Differential reflectance of natural and man-made materials at CO(2) laser wavelengths.

The differential reflectance of several naturally occurring and man-made materials at CO(2) laser wavelengths is determined. The computer-controlled measurement system has two CO(2) lasers and determines the differential reflectance of each material by measuring the ratio of the reflected signals at two wavelengths simultaneously. These results can be used to improve the accuracy of air pollution measurement systems which derive their return signals from topographic targets.

Laser absorption spectrometer: remote measurement of tropospheric ozone.

The laser absorption spectrometer (LAS) is an airborne instrument able to perform remote measurement of trace atmospheric gases. The instrument uses a pair of carbon dioxide laser-heterodyne receiver systems that are directed downward from an airplane and determines gas concentration by the differential absorption method. Configured to measure tropospheric ozone, the LAS has been used in conjunction with another instrumented aircraft to test the accuracy of this method of measurement. A complete description of the instrument is presented, and the results of extensive flight testing are summarized.

Optoacoustic detection using Stark modulation.

Stark modulation of the absorbed laser radiation in an optoacoustic detector (or spectrophone) is reported. Measurements were made over a range of total pressure between 760 Torr and 50 Torr. Greatly enhanced molecular discrimination is suggested due to the tuning ability of the Stark-shifted absorption. The background signal obtained by operating in this mode is more than 500 times smaller than that obtained by operating the same optoacoustic detector in the conventional chopped radiation mode. The responsivity of the optoacoustic detector and the absorption coefficient of C(2)H(4) are presented as a function of total pressure.

Remote measurements of ambient air pollutants with a bistatic laser system.

The ambient air pollutants ozone, nitric oxide, and ethylene have been monitored in the Pasadena area with a bistatic ir laser apparatus. These pollutants were measured with a differential absorption technique using selected wavelengths in the 9.5-microm, 5.2-microm, and 10.5-mum regions, respectively. The transmitted laser radiation was detected using both direct and heterodyne detection techniques. In the direct detection case cube corner retroreflectors provided the return, and the heterodyne detection responded to scattered radiation from various rough surfaces, ranging from 400 m to 1.9 km in distance from the apparatus. Significant departures from ambient background concentration levels were noticed in the region near a local freeway during periods of moderate and heavy traffic.

Water vapor absorption of carbon dioxide laser radiation.

An optoacoustic detector or spectrophone has been used to perform detailed measurements of the absorptivity of mixtures of water vapor in air. A C(12) O(2)(16) laser was used as the source, and measurements were made. at forty-nine different wavelengths from 9.2 microm to 10.7 microm. The details of the optoacoustic detector and its calibration are presented, along with a discussion of its performance characteristics. The results of the measurements of water vapor absorption show that the continuum absorption in the wavelength range covered is 5-10% lower than previous measurements.

Air pollution: remote detection of several pollutant gases with a laser heterodyne radiometer.

An infrared heterodyne radiometer with a spectral resolution of 0.04 reciprocal centimeters has been used to remotely detect samples of ozone, sulfur dioxide, ammonia, and ethylene at room temperature, and samples of nitric oxide at 390K. Each gas was observed in a background of nitrogen or oxygen at atmospheric pressure. Sensitivities to some of these gases are adequate for detection of ambient concentrations as low as a few parts per billion.

Interferometric measurement of large indices of refraction.

A method for determination of refractive indices which may be applied to thin flat plates of optical materials is considered. It is particularly suited for use with materials whose refractive indices are large (>1.8), but is not limited in the range of refractive index it can determine. The method uses an interferometer to measure the optical pathlength through a sample, and is shown to have moderate accuracy: +/-2 x 10(-4) in refractive index for a sample 0.5 mm thick. The effect of a nonideal sample is considered, and is shown to have only a small effect on the accuracy. The method has been applied to singlecrystal barium titanate in the visible spectrum, and tabulated results are given.