A magnetically controlled total immersion hydrometer is described. Changes in upthrust due to changes in density of the solution are balanced by adjusting the current in a suitably placed coil. A simple relationship between the coil current and the density increment permits the density of the solution as a function of concentration of solute to be investigated to a high degree of accuracy. The electrolytes of 1:1, 2:1, 1:2 valence types and four tetra-alkyl ammonium salts are investigated. In all these cases the density shows a linear function of concentration over the concentration range of 5.53 x 10N to 3.32 x 10N. The molar volumes at infinite dilution calculated from our experimental results show slightly higher values in most of the electrolytes investigated. However, in cases of KF, Na2CO3, Mgcl2, Sncl2 and KOH the values of the molar volumes deviate considerably from the presently available values. The electrostriction estimated on the basis of the densities of the molten state of the electrolytes is comparable to that estimated by Mukherjee. In cases of 1:1 electrolytes the electrostriction varies from 3 ml/moleto 11 ml/mole and in cases of 1:2 electrolytes from 44 ml/moleto 53 ml/mole with an exception of Na2CO3. The electrolytesof 2:1 valence type show electrostriction around 30 ml/mole with a number of exceptions. In cases of all the four tetra-alkyl ammonium salts the electrostriction is found negative around - 20 ml/mole.

The electronic band structure of a face-centred monatomic crystal is calculated by a plane wave method. A model pseudopotential is used depending on two adjustable parameters. The object of this work is mainly to investigate how the change of the potential affects the band structure, for the case of a potential similar in some respect to pseudo-potentials which have been Used for real metals. A detailed calculation is made for the points of symmetry and along the axis of symmetry within the Brillouin Zone. Five different sets of parameters for the pseudopotential are considered and the corresponding Energy v. Wave vector graphs are plotted. Also the coefficients of the Fourier expansion of the wove function, the so-called momentum eigen functions, are plotted against the wave vector k in an extended zone scheme. The features of the band structure which are independent of the potential and those which are sensitive to any change of it are found. Finally the results given by this model are compared with the band structure of actual elements having a face-centred cubic lattice.

In the first part of the thesis we consider two theoretical problems: (a) The Kroll-Watson result for laser assisted potential scattering of charged particle has been extended to the case where a uniform static magnetic field is also present, and the consequences examined. (b) The problem of the transition of an incoming plane wave state of a charged particle entering such a magnetic field, to occupy Landau levels is solved in both the adiabatic and the sudden cases. The cross section for potential scattering in presence of a magnetic field and the limit for B0 are derived. The second part of the thesis deals with laser assisted electron impact ionisation of helium atoms. The slow electron is described in a tree-state close-coupling formulation. Conditions for the observation of the predicted splitting of the "Erhardt" pattern of the triple differential cross section are discussed.

Some problems which arise in the analysis and design of multilayer filters are discussed in this thesis. The filters consist of sequences of parallel-sided media which reflect and transmit electromagnetic radiation. The cases considered are those appropriate to the optical region of the spectrum although the analysis is quite general. In the optical region, the refractive index of a thin film is generally measured by the Abeles method, which entails determining the angle of incidence at which the film and the bare substrate have the same value of Rp. The presence of a small amount of absorption can produce errors in measurements of this kind. Two ways of estimating the magnitude of this error are given. Considerable broadening of the reflectance band of a multilayer may be obtained by 'staggering' the layer thicknesses in such a way that they form either an arithmetic or geometric progression. Results are shown for fifteen, twenty-five and thirty-five layers. The presence of the narrow band transmission peaks exhibited by the symmetric filters is explained, and the advantages of the use of this type of filter as an interference filter arediscussed. A closed form expression for the matrix product of staggered layers is obtained for the case when the difference in thickness is small. A 'least squares' method of filter design is introduced. This method may be used either to design a filter automatically if no initial design is available, or to 'refine' an existing design. The method is applied to the design of antireflection coatings, beam splitters, low-and high-pass filters and broad-band high reflectance coatings. In addition, one or two well-known filter designs are used to test the method.

