Showing papers on "Diffraction efficiency published in 1969"

Coupled wave theory for thick hologram gratings

Abstract: A coupled wave analysis is given of the Bragg diffraction of light by thick hologram gratings, which is analogous to Phariseau's treatment of acoustic gratings and to the “dynamical” theory of X-ray diffraction. The theory remains valid for large diffraction efficiencies where the incident wave is strongly depleted. It is applied to transmission holograms and to reflection holograms. Spatial modulations of both the refractive index and the absorption constant are allowed for. The effects of loss in the grating and of slanted fringes are also considered. Algebraic formulas and their numerical evaluations are given for the diffraction efficiencies and the angular and wavelength sensitivities of the various hologram types.

Optical pulse compression with diffraction gratings

Abstract: The theory of the diffraction grating pair is developed by expanding the frequency dependence of the phase shift as far as the quadratic frequency term. The analogy between pulse compression and Fresnel diffraction is treated. The effect of the cubic phase term is discussed for ultrashort pulses having appreciable fractional bandwidth.

Electrical control of holographic storage in strontium‐barium niobate

Abstract: Single‐crystal Sr0.75Ba0.25Nb2O6 when used in conjunction with an externally applied electric field is shown to be a sensitive volume holographic medium capable of high‐resolution information storage. Optically induced refractive index changes of 5 × 10−4 have been observed with laser exposure of 14 J/cm2. A simple relation between the applied electric field and optical exposure is determined which allows electrical control of optically induced refractive index change. In addition to control of the optically induced effect it is found that the applied electric field can also be used to control the diffraction efficiency of the holographic reconstruction process.

Theoretical and Experimental Investigation of a New Type of Blazed Grating

Abstract: A rigorous electromagnetic theory of the diffraction of light by blazed lamellar gratings has been developed. It is applied to calculate the diffracted power distribution of four gratings (R1 − R4) whose grooves have the following depths and widths (b,l) in units of grating period a: (0.433, 0.750), (0.333, 0.667), (0.250, 0.500), and (0.200, 0.400). All four gratings are theoretically blazed in the minus-first order for 30° incidence and for the wavelength equal to the grating period. The blaze is, however, broad band, and the minus-first-order theoretical power-conversion efficiency (P−1) for the most interesting grating, R3, exceeds 0.8, 0.9, 0.95, and 0.98 in the wavelength bands 0.84 a−1.49 a, 0.85 a−1.47 a, 0.87 a−1.43 a, and 0.98 a−1.31 a, respectively, for linearly polarized light. These surprising performances, which far exceed those obtainable with echelette gratings insofar as the incident light is linearly polarized, have been experimentally verified with the help of a microwave interference spectrometer, and point to the potential usefulness of blazed lamellar-reflection gratings in far-infrared spectroscopy.

Diffraction efficiency of bleached, photographically recorded interference patterns.

Abstract: An experimental study has been made of techniques that can increase the diffraction efficiency of photographically recorded three-dimensional interference patterns. The efficiency is increased by using bleaching processes that convert the silver image into a dielectric image. Diffraction efficiency vs transmittance curves, chemical formulas of some bleaches, and the bleaching procedures are given. A maximum efficiency of 60%o has been achieved. Applications to holography and partitioned zone plates are demonstrated.

Recording holograms in luminescent materials.

Abstract: The fluorescein–boric acid glass organophosphor has been characterized as a transient photochromic hologram receptor medium in which an excited electronic state gives rise to the holographic grating. It is shown that the holographic signal depends upon dye concentration, sample thickness, and writing laser power. The decay rate of the hologram, after the writing laser is turned off, is determined by the excited state lifetime of 1 sec, while holographic rise times are in the order of 0.1 sec. Diffraction efficiencies are in excess of 0.2% at hologram writing powers of about 500 mW cm−2. It is thought that this can be improved by choice of either more highly doped systems or pure materials.

Amplitude and Phase Holograms Exposed on Agfa-Gevaert 1OE75 Plates.

Abstract: A new line of films and plates has recently been developed especially for holography. One of these, the Agfa-Gevaert 10E75 emulsion, has both relatively high resolution and good sensitivity to the red He–Ne and ruby laser lines.We have used 10E75 plates to record a variety of He–Ne laser holograms, and, since these plates are evidently not widely used, we thought it worthwhile to report on some of our results. In our experiments, the object was a back-lighted ground glass diffuser. The collimated reference beam and the object beam fell on the photographic plate making approximately equal angles with the normal to the plate. The spatial frequency of the carrier wave was approximately 500 1/mm; the optical path difference between the two beams was very nearly zero. All plates were developed for 5 min in Kodak D-19 developer. Figure 1 shows the typical dependence of diffraction efficiency

Efficiencies and bandwidths of intracavity acousto-optic devices

Abstract: Acousto-optic devices based on isotropic and anisotropic acoustic Bragg diffraction will be discussed in terms of their efficiency and bandwidth. The conflicting requirementos n the width W of the acoustic column with regard to efficiency and bandwidth determine the basic limitations of the devices. A scheme using the acousto-optic devices within a flat-field conjugate (FFC) angularly degenerate laser cavity has been experimentally demonstrated. The bandwidth of the new scheme is limited by the field angle of the FFC cavity instead of by W-1. The width W can be made as large as possible to increase the diffraction efficiency without decreasing the bandwidth. The new scheme provides means for high efficiency and large bandwidth in optical deflection and signal processing systems.

Radiance of Rectangular-Profile Gratings in S Polarization

Abstract: We treat gratings as arrays of lines or elements rather than as infinite periodic structures. Since we cannot calculate accurately the diffraction pattern of a single rectangular-profile line, we have constructed a simple model which assumes Fraunhofer diffraction from the various parts of the line. Three measured parameters, functions of the angle of incidence, determine the entire diffraction pattern with good accuracy except for large angles of diffraction. The radiance either of the single-line or of a grating of any number of lines is then given by the triple product of the squares of the incident amplitude, the single-line diffraction amplitude (or the effective single-line pattern) and the array factor. Spectral radiances in S polarization calculated for a set of 20-line rectangular-profile gratings are in good agreement with measured values. Even anomalous behavior is accurately predicted.

Diffraction anomalies for transmission gratings with laser illumination.

Abstract: Grating anomalies, i.e., large changes in the intensity of diffracted orders for small changes in the angle of incidence, were first observed by Wood for optical reflection gratings. He found that bright and dark bands appeared in certain orders as a function of the incident angle and that they apparently occurred only for light polarized with its electric vector per­ pendicular to the grooves (S polarization) and not for parallel (P) polarization. P anomalies have since been observed. Rayleigh formulated a theory which related the angles of incidence at which anomalies can occur to the grating param­ eters by the following equation: