Conventional interferometry is widely used to measure spherical and flat surfaces with nanometer level precision but is plagued by back reflections. We describe a new method of isolating the measurement surface by controlling spectral properties of the source (Spectrally Controlled Interferometry - SCI). Using spectral modulation of the interferometer's source enables formation of localized fringes where the optical path difference is non-zero. As a consequence it becomes possible to form white-light like fringes in common path interferometers, such as the Fizeau. The proposed setup does not require mechanical phase shifting, resulting in simpler instruments and the ability to upgrade existing interferometers. Furthermore, it allows absolute measurement of distance, including radius of curvature of lenses in a single setup with possibility of improving the throughput and removing some modes of failure.

No description available.

No description available.

This research is focused on the application of both new and established seismic interferometry techniques to a single area: the Altiplano in the Andes region. This area has already been widely studied in terms of its geological evolution. Nevertheless, a single accepted theory has not yet been developed to explain why the topography of the Andes incorporates such a large area of low relief at this altitude. The Altiplano is therefore an interesting zone to study. This research introduces and analyses new concepts and methodologies, such as retrieving surface and body waves between earthquakes by using interferometry. Nevertheless, several factors, such as the quality of recordings, the separation between sources, and the velocity gradient of the medium, had to be taken into account for body and surface wave retrieval. This research also analysed the retrieval of body waves by means of seismic interferometry applied to coda wave arrivals. Results show that due to the attenuation of S waves produced by the zone of partial molten material, when using S coda waves, seismic interferometry does not achieve the objective of wave retrieval. On the other hand, P coda waves gave good results. Also, the combined methodology of interferometry by cross-correlation and convolution was shown to account for the behaviour of the retrieved waves and provided an indication of how the distribution of sources affects the Green’s functions estimates for body waves in this area. Another point covered by this research was the analysis of passive recordings in order to retrieve surface and body waves. Results indicate that surface and body waves could be retrieved. However, in order to retrieve body waves, special circumstances are required, such as lateral continuity of the Moho, a relative strong Moho impedance contrast, and simplicity of the geologic structure because these factors will contribute to a strong signal like that obtained in critical reflections making interferometry results more successful.

No description available.

Thesis (MSc (Physics))--University of Stellenbosch, 2009. / The exciting field of ultrashort laser optics has experienced tremendous growth since it's inception. One of it's branches that has been of continuous interest is the characterization of ultrashort laser pulses ...

Atmospheric artifacts superimposed on interferometric synthetic aperture radar (InSAR) measurements have the potential to greatly impede the accurate estimation of deformation signals. The research presented in this dissertation demonstrates a novel InSAR time series algorithm, called HiRAPS algorithm, for effectively estimating high resolution atmospheric phase screens (APS) from differential InSAR measurements. In summary, the HiRAPS algorithm utilizes short time span differential interferograms and rearranges components of existing advanced InSAR techniques to identify a higher density of scatterers used to create the APS. The improved scatterer density allows one to estimate high spatial frequency atmospheric signals not recovered from existing InSAR time series techniques. The HiRAPS algorithm was tested with simulated and actual data, which contain phase contributions from linear and nonlinear deformation, topographic height errors, and atmospheric artifacts. Simulated differential interferograms were generated to have the same spatial and temporal baselines as the actual differential interferograms formed from RADARSAT-1 data over Phoenix, Arizona. The APS superimposed on simulated differential interferograms were then estimated and compared to simulated APS. The root mean square error (RMSE) between the estimated and simulated APS was calculated to qualitatively assess the different values obtained. The RMSE was 0.26 radians when utilizing the HiRAPS algorithm, compared to an RMSE value of 0.39 radians using an implementation of the permanent scatterer (PS) algorithm. The HiRAPS algorithm also showed its applicability for estimating high spatial frequency atmospheric signals for actual data. Sixty-six SAR images, starting from October 5, 2002 and spanning 5 years, were processed for this research. The APS pixel density obtained using the HiRAPS algorithm was 253 pixels per square kilometer, compared to 14 pixels per square kilometer utilizing the PS algorithm. The APS superimposed on the differential interferograms were estimated with both the proposed and PS algorithms. High resolution APS were estimated with the HiRAPS algorithm, whereas only low resolution APS were obtained with the PS algorithm. After estimating and removing estimated APS, the phase stability of APS-free differential interferograms was examined by identifying the permanent scatterers (PS). The final density of identified PS obtained with the HiRAPS algorithm was 453 PS per square kilometer, whereas the density of detected PS using the generic PS algorithm was 381 PS per square kilometer. The maximum difference in the deformation time series between the HiRAPS algorithm and the PS algorithm was less than 6 mm. However, the HiRAPS algorithm resulted in less apparent noise in the time series than the PS algorithm due to the precise estimation of APS. / text

