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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Deep UV Raman Spectroscopy

Patil, Raj January 2016 (has links)
This thesis examines the performance of a custom built deep UV laser (257.5nm) for Raman spectroscopy and the advantages of Raman spectroscopy with a laser in the deep UV over a laser in the visible range (532 nm). It describes the theory of resonance Raman scattering, the experimental setup for Raman spectroscopy and a few Raman spectroscopy measurements. The measurements were performed on biological samples oak tree leaf and lactobacillus acidophilus and bifidobacteria from probotioc medicinal capsules. Fluorescence free Raman spectra were acquired for the two samples with 257.5 nm laser. The Raman spectra for the two samples with a 532nm laser was masked with fluorescence. Raman measurements for an inorganic salt sodium nitrate showed a resonance Raman effect with 257.5 nm laser which led to enhancement in the Raman intensity as compared to that with 532 nm laser. Therefore we were able to demonstrate two advantages of deep UV Raman spectroscopy. First one is the possibility of acquiring fluorescence free spectra for biological samples. Second is the possibility of gaining enhancement in Raman intensity due to resonance Raman effect. It was observed that 257.5 nm laser requires optimization to reduce the bandwidth of the laser to get better resolution. The 257.5 nm laser also needs to be optimized to obtain higher power to get better signal to noise ratio. The experimental setup can also be further improved to obtain better resolution. If the improvements required in the setup are implemented, the deep UV Raman setup will become an important tool for spectroscopy.

SDN-Enabled Dynamic Feedback Control and Sensing in Agile Optical Networks

Lin, Likun January 2016 (has links)
Fiber optic networks are no longer just pipelines for transporting data in the long haul backbone. Exponential growth in traffic in metro-regional areas has pushed higher capacity fiber toward the edge of the network, and highly dynamic patterns of heterogeneous traffic have emerged that are often bursty, severely stressing the historical "fat and dumb pipe" static optical network, which would need to be massively over-provisioned to deal with these loads. What is required is a more intelligent network with a span of control over the optical as well as electrical transport mechanisms which enables handling of service requests in a fast and efficient way that guarantees quality of service (QoS) while optimizing capacity efficiency. An "agile" optical network is a reconfigurable optical network comprised of high speed intelligent control system fed by real-time in situ network sensing. It provides fast response in the control and switching of optical signals in response to changing traffic demands and network conditions. This agile control of optical signals is enabled by pushing switching decisions downward in the network stack to the physical layer. Implementing such agility is challenging due to the response dynamics and interactions of signals in the physical layer. Control schemes must deal with issues such as dynamic power equalization, EDFA transients and cascaded noise effects, impairments due to self-phase modulation and dispersion, and channel-to-channel cross talk. If these issues are not properly predicted and mitigated, attempts at dynamic control can drive the optical network into an unstable state. In order to enable high speed actuation of signal modulators and switches, the network controller must be able to make decisions based on predictive models. In this thesis, we consider how to take advantage of Software Defined Networking (SDN) capabilities for network reconfiguration, combined with embedded models that access updates from deployed network monitoring sensors. In order to maintain signal quality while optimizing network resources, we find that it is essential to model and update estimates of the physical link impairments in real-time. In this thesis, we consider the key elements required to enable an agile optical network, with contributions as follows: *Control Framework: extended the SDN concept to include the optical transport network through extensions to the OpenFlow (OF) protocol. A unified SDN control plane is built to facilitate control and management capability across the electrical/packet-switched and optical/circuit-switched portions of the network seamlessly. The SDN control plane serves as a platform to abstract the resources of multilayer/multivendor networks. Through this platform, applications can dynamically request the network resources to meet their service requirements. *Use of In-situ Monitors: enabled real-time physical impairment sensing in the control plane using in-situ Optical Performance Monitoring (OPM) and bit error rate (BER) analyzers. OPM and BER values are used as quantitative indicators of the link status and are fed to the control plane through a high-speed data collection interface to form a closed-loop feedback system to enable adaptive resource allocation. *Predictive Network Model: used a network model embedded in the control layer to study the link status. The estimated results of network status is fed into the control decisions to precompute the network resources. The performance of the network model can be enhanced by the sensing results. *Real-Time Control Algorithms: investigated various dynamic resource allocation mechanisms supporting an agile optical network. Intelligent routing and wavelength switching for recovering from traffic impairments is achieved experimentally in the agile optical network within one second. A distance-adaptive spectrum allocation scheme to address transmission impairments caused by cascaded Wavelength Selective Switches (WSS) is proposed and evaluated for improving network spectral efficiency.

