Biomedical imaging requires high resolution to see the fine features of a sample and fast acquisition to observe live cells that move. Optical coherence tomography (OCT) is a powerful technique which uses optical interference for non-invasive high resolution 3D imaging in biological samples. The resolution of OCT is determined by the length over which the light used will in- terfere. Unfortunately, dispersion hurts the imaging resolution by broadening interference features. A technique called quantum-OCT (QOCT)[1] is immune to dispersion but re- quires entangled photon pairs. The need for entanglement drastically reduces the number of photons available for imaging, making QOCT too slow to be practical. Chirped-pulse interferometry (CPI) is also immune to dispersion. A chirped pulse is one where the fre- quency, or colour, of the light changes from red to blue from one end of the pulse to the other. CPI relies on frequency correlations created by applying different chirps to two sep- arate pulses. This method had the disadvantage of being limited to a single predetermined chirp rate, and discarded 50% of the power. However CPI has better resolution than OCT, automatic dispersion cancellation, and 10,000,000 times the signal strength of QOCT [13]. A new, much more flexible and efficient method of CPI will be demonstrated by creating the frequency correlations entirely in a single pulse. This new method is referred to as non- linear chirped pulse interferometry (NL-CPI). The non-linear chirp required in NCPI is very difficult to produce using only conven- tional optics. In this thesis we document the construction and characterization of a new method of creating the desired chirp using a programmable pulse-shaper (PS). We build a PPS and then demonstrated its functionality by compressing a 105nm FWHM bandwidth pulse to under 17f s, near its transform limited time duration. We also show that the values given to the PPS for dispersion are accurate by calculating and then compensating the dispersion caused by various optical elements in the CPI interferometer. Conventional OCT systems are immune to dispersion common to both arms of the interferometer. Non-linear interferometers experience broadening due to this dispersion, making them more difficult to use with fibre based interferometers common in conventional OCT. We show that NL-CPI can compensate for dispersion common to both arms of the interferometer, making NL-CPI more appealing as a replacement for conventional OCT. In this thesis we experimentally implement and demonstrate a prototype setup using non-linear CPI for dispersion-cancelled imaging of a mirror, with a resolution comparable to conventional OCT systems. We then use the system to produce 2-D cross sectional images of a biological sample, an onion. Q-OCT has previously been used to image an onion[16], but required treating the onion with gold nano particles to achieve a useful signal. The onion we used had no special treatment. In addition our axial scanning rate is also 10000 times faster than Q-OCT.

Thermoacoustic engines convert thermal energy into acoustic energy with few or no moving parts, thus they require little maintenance, are highly reliable, and are inexpensive to produce. These traits make them attractive for applications in remote or portable power generation, where a linear alternator converts the acoustic power into electric power. Their primary application, however, is in driving thermoacoustic refrigerators, which use acoustic power to provide cooling at potentially cryogenic temperatures, also without moving parts. This dissertation examines the feasibility of a new type of thermoacoustic engine, where mean flow and an internal pulse combustion process replace the hot heat exchanger in a traditional closed cycle thermoacoustic engine, thereby eliminating the heat exchangers cost, inefficiency, and thermal expansion stresses. The theory developed in this work reveals that a large temperature difference must exist between the hot face of the regenerator and the hot combustion products flowing into it, and that much of the convective thermal energy input from the combustion process is converted into conductive and thermoacoustic losses in the regenerator. The development of the Thermoacoustic Pulse Combustion Engine, as described in this study, is designed to recover most of this lost thermal energy by routing the inlet pipes through the regenerator to preheat the combustion reactants. Further, the developed theory shows that the pulse combustion process has the potential to add up to 7% to the engines acoustic power output for an acoustic pressure ratio of 10%, with linearly increasing contributions for increasing acoustic pressure ratios. Computational modeling and optimization of the Thermoacoustic Pulse Combustion Engine yield thermal efficiencies of about 20% for atmospheric mean operating pressures, though higher mean engine pressures increase this efficiency considerably by increasing the acoustic power density relative to the thermal losses. However, permissible mean engine pressures are limited by the need to avoid fouling the regenerator with condensation of water vapor out of the cold combustion products. Despite lower acoustic power densities, the Thermoacoustic Pulse Combustion Engine is shown to be well suited to portable refrigeration and power generation applications, due to its reasonable efficiency and inherent simplicity and compactness.

