Alois J. Adams

Design of a light stimulator for fetal and neonatal magnetoencephalography.

The design, safety analysis and performance of a fetal visual stimulation system suitable for fetal and neonatal magnetoencephalography studies are presented. The issue of fetal, neonatal and maternal safety is considered and the maximum permissible exposure is computed for the maternal skin and the adult eye. The risk for neonatal eye exposure is examined. It is demonstrated that the fetus, neonate and mother are not at risk.

Calculation of spectral linewidth reduction of external-cavity strong-feedback semiconductor lasers.

It is shown that, to calculate the spectral linewidth reduction of an external-cavity semiconductor laser with strong external feedback, the complex laser field equation and the general linewidth-reduction equations must be modified to avoid inconsistencies. The resulting set of consistent equations and the consequent consistent linewidth reductions are discussed.

Development of a tunable, grating external cavity, strong feedback semiconductor laser with real-time wavelength monitoring

A novel tunable, grating external cavity, strong feedback semiconductor laser with real-time wavelength monitoring was designed, constructed, and tested. The wavelength monitoring was realized by recording the position of the second-order diffraction beam of the grating on a photodiode array. A wavelength tuning range of 16 nm from 648 to 664 nm, with a tuning resolution of better than 0.01 nm, was obtained. The verified tuning accuracy of the system was 0.1 nm, limited by the 0.1 nm accuracy of the monochromator used to calibrate the laser system.

Spectral reflectance of rice seedlings

The spectral reflectance of young rice plants was measured in the visible and near-IR region of the spectrum using a commercially available fiber optic contact probe and miniature spectrometer. This work aims to identify an empirical spectral index which changes when rice is exposed to increased levels of chloride anions in the irrigation water and soil. The ratio of near IR reflectance to that of green, R750/555 is known to be a quantitative measure of chlorophyll content in the leaf but int his study does not show a consistent shift for sample which are exposed to chloride levels equal to or less than 0.1 percent by mass of soil. However, leaf contact spectral reflectance measurements did reveal a significant and consistent increase in R750/555 along the length of the leaves, and this variation should represent an important factor in modeling remote and proximal sensing data.

Multi-Wavelength Laser Opacity Study of a Hybrid Rocket Plume

An instrumentation system was developed to measure the opacity of a hybrid rocket plume as a function of optical wavelength. The source consisted of collineated beams from two lasers, providing seven wavelengths in a single probe beam. Detection was accomplished with a spectrograph equipped with a photodiode array. Previous work with a two-wavelength system demonstrated the ability to follow the changes in opacity level of a hybrid rocket plume during the various stages of a typical firing cycle. The present work was to investigate the feasibility of using a multiple wavelength system to acquire more detailed information about the particulates present in the hybrid rocket plume. Qualitative analysis of the plume particulates was done by comparison of the relative extinction coefficients of the laser wavelengths with published extinction coefficient curves from Mie scattering theory. While it was found that light level fluctuations in the system prevent definitive conclusions, the data suggests that the particulate matter in the plume may consist of some optically transparent material. This is in contrast to the absorbing, soot-like material that might be expected in a hybrid rocket plume.

Optical fiber refractometer for measuring the dispersion of turbid fluids

An optical fiber with a section of its cladless core immersed in a fluid uses a refractive index (RI), n, matching method to measure n and (delta) n/(delta) (lambda) (dispersion) of the fluid. Current methods of measuring n and (delta) n/(delta) (lambda) often require light transmission through the fluid; thus turbidity, which diffuses and attenuates the light, restricts RI analysis. This device, which senses the minimum light remaining within the fiber core, is immune to such limitations. Temperature, a factor in any precise measurement of n, is the only accurate measurement needed; no critical system calibration is required. Tests were performed on clear and turbid edible oil samples, and the method matched the +/- .0001 RI unit accuracy of the Abbe refractometer. A tunable laser was used to measure the oil RI within the wavelength range of 543 to 633 nm, and the data fitted to Cauchys dispersion equation. Calculations, using (lambda) equals 589.3 nm, agree with Abbe measurements of the oil samples.