Measurements of the longitudinal and transverse direct current (d.c.) magnetoresistance of n-type InP samples (carrier density from and the alternating current (a.c.) conductivity of n-type InSb samples (carrier density from have been made at temperatures T down to 0.04 K and in magnetic fields H up to 70 kG. For H=0, the InP samples were nonmetallic. At low temperatures, the conductivity is due to nearest neighbour hopping (NNH) which is followed by variable range hopping (VRH) at lower T as described by the first, and second terms in the expression. In the NNH regime, it is necessary to plot In (p/T) against T1 and this yields values of the activation energy much larger than the traditional In p versus T-1 plots In the VRH regime, Mott's law (x = 1/4) is obeyed. Values of To obtained by considering the temperature dependence of the pre-exponential factor are found to be much higher than if the temperature dependence of this factor is ignored. Good agreement between the theory and experiment is achieved in both NNH and VRH regions if an enhanced dielectric constant is used. Magnetoresistance measurements in both the NNH and VRH regimes are analysed using the theories of Shklovskii and Efros (1984) and reasonable agreement is obtained. The anisotropy of the magnetoresistance in the NNH agrees closely with the expected H2 dependence. In the VRH, In(p(H)/p(0)) varies as T-3/4 and H2 as expected for hopping with a constant density of states at the Fermi level. The InSb samples are metallic-like in zero magnetic field. High magnetic fields are applied to shrink the donor wavefunctions (to induce the metal-insulator transition) and to locate the samples on the insulator side where the measurements are carried out. The d.c. resistivity was measured and at low temperatures was of a VRH type with 1/4 x 1/2, and T0 being magnetic field dependent. Reasonable agreement with the theory is found at high fields. The real and imaginary parts of the a.c. conductivity were measured in the frequency range of 110-105 Hz. The real part of conductivity was found to vary as where s is approaching 1 at low temperatures and high fields but decreasing as T increases. At the lowest temperatures was independent of T but at higher T the temperature dependence is stronger than the linear dependence predicted by the simple pair approximation theory. Data are interpreted in terms of multiple hopping of electrons which becomes important at high temperatures and/or low frequencies. The scaling formula; has been applied to discuss the results for the real part of the conductivity, where and are normalized values and f is a universal function obtained by Summerfield (1985). The scaling parameter -log10A is found to be 3.0 +/- 0.2.The relative dielectric constant, due to donors, calculated from the capacitive part was found to be a decreasing function as the frequency is increased and/or the temperature is lowered. At very low temperatures, depending on the magnetic field, however, a temperature-independent, but frequency-dependent behaviour is observed. The lowest temperature value of the dielectric constant was found to diverge as the magnetic field is reduced towards the metal-insulator threshold value.

Equations for the Faraday rotation and ellipticity in an anisotropic material are derived in terms of quantities related to the components of the high frequency magnetoconductivity tensor. The theory is valid for all orientations of H, (the magnetic field), and Eo, (the electric vector of the incident radiation), with respect to the crystal axes. The magnetoconductivity tensor is calculated for the [111] and [100] ellipsoid band models of a cubic semiconductor, assuming the scattering to be isotropic. The treatment is semi-classical, being based on the solution of the Boltzmann equation for a single valley which is an ellipsoid of revolution. It is convenient to consider axes such that H is along one axis. The tensors are therefore transformed bo systems in which H lies in a (100) or (110) plane, and Eo takes any orientation in the plane perpendicular to the field. The tensor for the isotropic model having spherical surfaces of constant energy is obtained as a special case. The series expansion for the current density inpowers of H is also developed to 0(H2), and the associated tensor coefficients evaluated for H in the (100) and (110) planes, as for the closed solution. Detailed calculations are made of the frequency, field and temperature dependence of the rotation and ellipticity in two specimens of n-type germanium, assuming the isotropic model. One is near intrinsic and accoustic phonon scattering is considered, while the other is moderately doped and ionized impurity scattering is assumed. Calculations are also made for the lattice scattering specimen only, using the [111] ellipsoid band model. An analysis is made of the anisotropy of the rotation and ellipticity as a function of the orientation of H and Eo, in addition to a consideration of the field and frequency dependence. Approximate expressions are derived and discussed in certain regions. Finally some calculations are presented for the same specimen, using the series expansion, and a comparison of the two treatments is made.

The application of Sample Grated Distributed Bragg Reflector (SGDBR) wavelength tunable lasers for swept-wavelength Optical Coherence Tomography (OCT) is explored. OCT is a method of measuring reflectivity versus distance into samples under test with a focused infrared light source. Swept wavelength OCT requires a laser light source that is capable of sweeping its wavelength quickly over the entire wavelength range of the tunable laser. Fast sweeping of the laser's wavelength enables real-time imaging of a wide surface area of the surface under test. This thesis will show that SGDBR lasers can be designed to meet the fast wavelength ramp speeds of swept wavelength OCT and to even exceed the capability of present swept-wavelength OCT source solutions. SGDBR lasers were originally developed for telecommunications applications using Wavelength Division Multiplexing. In the telecommunications application, the wide wavelength tuning range of the device (1520-1575 nm) is utilized but the devices are only required to change wavelength over 50 ms time intervals. Research on SGDBR lasers has shown that wavelength switching speeds of 5 ns have been obtained using pre-distortion of the current drive waveforms. This thesis explores the inherent modulation speed of chip-level and packaged SGDBR lasers and the associated capability to make high speed continuous wavelength ramps for swept wavelength OCT. It will be shown that frequency modulation speeds of over 100 MHz can be accomplished with the laser drive and packaging techniques presented in this work. The result of the work shows that SGDBR lasers are very promising sources for swept wavelength OCT applications. In order to understand the present generation OCT application in more detail, work is first presented demonstrating the capability of white-light interferometry OCT in a meat tenderness measurement application. White light interferometer measurement OCT has been the standard solution for OCT measurements for at least 15 years. Measurement of a range of beef samples was done in conjunction with the college of Agriculture. Results show that the OCT setup has a penetration depth of up to 1.5 mm. The work did not show strong correlation between OCT measurement signatures and meat tenderness. The work helped to understand the OCT measurement and clearly pointed out the value of increased measurement speed using swept wavelength OCT and the potential use of SGDBR lasers as the swept wavelength source. One of the conclusions drawn from this application of OCT measurements is that the process can be improved using a faster measurement technique. The thesis then studies the characteristics of the SGDBR laser and how they map into the characteristics needed for swept-wavelength OCT applications. A major part of the work was design of both chip-level and package-level sources that were used to evaluate the laser characteristics. Specific properties of this SGDBR laser are measured: wavelength tuning characteristics, optical laser linewidth, amplitude modulation speed, frequency modulation speed and wavelength switching speed on each of the control inputs to the SGDBR device In the end, it is shown that SGDBR lasers can improve the wavelength ramp speeds in OCT. Device concerns include the laser linewidth and its limitations for swept wavelength OCT. This work provided the basis for other graduate students to build up a more complete implementation of an OCT measurement system.

