhanced mass removal was indicative of a phase explosion mechanism. Spatial images of plasma emission were measured to study the dynamics of plasma expansion.

Propagation of the shock wave generated during pulsed laser ablation in cavities was measured using laser shadowgraph imaging and compared with laser ablation on a flat surface. The cavities were fabricated in fused silica with the same diameter and variable depths to provide aspect ratios (depth/diameter) of 3 and 6. It was found that outside the cavity, after ~30 ns the radius of the expanding shock wave was proportional to t2/5, corresponding to a spherical blast wave as predicted by the Sedov–Taylor solution. The calculated pressures and temperatures of the shocked air outside of the cavities were higher than on the flat surface. The incident energy driving the shock wave outside the cavity was smaller than that on the flat surface; the greater the cavity aspect ratio, the smaller the energy supporting the shock wave. Plasma–wall interactions are discussed to explain the sharp decrease of the energy driving the shock wave outside the cavity.

The flow passing a single sphere moving in a micro–tube is investigated theoretically. Two cases are studied. Case I is for a single sphere moving along the centreline, while case II is for a single sphere moving parallel to the centreline of a micro–tube. The range of Knudsen numbers to be studied lies between 0.01 and 0.1 so that the Navier–Stokes equations with slip boundary conditions are the appropriate system to be analysed. The stream–function method is used to obtain analytic solutions for case I, while the reflection method is used for case II. The effects due to the slip boundary conditions on the flow field, resultant force on the sphere, pressure drop over the sphere, terminal velocity of the sphere, etc., are calculated and discussed.

Light scattering from nonspherically symmetric pure dielectric structures is examined. From the finite element full-wave analysis, it is found that teardrop-shaped scatterers can focus visible light to a ∼10 nm spot with an intensity enhancement ∼10(5) when the incident light is radially polarized.

Laser induced breakdown spectroscopy (LIBS) is an effective technique for real-time chemical analysis of samples in the laboratory and in the field. The performance of LIBS can be significantly improved by replacing the conventional LIBS configuration from single pulse laser to double pulse laser ablation. Corsi et al. showed that by firing two lasers with microsecond order delay can increase LIBS sensitivity [M. Corsi, G. Cristoforetti, M. Giuffrida, M. Hidalgo, S. Legnaioli, V. Palleschi, A. Salvetti, E. Tognoni, C. Vallebona, Three-dimensional analysis of laser induced plasmas in single and double pulse configuration, Spectrochimica Acta, Part B 59 (2004) 723–735] [1] . By studying plume evolution, they attribute this enhancement to the faster plume expansion in double pulse laser ablation. Blast wave theory was used in Corsi's paper to explain the higher expansion speed observed in double pulse laser ablation. However, it is questionable whether the blast wave theorem applies in laser ablation where the shockwave is driven by a vapor plume of mass. We introduce an alternative way to explain the faster plume expansion during double pulse laser through a more general thermodynamic relation.

To achieve precise nano-droplet ejection, the existing microscale inkjet module could be scaled down to nanoscale, including both the fluidic channel and the pressure driver. While 2D/3D nanoscale fluidic channels are currently available, a nanoscale pressure driver providing high enough power intensity to overcome surface tension for nano-droplet ejection is still lacking. In this study, laser induced nanoscale confined heating with nano-nozzles are constructed and demonstrated as a simple and robust approach to achieve the required pressure driver. For the heating with continuous laser, micro spray composed with nano-droplets can be induced from the nano-nozzles. For the heating with nanosecond laser of adequate pulse energy, drop-on-demand ejection of droplets with similar diameter as the apertures of the nano-nozzle can be achieved.Copyright © 2012 by ASME

A methodology is proposed, which is capable of determining the near field thermal radiation based on the Wiener chaos expansion. The approach has no explicit constraints on the geometry and temperature distributions of the system and can be easily included with classical electrodynamics simulations. A specific application is made for the near field thermal radiation between two plates and the results are in very good agreement with the classical solutions obtained from Green’s function method. Also, by comparing the resulting solutions with the solutions from Green’s function method, a new point of view for interpreting the results for the near field thermal radiation in terms of a chaos expansion is provided.

Micro Fresnel zone plate has showed a potential in the recent few years for precise nanoscale detection and fabrication. In this study, nano-patterns have been generated on photoresist and copper films through coupling a micro Fresnel zone plate with pulsed light sources. To understand the near field and far field optical energy transport from the zone plate to the target along with the resulting thermal energy transport, a series of experimental measurement of the size and shape of nano-patterns generated on targets under different experimental conditions was conducted. In addition, a theoretical optical analysis for the light focusing in the near field range to the target along with the heating process of the target is established.

Nano-patterns are generated on semiconducting and metallic surfaces through coupling an apertured near field scanning optical microscope (NSOM) with a pulsed laser source in this study. To understand the dominant mechanisms for the generation of the nano-patterns, a series of experimental measurement of the size and shape of nano-patterns generated on targets under different experimental conditions with different targets is conducted. The characteristic dimensions of nano-patterns show dependence on optical properties of the target material. The qualitative trend of the variation of nano-patterns as a function of laser and material conditions indicates that the dominant mechanisms for the generation of nano-patterns through a combination of nanosecond laser and an apertured NSOM under different conditions studied is near field laser-material interaction.Copyright © 2009 by ASME

Different nano-patterns have been generated with the same near field scanning optical microscope (NSOM) tips with multiple femtosecond laser pulses in different background gases. It is demonstrated that significant energy was transferred from the NSOM probe to a pure silicon surface for the generation of nano-protrusions and nano-craters, which shows the possibility of nano-fabrication with the present experimental configuration. In order to understand the heating effect of the target and the relationship between the generations of nano-craters, a corresponding theoretical analysis considering the wave format light propagation within a single tapering NSOM probe (first order approximation) and the subsequent light absorption in a target is established. This analysis show that electron temperature of around the nano-scale laser spot of target can be very high (>∼10,000 K) during the laser pulse. However, both the photoexcited electron number density and lattice temperature are much less the threshold for a thermal and non-thermal evaporation. Therefore, supplementary mechanisms in additional to pure pulsed light absorption are required for generation of nano-craters on a target if a single tapering angle NSOM probe is applied.Copyright © 2008 by ASME

Pulsed laser ablation (266 nm) was used to generate metal particles of Zn and Al alloys using femtosecond (150 fs) and nanosecond (4 ns) laser pulses with identical fluences of 50 J cm−2. Characterization of particles and correlation with inductively coupled plasma mass spectrometer (ICP–MS) performance was investigated. Particles produced by nanosecond laser ablation were mainly primary particles with irregular shape and hard agglomerates (without internal voids). Particles produced by femtosecond laser ablation consisted of spherical primary particles and soft agglomerates formed from numerous small particles. Examination of the craters by white light interferometric microscopy showed that there is a rim of material surrounding the craters formed after nanosecond laser ablation. The determination of the crater volume by white light interferometric microscopy, considering the rim of material surrounding ablation craters, revealed that the volume ratio (fs/ns) of the craters on the selected samples was approximately 9 (Zn), 7 (NIST627 alloy) and 5 (NIST1711 alloy) times more ablated mass with femtosecond pulsed ablation compared to nanosecond pulsed ablation. In addition, an increase of Al concentration from 0 to 5% in Zn base alloys caused a large increase in the diameter of the particles, up to 65% while using nanosecond laser pulses. When the ablated particles were carried in argon into an ICP–MS, the Zn and Al signals intensities were greater by factors of ∼50 and ∼12 for fs versus ns ablation. Femtosecond pulsed ablation also reduced temporal fluctuations in the 66Zn transient signal by a factor of 10 compared to nanosecond laser pulses.

A study was made of the cooling of the laser induced vapor plume in background air. The temperature and size variations of the vapor plume were determined from spectroscopic measurements during the first few tens of microseconds after the laser pulse. Experiments were carried out over a range of laser spot sizes and energies. The energy transport by thermal radiation from the vapor plume to the background air and to the test sample was formulated. Spectral line by line calculations were made by (a) calculating the detailed line emission profiles (valid for all optical depths), as well as by (b) dividing the lines into being either optically thin or optically thick. The calculations agreed with one another and with the experimental results for the decreasing vapor plume temperature. It was also shown that for optically thin conditions, which are often valid for small vapor plumes, the variation of the surface reflectivity of the test sample had very little effect on the cooling process. For optically thin conditions, the temperature decrease of the vapor plume was independent of the plume size, shape, and position. For larger optical thicknesses of the vapor plume, the calculations showed that the reflectivity of the sample surface and the size of the vapor plume would dramatically affect cooling of the vapor plume.

Based on full wave simulations, ∼0.3 λ and ∼0.24 λ imaging resolutions can be achieved for incoherent transverse and longitudinal point dipoles, respectively, when the dipoles are on an aluminum oxide base with a fused silica microsphere as the imaging lens. These high spatial resolutions (better than 0.5 λ) can be attributed to almost 90° light acceptance angle of the microsphere and the solid immersion effects from the microsphere/base material. These simulation results can explain the ≳0.3 λ and ≳0.24 λ minimum resolvable center to center separation distance for thin metallic nanostructures and elongated metallic nanostructures, respectively, which is equal to ≳0.1–0.14 λ edge to edge distance observed in previous microsphere imaging experiments.

Time resolved thermoreflectance imaging with a nanosecond laser is applied to study the transient thermal response of near field scanning optical microscope (NSOM) probes driven by either microsecond (μs) or nanosecond (ns) laser pulses. It is found that when the laser energies are the same, μs and ns laser pulses show similar trend of close to adiabatic heating during the laser pulse and close to conductive cooling after the laser pulse. The peak temperature is almost linear with respect to input laser energy for the energy selected. The peak temperature of the NSOM probe is increased when the aperture size of the probe is smaller and when the incident laser wavelength is shorter. However, compared with μs laser pulses, small physical damages appear around the NSOM aperture, which gradually decreases the optical-thermal energy conversion efficiency in the NSOM probe when ns laser pulses are applied.

A new methodology for generating core–shell micro/nanoparticle (CSPs) based on laser ablation in liquid is developed. This new method showed no observable restriction for generating core and shell materials of different combinations. However, to form a high-quality shell with the new method, the adhesion energy between the core and the shell material should be as high as possible. The obtained thickness and smoothness of the shell are also affected by amount of ablation time and the applied laser energy. Based on the test, smoother (i.e. with less condensed island growth) and thicker shell can be achieved with longer ablation time and lower ablation energy. The developed new methodology can be directly extended to the generation of multiple layered core–shell micro/nanoparticles with different configurations through introducing more ablation targets in the liquid.

A fabrication method based on negative tone lift off EBL is developed for constructing nano-structures at end faces of multimode optical fibers. With this new approach, precise and robust nano-structures with high spatial resolutions can be fabricated with minimum damage to the optical fiber face during the fabrication process. Based on this approach, high numerical aperture micro Fresnel zone plates (MZP) with focal lengths ?3??m were fabricated on the face of an optical fiber. The focusing characteristics of the fabricated MZP showed good consistency with the numerical simulations at the specified wavelength (?405?nm).

Long distance guidance and focusing of infrared (IR) nanosecond-pulsed laser light in a hollow plasma channel formed with femtosecond pulsed laser plasma filaments is examined with numerical experiments. Numerical models show that a thick hollow plasma channel can provide low loss long distance (>100 m) guidance of the IR nanosecond-pulsed laser beam. The effectiveness of guidance is determined by the electron number density, thickness of the plasma filament shell and the size of the inner radius of the hollow plasma channel. The hollow plasma channel can be thought of as an open-space optical fibre. The required thickness of the plasma channel with specified electron number density and the inner radius can be estimated with modal analysis, similar to that used for optical fibres. In addition, with a small tapering angle in the hollow plasma channel, the guided light can be moderately focused during long distance propagation. Owing to the rapid decay of electron number density of a plasma channel in free space, the delay time between the generation of the plasma channel and the guided light along with the duration of the guided light are better to be maintained within a few nanoseconds.