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For routine quantitative spectrographic analysis of phosphorus, using the line at 2136A, the Geiger-Muller photoelectron counter has certain advantages over both the photographic plate and the electron multiplier photo-tube. The construction of the counters and the methods of electrically shielding and mounting them on the Littrow spectrograph are briefly described. The adjustments of counter orientation, slit widths, and focus are discussed with reference to the analyses of ferrous alloys where good resolution is necessary. Because of the absorption of radiation by quartz at low wave-lengths, both absolute and relative intensities are dependent upon the position of the arc on the electrode surface. This effect, which results in appreciable error in the measured percentage composition of a sample, is investigated photographically and with G-M counters, and several methods of reducing the effect are discussed. The effect of temperature changes of the dispersing prism on line position is investigated and a suitable method of control is mentioned. Preliminary consideration of this direct-reading method shows that it seems possible to reduce the various errors so that the source fluctuation is the controlling factor.

The spectrum of eleven-times ionized barium was generated in a triggered, high-voltage, vacuum spark and photographed with the National Bureau of Standards 10.7-m grazing-incidence spectrograph. The spectral lines of the transition array 4d9–4d85p were identified in the range of 100–125 A. Thirty-nine lines of this array have been classified as transitions from thirty-two levels of the 4d85p configuration to the 4d9 2D ground term. Radial energy integrals were fitted to the observed levels of 4d85p, and the relative intensities in the array were calculated with fitted eigenvectors. These intensities were in good qualitative agreement with the relative intensities that had been visually estimated on the photographic plate. Least-squares-fitted values for the energy parameters and their ratios to the calculated Hartree–Fock (HF) values are given.

In all methods of photographic optical processing presented here, the carrier frequency is derived from an intensity speckle pattern, the advantage of which is to spread out information in the Fourier plane. Furthermore, they are based on the fact that the Fourier spectrum of two laterally translated speckle patterns displays Young’s fringes, the visibility of which represents the correlation of the speckle patterns. The problems of comparing intensities of two transparencies, multiplexing optical signals, and detecting small translations of a diffuse object will be successively considered. The optical process of comparing two transparencies A and B is the following. The two signals are modulated by the same speckle pattern and recorded successively on a photographic plate which is laterally translated between the exposures. After processing, H displays Young’s fringes at infinity. If the intensity distributions of A and B are not identical, the two corresponding speckle images are not completely correlated and therefore the fringe visibility is not maximum. The difference A–B can easily be obtained by filtering the minima of the fringes. For multiplexing operations, each of the signals to be stored is modulated by a speckle pattern and recorded at least twice on a photographic plate which is laterally translated between successive exposures. The amount of translation given to the plate is different for each of the signals. The spectrum of the photographic record has as many fringe systems as the signals. By filtering the maxima of a particular fringe system, the corresponding signal is reconstructed and the others are removed. Small translations of a diffuse object can be detected by illuminating the object with a speckle pattern and recording its image before and after the motion in the same way as above. The decorrelation of the two recorded speckle patterns is only due to the motion of the object which can thus be revealed by the visibility of the corresponding Young’s fringes. With such a method it is not possible to detect the direction of the translation suffered by the object. We suggest therefore an interferometer consisting of a Michelson interferometer in which both mirrors are replaced by two scattering surfaces O1 and O2 shifted longitudinally. The interferometer is illuminated by a parallel beam of laser light, and a photographic plate twice records (before and after the translation of one of the surfaces) irradiances lying in the Fourier plane of O1 and O2. After processing, H exhibits Moire fringes. These fringes are rectilinear if the translation suffered by the object is lateral and they are circular if the translation is longitudinal. The sensitivity of the interferometer depends only on the geometrical characteristics of the recording setup.

A large Wadsworth grating spectrometer designed primarily for photoelectric recording is described. Important features of the instrument are an arrangement which permits any wavelength interval up to the full range of the spectrometer to be scanned in one continuous operation and a wavelength scale which is linear over the entire spectral range (2000 to 14,000A). The linear scale results in part from scanning the spectrum on the grating normal, a condition which leads also to minimum aberrations in the spectral image. Provision is made for indicating on the spectrum record reference marks which denote equal increments of wavelength. Multiplier photo-tubes, operating at liquid nitrogen temperature, are used in the photoelectric recording system. The scanning slit (or photographic plate) is maintained automatically on the focal curve by a simple focusing device. The spectrometer is fully adaptable to photographic work and may be converted from photoelectric recording to photographic recording (or vice versa) in about five minutes.

