Showing papers on "Diffraction efficiency published in 1977"

Grating efficiency theory as it applies to blazed and holographic gratings.

Abstract: Recently developed rigorous theories have been used to investigate the diffraction efficiency behavior of both blazed and holographic gratings. In order to assist designers of spectrometric systems we have covered a complete range of blaze angles for triangular grooves and modulations for sinusoidal groove shape in first and second orders. Several types of mountings are included together with the role played by finite conductivity of aluminum. Useful classifications of both types of gratings are given, as they apply from the near uv to ir regions. Comparisons showing the close agreement between theory and experiment are presented.

Volume hologram recording and charge transfer process in Bi12SiO20 and Bi12GeO20

Abstract: Bi12SiO20 and Bi12GeO20 are photoconductive and electro‐optic crystals in which hologram recording is performed using the photorefractive effect; their sensitivity and optical quality are comparable with the high‐resolution photographic plate. Hologram formation and erasure are analyzed in terms of a simple two‐level charge transfer model. The photocarrier’s displacement length, comparable with fringe spacing and the nearly unity quantum efficiency, allows the attainment of the ultimate photosensitivity. The trapping centers concentration being much smaller than the absorption centers concentration, the saturation recording time and diffraction efficiency are found limited only by the trap‐filling mechanism.

Analysis of multiwave diffraction of thick gratings

Abstract: A general coupled-wave formalism describing the multiwave diffraction properties of thick gratings is presented. The analysis is applicable to refractive-index-modulated and/or absorption-modulated gratings of any modulation strength. The gratings may be slanted, nonuniform with thickness, nonsinusoidal, and lossy. The incident wave (of arbitrary polarization) may be at any angle of incidence including all Bragg angles. Example multiwave diffraction efficiency characteristics are calculated for some representative grating thicknesses and refractive-index modulations for sinusoidal, square-wave, and sawtooth gratings.

High‐sensitive holographic storage in Ce‐doped SBN

Abstract: High optical sensitivity is observed in 0.1 wt% Ce‐doped strontium barium niobate (SBN) crystals in the absence of an external electric field. Only 5–10 mJ/cm2 of incident 0.488‐μm radiation is required to produce 10% diffraction efficiency, while the energy to erase holograms from the 80% to its 1/e diffraction efficiency level is 30–40 mJ/cm2 at the same wavelength. Holograms stored in Ce‐doped SBN persist at least one month (decay time constant) if kept in the dark at room temperature.

Diffraction grating transmission efficiencies for XUV and soft x rays.

Abstract: Efficiencies for diffraction of 45–275-eV x rays into orders by interferometrically formed, electrodeposited, gold transmission gratings have been measured on the 4° beam line at the Stanford Synchrotron Radiation Project (SSRP). Anomalous dispersion affects the observed efficiency since the gold is partially transmitting to x rays. Model calculations which include anomalous dispersion are in good agreement with observations. With a suitable choice of material and thickness, a grating can be optimized for a given wavelength range by reducing the zero order transmission and enhancing the higher orders. Even orders are suppressed for a grating with equal slit and wire sizes.

X-ray efficiencies of blazed gratings in extreme off-plane mountings.

Abstract: The measured first order diffraction efficiencies in the X-ray wavelength region of a blazed grating ruled with 3600 grooves/mm are reported. The grating is used in an extreme off-plane configuration which means that the incident beam is nearly parallel to the grooves. It appeared that in this configuration the efficiencies are between 40% and 70% of the reflection coefficient of the selected grating material.

Spectrum Analysis Using Acousto-Optic Devices

Abstract: A tutorial review is presented covering the real-time optical Fourier spectrum analysis of a wide band of electrical signals by means of acousto-optic diffraction. Topics include frequency dispersion, spatial modulation, weighting functions, frequency resolution, sidelobe level, optical background level, acousto-optic bandshapes, normal and birefringent acousto-optic diffraction, figures of merit, diffraction efficiency, nonlinearities and spurious responses, dynamic range and output characteristics.