A new interferometric method which indirectly measures the total chromatic dispersion of a single mode fiber is demonstrated. The technique utilizes a short length of fiber, an unmodulated broadband source, simple low frequency electronics, and a standard interferometer. The concept of this measurement is based on the behavior of the uncorrelated individual bursts of light from the elemental emitters that constitute a thermal source. Their propagation through a dispersive media, e.g., silica fiber, which is placed in one arm of the interferometer, is delayed and broadened. They will interfere with their counterpart from the other arm, generating a train of time-varying fringes as one mirror of the interferometer is uniformly translated. The local frequency of the fringes at a given position of the moving mirror is a direct measure of the instantaneous wavelength, while the mirror position itself demarks the corresponding relative delay. A colinearly launched HeNe laser beam is used as a reference to calibrate the other source's fringe width and location of the mirror. In this experiment, an edge-emitting LED of λo = 830 nm and Δλ = 60 nm was used. The tested fibers had a length of 27.9 cm and 38.3 cm, which made the width of the crosscorrelation function approximately 100 times greater than the source's coherence length. The speed of the mechanically driven mirror set the frequency of the HeNe fringes to approximately 800 Hz with an r.m.s. fluctuation around the mean of 0.2%. The SNR of the HeNe fringes was four times larger than the LED's. Ten different runs for each fiber were executed. Data from the two sets of simultaneous measurements of delay versus wavelength were used to fit the best linear and quadratic polynomials with a minimum residual mean error square. The derivative of this function with respect to wavelength gave the dispersion relation. The accuracy of measured delay and wavelength were 0.1 ps and 6 nm, respectively. The dispersion value and its standard error for the best linear fit was approximately 117 ∓ 2 ps/km nm. The standard error for the quadratic fit was much larger due to the high noise level accompanying signal. A thorough investigation of the noise sources, accuracies, standard error of the polynomial's coefficient, and SNR analysis is conducted. This measurement is simple and has the potential of achieving substantially higher accuracy--especially for the longer wavelength region where dispersion is minute.

A new instrument, the liquid crystal point diffraction interferometer (LCPDI), has been developed for the measurement of phase objects. This instrument maintains the compact, robust design of Linnik's point diffiaction interferometer (PDI) and adds to it phase stepping capability for quantitative interferogram analysis. The result is a compact, simple to align, environmentally insensitive interferometer capable of accurately measuring optical wavefronts with very high data density and with automated data reduction. This dissertation describes the theory of both the PDI and liquid crystal phase control. The design considerations for the LCPDI are presented, including manufacturing considerations. The operation and performance of the LCPDI are discussed, including sections regarding alignment, calibration, and amplitude modulation effects. The LCPDI is then demonstrated using two phase objects: a defocus difference wavefront, and a temperature distribution across a heated chamber filled with silicone oil. The measured results are compared to theoretical or independently measured results and show excellent agreement. A computer simulation of the LCPDI was performed to verify the source of observed periodic phase measurement error. The error stems from intensity variations caused by dye molecules rotating within the liquid crystal layer. Methods are discussed for reducing this error. Algorithms are presented which reduce this error; they are also useful for any phase-stepping interferometer that has unwanted intensity fluctuations, such as those caused by unregulated lasers. It is expected that this instrument will have application in the fluid sciences as a diagnostic tool, particularly in space based applications where autonomy, robustness, and compactness are desirable qualities. It should also be useful for the testing of optical elements, provided a master is available for comparison.

Bacterial adhesion is the first step of biofilm formation that plays various roles in the environment and the human body. Examples of undesirable roles of biofilm formation include metal rust, sewage sludge and bacteria-related diseases. Desirable roles are biofiltration and bioremediation.For a decade, Atomic Force Microscopy (AFM) has been the primary tool used to study the adhesion and elastic properties of individual bacteria. In this work we show it is possible to use a Surface Forces Apparatus (SFA) to measure elastic and adhesive properties of small collections of surface bound bacteria. The measurements are conducted with incomplete, patterned bacterial films and we have developed a protocol to image the contact area with AFM after the experiment. Using the SFA, we measured the force profile between a P. Aeruginosa PAO1 film and a bare mica surface. We repeated the measurement in the same contact position for up to ten days to determine the effect of desiccation on the film material properties, and then moved to the new contact area to measure the film thickness and elastic properties. A large shrinkage of the bacterial film thickness was measured during the first few days due to the bacterial film desiccation and rearrangement. The proportion of shrinkage depends on factors such as the bacterial film coverage, roughness, temperature and relative humidity. Thickness compressibility was estimated from the force curves. As a force approximation, the stress at the center of the contact (σ) and the area of the contact were estimated by applying the Hertz model. Since the film is incomplete the calculated area in contact was reduced by a factor estimated from the optical image of the contact zone. Adhesiveness was measured in receding force profiles. Maximum adhesive force was detected in the first day, due to the high capillary force, decreased by the bacterial film desiccation and increased again due to the conditioning film.