<p> Using a Q-spoiled Nd-glass laser, an experimental investigation of frequency doubling in NiSO4•6 H2O was carried out. The frequency doubling was observed to occur at a phase matching angle of 56° ± 1°. Experimentally, it is shown that the fundamental frequency at λ = 1.06 μm is an O-ray while the doubled frequency at λ = .53μm is an E-ray. Since the amplitude for electric dipole frequency doubling in NiSO4•6 H2O is zero, these observations are unusual. The observations are attributed to magnetic dipole and/or electric quadrupole frequency doubling. Evidence to support this view comes from the magnitude of the effect and from its azimuthal dependence. The electric quadrupole type frequency doubling is consistent with the data only if the susceptibility coefficients satisfy the relation QאEE =1/2 (QאEE - QאEE ) 1212 1111 1122 </p> / Thesis / Doctor of Philosophy (PhD)

The spatial frequency doubling illusion (FDI) occurs when the contrast of a low spatial frequency sinusoidal grating is modulated at high temporal frequencies – its apparent spatial frequency increases. Earlier suggestions were that the FDI is generated by a specific class of retinal ganglion cells, which are preferentially lost in the early stages of glaucoma. Based on this linking theory, frequency doubling perimetry (FDP) was developed and several clinical reports confirmed its high efficiency in diagnosing early glaucomatous vision loss. However, this linking theory is not universally accepted and newer suggestions posit that the illusion arises because of temporal frequency related difficulties in temporal phase encoding ability. This thesis psychophysically examines the spatiotemporal characteristics of both the FDI and temporal phase encoding ability with achromatic and equi-luminant (both red-green (RG) and blue-yellow (BY)) gratings at a range of spatiotemporal parameters including those eliciting the FDI. (For complete abstract open document)

The spatial frequency doubling illusion (FDI) occurs when the contrast of a low spatial frequency sinusoidal grating is modulated at high temporal frequencies – its apparent spatial frequency increases. Earlier suggestions were that the FDI is generated by a specific class of retinal ganglion cells, which are preferentially lost in the early stages of glaucoma. Based on this linking theory, frequency doubling perimetry (FDP) was developed and several clinical reports confirmed its high efficiency in diagnosing early glaucomatous vision loss. However, this linking theory is not universally accepted and newer suggestions posit that the illusion arises because of temporal frequency related difficulties in temporal phase encoding ability. This thesis psychophysically examines the spatiotemporal characteristics of both the FDI and temporal phase encoding ability with achromatic and equi-luminant (both red-green (RG) and blue-yellow (BY)) gratings at a range of spatiotemporal parameters including those eliciting the FDI. (For complete abstract open document)

The purpose of this study is to develop a solid-state blue laser which has advantages of high power, short wavelength, and compact. It can be applied in micromaching, LIDAR, underwater ranging, biochemical techniques, and so forth. We increased the peak power of the laser effectively by a low-cost, small, and easy-use passive Q-switching technique. In addition, intracavity frequency-doubling is an economic way to achieve non-linear frequency conversion for blue generation. By integrating of these two techniques, we develop a compact all solid-state high-power blue laser with 83 W peak power at 473 nm. Restricted to reabsorption loss, the optical to optical conversion efficiency of 4F3/2 ¡÷ 4I9/2 quasi-three-level laser is lower than 4F3/2 ¡÷ 4I11/2 four-level laser for Nd:YAG crystal. The reabsorption loss will change with the temperature variation of the gain medium, it enormously affects to the performance and stability of quasi-three-level lasers. Therefore, in addition to make systematic studies of the conversion efficiency of KNbO3, BBO, LBO as the intracavity SHG crystals for generation of high-power blue laser, we use the numerical analysis to investigate the influence of reabsorption loss to quasi-three-level passive Q-switching laser. At present, blue laser with peak power of 83 W and pulse width of 10.6 ns was generated as a result. To our knowledge, the compact all solid-state high-power pulsed blue laser is demonstrated for the first time by integrating of passive Q-switching and intracavity frequency-doubling simultaneously.

In this thesis the development of a high efficiency harmonic re-radiator, consisting of a diode doubler and conjugate-matched receive and transmit antennas, is described. Diode-based frequency multipliers and rectifiers, coupled with antennas, are of interest for quasi-optical applications, for energy-scavenging and for sensing applications. The device studied operates by receiving an interrogating signal at a frequency of 1.3 GHz and re-radiating a signal at 2.6 GHz. The primary goal of this research was to develop a passive, miniature and effective frequency doubler integrated with planar antennas. The system is referred to as a frequency doubling reflectenna, (FDR). Prediction of accurate performance was achieved by employing precise modeling and measurement methods. The FDR can be utilized in data collection applications. The footprint of the FDR is occupied primarily by the receive and transmit antennas. Therefore, a significant portion of the research focused on the development of compact and efficient planar antennas, which would provide for a miniature FDR. A first-generation FDR design was designed, which utilized quarter-wavelength shorted microstrip patch antennas. The choice of antennas provided a small prototype with dimensions equal to 44 mm by 17 mm. In order to further reduce the size of the harmonic re-radiator, meandered planar antennas were investigated and optimized for efficient operation. A second-generation FDR design, which utilized meandered microstrip patch antennas, was produced and a size reduction of 75% was achieved. Both first- and second-generation harmonic re-radiator designs were designed for low input power operation and provided maximum measured conversion efficiencies of approximately 4.5% and 1.8%, with the input to the diode doubler at -14.5 and -17.5 dBm, respectively. Re-configurable microwave devices, which dynamically operate at different frequencies, are often desirable for sensing applications. Therefore, to conclude this research, a tunable FDR was realized using a semiconductor varactor that provided the dynamic capacitance required for the tunability.

