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.
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.
Abstract
We report high resolution nonlinear laser spectroscopy studies of excitation relaxation
associated with the excitonic optical nonlinearity at room temperature and low temperature in
GaAs/AlGaAs multiple quantum wells. Using a new method of cw frequency domain four wave
mixing, we show that relaxation of the room temperature nonlinear optical response is
characterized by free carrier recombination and ambipolar diffusion. At low temperature, the
excitation relaxation for localized excitons is dominated by phonon assisted tunneling. In addition,
we use four wave mixing methods to eliminate contributions to the excitation line shape from
inhomogeneous broadening. The observed line shape is highly asymmetric and shows the presence
of spectral diffusion due to the phonon assisted tunneling associated with the excitation relaxation.
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