No description available.

No description available.

No description available.

No description available.

This work describes the use of a broadband spectral source for nonlinear spectroscopy to characterize various materials with potential applications in confocal microscopy, biological sample markers, optical limiting devices and optical switches. The goal is to study the spectrum of nonlinear absorption and the dispersion of nonlinear refraction as well as the dynamics of the nonlinearities by means of femtosecond excite-­probe experiments. The principle is quite simple: if a sample is under the influence of a strong fs excitation pulse and a pro be pulse beam is incident at the same time, or shortly after (within the decay time of the nonlinearity), then the probe pulse will sense the nonlinearity induced by the excitation. If the probe pulse is broadband, a femtosecond white-light continuum (WLC) in our case, we can monitor the nonlinearity induced over the entire continuum spectrum in one laser "shot". The use of femtosecond laser pulses to generate WLC will provide femtosecond time resolution for time-resolved spectroscopy. We built the nonlinear spectrometer and allowed for many degrees of flexibility in terms of choice of wavelengths for pump and probe beams and a dual detection system to cover both visible and infrared spectral ranges. We have the possibility of performing broad band spectral measurements using a spectrometer or selected narrow bandwidth probes incident on Si or Ge photodiodes for improved S/N ratios. The intrinsic properties of the continuum probe demand a careful characterization of its spatial and temporal profile. Know ledge of the dispersion of the index of refraction in various optical elements, including the sample itself, is also required for a correct analysis of the transient absorption raw data, especially for short time-scale dynamics of nonlinear processes. We tested the system using well-characterized semiconductor samples, and the results came out in excellent agreement with those from previous picosecond Z-scan measurements and theoretical modeling. With confidence, we can now measure various organic dyes with enhanced two-photon and excited-state absorption. Our setup is used to conduct a systematic study on similar compounds with modified molecular structures in order to learn about structure-property relations and draw guidelines for future design work.

No description available.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Call number: LD2668 .T4 1955 O88 / Master of Science

Call number: LD2668 .T4 1955 M32 / Master of Science

In an industrial application a GFAAS method for monitoring the Rh concentration in process streams is being used. Matrix effects are known to exist with the application of this technique; in fact, it was observed that different solvents lead to different results. Therefore, standard additions have to be employed for quantitative determinations, resulting in high costs and long analysis times. In an attempt to understand these interfering effects, fractional factorial designs were proposed to determine whether any GFAAS parameter was responsible for, or related to, the matrix effects. Seven GFAAS parameters were investigated: final temperature, ramp time and hold time of the transitions step (from the dry step); final temperature, ramp time and hold time of the ashing/pyrolysis step; ramp time of the atomisation step. The results showed that the matrix effects were not related to any specific parameter. A complete factorial design was implemented to demonstrate the fundamental role of the atomisation temperature. SEM analysis showed that the surface of the graphite tubes might be affected in different ways by different solvents. A Principal Component Analysis demonstrated that the matrix effects may be related to the viscosity and melting point of the solvents and may be independent of their molar mass. To identify the origins of these effects, an investigation on the link between the tube surface-sample matrix interactions and the physical properties of the matrices is recommended. Since GFAAS parameters cannot compensate for the matrix effects, standard additions remain the preferred mode of operation as it accounts for the effects in-situ. / Chemistry / M.Sc. (Chemistry)