Doubly modulated on-axis thick hologram optical element

Abstract: An on-axis thick phase holographic optical element for use as a lens is fabricated by incorporating two off-axis holograms of two point sources located on opposite sides of the plate made by use of reference beams having a common angle with respect to the photographic media and complementary curvatures in the two cases. The element may be formed either by forming the two holograms in a single photographic emulsion, incoherently relative to one another, using a double exposure technique, or by forming the holograms on two physically separated media and then joining them to one another with their emulsion sides in contact. The resultant elements enjoy the low dispersion and aberrations like a conventional on-axis thin holographic optical element and the high diffraction efficiency like a thick hologram and additionally provide an extremely high ratio of diffracted to undiffracted light energy in the on-axis image.

Plastic recording media for holography at 10.6 μm

Abstract: A search for recording media suitable for holography at wavelengths comparable to the 10.6 μm of a CO2 laser has led to the successful use of Saran Wrap plastic films and of thick acrylic plates. Holographic phase recording has been made with a 1-W single mode cw CO2 laser yielding incident intensities up to 3.5 W/cm2. Holographic reconstruction at a wavelength of 632.8 nm has given a diffraction efficiency up to 20%. At a wavelength of 10.6 μm, reconstruction by reflection on the silver-coated surface of an acrylic plate had a diffraction efficiency of 0.5%. It was observed that the recording is less linear on acrylic plates than on Saran Wrap films.

Device to control introduction of diffracted beam by means of diffraction element

Abstract: According to the present invention in the image forming light path a direction-selective diffraction element is provided in such a manner that the image forming beam having entered into said diffraction element is diffracted by means of the diffraction grating structure of said diffraction element and devided into a plurality of beams, whereby at least one of the diffracted beams is led to a photo detecting device while the not diffracted beam is made use of as the image forming beam.

Photodielectric polymer for holographic recording

Abstract: A novel photodielectric polymer system suitable for recording high resolution volume phase holograms is described. Highly reactive monomers that polymerize rapidly when inserted between two substrates allow for simple and convenient preparation of recording layers ranging from 10microm to 3 mm. The materials have superior chemical and dimensional stability and have in situ self-developing capabilities. During recording the polymer cross-links in the irradiated regions causing changes in index of refraction. Experimental measurements reveal that the diffraction efficiencies may exceed 90%, that the resolution is in excess of 2000 lines/mm, that the angular selectivity may be as high as several minutes of arc, and that the noise characteristics are comparable to those of high quality photographic emulsions. The hologram formation mechanism along with experimental results of exposure sensitivities, diffraction efficiencies, SNRs, and angular discrimination are presented.

On simultaneous blazing of triangular groove diffraction gratings

Abstract: Numerical results for plane-wave scattering from a perfectly conducting diffraction grating with triangular groove profile show that simultaneous blazing with 100% efficiency in both polarizations is obtainable in a Littrow arrangement. The range of angles of incidence, for which such simultaneous blazing occurs, is considerably narrower than that obtainable with a rectangular groove profile.

Volume Amplitude Holograms in Photodichroic Materials

Abstract: A theoretical analysis is made of the process of writing volume holograms on photodichroic materials. The real form of the recorded diffraction gratings at large exposures is found. Expressions are derived for the diffraction efficiency of transmission and reflection gratings for the case of pure amplitude recording and the results of some numerical calculations are presented. Maximum diffraction efficiencies for different parameters of the recording medium are determined.

Bragg effect waveguide coupler analysis.

Abstract: We present an approach to the analysis of a holographically produced grating coupler, in which we separate the coupling problem into independent slab waveguide and diffraction grating problems. Considering the guiding structure as a slab waveguide, we obtain the parameters of the propagating modes of the coupler through conventional analysis. The diffraction efficiency of the grating orders are then calculated by using the thin grating decomposition method (TGD). Utilizing the propagating mode angles of the waveguide and the calculated diffraction efficiencies of the grating, we are able to calculate the radiation loss coefficient and therefore the coupling efficiency of the holographic waveguide coupler.

Design Procedure for Wide Bandwidth Acousto-Optic Modulator

Abstract: In this paper, we give the design equations and a procedure for the complete specification of the design parameters for a wide bandwidth acousto-optic modulator (AOM). Although the modulating medium, transducer material, and bonding agents determine the modulator performance, we concentrate here on the question of how to design an AOM, given specifications on its minimum modulation bandwidth, diffraction efficiency, and the maximum ellipticity of the output beam.

Large-size distortion-free computer-generated holograms in photoresist.

Abstract: Holograms, derived from computer calculations (e. g., Ref. 1) have gained interest for a number of applications, like spatial filtering, and, in particular, for interferometric testing of aspheric surfaces in optics production due to their potential to create physically wavefronts from just a mathematical description. The most common way of making the hologram is to have the pattern, which has been calculated by the computer, drawn in a large scale by a plotter. The drawing is reduced photographically onto high-resolution film in one or two steps by a factor of 20-400. In the special application to generating wavefront standards for testing aspheric optical elements, computer-generated holograms are handicapped by several serious technical de­ ficiencies. Their low space-bandwidth product limits the diffraction angle and/or wavefront accuracy' and, hence, requires the use of additional optical elements for the testing of deep aspherics (e. g., Refs. 6, 10, 12, 14, 15, 17). Position nonlinearities of the plotting device, aberrations of the reducing lens, and minute scale errors in the demagnification process cause errors in the wavefront generated which are much larger than the accuracy of λ/10 or λ/20 usually re­ quired for wavefront standards. The space-bandwidth product of ordinary holograms generated in laser light by a signal wavefield and a coherent off-axis reference beam may easily be 10 and more along one coordinate if the carrier frequency is, say, 1000 cycles/mm and the plate is 10 cm wide. Data on display devices used for drawing computer-generated holograms indicate that plotters of different brands may provide between 900 × 900 and 6000 × 6000 or 7000 × 7000 discrete pen positions (e. g., Refs. 8, 18, 19), of which only about 1500 have been regarded as suffi­ ciently distortion-free. The paper size may be up to about 1 m. Plotting time for the largest type is about 10 h. Also the use of cathode-ray tube displays with, e. g., 1024 X 1024 points, a laser beam recorder with about 1400 × 1400 dis-

Theory of hologram formation in photorefractive media

Abstract: A theory for the formation of phase holograms in lithium niobate and similiar materials is presented. The experimental situation considered is that of an open‐circuited crystal with no applied voltage. The present theory differs from previous theories in that the electric field is treated self‐consistently in agreement with basic electrostatic laws. It is found to be important to account for the dark conductivity of the crystal. Several new results are obtained: The dependence of stationary‐state diffraction efficiency on light intensity is predicted. The influence of previous illumination of the crystal is investigated. It is shown that the phase shift between the interference pattern and the refractive‐index pattern changes during hologram recording. Nonlinear effects occurring at high modulation indices are evaluated. The effect of piezoelectricity on hologram recording is discussed.

Holographic diffraction gratings with asymmetrical groove profiles

Abstract: Gratings with a sinusoidal profile, as they are obtained in photoresist by holographic interference techniques, can provide very high efficiency values for wavelengths of about the same dimension as the groove spacing When the high dispersion following from the high groove density is undesirable and broadband efficiency is required, asymmetrical groove profiles become necessary We report on a method of Fourier synthesizing an asymmetrical profile by superimposing two sinusoidal exposure distributions of spatial frequency ratio 1:2 Amplitudes and the relative phase of the two interference exposures are obtained from a calculation optimizing diffraction efficiency by optimizing the combined action of the diffracted fields The technical realisation of the method, comprising, eg, exact phase control of the two individual exposures, is described in detail As an example, experimental results are reported for a grating of 600 grooves/mm blazed for λ = 340 nm The diffraction efficiency obtained in the +1 order is 67 per cent, and this value is higher by a factor of 95 than that of the −1 order

Measuring concave diffraction grating efficiencies at grazing incidence.

Abstract: The efficiency of a concave diffraction grating in a given order is obtained by measuring the intensities of the diffracted and incident beams and taking their ratio. A valid measurement requires that both the incident and diffracted beams be collected, in their entirety, by the detector. At grazing incidence, however, the diffracted beam may spread beyond the detector due to aberrations. In addition, the diffracted beams of consecutive orders may overlap so that unambiguous efficiency measurements cannot be made. The effect of aberrations on efficiency measurements has been studied, using ray tracing, for the geometry of the measuring instrument in use at the Naval Research Laboratory. This instrument, a reflectometer wherein the detector rotates around the grating at a given distance, is attached to a VUV monochromator which furnishes a diverging beam. The main effect of aberrations for this instrument is a spread of the diffracted beam in the direction of dispersion. The width of the diffracted beam is wavelength dependent and is minimal at the horizontal focus, spreading to longer and shorter wavelengths. Reducing the divergence of the incident beam reduces the spread but, for small radius gratings, not always sufficiently so that the entire diffracted beam can be collected by the detector. The distance from the detector to the grating can also be adjusted to aid in collecting all the diffracted beam. Some results of the ray tracing studies will be presented, and the effect of the f-number of the incident beam and the detector distance will be discussed.

Attenuated thick hologram gratings. Part I: Diffraction efficiency

Abstract: In this paper volume hologram reconstruction is considered as an electromagnetic scattering problem that leads to a characteristic integral equation. Our main attempt is the calculation of diffraction efficiency for attenuated gratings, that is compared with those of unattenuated gratings, to point out the influence of grating attenuation. In this respect the solution in the first Born approximation is found to be sufficient for diffraction efficiency calculations of attenuated gratings.

Phase-hologram material by using four-center-type photopolymerization in the crystalline state

Abstract: A new dry-process recording material using photopolymerization in the crystalline state is proposed as an ideal material for holographic interferometry, especially for real-time holographic interferometry. The performance of the complex recording material comprising m-PDA as a photopolymerizing reactant and picramide as a spectral sensitizer were evaluated. The development of this complex recording material is accomplished simply by heating it; fixation occurs at room temperature. We were able to make a holographic grating with resolution up to 1930 lines per millimeter using this material with a He-Cd laser oscillating at 442 nm. The maximum diffraction efficiency and the sensitivity corresponding to a 30% diffraction efficiency as a volume phase hologram were estimated as 36.3% and 5.6 mJ/cm2, respectively.

Photodielectric Polymers for Holographic Use

Abstract: The use of polymeric materials as “thick” recording media for holographic applications is discussed. These materials offer some interesting applications owing to their high diffraction efficiency, high storage density, excellent angular and spectral discrimination, as well as in situ real-time recording. The present state of art is outlined, as are prospects for the future.

On the Hologram Recording Based on the F→Z1 Colour Centre Conversion in KCl:Ca and KBr:Ca Crystals

Abstract: Use of the F ? Z1 colour centre conversion for hologram recording in KCl and KBr single crystals doped with Ca has been studied. A new technique for measurement of the H-D curve (optical density versus exposure energy) has been described. Further, measured diffraction efficiency values for holograms by taking advantage of the H-D curves are presented. The readout of the hologram was observed to be destructive, and experimental data describing this property are also given.

Infrared Laser Heating For Thermoplastic Recording

Abstract: IR laser heating for thermal development and erasure of data is presented with results showing holographic diffraction efficiency, signal to noise ratio, thermoplastic surface condition, recording area size and IR energy requirements.