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Spectroscope incorporates two prisms combined with holographic grating as dispersing element. This provides high dispersion with selective undeviated wavelength. Prisms with different indices of refraction and/or angles for construction and reconstruction may be used. Also, different prisms for input and output may be used.
The authors report the first demonstration of holographic techniques in the vacuum ultraviolet spectral region. Holograms were produced with coherent 1182 A radiation. The holograms were recorded in polymethyl methacrylate and read out with an electron microscope. A holographic grating with a fringe spacing of 836 A was produced and far-field Fraunhofer holograms of sub-micron particles were recorded.
A coarse resolution spectrum of the Orion Nebula between 65 and 125 microns is presented which closely fits the color dependence of a 75 K blackbody. A high resolution search for O III at 88.16 microns yields an upper limit below theoretical predictions. Observations were carried out in November, 1974, using the 31 cm gyrostabilized telescope mounted in the NASA Lear jet. The instrument employed was a fully liquid helium cooled grating spectrometer with a 3 mm entrance slit that gave a square beam on the sky, 5 arc minutes in diameter. The results are presented.
The peak pulse power was increased by operating an array of three homostructure Ga As lasers in the laser device. A spatial filter in the laser device selects the spatially coherent, free running, mode. The optical peak power is 5 watts, which is three times the peak power of a single laser in the array. The far-field distribution of the three laser array is a single Gaussian beam of spatial coherence without sidelobes or grating lobes. The length of the optical pulses of spatial coherence was increased to 200 ns by improved heat transfer from the p-n junctions of the lasers to the metal housing of the pulse transformer, and by doubling the core area and increasing the turns of the primary windings of the pulse transformer. The mechanical stability of the laser device was improved and the transition from mechanical alignment to electro-mechanical alignment control, was facilitated.
We report the first demonstration of holographic techniques in the vacuum ultraviolet spectral region. Holograms were produced with coherent 1182-A radiation. The holograms were recorded in polymethyl methacrylate and examined with an electron microscope. A holographic grating with a fringe spacing of 386 A was produced and far-field Fraunhofer holograms of submicron particles were recorded.
The Orion nebula spectrum was obtained using an airborne cooled grating spectrometer in the spectral range from 80 to 125 microns at a resolution of 8 microns. The spectrum, corrected for instrument profile and atmospheric water vapor absorption, could be fit by the 60 and 100 K black body curves. The results are in good agreement with those of Erickson et al. (1973) and are consistent with a thermal emission spectrum produced by cool interstellar grains radiating at a wavelength much longer than the grain size.
Spectral absorption measurements involving pure nitrous oxide were performed with the aid of a commercial grating spectrophotometer. A multiple reflection cell with a path length of 1.25 m was used in the investigation. The tests were conducted at pressures in the range from 5 to 8 atm. The obtained data were used to determine the apparent spectral absorption coefficients. Questions regarding the validity of a line approximation relation are discussed.
The double ribbon flare of 1973 June 15 was observed in the XUV wavelength region with the NRL objective grating spectroheliograph during the Skylab missions. The Fe XXIV emissions at 192.1 and 255.2 A are prominent in the early phase of the flare. The Fe XXIV emission is centered over the neutral line, forming a bridgelike structure between magnetic regions of opposite polarity. This is unlike the emission pattern of He II, the transition zone ions, and Fe IX-XVI, which are relatively brighter in the adjacent flare ribbons overlying strong vertical magnetic field. An electron density of 5 times 10 to the 10th per cu cm for the Fe XXIV emission region is deduced from the observational data, and the cooling rate is briefly discussed.
The S-054 X-ray telescope, which operated successfully throughout the eight-month Skylab mission, is a grazing incidence instrument with a spatial resolution of the order of 2 arc sec on axis. The total wavelength range observed by the instrument is 2 to 60 A. Crude spectral resolution within this range is achieved by means of a series of six X-ray filter materials. A spectrographic mode of operation, employing an objective grating, is used to obtain spectra of flare events and selected coronal features.
The paper describes the use of nonlinear optical techniques for the generation of coherent radiation at ultraviolet, vacuum ultraviolet, and soft X-ray wavelengths. Mixtures of metal vapors and inert gases, and other mixed gas systems, allow generation to regions of the spectrum where nonlinear optical crystals are opaque; and also allow generations at high incident power and energy densities. Progress is reported on programs aimed at efficient conversion from 1.064 microns to 3547 A, and from 3547 A to 1182 A. To date, the shortest wavelength generated by this technique is 887 A. Theoretical considerations indicate that generation into the soft X-ray region should be possible. Using 1182 A radiation, a holographic grating with a fringe spacing of 836 A has been constructed and examined on an electron microscope.
