Study of propagation and detection methods of terahertz radiation for spectroscopy and imaging

The applications of terahertz (THz, 1 THz is 1012 cycles per second or 300 pm in wavelength) radiation are rapidly expanding. In particular, THz imaging is emerging as a powerful technique to spatially map a wide variety of objects with spectral features which are present for many materials in THz region. Objects buried within dielectric structures can also be imaged due to the transparency of most dielectrics in this regime. Unfortunately, the image quality in such applications is inherently influenced by the scattering introduced by the sample inhomogeneities and by the presence of barriers that reduces both the transmitted power and the spatial resolution in particular frequency components. For continued development in THz radiation imaging, a comprehensive understanding of the role of these factors on THz radiation propagation and detection is vital. This dissertation focuses on the various aspects like scattering, attenuation, frequency filtering and waveguide propagation of THz radiation and its subsequent application to a stand-off THz interferometric imager under development. Using THz Time Domain spectroscopic set-up, the effect of scattering, guided THz propagation with loss and dispersion profile of hollow-core waveguides and various filtering structures are investigated. Interferometric detection scheme and subsequent agent identification is studied in detail using extensive simulation and modeling of various imaging system parameters

Synthesis Technique of Thickness-Customizable Multilayered Frequency Selective Surface for Plasma-Based Electromagnetic Structures

This dissertation provides a synthesis technique for the design of thickness-customizable high-order (N ≥ 2) bandpass frequency selective surface (FSS) and its application in realizing versatile multi-layered FSS and absorbers. Admittance inverters layers are used to synthesize the transfer response of the filter given desired characteristics such as filter type, center frequency, and bandwidth. These inverter layers are essentially electromagnetic coupling interlayers that can be adjusted to customize the thickness of multilayered FSS without degrading the desired filter performance. A generalized equivalent circuit model is used to provide physical insights of the proposed design. This synthesis technique is adopted to deliver a versatile implementation capability of high-order FSS filters using various dielectric spacers with arbitrary thicknesses. Such technique enables the realization of spatial filters with variable size, while maintaining the desired filter response. To highlight the significance of the proposed synthesis technique, its concept is applied to two practical problems including the design of compact switchable FSS and adaptive/tunable microwave absorbers as it may allow simpler integration of active components that require specific physical dimensions. In the first practical problem, the feasibility of deploying plasma switchable compact spatial filter in harsh electromagnetic radiation environments is investigated. The proposed FSS integrates contained plasma (plasma-shells) as active tuning elements. These ceramic, gas-encapsulating shells are ideal for high-power microwave and electromagnetic pulse protection because they are rugged, hermetic, operable at extreme temperatures, and insensitive to ionizing radiation. A 2D periodic second-order switchable spatial filter is implemented. It is composed of electrically small Jerusalem cross structures embedded with discrete plasma shells strategically located to effectively switch the transfer function of the filter. This technique is used to realize compact low profile second order band pass spatial filter operating at S-band. It also has the ability to switch its transfer function within 20 to 100 ns while enabling in-band shielding protection for aerospace or terrestrial electromagnetic systems subjected to high power microwave energy (HPME) and high electromagnetic pulse (HEMP) in harsh space environment. Experimental results are shown to be in good agreement with simulation results. The second practical problem is addressed by deploying a large-scale adaptable compressed Jaumann absorber for harsh and dynamic electromagnetic environments. The multilayered conductor-backed absorbers are realized by integrating ceramic gas-encapsulating shells and a closely coupled resonant layer that also serves as a biasing electrode to sustain the plasma. These active frequency selective absorbers are analyzed using a transmission line approach to provide the working principle and its frequency tuning capability. By varying the voltage of the sustainer, the plasma can be modeled as a lossy, variable, frequency-power-dependent inductor, providing a dynamic tuning response of the absorption spectral band. To study the power handling capability of the tunable absorber, dielectric and air breakdowns within the device are numerically emulated using electromagnetic simulation by quantifying the maximum field enhancement factor (MFEF). Furthermore, a comprehensive thermal analysis using a simulation method that couples electromagnetics and heat transfer is performed for the absorber under high power continuous microwave excitations. The maximum power level handling capability of the microwave absorber has been numerically predicted and validated experimentally

Light manipulation in multilayered photonic structures

L'abstract è presente nell'allegato / the abstract is in the attachmen

Nanophotonic Structures: Fundamentals and Applications in Narrowband Transmission Color Filtering

The optical properties of materials can be manipulated by structures roughly the size of the wavelength of light of interest. For visible wavelengths, many different types of structures sized on the order of 10s-100s of nanometers have been used to engineer materials to produce a targeted optical response. Multilayer stacks of nanoscale metal and dielectric films are a widely explored geometry that has been used to make composite materials with effective optical properties that vary significantly from their constituent films. In this thesis, carefully designed multilayer stacks were used to induce artificial magnetism in non-magnetic materials, opening new directions for tailoring wave propagation in optical media. By perforating these multilayer structures with an array of sub-wavelength slits, these nanophotonic structures were shown to be able to function as narrowband transmission color filters. Using numerical optimization methods, these narrowband filterswere further refined and simplified to only require a single thin film sandwiched between two mirrors to achieve this high resolution spectral filtering. Novel methods were used to fabricate these ultracompact narrowband transmission color filters, which were shown to possess extremely narrow transmission resonances that can be controllably pushed across the visible and near IR parts of the spectrum. These mirrored color filters have footprints as small as 400 nm, well below the size of state-of-the-art CMOS pixels, inviting the possibility for integrating multi- and hyperspectral imaging capabilities into small portable electronic devices.</p

Linear and nonlinear optical properties of metal-dielectric multilayer structures

The object of the present research is to design and fabricate metal-dielectric thin film multilayer structures that make use of the nonlinear optical (NLO) response of Ag for efficient nonlinear absorption for sensor protection. These structures employ structural resonances to overcome the challenges of reflection and absorption that limit access to this large NLO response. The research consists of three parts: first, we present a comprehensive analysis of the contributions to the nonlinear optical response of Ag. Second, we present a systematic investigation of the linear optical properties of Metal-Dielectric Photonic Band-Gap (MDPBG) structures, including optimization of the structure for a particular transmittance spectrum. Third, we study the linear and nonlinear optical properties of Induced Transmission Filters (ITFs). Each of these parts includes experimental results backed by modeling and simulation.Ph.D.Committee Chair: Bernard Kippelen; Committee Member: David Citrin; Committee Member: Farrokh Ayazi; Committee Member: Gee-Kung Chang; Committee Member: Ken Sandhag

Photosensitive Materials: Optical properties and applications

Les matériaux photosensibles sont des matériaux (organique ou inorganique) dont l’indice de réfraction peut être localement modifié lorsqu’ils sont soumis à une excitation lumineuse dont une partie de l’énergie est absorbée par ce matériau. La majorité des travaux réalisés dans ce domaine a longtemps concerné des applications d’optique guidée (fibre ou guides planaires). L’apparition récente de nouveaux matériaux a rendu possible l’utilisation de ce phénomène de photosensibilité dans des composants optiques massifs en permettant notamment la réalisation d'hologrammes de volume à hautes performances. Dans le cadre de ces travaux, un verre inorganique a fait l’objet d’études approfondies : il s’agit d’un verre photo-thermo-réfractif (PTR), pour lequel la variation d’indice est obtenue par exposition à un rayonnement ionisant suivie d’un traitement thermique. La nature même du matériau lui procure des propriétés compatibles avec les contraintes des applications lasers à haute énergie.La première partie de ce manuscrit présente donc l’ensemble des travaux qui ont été réalisés sous ma responsabilité dans le but de mettre en évidence l’inter-relation qui existe entre les propriétés optiques (photosensibilité, absorption, diffusion, interaction laser-matière, propriétés spectrales) et les propriétés structurales de ces verres. La deuxième partie de ce manuscrit présente différentes applications de ces verres d’un point de vue composants, que ce soit pour du filtrage à bande très étroite, la fabrication de masques de phase volumiques, l’étirement ou la compression d’impulsions ultra-courtes ou le développement de nouveaux designs de sources lasers. Enfin, la troisième partie de ce manuscrit présente l’ensemble des réalisations dans lesquelles j’ai été impliqué durant ces 10 dernières années, que ce soit en termes de production scientifique, de management de projets ou d’encadrement de recherches

Light scattering and roughness properties of optical components for 13.5 nm

Die stetige Reduzierung der Belichtungswellenlängen in der optischen Lithographie, motiviert durch die Herstellung immer kleinerer Halbleiterbauelemente, zieht enorme Herausforderungen an optische Komponenten nach sich. Insbesondere Streulicht an optischen Oberflächen stellt durch die starke Wellenlängenabhängigkeit gegenüber Oberflächenimperfektionen (~1/λ4) einen kritischen Faktor dar. Das Ziel dieser Arbeit besteht daher in der Untersuchung der Rauheits- und Streulichteigenschaften von Mo/Si Mehrschichtsystemen für die nächste geplante Lithographiewellenlänge 13,5 nm. Neben der Charakterisierung und Klassifizierung der wesentlichen Streulichtmechanismen wurden neue Lösungsstrategien erarbeitet, um Streulicht von Mehrschichtsystemen gezielt zu minimieren. Darüber hinaus wurde ein neuartiges Messverfahren entwickelt, welches basierend auf winkelaufgelösten Streulichtmessungen eine flächendeckende Charakterisierung der Oberflächenrauheit großer und komplex geformter EUV-Substrate ermöglicht. Somit können die Grenzen klassischer, hochauflösender Rauheitsmessverfahren, wie der Rasterkraftmikroskopie, überwunden werden, die aufgrund ihrer langen Messzeiten in der Regel nur für stichprobenartige Messungen geeignet sind. Im Zusammenspiel mit der Modellierung der Streulichteigenschaften des Mehrschichtsystems können so schon vor der Beschichtung Aussagen über den späteren EUV-Reflexionsgrad getroffen werden. Dadurch wird bereits früh im gesamten Herstellungsprozess eine zielgerichtete Optimierung möglich. Ein weiteres, sehr junges Forschungsfeld sind optische Komponenten für eine Wellenlänge von 6,x nm, die derzeit als nächste Lithographiewellenlänge nach 13,5 nm intensiv diskutiert wird. Um eine erste Abschätzung der Streulichteigenschaften und kritischen Rauheitsparameter zu ermöglichen, wird am Ende der Arbeit auch auf die Rauheitsentwicklung von Mehrschichtsystemen für diesen Wellenlängenbereich eingegangen

High-Peak-Power Fiber-Laser Technology for Laser-Produced-Plasma Extreme-Ultraviolet Lithography.

This dissertation studied and demonstrated, for the first time, the feasibility of using a fiber laser as a practical EUV driver for next generation lithography. Our specially-designed fiber laser successfully emulated the same conversion efficiency achieved by the solid-state lasers, which was not believed possible before this study. An innovative spectral combining scheme was also developed to accommodate the broad linewidth from a high-peak-power fiber-laser with concurrent MW-peak power and multi-kW average power, as required to reach the EUV power for high-volume manufacturing. The concept of a single-emitter-fiber-integrated module (SEFIM) was realized. Using an 80-μm-core Yb-doped large-mode-area fiber, we achieved a record high peak power 6MW with 110-ps pulses and 6 mJ energy with 6-ns pulses, giving a near-diffraction-limited mode quality of M^2~1.3. These pulse parameters will provide sufficient intensities for optimal EUV generation using Sn targets. High average power 140 W is also achieved with proper forced cooling arrangements. Implementation of arbitrary waveform generator as the seed driver also provided pulse temporal-shaping capability, providing an instrumental tool for the study of plasma dynamics. The first 13.5-nm EUV generation was demonstrated using our single emitter module, with a conversion efficiency 1% at a intensity of 1.0 × 10^10 W/cm2, using a solid-Sn planar target. Conversion efficiency was limited by the highest achievable laser intensity at the time. The second demonstration, using the improved SEFIM and Sn-doped water-droplet targets, achieved a conversion efficiency of 2.1% at a intensity of 8.8 × 10^10 W/cm2. The intrinsic advantages of this mass-limited target greatly are debris mitigation and compatibility with high repetition rate power scaling. We developed a new high power spectral beam combing scheme based on sharp spectral- edge multi-layer dielectric filters, which does not use spectral spatial dispersion and, therefore, is free from the constraints on laser linewidth and beam size inherent in conventional diffraction-grating-based beam-combining approaches. This scheme is particularly well suited for high energy pulse power combining, as experimentally demonstrated in >91% efficient combination of three nanosecond-pulse fiber laser beams with a combined power and energy of 52 W and 4.0 mJ repectively.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/60738/1/kchou_1.pd