Methods are discussed for finding the optimum configuration of an inplane Czerny–Turner-type spectrograph. An asymmetry parameter is used which involves a lateral movement of the grating, perpendicular to the rulings. This displacement improves image quality at the center of a fixed photographic plate, and we find that the grating position for best imaging varies with angle. The optimum relationship between grating angle and position is derived by ray tracing for a specific 4-m instrument and the image widths are found to be superior to those calculated for configurations based on analytical expressions. Ray tracing is used to derive a compromise configuration with a fixed plate and a fixed grating for which the image quality is maximized at the photographic plate-center for all useful grating angles, and falls off symmetrically toward each end of the plate. For this configuration, it is necessary only to refocus the entrance slit as the grating is rotated to scan wavelengths.

An apparatus for photographing Raman spectra of low-pressure gases at high dispersion is described. A multiple reflection Raman tube, 2 m long, is irradiated by two water-cooled Pyrex mercury arcs operated at 30 amp, and surrounded by a magnesium oxide diffusing screen. A two-prism glass Littrow spectrograph, f/42, gives a reciprocal linear dispersion of 10.5 cm−1 per mm; its speed is increased fifteen-fold by a cylindrical lens in front of the photographic plate. Rotation-vibrational spectra of gases at 1–3 atmos pressure can be photographed with a resolution of 1 cm−1. Various aspects of high-resolution Raman spectroscopy of gases are discussed.

Microanalytical apparatus has been designed and constructed for the purpose of the study of diffusion in metals and alloys and the analysis of segregates and inclusions. Versatility in changing photographic plate and sample speeds was included in the design. Based on mechanical considerations, the relative importance of factors, such as size of sparked area, lengths of spectrograph and microphotometer slits and the ratio of plate speed to sample speed are discussed. The width of the sparked area was 0.6 mm and uniform. Calculations of apparent concentration were performed to verify the experimental discrimination factors. The most important factor was found to be the width of the sparked area. No advantage was seen in using a speed ratio greater than 10:1.

Use of the image orthicon tube as a detector in spectroscopy provides rapid response at controlled instants and, for short exposure times, greater light sensitivity than the photographic plate. The application of the orthicon spectrograph to the study of transient or rapidly varying light sources is discussed.

Three properties of any recorder are of primary importance in electron microscopy: (1) its spread function, (2) its signal-to-noise characteristics (or, detective quantum efficiency, DQE), and (3) its sensitometric curve shape. Photographic materials are found to have spread functions that are not limiting under normal conditions. The remaining two factors are investigated by analysis of mathematical models and comparison with experimental results. Most photographic materials are found to be near-perfect detectors, in that they record the input signal without appreciable loss and do not seriously add to the input noise. They have similarly shaped curves of density vs electron exposure. It is shown that to optimize the recording step in electron microscopy, it is advantageous to be able to select speed–granularity combinations at will, if DQE can be kept high. Variations in the processing of a commercial photographic plate are found to accomplish this effect.

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A new technique for holographic multiplexing is described. The advantages of the technique are that a single carrier is used, a volume hologram is not necessary, and the entire area of the photographic plate can be exposed to record the holograms of each of the signals to be multiplexed. The technique can be used for relatively noise-free, high-resolution holographic multiplexing of digital and continuous-tone signals.

Bryngdahl pointed out that a photographic plate, exposed to fine interference fringes and processed with high gamma, can record an amplification of the original phase difference. Interferograms obtained with this technique are shown. With a Mach-Zehnder two-beam interferometer, 14-fold phase-difference amplification was observed. Sources of experimental errors encountered in practice are discussed.

Fourier harmonics in the form of Young’s interference fringes, may be added together by successive exposures on a photographic plate. In the synthesizer to be described, an optical system using a Wollaston prism generates the Young’s fringes with adjustable spacing, position, and intensity. This provides the necessary variations of frequency, phase, and amplitude of the harmonics simply by setting dials. The apparatus is potentially capable of adding a few hundred harmonics, as can be shown by preliminary experimental results. Spherical aberration in the optical system merely remains to be corrected.