This thesis presented the research, design and fabrication associated with a unique application of rectenna technology combined with lock-in amplification. An extremely low-power harmonic transponder is conjoined with an interrogator base-station, and utilizing coherent demodulation the Remote Lock-In Amplifier (RLIA) concept is realized. Utilizing harmonic re-radiation with very low-power input, the 1st generation transponder detects a transmitted interrogation signal and responds by retransmitting the second harmonic of the signal. The 1st generation transponder performs this task while using no additional power besides that which accompanies the wireless signal. Demonstration of the first complete configuration provided proof of concept for the RLIA and feasibility of processing relevant information under "zero" power operating conditions with a remote transponder. Design and fabrication of a new transponder where the existing zero-bias transponder was modified to include a DC bias to the diode-based frequency doubler is presented. Applied bias voltage directly changed the impedance match between the receiving 1.3 GHz antenna and the diode causing a change in conversion loss. Testing demonstrated that a change in conversion loss induces an amplitude modulation on the retransmission of the signal from the transponder. A test of bias sweep at the optimal operating frequency was performed on the 2nd generation transponder and it was seen that a change of ~ 0.1 V in either a positive or negative bias configuration induced an approximate 15 dB change in transponder output power. A diode-integrated radar detector is designed to sense microwaves occurring at a certain frequency within its local environment and transform the microwave energy to a DC voltage proportional the strength of the signal impinging on its receiving antenna. The output of the radar detector could then be redirected to the bias input of the 2nd generation transponder, where this DC voltage input would cause a change in conversion loss and modulate the retransmitted interrogation signal from the transponder to the base station. When the base station receives the modulated interrogation signal the information sensed by the radar detector is extracted. Simulations and testing results of the fabricated radar detector demonstrate capability of sensing a signal of approximately -53.3 dBm, and accordingly producing a rectified DC voltage output of 0.05 mV. A comparison is made between these findings and the transponder measurements to demonstrate feasibility of pairing the radar detector and the 2nd generation transponder together at the remote sensor node to perform modulation of interrogation signals.

This thesis deals with the analysis of a planar antenna operating at two frequencies with use frequency doubling. The design and simulation of the antenna in ANSOFT Designer is described. The antenna is designed for two operating frequencies 900 MHz and 1.8 GHz. The antenna is required to operate TM10 mode and TM01 modes.

L’auto-doublage de fréquence dans des cristaux optiques non linéaires dopés avec des ions ytterbium est actuellement le meilleur moyen d’obtenir une émission efficace dans le vert, tout en garantissant une bonne compacité, un faisceau faiblement divergent et une bonne monochromaticité. Deux nouvelles matrices ont été étudiées en ce sens : BaCaBO3F un oxyfluorure à fusion congruente, et LaxGd1-xSc3(BO3)4 un membre de la famille des huntites à fusion non congruente mais pouvant être obtenu par la méthode Czochralski. Après l’étude des conditions de synthèse et de croissance, les propriétés optiques de l’ion ytterbium dans ces matrices ont été caractérisées, et l’effet laser en régime continu autour de 1µm a été démontré pour la première fois. Pour améliorer les performances d’auto-doublage de fréquence dans des cristaux de YCa4O(BO3)3:Yb, deux pistes ont été envisagées : stabiliser l’émission laser infra-rouge en travaillant sur la cavité résonnante (traitement de surface des optiques), et améliorer le rendement de conversion de Génération de Seconde Harmonique de type I en effectuant le premier suivi expérimental de la courbe d’accord de phase hors des plans principaux à 1064nm. / Self-frequency-doubling in nonlinear optical crystals doped with ytterbium ions is actually the best way to combine both efficient emission in the green region, low divergent beams and good monochomaticity. Two new compounds have therefore been studied: BaCaBO3F a congruent melting oxyfluoride and LaxGd1-xSc3(BO3)3 a huntite-type crystal with incongruent melting that can however be obtained by the Czochralski method. We first studied the synthesis and growth conditions, and then the optical properties of the ytterbium doped crystals. Laser effect in continuous wave operation mode was demonstrated for the first time. In order to improve the self-frequency-doubling performances of the Yb:YCa4O(BO3)3 crystals, we focused on both stabilizing the 1µm laser emission (special anti-reflection coatings) and on maximizing the type I Second Harmonic Generation process at 1064nm (first direct measurements of both the conversion efficiency and the phase-matching directions out of the principal planes).