Frequency Combs for Spectroscopy in the Vacuum Ultraviolet

Carlson, David R. January 2016 (has links)
This dissertation explores frequency comb spectroscopy and, in particular, its extension to the vacuum-ultraviolet (VUV) and extreme-ultraviolet (XUV) wavelength regimes through a technique called intracavity high harmonic generation (IHHG). By combining the techniques of passive pulse amplification in an enhancement cavity with high harmonic generation, IHHG enables the direct conversion of near-infrared radiation to the VUV/XUV while still maintaining the underlying comb structure .As part of this work, a series of numerical simulations was performed to investigate the plasma that is formed in the IHHG process and its implications for the resulting VUV comb. It was demonstrated that a fundamental limitation to the performance of IHHG experiments is due to the single-pass ionization phase shift acquired by the pulse circulating in the enhancement cavity. Furthermore, we showed that a static background plasma accumulates between pulses and complicates cavity stabilization. Insights gained from the simulations led to the development of a novel pump-probe technique using the enhancement cavity that allowed a direct measurement of the intracavity plasma and its decay dynamics in real-time. Because the plasma lifetime plays such a crucial role in the operation of these cavities, it was important to have a method to test ways of reducing it. To build on our initial IHHG results showing record-level powers in the XUV, we implemented a fully phase-coherent dual comb spectrometer consisting of two identical IHHG systems operating in parallel. The system is designed for precision spectroscopy in the VUV and is based on a pair of homemade ytterbium fiber lasers that use a parabolic amplification scheme to achieve 80 fs pulses after amplification to 50 W of average power. Initial dual comb data showing system performance at the fundamental frequency and third harmonic are presented.

Characterizing the Transient and Stationary Response of the TAU 2 Camera

Wilhite, Jeffrey Ryan January 2016 (has links)
The purpose of this research is to learn how a FLIR Tau 2 infrared camera reacts to stimuli to, later on, preform a calibration of the camera. This included measuring the line spread function (LSF), quantifying the thermal blooming, looking at the response to thermal changes in the focal plane array (FPA), and measuring the response of different temperature and speed sub-pixel objects streaking across the FPA to backtrack what the actual size, speed, shape and temperature of unknown objects were. This work will provide information to help in performing a calibration on the camera necessary to be able to get performance similar to that of a cooled sensor out of an uncooled sensor. There was not enough time to fully understand the reaction of the camera to different stimuli, which would require much more effort, but there was a large amount of information gathered that can greatly increase the understanding of the camera and help in performing calibration of the camera later on.

Study of Optical Destruction Techniques for Optical Discs

Choi, Taeyoung January 2008 (has links)
The topic of this dissertation is on the investigation of optical techniques for completely destroying data stored in optical discs. Complete and secure destruction of data is important when disposal of an optical disc containing sensitive and possibly classified information is concerned, since some information can be retrieved even from a fragment of a disc. After several candidate techniques and related systems are examined and fundamental system components are identified, an optical data destruction (ODD) system using a focused high power laser beam is devised, and a prototype system is designed and constructed. The ODD system uses a high power laser diode (HPLD) to expose data marks on optical discs and maintains the focused laser beam on a data layer by a focus servo using a diffractive optical element (DOE).The optical characteristics of the beam emitted from an HPLD are thoroughly investigated, and a few methods of modeling an HPLD beam in an optical system are studied. With the understanding of the HPLD beam properties, a limited-divergence raytracing (LDRT) model is developed to predict the propagation behavior of the HPLD beam in an optical system and shows good agreement with the real HPLD beam. This LDRT method is used to model the HPLD beam in the ODD system and simulate the resultant focus error signal with and without fabrication errors.The DOE focus sensor overcomes the problems in conventional focus sensors associated with the use of an intense line beam. The DOE comprising two angled gratings is designed to use only two weak 3rd order beams for focus sensing and fabricated on a chrome-coated glass substrate using a maskless lithography tool.The constructed ODD system is then used to perform destruction tests on various optical discs, which are examined using static and dynamic methods of data observation and retrieval. The observations show that data marks are optical invisible or completely covered with numerous micro-bubbles. These test results demonstrate that secure and complete destruction of data on optical discs is achieved using an ODD system. Successful destruction, however, depends greatly on exposure conditions and the type of optical media.

