A common form of the expression for NETD (Noise Equivalent Temperature Difference)* for FLIR (Forward Looking InfraRed) sensors suggests that the sensor SNR (Signal to Noise Ratio) is inversely proportional to the square of the f-number of the imaging optics. This is an incorrect conclusion in the case of nearly BLIP systems since the detectivity of an appropriately cold shielded detector array varies with f-number in such a fashion as to eliminate the f-number dependence to the first order. It is more appropriate to consider
The August 1977 SPIE Annual Symposium devoted one of its seminars to Laser Engineering. What is laser engineering? To answer that, one must decide what engineering is and how it is distinguished from development or research. Without getting enmeshed in a web of confusing semantics and nuances, one can say without controversy that the term "engineering" is commonly used when there is considerable economic activity in existence or in prospect, and when hardware, structures, or products result. Of course, there can be rather close coupling between engineering and science. The engineering of a new accelerator for basic high energy research or a basic materials research program to obtain improved semiconductor devices are two examples.
This paper presents the phenomenology of different approaches to the frequency-shifting (upconversion) of infrared radiation into the visible and discusses the practical aspects of designing systems to upconvert IR images. The recently discovered process of upconverting infrared radiation into the visible or the ultraviolet using two-photon-pumped alkalimetal vapors and the more familiar method of frequency mixing using single-photon-pumped nonlinear crystals are described and compared. In addition to these coherent processes, the use of quantum-counter action in certain crystals to convert an IR photon into a visible photon by an incoherent process is discussed. The important performance parameters of an IR imaging system are discussed briefly and the considerations and constraints involved in the design of coherent and incoherent image upconverter systems are presented. Using this background, practical system designs are developed for both active and passive imaging. The expected performances of these systems are compared with those of IR imaging systems based on direct-detection of IR photons with semiconductor detectors.
The design and performance of optical cables, connector hardware and communication systems are governed by the light transmission and coupling characteristics of waveguide fibers. These characteristics depend upon waveguide design and materials as well as manufacturing tolerances. Measurement methods and limitations are discussed, and use and interpretation of waveguide specifications in designing optical links and predicting overall performance are shown.
The second harmonic of the Nd:YAG output wavelength (1,064 nm) can be produced with both CD*A and KD*P with efficiencies approaching 50% when the crystal indices of refraction are equal at the fundamental and second-harmonic frequencies - the so-called "phase-matching" condition. For Type I doubling processes, this condition can be satisfied by allowing the ordinary index of refraction at the fundamental wavelength to be equal to the extraordinary index at the doubled frequency. For Type II doubling, the necessary condition is that the extraordinary index at the second harmonic be the average of the extraordinary and ordinary indices at the fundamental. For CD*A, phase matching can be accomplished via the Type I process with 0m=90° by elevating the crystal temperature to ~100 deg C, depending on the deuteration level of a specific crystal. For a 21-mm-long CD*A crystal, the width of the temperature versus efficiency curve is 3.25 C FWHM. Ninety-degree phase matching allows efficient doubling with incident beam divergences an order of magnitude greater than diffraction limited and does not introduce walkoff resulting from double refraction. Data are presented showing doubling efficiency as a function of crystal length and incident average power density, including considerations of efficiency and average power saturation. Type II KD*P phase matches at room temperature with 0m=53°36'. To obtain efficient doubling in this case, the incident fundamental beam divergence must be close to diffraction-limited. The angular halfwidth of a 25-mm crystal is 1 mr FWHM for rotation about the ordinary axis. Compared to CD*A, the use of KD*P is advantageous because of its ready availability, high damage thresh-old, high saturation levels and usefulness at room temperature. Using a 3.0-J pulsed Nd:YAG laser with a repetition rate of 10 pps, 10.5 W of 532-nm power has been achieved.
The problem of obtaining high yields in the manufacture of HeNe lasers is compounded as the number of specified performance parameters is increased. This problem is especially difficult when lasers have a low noise specification. Some common kinds of noise encountered in HeNe lasers are discussed along with ways of eliminating or reducing such noise. A case history describing improvements in performance and production yields of one laser model is given.
There has been a strong need for a rapid automated technique to count bacteria in urine. This paper demonstrates that the optical scattering pattern analysis for a collection of heterogeneous particles in a tenuous solution can be effectively applied to species identification and concentration estimation for bacteria. The scattering patterns are measured with latex spheres and bacteria (Escherichia coli and Staphylococcus aureus). They agree well with theoretical calculations using the Mie theory and the Rayleigh-Debye approximation, taking into account size distribution and random orientation. The parameters such as average size, axial ratio, size variation and refractive index are estimated to give a good agreement between the theory and the measurement. The values of the parameters agree with those in the literature. The scattering pattern is found to be sensitive to the aggregation of scatterers. The parameters obtained from the scattering pattern analysis are used to improve the estimation of bacterial concentrations by turbidimetry. The estimated values agree within a factor of 10 with those obtained by conventional culturing technique.
The Dynalyzer ll can be used as a troubleshooting aid, or as a calibration tool for diagnostic x-ray generators. The High Voltage Unit can measure anode current and filament current as well as kVp. The Digital Display has features to provide accurate numerical values to these parameters. The operation of the system in typical applications is discussed.