No description available.

Detection within the deep ultraviolet (DUV) region (˜200-280 nm) offers unique fundamental advantages to probe certain optical traces. Therefore, many applications have emerged including flame and missile detection, and non-line of sight and space-to-space communication. Ga2O3 has become a natural choice for DUV detection owing to its intrinsic ultra-wide optical bandgap (˜4.85 eV), extrinsic n-type dopability, and excellent chemical and physical stability. However, Ga2O3 has no viable p-type doping to date, and fabricated photodetectors show only partial coverage of the entire solar-blind region (˜200-245nm). Furthermore, there is a limited understanding of how various growth parameters for ß-Ga2O3 and its alloys impact the material properties (i.e. defects), and how these ultimately play a role in functional device characteristics. This dissertation aims to address the aforementioned challenges with systematic studies spanning across epitaxial growth by molecular beam epitaxy (MBE), device fabrication, and characterization, leading to a comprehensive understanding of how these impact the optical, structural, compositional, and device properties. The experiments start with homoepitaxial and heteroepitaxial growth of Ga2O3 on bulk n-Ga2O3, sapphire, and advance to the growth on Si by MBE for monolithic integration. A novel nucleation technique of Ga2O3 on n-Si substrate allowed achieving one of the fastest functional DUV photodetectors with high responsivities. Furthermore, bandgap engineering via alloying Ga2O3 with In and Sn improved the DUV coverage, extending the cut-off wavelength beyond ˜245 nm, while benefitting higher responsivities. A record-setting photoresponsivity (˜35 kA/W) among planar devices was achieved with Sn alloying. The mechanisms leading to the unusually high photoconductive gains in these devices were investigated to determine the root cause. Point defects, particularly gallium vacancy-related complexes, are identified as the most likely source of ultra-high gains by hole-trapping at space-charge-region of Schottky barrier photodetectors. Moreover, a direct trade-off between bandwidth and responsivity was observed due to these complexes.

Surface acoustic wave (SAW) devices have provided solutions to many sensor applications. With the increasing use of the electromagnetic spectrum, the adoption of higher frequencies for new developments is becoming a necessity. SAW devices represent a solution for advancing many emerging sensor's needs given their inherent advantages such as: wireless operation, low cost, and ease of fabrication. However, the SAW technology has been typically limited to frequencies under 3 GHz due to size limitations, increased SAW losses, and the need of an interrogation system suitable for reading SAW sensors at higher frequencies. This dissertation presents the work done to push up the frequency limitations of SAW sensors by using the harmonic response of a SAW device to sense temperature and strain at 4.74 GHz. Transducer configurations for harmonic response are studied using the theory on SAW transduction. The development of 4.3 GHz harmonically operated SAW devices is presented as initial work and part of a NASA SBIR project to investigate the feasibility of the harmonic operation concept applied to the Wireless Avionics Intra-Communications (WAIC) band. Measurements of the devices at fundamental and harmonic frequencies were validated using the coupling of modes (COM) model. 4.74 GHz SAW devices were fabricated using a SAW mask provided by Pegasense, LLC. This mask, designed for 4.3 GHz devices using LN YZ cut, was used to fabricate higher frequency devices using LN YX 128 cut. Temperature and strain SAW sensors harmonically operated at 4.74 GHz were fabricated. Finally, a 4.74 GHz SAW interrogation system is developed, the UCF SAW SDR software is improved, a transceiver is fabricated, and the interrogation of 4.74 GHz harmonically operated SAW temperature and strain sensors is demonstrated.