A theory of holographic imaging is formulated in terms familiar from conventional optics. The effects of the curvatures and off-axis angles of the reference and read-out waves are described by equivalent thin lenses and prisms. The formation of the true-image wavefield is found to be completely analogous to the conventional imaging of the object wavefield by the equivalent lenses and prisms. To explain the conjugate image, we introduce the concept of time reversal. The conjugate-image wavefield is the time-reversed object wavefield conventionally imaged by equivalent lenses and prisms (and a plane mirror). The finite size and resolution of the photographic plate are taken into account. The size of the plate determines the effective aperture of the equivalent lenses and prisms, it is equivalent to a diaphragm in the hologram plane. The modulation transfer function of the plate has the same effect as a diaphragm inserted in the imaging bundle during the recording (or the reconstruction) with its center at the reference (read-out) point. The two diaphragms limit the field of view and the resolution.

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A method for measuring the relative intensities of spectral lines is described in which a step diaphragm is substituted for the slit of a spectrograph. A continuous source of light then produces on the photographic plate a set of bands over which the intensity of the light varies as the widths of the openings in the step diaphragm. Necessary precautions in the use of the method are noted. Results from this method are compared with those obtained by varying the distance to the source. Possible errors in measurements on relative intensities of spectral lines due to the Eberhard effect and to the use of an intermittent source are mentioned.

We describe a new technique of image multiplexing which employs a random diffuser. The same diffuser is used to modulate all of the signals to be multiplexed. The signals are recorded on the same frame, making the entire area of the photographic plate available for all of them. The decoding is done by putting a binary filter in the Fourier plane where each signal produces a system of rectilinear fringes. We get the product of the signal function and the diffuser function as the retrieved image. The maximum number of signals that can be stored without cross talk is a function of the number of exposures for each signal and the interexposure displacement of the signal on the photographic plate. This is limited by the dynamic range of the photographic emulsion and the precision of the displacements of the photographic plate.

The intensity of the astigmatic spectral image formed by a concave grating is a maximum at the center and drops off to zero at the ends of the line. Inasmuch as the intensity distribution can be known from the value of the astigmatism factor, G. H. Dieke has suggested using such an image as a means for calibrating a photographic plate in intensity measurements. It has been the purpose of this investigation to develop the method in detail, to apply it to the calculation of relative intensities, and to compare the results with those obtained from one or another of the standard methods now in use. Under proper conditions the astigmatism method has the great advantage of simplicity, and it was found to yield results which compare favorably with those obtained by other means.

The information on a hologram is reduced when the hologram is recorded on only an array of small areas on the photographic plate. When looking at such a hologram the observer has the annoying sensation of observing the object through a screen. A method is shown for eliminating this “screen-effect”. The relation between the information reduction and loss of resolution is given. The number of resolvable points on the hologram needed for a reconstruction of given resolution is also computed. Apart from a numerical factor, the formula is identical to one derived for integral photography.

An expression derived for hologram exposures made along the straight-line portion of the H–D curve of a photographic plate shows that the relationship between the luminance of the reconstructed hologram image and the luminance of the original object depends on the value and sign of the gamma of the photographic processes.To check the theory, several holograms of different exposures were superimposed on Kodak 649-F plates that were pre-flashed with a uniform illuminance so the H–D curve of the photographic process is straight. The calculated and measured luminance ratios of the different reconstructions agree within experimental error. Since the gamma of the usual photographic process is positive, instead of negative, even if the gamma of the photographic process is equal to 2, it is not valid to assume that the relative luminance of the reconstruction of a given superimposed hologram is proportional to the product of the exposure due to the object beam and the exposure due to the reference beam used in the making of the hologram. This assumption would be valid for all fringe contrasts only if gamma were −2.

Atmospheric contamination by lead presents acute problems in analysis and control to the chemical industry. A mobile instrument of extreme sensitivity has been developed which furnishes a rapid indication and an approximate assay of localized relatively high concentrations of lead, combined or elemental. Samples are drawn through a condensed spark discharge adjusted to minimize air lines and to excite the lead spectrum which is photographed with a small quartz instrument. Visual examination of a series of exposures provides data on lead concentration as a function of time and location. A sensitivity of better than one part in 20 million can be maintained in routine operation. Instantaneous response has been realized by substitution of the photoelectric Geiger counter for the photographic plate, as described in detail in the following paper.