Modeling Scatter in Composite Media

Fest, Eric January 2008 (has links)
A theoretical model of optical scattering in materials consisting of densely packed spherical particles is developed that can be used to predict its optical properties given its physical characteristics. The inputs to this model are the waveband of interest, the complex refractive indicies and particle size distribution of the materials that comprise the media (including any contaminants), the density and sizes of any pores in the media, and the dimensions of the media slab. The outputs of this model are the specular transmittance and emissivity vs. wavelength of the media, and it's Bidirectional Scattering Distribution Function (BSDF) versus scatter angle, wavelength, and incident polarization. The results of this model are compared to measured transmittance and BSDF data.

Time Domain Spectroscopy of Graphene

Roberts, Adam January 2012 (has links)
This dissertation describes the response of graphene and graphene fragments to ultrafast optical pulses. I will first describe how we created few-cycle optical pulses for interacting with the graphene lattice. These pulses are created through filamentation based pulse compression. I studied how the filamentation process can be optimized through simple means to create the shortest possible pulse. I then examine the extent to which graphene can withstand irradiation from intense ultra-fast pulses. I examine both the high intensity regime at which a single laser pulse will ablate the graphene and a more moderate regime that slowly degrades the graphene from long term exposure to ultrafast pulses. The knowledge lets us both identify a safe working regime for driving the graphene lattice with optical fields as well as use ultrafast lasers to create graphene nano-fragments down to 2nm. Next, I explore the ultrafast dynamics of photo-excited graphene. Graphene undergoes electronic band renormalization after photo exciting carriers. By measuring a differential transmission spectrum, small changes to the band structure can be quantified. I will explain how screened exchange and electron phonon self energies provide corrections to the band structure for different times after carrier excitation. Lastly, I will describe measurements that determine the extent of electron-electron correlations in graphene fragments. By measuring the energy of the two photon state and comparing it the lowest energy one photon state in graphene fragments, we can determine the strength of the correlations in graphene systems.

Pixelated Mask Polarization Based Spatial Carrier Interference Microscopy

Wiersma, Joshua Thomas January 2012 (has links)
The following dissertation demonstrates the advantages of using a camera with a pixelated polarization mask allowing spatial carrier phase shifting in interference microscopy. An interference microscope in the Michelson and Linnik configurations integrates a camera equipped with a pixelated polarization mask. The camera utilizes polarization to simultaneously capture four phase shifted interferograms. Each set of four phase shifted fringe patterns permits the calculation of fringe contrast and phase at a point in the vertical scan of a test surface. The use of a short coherence source enables construction of a coarse surface profile by estimating the localization of the peak fringe contrast over the vertical scan. The coarse profile allows unwrapping of the less noisy, though circumstantially ambiguous, phase data. Established phase shifting interference microscopy methods utilize temporal phase shifting techniques. Temporal methods contrast spatial methods by acquiring each set of interferograms necessary for calculating fringe contrast and phase by scanning the test object. The scanning changes the optical path difference between the interferometer arms thus inducing the phase shifts. While both methods scan the test surface, spatial methods acquire all of the information needed to calculate fringe contrast and phase simultaneously while the temporal methods require data from multiple points in the scan. Furthermore, the focus and fringe contrast also change between phase shifts and introduce a small error in temporal methods. However, the largest source of error results from the time taken between capturing the phase shifted frames comprising each set where environmental disturbances such as vibration can change the fringe pattern. The subsequent work shows the practicality of performing interference microscopy with a pixelated polarization mask as well as the technique's relative vibration insensitivity.

