Carbon monoxide adsorbed on Cu(100) Studied by infrared spectroscopy

Derivative luminescence spectrometry

Optical apparatus for forming correlation spectrometers and optical processors. The optical apparatus comprises one or more diffractive optical elements formed on a substrate for receiving light from a source and processing the incident light. The optical apparatus includes an addressing element for alternately addressing each diffractive optical element thereof to produce for one unit of time a first correlation with the incident light, and to produce for a different unit of time a second correlation with the incident light that is different from the first correlation. In preferred embodiments of the invention, the optical apparatus is in the form of a correlation spectrometer; and in other embodiments, the apparatus is in the form of an optical processor. In some embodiments, the optical apparatus comprises a plurality of diffractive optical elements on a common substrate for forming first and second gratings that alternately intercept the incident light for different units of time. In other embodiments, the optical apparatus includes an electrically-programmable diffraction grating that may be alternately switched between a plurality of grating states thereof for processing the incident light. The optical apparatus may be formed, at least in part, by a micromachining process.

Optical apparatus for forming correlation spectrometers and optical processors

Kreuzer has demonstrated the feasibility of detecting atmospheric pollutants using acoustic signals produced by volumetric absorption of infrared radiation. We have investigated a substantial improvement of this technique wherein the optical excitation beam is modulated at a frequency corresponding to a natural acoustic resonance of the sample chamber. Acoustic amplification factors exceeding 100 have been observed.

Acoustic amplifier for detection of atmospheric pollutants

Three methods of remote air pollution detection-Raman backscattering, resonance backscattering, and resonance absorption-are discussed and compared. Theoretical expressions are derived for the minimum detectable pollutant concentration, and in each case the depth resolution and the problems of interference, pump depletion, and background noise are discussed. A brief discussion of possible laser sources is included, numerical examples of the detectabilities based on present technology are given. The atmospheric transparency limits the useful range to a few kilometers for the Raman and resonance backscattering schemes. For the resonance absorption technique the useful range can be as great as 50 kilometers.

Comparison of laser methods for the remote detection of atmospheric pollutants

The theory and performance are described of a small portable second derivative spectrometer, the d2spectrometer The physical principles of the apparatus permit detection of gases by absorption spectrometry with sensitivities two or more orders of magnitude greater than is attainable by use of more conventional spectrometers When the spectrometer is used with a readily portable absorption cell having a 772-m folded light path, some common air pollutants are detectable in concentrations of parts per 100 million or less Other designs of absorption cell permit measurement of ammonia in blood or in expired air

The derivative spectrometer.

The method of spectrometric determination of gas concentration by use of a mask is examined and described. Calibration curves for four gases, NH(3), C(6)H(5)CH(3), NO(2), and SO(2), are reported in detail, and results are included for C(6)H(6), NO, and SiF(4). The calibration curves are shown to be linear in a log-log plot over ranges of practical interest. The slopes are reproducible. The technique used in making masks is described. The proposed manner of making measurements involves the use of a small reference cell containing a sample of the gas being measured. When such a method of measurement is used, several gases of practical importance are concluded to be determined as to concentration to a few parts per billion with a precision of 10% or less, if path lengths of the order of several hundred meters are used. The results appear to be independent of the presence of unknown absorbing gases under many circumstances.

Molecular correlation spectrometry.

A STUDY of the fluid dynamics of ablating bodies has been pursued at the University of Florida for the past three years In this study, blocks of soluble material have been mounted on suitable supports located under water on the prow of a small skiff, which is then propelled at known constant speed by use of an outboard motor The changes in shapes of the soluble specimens have been observed as a function of the boat speed, the time, the initial model shape, and its material composition In early experiments, models of salt which had an initial cylindrical symmetry about the direction of relative motion of the water—square-ended cylinders, or ogives—were found to erode to a shape that seemed to change very little with time but for scale The shape could be described in terms of the coordinates x and y, where the lateral dimension y is measured vertically from the line of cylindrical symmetry of the model at a distance x measured along that axis from the forward tip of the shape The relation between y and x was found to be

Terminal shapes of ablating bodies

A was made some years ago of the evidence of the nature of air flow over the surfaces of meteorites during their flight through air when they entered the earth's atmosphere That evidence is left on the surface in the form of flow lines due to streaming of molten rock or iron oxide, just before the bodies in question were decelerated enough for ablation to cease In that study the suggestion was made, as based on the observations, that the shallow pits that have often been observed on meteorites, particularly iron ones, might have been caused by peculiarities of the air flow over the meteorite surface rather than by inhomogeneities of the meteorite material In particular, it seemed likely that a pit would form in a surface if the flow that causes ablation can exist in the form of a "bound vortex/ that is, a vortex with axis having a horseshoe shape which is held in one place on the ablating surface by the pressure gradients of the fluid flow The pit would be formed at the apex of the horseshoe; the ends of the vortex would trail off to infinity in the wake The horseshoe shape was concluded to be essential for the purpose of satisfying the continuity relation for the reversed flow implicit in any assumed vortex As a rather direct method for demonstrating that vortices of the type proposed actually exist over the surface of an ablating body and that, when they do, pits will be formed, tests were made by use of steady water flow over the surface of large salt blocks such as are fed to cattle The relation between bound vortices and surface pits was verified in that pits were formed where bound vortices were predicted to exist, and not where they were absent Figure 1 shows one of the pitted blocks The evidence of the horseshoe shape of the bound vortex, presumed to have carved the pit, is clear in the shape of the lower one The question was posed how the ablation rate beneath a vortex could possibly be as great as that where no vortex exists; presumably, ablation rate depends on flow speed, which, in a vortex and especially inside a pit, certainly is less than it would be outside An answer might be obtained if the flow about the pitted shape were studied in air flowing with the same Reynolds number as the water that shaped the block, under conditions of dynamic similarity, t For measurement of the air flow inside the pit, a special velocity probe was made It consisted of two lengths of 0046-in capillary tubing, each length closed at one end and pierced with a small hole in a side as near to the closed end as possible The two tubes were soldered together with the

Flow in pits of fluid-dynamic origin

In the paper by Grum et al. the point was made that derivative spectrometry is analytically very powerful; and a great deal of very persuasive data were adduced to support that statement. Those who have had experience in modern spectrophotometry could hardly agree more with the assertions of the authors. In one respect, however, the paper has left out a rather important fact. The authors say: \"The field . . . is surprisingly new. And, to the best of our knowledge, only one' derivative spectrophotometer is commercially available for this specific purpose.\" The reference they include is to a Perkin-Elmer publication. Some other spectrometers are also stated to have the derivative capability. I would like to point out that there is currently in production and for sale, a second instrument, namely a second-derivative spectrometer, the model III d analyzer. It is manufactured by Spectrometries of Florida, P.O. Box 517, Pinellas Park, Florida 33565. This instrument, originally developed for use in air pollution applications, is capable of recording the second-derivative signal between about 190 nm and 310 nm. It has an absorption cell providing a 24-m absorption pathlength and records many pollutant gases down to concentrations as low as parts in 10 depending on the gas. The model III instrument records directly and in real time the concentrations of SO2, NO, NO2, and O3— and if desired, it could be arranged to record any number up to

David T. Williams

Papers

The derivative spectrometer.

Molecular correlation spectrometry.

Terminal shapes of ablating bodies

Flow in pits of fluid-dynamic origin

Comment on: Derivative Absorption and Emission Spectrophotometry.