A Two-Meier Vacuum Spectrograph—The construction and operation of an optical vacuum-grating spectrograph capable of accommodating a grating of two meters radius of curvature is described. Means are provided for introducing and removing the photographic plate as well as altering the focus and inclination of the grating while the vacuum is maintained.Doublet Separations in C ii.—The following doublets in Fowler’s series have been resolved and the frequency separation measured. (2π1 − 3σ)(2π2 − 3σ) Δν =64 in the second order of the grating and 60 in the third order. (2π1 − 3δ)(2π2 − 3δ) Δν =64.5 in 2nd order. For lines λ1335 Δν = 65 and lines λ = 1036 Δν = 62 showing that since the 1036 line belongs to Cii probably 1335 does also.Doublet Separation in Si iii.—In these series the following doublet is resolved. (3σ1 − 4π) (3σ2 − 4π) Δν = 153.

An expression derived for hologram exposures made along the straight-line portion of an H–D curve of a photographic plate gives the first-order transmittance of a hologram made of several object points exposed simultaneously (conventional holograms). This expression is compared with a similar expression derived previously for holograms made of several object points exposed sequentially (synthetic holograms). Theory and experiments show the effect of the nonlinearity of the photographic process on the contrast of the reconstruction of conventional holograms. Synthetic and conventional holograms are studied theoretically and experimentally to determine how the total amount of light in the reconstruction image depends upon the number of object points when the total amount of light in the object is constant. It is shown that the reconstructed image formed by a conventional hologram contains more light than the image formed by a synthetic hologram of the same number of object points. Both synthetic and conventional holograms are also studied to determine the ratio of reference-beam illuminance to object-beam illuminance that maximizes the amount of light in the reconstructed image.

A method of determining the spherical aberration of a lens is given which requires relatively simple apparatus and which gives directly the retardation of different portions of the wave-front referred to any point along the axis andintermsof the wave length of the light employed. Data are given from which a convenient self-contained apparatus can be built to serve as an attachment on an optical bench of usual design. The method is based upon interference phenomena and the bench does not need to be provided with scale or micrometric measuring devices. With the attachment built as suggested, in addition to its dimensions, the measuring of the photographic plate gives all the data required and the one necessary exposure provides a permanent and complete record of the test.

It is now well known that a system of interference fringes photographed on a photographic plate has very interesting properties when used as a diffraction grating. This paper considers two cases. One is when the photographic plate is a plane surface; the aberration properties of this are worked out as a function of wavelength. There are three positions for which the spherical aberration is zero. Of these, one is of little interest as this is simply zero-order position. Another case considered was that of a photographic plate in the form of a concave spherical surface. In this case, there are three positions at which the spherical aberration is zero. The nature of variation of spherical aberration between these zero-aberration positions is presented in the form of curves computed from the theory of these gratings.

A photoelectric means for recording an extended spectral region as a function of time has been developed. With this method, the recording procedure imposes no limitations on the time resolution other than that defined by the minimum detectable energy. The optical portion of the device, which includes the time-resolving mechanism, is very similar to a conventional photographic time-resolving spectrograph. However, the photographic plate has been replaced by a television camera which is used in much the same way. In fact, direct analogies can be drawn between the photographic plate and the storage surface of the television camera tube and also between the photographic developer and the scanning electron beam in the camera tube. The method is capable of sensitivities of the order of 103 times those available with Tri-X film in the visible. In addition, the usual cumbersome photographic calibration procedures are avoided since intensities are recorded as vertical deflections, yielding records similar in appearance to those obtained from strip chart recorders.

This paper reports another phase of the program being followed by the Inspection Division of Socony-Vacuum Laboratories, Technical Service Department, which is designed to reduce the size of samples and to improve the efficiency of spectroscopic analyses. Two wave-length ranges are recorded from a single exposure by the use of an auxiliary mirror system in a Littrow-type prism spectrograph.Radiation incident on the upper half of the prism-lens aperture receives the dispersion and collimation to produce the normal ultraviolet spectrum on the photographic plate. A system of two mirrors, interposed before the lower half-aperture, provides an additional angular deviation and increase in path length to produce a visible spectrum adjacent to the ultraviolet spectrum.The instrument described was designed for use with a Bausch and Lomb large Littrow spectrograph. Its purpose is to record, in one exposure, a spectral range sufficient for the detection and semiquantitative estimation of all the elements, except boron, which can be excited in an arc. Through the use of the auxiliary unit, the range 2530 to 3500A and any 4000 angstroms between 3540 and 10,000A are covered in one exposure, including, for example, the four phosphorus lines and the potassium lines at 7665 and 7699A.The elimination of an extra exposure results in substantial reductions in analytical time and in the required size of samples, thereby achieving very desirable economies in the costs of spectroscopic analyses.