The effect of uncertainty in gas composition on the accuracy of gas-phase thermometry using Laser-Induced Thermal Grating Spectroscopy, LITGS, is studied. Temperatures are obtained from measurements of the sound speed derived from the frequency of oscillations &fnof;_OSC imposed upon the LITGS signal arising from the transit of acoustic waves across the density modulation feature. The dependence of the sound speed, c_s on &radic;&gamma;/m, where &gamma; is the ratio of specific heats and m is the mean molecular mass leads to a dependence upon gas composition. LITGS signals were generated in acetone vapour in a variety of gas mixtures in a temperature controlled cell at 4 bar total pressure using pump pulses from a frequency quadrupled Q-switched Nd:YAG laser at 266 nm and a cw diode pumped solid state probe laser at 671 nm. Studies were undertaken of the variation in &fnof;_OSC with gas composition using gas mixtures of O₂ and N₂ with component concentrations in the range 0-100 &percnt;, and was found to agree with theoretical predictions. Measurement precision of the data (one standard deviation in 50 measurements) was found to be typically &plusmn; 1.7 &percnt; for measurements at 4 bar total pressure. The effect of varying concentrations in exhaust gas residuals (EGR) typical of pre-ignition gases in a spark ignition internal combustion engine were studied using synthetic air (N₂/ O₂ mixtures) containing variable amounts of simulated EGR components, CO₂ and H₂O. The effect of variation in CO₂ concentration in dry synthetic air was measured at 4 bar and 30&deg;C and found to agree with theoretical predictions. Experiments conducted at 30&deg;C, with the addition of a saturated vapour pressure of water indicate that the effect of a saturated vapour pressure of water on the oscillation frequency in synthetic EGR is on the borderline of resolution. The effect of variable amounts of typical hydrocarbon fuel vapour on &fnof;_OSC was studied using 2,2,4-trimethyl-pentane in gas mixtures composed of synthetic air and variable amounts of EGR and water vapour at 80&deg;C. Kinetic theory was used in order to model the dependence of the oscillation frequency &fnof;_OSC on various gas compositions containing fuel and EGR, in order to construct an error surface for comparison with experimental measurements. Experimental data were found to agree with the model predictions to within experimental error for a representative data set within the range of calculated values. The results indicate that uncertainties in temperature values derived from LITGS thermometry can be estimated with confidence within reasonable estimates of composition variations in an internal combustion engine, and should lead to absolute temperature accuracy of within 2-3 &percnt;.

Ces dernières années, les métamatériaux acoustiques sont largement étudiés pour leur intérêt dans la réalisation de divers types de contrôle des ondes à une échelle sub-longueur d’onde. En particulier, les métasurfaces acoustiques ont montré leur capacité à manipuler des ondes en limites de milieux de propagation via les processus de réflexion, de transmission et de réfraction. Contrairement au régime linéaire qui concerne l’immense majorité des travaux sur les métamatériaux acoustiques, les études sur les propriétés non linéaires des métamatériaux, de surcroit des métasurfaces, restent peu nombreuses, malgré la possibilité de générer des phénomènes acoustiques riches et variés. Les principaux freins au développement des métamatériaux non linéaires sont l'efficacité généralement faible de la réponse non linéaire et le manque de contrôle sur cette non-linéarité. Les travaux de recherche présentés ici ont donc pour objectif de concevoir des architectures de métasurfaces élastiques, permettant un contrôle des ondes acoustiques dans le régime non linéaire. En particulier l’effet de conversion d’une onde fondamentale vers son deuxième harmonique est étudié dans le processus de réflexion et de transmission unidirectionnelle. Cela nécessite le design de la non-linéarité élastique, qui est réalisé à base de modélisations discrètes de systèmes masses-ressorts et d'architectures composées d'éléments tournants. Les métasurfaces ainsi conçues, résonantes et à non-linéarité contrôlée, permettent de générer des effets non linéaires acoustiques inhabituels, potentiellement intéressants pour la manipulation d'ondes acoustiques. / In recent years, acoustic metamaterials have proven to be of great interest for their ability to achieve a variety of wave control at sub-wavelength scale. In particular, acoustic metasurfaces have shown their ability to manipulate waves from the boundaries of propagation media, via the reflection, transmission and refraction processes. Unlike the linear regime which has been extensively investigated in acoustic metamaterials, studies of the nonlinear acoustic properties of metamaterials, especially nonlinear acoustic metasurfaces, are quite scarce, despite the possibility to lead to a rich and diverse set of non-trivial acoustic phenomena. The key limitations in the development of nonlinear acoustic metamaterials are the typically weak efficiency of their nonlinear response together with the lack of control on this nonlinearity. This PhD research is thus dedicated to the design of nonlinear elastic metamaterial and metasurface architectures, enabling acoustic wave control in the nonlinear regime. Specifically, the conversion effect from a fundamental wave to its second harmonic is studied through the one-dimensional scattering process (reflection and transmission) by metasurfaces. This requires the elastic nonlinearity management, realized via the discrete modeling of lumped-element systems and architectures made of rotating units. Such designed metasurfaces, resonating and with harnessed nonlinearity, can create unusual nonlinear acoustic effects, potentially interesting for wave control. This research open the path to a more systematic study of nonlinear acoustic wave manipulation by metamaterials.