Jeffrey Thomas Remillard

Ellipsometric study of a palladium catalyst during the oxidation of carbon monoxide and methane

Spectroscopic ellipsometry is used to monitor the surface of a thick Pd‐film catalyst during the oxidation of either carbon monoxide or methane. Dense PdO layers form under sufficiently lean conditions (excess oxygen) for both reactions. A stable metal surface exists in the case of CO, but a very porous PdO layer develops in the case of methane, under rich conditions. There is a large hysteresis in the conditions for PdO formation in the case of CO oxidation. Spontaneous oscillations in catalytic activity and Pd‐surface composition occur for both reactions, the higher activities corresponding to O‐atom‐rich or PdO‐rich surfaces for CO or methane oxidation, respectively.

Sub-Doppler resolution limited Lamb-dip spectroscopy of NO with a quantum cascade distributed feedback laser

A quantum cascade distributed feedback laser operating at 5.2 microm is used to obtain sub-Doppler resolution limited saturation features in a Lamb-dip experiment on the R(13.5)1/2 and R(13.5)3/2 transitions of NO. The dips appear as transmission spikes with full widths of ~ 4.3 MHz. At this resolution the 73 MHz _-doubling of the R(13.5)3/2 line, which is normally obscured by the 130 MHz Doppler broadening, is easily resolved.

Using a Wavelength-Modulated Quantum Cascade Laser to Measure NO Concentrations in the Parts-per-Billion Range for Vehicle Emissions Certification

Measurements of NO concentrations at sub-ppm levels in vehicle exhaust are needed for emissions certification of future ultra-low emission vehicles. We demonstrate a wavelength-modulation, laser-based, NO detection system suitable for this purpose. A quantum cascade distributed feedback laser (QC-DFB) operating continuous wave (cw) at ∼100 K is frequency modulated at f = 10 kHz and locked to the center of a transition at ∼1921 cm−1 in the fundamental band of NO. The demodulated signal at 2f of the beam passing through the sample cell directly measures the NO concentration. The cell is a multipass Herriott-type with a 100-m path length. Doppler broadening, pressure broadening, and unresolved Λ doubling combine to yield a pressure for optimum sensitivity of 100 torr and a modulation amplitude of ∼600 MHz. A flowing gas system is used to avoid problems with adsorption and desorption of NO from the cell walls. The reduced pressure eliminates interference from other gas species. Detection of NO concentrations in the few parts-per-billion (ppb) range is demonstrated in diluted exhaust-gas bag samples collected in the vehicle certification process.

Pedestrian detection in near-infrared night vision system

Several premium automotive brands offer night vision systems to enhance the drivers ability to see at night. Most recent generation night vision systems have added pedestrian detection as a feature to assist drivers to avoid potential collisions. This paper reviews pedestrian detection based on two different sensing technologies: active night vision operating in the near-infrared (NIR) region of the electromagnetic spectrum, and passive night vision operating in the far-infrared (FIR) spectrum. It also discusses the pros and cons of each type of night-vision system with-respect-to the pedestrian detection capability, the effectiveness for collision avoidance, and the commercial attractiveness. The paper introduces an enhancement to the NIR active lighting scheme that significantly improves the pedestrian detection performance. With improved pedestrian detection performance, we argue that the NIR night vision system is more effective at improving night-time driving safety and may achieve broader market acceptance.

Demonstration of a high-temperature fiber-optic gas sensor made with a sol-gel process to incorporate a fluorescent indicator

To make a gas sensor suitable for use at high temperatures, we have used a sol-gel-processing technique to bond a copper-exchanged zeolite fluorescence indicator onto the end of an all-silica optical fiber. Experimental results from single-fiber prototype sensors show they can be used to measure either the oxygen concentration or the equivalence ratio for gas mixtures containing weak or strong reductants, respectively.

Diode laser illuminators for night-vision applications

We describe a prototype night vision system for automotive applications that uses a high power near-infrared (NIR) diode laser, compact optics, and a CCD camera. Because NIR radiation is invisible to the human eye, a high-beam illumination pattern can be formed permitting a clear view of objects on both sides of the roadway, even in the presence of oncoming traffic. A narrow band-pass filter in front of the camera passes only the laser wavelength and prevents blooming of the image due to the headlights of other vehicles. This system permits drivers to see objects at night (such as debris or pedestrians) that are in close proximity to oncoming vehicles. The diode laser operates at 810 nm and emits 5 - 10 W. The illuminator distributes the laser light using a combination of refractive, reflective, and holographic optics in a manner that meets the standards for Maximum Permissible Exposure. We discuss the performance of our prototype system as a function of laser power and camera field-of-view and sensitivity, and we provide comparisons with a commercially available automotive night-vision system that uses a thermal-imaging camera.