Current results from the TO27 experiment which was performed on the first two Skylab missions are presented. The purpose of the experiment was to determine the change in optical properties of various transmissive windows, mirrors, and diffraction gratings caused by the deposition of contaminants found about the orbital assembly and to measure the sky brightness background caused by solar illumination of particulate contaminants. The sample array system containing 248 optical surfaces and exposed outside the orbital workshop did not collect any significant contaminants. Only trace amounts of surface deposited contaminants have been seen, in all cases the measurement was near the limiting sensitivity of the instrument. Unfortunate performance compromises and the relative cleanliness of the assembly on the anti-solar side appeared to place the amount of available surface contaminants near the limiting sensitivity of the sample array. Mass spectroscopy on the trace contaminants show the presence of high molecular weight species, up to 773 amu. The data suggests the presence of condensed aromatics.
The far infrared spectra of H II regions are investigated. A liquid helium cooled grating spectrometer designed to make observations from the NASA Lear Jet is described along with tests of the instrument. The observing procedure on the Lear Jet telescope is described and the method of data analysis is discussed. Results are presented from a search for the (O III) 88.16 micron line. An upper limit on the emission in this line is obtained and line detection is described. Results are compared to theoretical predictions, and future applications of fine structure line observations are discussed. Coarse resolution results are given along with calibration problems. The spectra obtained are compared to models for dust emission.
An ion drift meter, extreme ultraviolet spectrometers, an extreme ultraviolet grating photometer, and a soft particle spectrometer were developed.
Utilizing round optical fibers as communication channels in optical communication networks presents the problem of obtaining a high efficiency coupling between the optical fiber and the laser. A laser is made an integral part of the optical fiber channel by either diffusing active material into the optical fiber or surrounding the optical fiber with the active material. Oscillation within the active medium to produce lasing action is established by grating the optical fiber so that distributed feedback occurs.
A new observatory for meteor research which provides data for study of meteor heights, velocities, orbits, and meteoroid abundances is described. The observing equipment is automated to take advantage of the long periods of favorable observing weather common to the region. Four K-24 cameras, electrically operated, provide the triangulation observations, and four Maksutov f/1.3 cameras with blazed transmission grating provide spectral coverage. The patrol cameras have operated for a year and a half, and approximately 6,000 frames have been exposed by 9 March 1975. Meteor trails appear on 260 of these frames. Sixty-eight trails are of meteors photographed from two locations and thus allow trajectory and orbit determinations for 34 meteors. Photoelectric sensors initiate the 2-second spectrograph exposures, and electrical controls open and close the observatory at present times.
The results of a number of theoretical and experimental studies relating to multiple hologram recording in lithium niobate are reported. The analysis of holographic gratings stored in lithium niobate has been extended to cover a more realistic range of physical situations. A new successful dynamic (feedback) theory for describing recording, nondestructive reading, erasure, enhancement, and angular sensitivity has been developed. In addition, the possible architectures of mass data storage systems have been studied.
Spatially coherent radiation from a monolithic array of three GaAs lasers in a free-running mode is reported. The lasers, with their mirror faces antireflection coated, are operated in an external optical cavity built of spherical lenses and plane mirrors. The spatially coherent-beam formation makes use of the Fourier-transformation property of the internal lenses. Transverse mode control is accomplished by a spatial filter. The optical cavity is similar to that used for the phase-controlled mode of spatially coherent-beam formation; only the spatial filters are different. In the far field (when restored by an external lens), the intensities of the lasers in the array are concentrated in a single laser beam of spatial coherence, without any grating lobes. The far-field distribution of the laser array in the free-running mode differs significantly from the interference pattern of the phase-controlled mode. The modulation characteristics of the optical waveforms of the two modes are also quite different because modulation is related to the interaction of the spatial filter with the longitudinal modes of the laser array within the optical cavity. The modulation of the optical waveform of the free-running mode is nonperiodic, confirming that the fluctuations of the optical fields of the lasers are random.
This paper reports the detection of the fine-structure forbidden line of O III at 88.16 microns in emission from M 17 (the Omega Nebula), which is an optically bright galactic H II region and a strong thermal radio source. The observations were made using an airborne 30-cm telescope and a liquid helium-cooled grating spectrometer with Ge:Ga photoconductive detectors. The line intensity is found to be 2.2 (+1.0, -0.7) by 10 to the -15th power W/sq cm. The results are compared with those of a search for the present line in M 42 as well as with theoretical predictions of the line intensity.