Over the past ten years we have seen a vast increase in interest and research related to air pollution as a facet of the general environmental awareness. The buzz words fly thick and fast, and amidst all the rhetoric, it is difficult to know if any really significant scientific contributions have been or are being made. This issue, devoted in part to environmental optics, shows the SPIE's awareness of the field although this coverage is by no means even partially complete. It also offers me a forum from which to state at least one opinion on the realities of the situation.
Raman Lidar techniques have been discussed theoretically and sensitivities for various pollutants have been predicted. The results of the present real Raman Lidar indicates pollutant levels between 40-700 ppm is the present sensitivity but very realistic projections based on this data suggest sensitivities between 0.4 - 7 ppm could be reached if nondispersive detection techniques were used.
It has been shown experimentally that a measurement of the Raman shifted component of the laser backscatter from atmospheric nitrogen will give a direct determination of transmission as a function of range. This type of single-ended device, when operating in a radar-like mode, can satisfy the need to accurately measure atmospheric transmission. A major difficulty in the interpretation of pulsed lidar backscatter data is that unless a priori information is available concerning the relationship between the volume backscattering coefficient and the attenuation coefficient, the received intensity cannot be easily evaluated as transmittance. The backscatter coefficient for Raman scattering, however, depends only on the Raman cross-section of the specific molecule used and the number density of that molecule. In the lower atmosphere the density of atmospheric nitrogen is constant. A measurement of Raman scattering from nitrogen will therefore give a direct determination of transmission as a function of range. Experiments were conducted over a 1/4-mile range and produced consistent results for transmissions down to as low as 2 percent when compared with simultaneous double-ended reference transmissometer data. The laser Raman transmissometer system is now computer controlled and produces real time data displays.
Long path infrared spectroscopy of air pollutants is operationally classified into several system types: Long folded path samplers, two station remote instruments using either a remote source or a remote retroreflector, and one station remote instruments using either natural sources, laser backscatter, remote fluorescence, or passive measurement of sample thermal emission. The operational requirements of each system are described, as are their advantages, disadvantages, and one example each of their results. A comparison of their overall performance reveals that the best system now available would be a two station remote device with an array of distal retroreflectors, employing a correlation Fourier Transform Spectrometer as a receiver. The main application of such a system would be the detection of widely dispersed pollutants at extremely low concentrations.
The optical and mechanical design of a derotator unit employing a Delta prism are described. Comparisons with other derotation prisms demonstrate the space and weight advantages of the Delta in collimated light. Curves showing the dependence of input FOV and apex angle on refractive index are presented. The small size and single-piece construction of the D elta facilitate a mounting design which is environment resistant and enables precise adjustment.
In the study of Optical Behaviour of Materials, spectroscopic instruments are used for irradiation of samples as well as for analyzing emitted radiation. Many of these instruments use prisms or gratings as dispersing components. There are a few basic types of these instruments utilizing the above dispersing components. Again depending on the region, these instruments use either plane gratings or concave gratings. Generally speaking, plane grating instruments are used above 2000 A, whereas concave grating instruments are used in the vacuum ultra violet region. Many of these instruments have ingenious scanning mechanisms to display the wavelength or the wave number linearly. The present article tries to review some of the basic principles of these instruments as well as recent progress in this field.
Descriptions of bore-hole cameras with several applications are presented. Their main feature is to inspect, by photographic recording, the walls of confined places, such as drillings in foundation and geological engineering, and inspection through small holes of restricted areas -as in medicine and industry. Development of a compact holographic system was achieved, which enables recording the three dimensions with high resolution and good contrast. It is believed that in the future, integrated optics will be applied, and micro-miniature photographic cameras will be developed for the mentioned and many other applications.
The thermal properties of certain pressed materials have been measured. In particular, specific heat measurements on hot-pressed and single crystal cadmium sulfide have been made between 1 and 20 K. An anomalous specific heat in the pressed material was observed below 1.5 K, and it is believed to be associated with the electronic structure of defects. The thermal conductivity of hot-pressed cadmium sulfide and hot-pressed magnesium fluoride has been measured in the temperature range 2 to 90 K. The results are compared with the single crystal data. The data are analyzed with a model that includes phononphonon interactions, pointdefect scattering, dislocation scattering, and boundary scattering. The sound velocity and ultra-sonic attenuation of hot-pressed CdS and hot-pressed MgF2 have been measured between 4 K and room temperature.
The test results presented were obtained over a 9 month period at the Naval Electronics Laboratory Center at San Diego. The test objective was to assess the structural and other physical property characteristics of incoherent, plastic jacketed, glass fiber-optic cable types of current manufacture. Tests were conducted to evaluate the capabilities of these type products to sustain structural integrity and operability after subjection to test exposures simulating Naval shipboard environmental conditions. A total of 29 types of tests were performed utilizing over 200 fiber-optic cables. A major part of this task involved the development of diagnostic test techniques for the evaluation of the test induced cable property modifications. A final report detailing the fiber-optic cable performance obtained in this test program is available by writing to the Library, Naval Electronics Laboratory Center, San Diego, California 92152. The report is entitled "Fiber-Optic Cable Test Evaluation" and identified as NELC TR-1869.