The general problem of remote detection for laser stimulated luminescent systems is considered. A simple optical model is employed to calculate the maximum practical range of detection for several such luminescent systems. Some experimental verification of the model is included. Consideration is also given to the practicality of using such a system for the remote detection of casual oil spills. The results of this study indicate that laser-induced fluorescence is a practical technique for the remote detection of pollutants. The ranges calculated from the simplified model are, in general, greater than those reported in the literature, but appear to be realizable.
A battery-powered scene recording radiometer system has been developed for relating spectral variability and target composition. A remote controlled filter wheel radiometer is interfaced with a Hasselblad 500 EL camera, so that the silicon detector is directed toward the camera's viewing glass. Signal detection at discrete wavelength bands is achieved by successively rotating interchangeable interference filters that interdict the view of the detector. Filter positioning is controlled by coding holes drilled in the filter wheel disk which are interpreted by a bank of opposing light emitting diodes and phototransistors. Upon obtaining a photographic record of the scene, the camera is automatically advanced.`
A new system of quantitative analytical spectroscopy using a continuously scanning tunable dye laser is proposed. This system can detect simultaneously many components of pollutant gases by one scan. The maximum number of detectable gases and the sensitivity of the detection is analyzed. The absorption spectrum is calibrated to the output of the laser, to the standard spectrum (Na), and the interpolating Fabry-Perot interferometer. The gas concentration is calculated by the method of least squares. A fundamental experiment by using a rhodamine 6G dye laser is done. Three kinds of gases, NO2, 12 and Br2, are separately analyzed quantitatively.
Two methods have been proposed for remote identification of oil slicks on water using an airborne lidar system. Both techniques require estimating the time decay of physical quantities from the measured return signal pulse. The purpose of this paper is to suggest the use of a Fast Fourier Transform technique to deconvolve the oil-fluorescence-on-water Raman decay time from the return pulse. This is a convolution of the required time varying signal with pulse shape, pulse broadening due to surface scattering, and instrument response. It is shown that the method yields results in agreement with those of Measures, Houston and Stephenson. The FFT method is faster and requires little storage and could be implemented in real time on airborne minicomputers or microcomputers.
The fabrication and assembly of a point symmetric, rotational shear interferometer with 180-degree rotation is given. It has been used to photograph the Michelson Stellar interferometer fringes in white light without the use of an image intensifier at a large astronomical telescope.
Intercomparison of the optical properties of diamond-turned, evaporated and sputtered metal mirrors is made with specific reference to surface and bulk physical structure. In most applications, absorption and scattered light are important optical parameters. Both of these characteristics are directly related to surface microtopography which is a direct product of the finishing methods employed. For laser applications, the threshold for damage is also often critical. The properties influencing laser damage include surface microtopography, as well as bulk physical and chemical structure. Diamond turning, in addition to its very attractive manufacturing advantages, can produce optically superior components. Nearly intrinsic values of pulsed laser damage threshold and absorption have been measured on diamond-turned copper mirrors.
Certain applications in coherent optical processing of two-dimensional signals require the operation of imaging a signal in one dimension while simultaneously Fourier transforming it in the other. Such parallel operations can be performed by a number of different system designs. This paper presents a method of analyzing such systems by treating each dimension independently and using three basic component subsystems. The method simplifies mathematical analysis of system operation and facilitates intuitive design for particular applications.
A heterodyne correlation radiometer is considered for the sensitive detection of radiating species whose Doppler shift is known, but whose presence we wish to affirm. Such radiation (which may be actively induced) can arise, for example, from remote molecular emitters, impurities and pollutants, trace minerals, chemical agents, or a general multiline source. A radiating sample of the species to be detected is physically made a part of the laboratory receiver, and serves as a kind of frequency-domain template with which the remote radiation is correlated, after heterodyne detection. The system is expected to be especially useful for the detection of sources whose radiated energy is distributed over a large number of lines, with frequencies that are not necessarily known. Requirements for local oscillator stability and tunability are less stringent than in the conventional heterodyne system and the use of a multiline local oscillator may be advantageous. It is shown that the minimum detectable power is expressible in a form similar to that for conventional heterodyning (for both quantum-noise-limited and Johnson-noise-limited detectors). The notable distinction is that the performance of the proposed system improves with increasing density of detected remotely radiating signal lines and increasing radiation power from the local sample. Performance degradation due to undesired impurity radiation is considered and shown to be tolerable in most cases. The technique should be applicable over a broad frequency range from the microwave to the optical, with its most likely use in the infrared.
A sensitive spectrometer for the measurement of circular polarization of emission, utilizing a photoelastic modulator, is presented. This spectrometer, when augmented by a superconducting magnet and dewar assembly, provides an excellent system for studying magnetically induced circular polarization of emission (MICE). In order to exemplify both the system and the usefulness of MICE, a partial analysis of the MICE observed from Ru-(4,7-dipheny1-1,10-phenanthroline)3C12 dispersed in a polymethylmethacrylate (PMM) matrix in the 2 to 100 K temperature range is reported. Also presented is a discussion of the effects of photoselection on the observed MICE for these D3 symmetry complexes. It is found that MICE is more sensitive to the detailed nature of the levels involved in emission than a combination of zero field techniques. MICE should prove to be an exceptionally useful tool for probing excited states of inorganic complexes.
Design parameters for Si02-Si film-substrate single reflection retarders for several mercury spectral lines are presented. An example of an angle-of-incidence tunable retarder (AITR) capable of multiple wavelength operation (MWO) is reported. Simple, approximate formulae for calculating film-substrate retarder design parameters (least film thickness d' and incidence angle are presented.