Nanocomposites for High-Speed Optical Modulators and Plasmonic Thermal Mid-Infrared Emitters

Demir, Veysi January 2015 (has links)
Demand for high-speed optical modulators and narrow-bandwidth infrared thermal emitters for numerous applications continues to rise and new optical devices are needed to deal with massive data flows, processing powers, and fabrication costs. Conventional techniques are usually hindered by material limitations or electronic interconnects and advances in organic nanocomposite materials and their integration into photonic integrated circuits (PICs) have been acknowledged as a promising alternative to single crystal techniques. The work presented in this thesis uses plasmonic and magneto-optic effects towards the development of novel optical devices for harnessing light and generating high bandwidth signals (> 40GHz) at room and cryogenic temperatures (4.2°K). Several publications have resulted from these efforts and are listed at the end of the abstract. In our first published research we developed a narrow-bandwidth mid-infrared thermal emitter using an Ag/dielectric/Ag thin film structure arranged in hexagonal planar lattice structures. PECVD produced nanoamorphous carbon (NAC) is used as a dielectric layer. Spectrally tunable (>2 μm) and narrow bandwidth (<0.5 μm) emission peaks in the range of 4-7μm were demonstrated by decreasing the resistivity of NAC from 10¹² and 10⁹ Ω.cm with an MoSi₂ dopant and increasing the emitter lattice constant from 4 to 7 μm. This technique offers excellent flexibility for developing cost-effective mid-IR sources as compared to costly fiber and quantum cascade lasers (QCLs). Next, the effect of temperature on the Verdet constant for cobalt-ferrite polymer nanocomposites was measured for a series of temperatures ranging from 40 to 200°K with a Faraday rotation polarimeter. No visual change was observed in the films during thermal cycling, and ~4x improvement was achieved at 40°K. The results are promising and further analysis is merited at 4.2°K to assess the performance of this material for cryogenic magneto-optic modulators for supercomputers. Finally, the dielectric constant and loss tangent of MAPTMS sol-gel films were measured over a wide range of microwave frequencies. The test structures were prepared by spin-coating sol-gel films onto metallized glass substrates. The dielectric properties of the sol-gel were probed with several different sets of coplanar waveguides (CPWs) electroplated onto sol-gel films. The dielectric constant and loss-tangent of these films were determined to be ~3.1 and 3 x 10⁻³ at 35GHz. These results are very promising indicating that sol-gels are viable cladding materials for high-speed electro-optic polymer modulators (>40GHz).

High Precision Optical Surface Metrology using Deflectometry

Huang, Run January 2015 (has links)
Software Configurable Optical Test System (SCOTS) developed at University of Arizona is a highly efficient optical metrology technique based on the principle of deflectometry, which can achieve comparable accuracy with interferometry but with low-cost hardware. In a SCOTS test, an LCD display is used to generate structured light pattern to illuminate the test optics and the reflected light is captured by a digital camera. The surface slope of test optics is determined by triangulation of the display pixels, test optics, and the camera. The surface shape is obtained by the integration of the slopes. Comparing to interferometry, which has long served as an accurate non-contact optical metrology technology, SCOTS overcomes the limitation of dynamic range and sensitivity to environment. It is able to achieve high dynamic range slope measurement without requiring null optics. In this dissertation, the sensitivity and performance of the test system have been analyzed comprehensively. Sophisticated calibrations of system components have been investigated and implemented in different metrology projects to push this technology to a higher accuracy including low-order terms. A compact on-axis SCOTS system lowered the testing geometry sensitivity in the metrology of 1-meter highly aspheric secondary mirror of Large Binocular Telescope. Sub-nm accuracy was achieved in testing a high precision elliptical X-ray mirror by using reference calibration. A well-calibrated SCOTS was successfully constructed and is, at the time of writing this dissertation, being used to provide surface metrology feedback for the fabrication of the primary mirror of Daniel K. Inouye Solar Telescope which is a 4-meter off-axis parabola with more than 8 mm aspherical departure.

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