Loss mechanisms in optical light pipes

A geometrical optics approach is used to develop a theoretical model for analyzing loss mechanisms in optical light pipes. Five mechanisms are identified: intrinsic absorption, bulk scattering, losses that are due to roughness at the core-cladding interface, losses that are due to large-scale defects at the core-cladding interface, and losses that are due to absorption in the cladding material; and the effects of each of these on light-pipe transmission are considered. An approximate model appropriate for slightly rough surfaces is used to estimate the loss that is due to interface roughness. Optical experiments on commercially available light pipes are done to quantify the various loss processes. These experiments indicate that the interface effects play an important role in limiting the transmission in high-quality light pipes. From the optical measurements a rms interface roughness height in the 30-70-A range is deduced, and these values are confirmed by direct surface profilometry with an atomic force microscope.

Diode-laser-illuminated automotive lamp systems

We have utilized the high brightness of state-of-the-art diode laser sources, and a variety of emerging optical technologies to develop a new class of thin, uniquely styled automotive brake and signal lamps. Using optics based on thin (5 mm) plastic sheets, these lamps provide appearance and functional advantages not attainable with traditional automotive lighting systems. The light is coupled into the sheets using a 1 mm diameter glass fiber, and manipulated using refraction and reflection from edges, surfaces, and shaped cut-outs. Light can be extracted with an efficiency of approximately 50% and formed into a luminance distribution that meets the Society of Automotive Engineers (SAE) photometric requirements. Prototype lamps using these optics have been constructed and are less than one inch in thickness. Thin lamps reduce sheet metal costs, complexity, material usage, weight, and allow for increased trunk volume. In addition, these optics enhance lamp design flexibility. When the lamps are not energized, they can appear body colored, and when lighted, the brightness distribution across the lamp can be uniform or structured. A diode laser based brake lamp consumes seven times less electrical power than one using an incandescent source and has instant on capability. Also, diode lasers have the potential to be 10-year/150,000 mile light sources.

Evanescent-wave scattering by electrophoretic microparticles: a mechanism for optical switching.

The total internal reflection of light occurring at the interface between glass and a low-index liquid containing suspended microparticles can be electrically controlled. The particles are charged and the glass is coated with a thin, transparent conductor. When the conductor is biased to attract the particles, they scatter and absorb light from the evanescent optical field near the interface, thus reducing the reflectivity. When the conductor is biased to repel the particles, total internal reflection is achieved. Experimental results are given for the time, voltage, and angle-of-incidence dependence of the reflectivity at the interface between an In-Sn-oxide-coated glass surface and a suspension of 0.47-µm-diameter silica particles in acetonitrile. The switching is found to be fast (~ 100 ms) and reproducible. In certain conditions the on/off ratio for a single reflection can be as large as 2:1. A simple theoretical model is developed to interpret these experiments. The model gives a reasonable fit to the data and allows one to extract information such as the particle mobility and the particle density in the evanescent-wave region.

Degradation of Urethane-Foam-Backed Poly(Vinyl Chloride) Studied Using Raman and Fluorescence Microscopy

Urethane-foam-backed poly(vinyl chloride) (PVC) degrades through dehydrochlorination, a process that results in the formation of conjugated polyene sequences within the backbone of the polymer. Raman spectroscopy at 633 nm and a combination of fluorescence spectroscopy and microscopy with blue excitation have been used to quantify the temporal degradation of two commercial foam/ vinyl composites. Since the resonance behavior of polyenes depends on their conjugation lengths, the Raman and fluorescence measurements were most sensitive to polyenes with conjugation lengths of ≥20 and ∼10, respectively. Durability tests were performed by weathering samples in the field for 35 months and in ovens at temperatures of 100 and 120°C for ∼500 h. For the field-weathered samples, the integrated fluorescence intensity correlates well with the polyene concentration as determined by Raman measurements, which suggests that for these aging conditions the kinetics controlling the steady-state populations of short- and long-length polyene sequences are similar. The results from the laboratory-weathered samples are consistent with the conclusion that short-conjugation-length polyenes form first and then propagate to longer conjugation lengths as degradation progresses. Most importantly, this work demonstrates that the relatively simpler fluorescence imaging techniques can be extremely useful in determining the comparative weatherability of different foam/vinyl composites.