Current research shows that pulse combustion impingement drying is an improvement over the steady impingement drying currently in commercial use. Pulse combustion impingement has higher heat transfer rates and a lower impact on the environment. Commercialization of pulse impingement drying is the goal of the Pulsed Air Drying group at IPST. To that end the objective of this project is to develop a system that will allow researchers to measure heat transfer rates at the impingement surface from the impinging air. A water cooled impingement plate with temperature and heat flux measuring capabilities was developed which accurately measures and records the desired information. The impingement plate was tested and its results were verified by comparison with previous literature. Finally a preliminary comparison between steady and pulse combustion impingement was carried out. The study shows pulsed combustion impingement to be superior to steady impingement.

The objective of the proposed research is to develop multiwavelength lasers as cost-efficient sources for broadband optical access networks. Todays telecommunications networks have widely adopted optical fiber as the backbone transmission medium. Optical fiber systems are promising candidates for the broadband access networks to offer high-speed and future-proof services. To harness the available bandwidth in fiber and to meet the ever-growing bandwidth demand, wavelength division multiplexing (WDM) techniques have been investigated. There have been intense research activities for the creation of new low-cost laser sources for such emerging applications. In this context, multiwavelength fiber ring lasers have been significantly investigated as they present many advantages, including simple structure, low-cost, and selectable multiwavelength operation. We propose a new laser system architecture that emits alternate multiwavelength picosecond pulses operating at room temperature. Optical signal generation is based on a single active component, an unbalanced Mach-Zehnder interferometer, inserted in an actively mode-locked erbium-doped fiber ring laser to provide both intensity modulation and wavelength-selective filtering. Time and frequency controls of the light emission are reached by inserting an additional modulator and a periodic filter in the cavity. This approach focuses on the application of multiwavelength lasers as sources for WDM passive optical networks.

The operation of pulse tube cryocoolers (PTCs) is based on complicated and poorly-understood solid-fluid interactions involving periodic flows of a cryogenic fluid in a flow loop that includes components filled with micro porous structures. CFD simulation is the current trend in modeling of pulse-tube cryocoolers. Such simulations can only be meaningful if correct closure relations are available. The objective of this investigation is to measure and empirically correlate the axial hydrodynamic parameters for two widely used cryocooler regenerator structures. A test section will be designed, constructed and instrumented for the measurements. Porous structures tested will include 325 and 400-Mesh stainless screens, each at two different porosities. Tests will be performed with helium as the working fluid, over a wide range of parameters. The longitudinal permeabilities and Forchheimer s inertial coefficients will then be obtained in an iterative process where agreement between the data and the predictions of detailed CFD simulations for the entire test sections and their vicinity are sought. Empirical correlations representing the longitudinal permeability and Forchheimer s coefficient in terms of relevant dimensionless parameters will then be developed.

The main contributions of this thesis to the field of ultrashort pulse measurement are a new set of experimental tools to measure the spatio-temporal fields of femtosecond pulses, and a new simplified formalism to describe such fields in the presence of distortions. More specifically, we developed an experimental technique based on scanning-wavelength digital holography and frequency-resolved optical gating that allows the complete measurement of the electric field E(x,y,t) of trains of identical femtosecond pulses. A related method, wavelength-multiplexed digital holography, is also introduced. It achieves a single-shot measurement of the three-dimensional field E(x,y,t) but at a reduced resolution using a simple experimental apparatus. Both methods can be used to measure various spatio-temporal distortions that often plague femtosecond laser systems, in particular amplified ones. Finally, to unambiguously and intuitively quantify such distortions, we introduce normalized correlation coefficients so that a common language can be used to describe the severity of these effects.

This paper discussed a way of applied stress to control the photonic crystal fiber dispersion curve, so that it can act on the anomalous dispersion or normal dispersion region area. By this way, we can design the pulse compressor and pulse stretcher for higher peak power laser system. Recently, high-power shortpulse laser has become an indispensable tool in many field, using short-pulse laser oscillator, combined with chirped-frequency amplification technology to produce high-power short-pulse laser system can be used for industrial or medical applications. The all-fiber laser system not only provide better pulse quality and also increased pulse laser system on the stability of the environment.

This research attempts to ignite metal halide lamps once with a single-pulse to avoid the problems of uncomfortable light strobes and irregularly high voltage and current stresses on circuit components caused by multiple strikes in conventional electronic ballasts. Metal halide lamps with single-pulse ignition, however, have difficulty in sustaining the lamp arc when operated with a low-frequency square-wave current. Experimental results indicate that the lamp exhibits an extremely small equivalent resistance as the electrode gap has being broken down. In this stage, the ballast has to keep the lamp current not declining to zero in the first half cycle. On the other hand, the lamp acts like open-circuited during commutation when driven by an alternating current. A sufficient energy from the ballast is needed to continue the arc in the next half-cycle. The transition waveform of the lamp arc current after being broken down is analyzed and the required energy for sustaining the lamp arc is calculated accordingly. Based on the investigation results, a starting scenario with appropriately designed circuit parameters for single-pulse ignition can be figured out. The starting scenario has been experimentally implemented on a 70 W metal halide lamp to demonstrate that the metal halide lamp can be successfully started up with single-pulse ignition.

Nonlinear optical microscopy (NLOM) offers many advantages when imaging intact biological samples. By using ultrafast lasers in the near infrared and two photon excitation (TPE), signal production is limited to the focal volume and provides an excellent means for rendering thin, microscopic images from within the sample. Exogenous fluorophores/lumiphores may be used as efficient contrast agents to tag specific targets and provide enhanced signal. The efficiency of the TPE process in these contrast agents is broadly assumed to vary inversely with the laser pulsewidth, τ. In this work, we investigate the TPE efficiency of transform limited broadband (~133nm, ~10fs) and narrowband (~11nm, ~170fs) pulses in the generation of twophoton luminescence from semiconductor nanocrystals or quantum dots (QD’s) both theoretically and experimentally. Compared to standard organic dyes, QD’s possess a relatively broad, uniform spectral response that enables better use of the full bandwidth from the broadband laser. Theoretical calculations including both degenerate and non-degenerate TPE indicate a rolloff from the 1/τ behavior as the pulses’ spectral bandwidth becomes broader than the absorption spectra of the QD’s. Experimentally measured enhancement in luminescence intensity while using a broadband pulse is compared with the simulated enhancement in two-photon luminescence. A combination of increased understanding of the excitation processes in NLOM and proper selection of contrast agents will help in advancing the role of broadband ultrafast lasers in NLOM.

Nonlinear optical microscopy (NLOM) utilizing femtosecond laser pulses is well suited for imaging living tissues. This work reports on the design and development of an optical fiber based multispectral NLOM developed around a laser generating broadband sub-10-fs pulses. An all-mirror dispersion-compensation setup is used to correct for quadratic and cubic phase distortions induced within the NLOM. Mouse tail tendon was used to characterize sub-10-fs pulses by interferometric autocorrelation. This is an effective method for characterizing dispersion from the optical system, immersion medium, and wet biological sample. The generation of very short autocorrelations demonstrates the ability to compensate for phase distortions within the imaging system and efficient second-harmonic upconversion of the ultrashort pulse spectrum within collagen. Reconstruction of ultrashort pulses at the focal plane of the objective allows the excitation of multiple fluorescent probes simultaneously. Multiple fluorescent probe excitation and spectral discrimination is demonstrated using mixtures of fluorescent dye solutions and an in-vitro angiogenesis model containing human umbilical vein endothelial cells (HUVEC’s) expressing multiple fluorescent proteins. Sub-10-fs pulses can be propagated through polarization-maintaining single mode fiber (PMF) for use in NLOM. We demonstrate delivery of near transform-limited, 1 nJ pulses from a Ti:Al2O3 oscillator via PMF to the NLOM focal plane while maintaining 120 nm of bandwidth. Negative group delay dispersion (GDD) introduced to pre-compensate normal dispersion of the optical fiber and microscope optics ensured linear pulse propagation through the PMF. Nonlinear excitation of multiple fluorophores simultaneously and polarization sensitive NLOM imaging using second harmonic generation in collagen was demonstrated using PMF delivered pulses. Two-photon excited fluorescence spectra and second harmonic images taken with and without the fiber indicates that the fiber based system is capable of generating optical signals that are within a factor of two to three of our traditional NLOM.