Showing papers on "Diffraction efficiency published in 1973"

Calculation of diffraction efficiency in hologram gratings attenuated along the direction perpendicular to the grating vector

Abstract: A thick hologram grating with modulation that decreases along the direction perpendicular to the grating vector has been analyzed using coupled-wave theory developed by Kogelnik. General solutions of two predominant waves, undiffracted and first-order diffracted waves, are given for transmission and reflection types of hologram gratings. Calculated efficiency of diffraction for some special cases is compared with that for the uniform grating. The influence of the attenuation of grating modulation upon the validity of the theory when applied to the Bragg reflection is also discussed.

Diffraction by thick, periodically stratified gratings with complex dielectric constant

Abstract: This paper extends Burckhardt’s solution for diffraction from a thick grating to include complex dielectric constants and nonsinusoidal stratifications. This allows any realistic periodic structure to be handled. Computed results are compared with coupled-wave theory, as described by Kogelnik, with emphasis on strongly absorbing gratings such as those made by photographing an interference pattern. Finally, some experimental holographic data are compared with computations that take into account the photographic nonlinearity between exposure and dielectric constant.

Properties of Holographic Gratings Photoinduced in Polymethyl Methacrylate

Abstract: Polymethyl methacrylate, PMMA, sensitized for lambda = 0.325 microm, is shown to exhibit a peak refractive index change of 2.3 x 10(-3). The index change has been characterized in relation to its sensitivity, temperature dependence, and development time. The sensitivity of the material is shown to be 1.7 x10(-4) alpha, where alpha is the intensity absorption coefficient. Laser light scattered by an exposed region is found to produce a double ring pattern due to the graininess of the index variation. Three-dimensional holographic diffraction gratings were made in the PMMA, and its diffraction efficiency was measured as a function of thickness, refractive index change, and reconstruction angle. The efficiencies measured agree fairly well with the theoretical sin(2) curve; however, higher peak diffraction efficiencies were obtained further out on this oscillatory curve. A maximum diffraction efficiency of 96% was obtained. Angular sensitivity measurements indicated that the effective thickness of the grating was less than its actual thickness due to the nonuniformity of the index variation with thickness. Potential applications as a dielectric waveguide, diffraction grating, and wavelength selector are discussed. Scattering, the relatively small maximum index change, and poor reproducibility are the chief limiting factors.

Acousto‐optical light diffraction in thin films

Abstract: The diffraction of optical guided waves in thin films through an acousto‐optic effect is treated. The diffraction of the bounded optical waves in thin films is a rather complicated phenomenon as compared with that of the free waves in bulk media. An expression for the diffraction efficiency has been derived using coupled‐wave equations. Acousto‐optical figure of merit and the mode coupling factor applicable to the diffraction in thin films are defined. The TE0 and TM0 waves in an As2S3 film deposited onto a LiNbO3 substrate were diffracted by Rayleigh waves with 93 and 72% efficiency at electrical input powers of 150 and 50 mW, respectively. The present experiment revealed that approximately 5% of the total acoustic power penetrated into the film and took part in the diffraction.

Holographic Optical Element for Visual Display Applications

Abstract: Off-axis and off-bisector reflection-type holographic visual display elements have been recorded in dichromated gelatin deposited on planar or spherical shell substrates of glass or Plexiglas. A procedure for bonding gelatin to Plexiglas is given. Holographic elements are recorded at the argon wavelength of 514.5 nm and reconstructed with spectral lines from a low pressure mercury arc lamp. Measured image characteristics for a flat substrate hologram agree with ray-tracing calculations. A swelling of the gelatin by approximately 6.6% after processing does not perceptibly affect the dispersion, astigmatism, or distortion in the image, that is, the grating equation depends on the spacing between the fringes on the surface of the gelatin and is not affected by the swelling or shrinking. However, the Bragg equation depends on the distance normal to the fringe planes and is affected by thickness changes of the gelatin. Therefore, this thickness change is taken as an independent parameter and used to adjust the wavelength for maximum diffraction efficiency, without affecting the image angle. Data reveal a near linear relationship between the dichromate concentration of 0.5–10% used to photosensitive the gelatin and the display wavelength of maximum diffraction efficiency. Lateral dispersion is 0.12 ± 0.01°/nanometer for both planar and spherical shell substrate elements recorded in quite similar geometry, but their astigmatisms are not alike.

Laser Doppler velocimeter with optical frequency shifting

Abstract: A bi-directional laser Doppler velocimeter utilizing optical frequency shifting has been developed. Optical frequency shifting is achieved by using a rotating radial grating. A high diffraction efficiency permits the system to be used in the fringe mode. The zero velocity frequency shift can be varied from 0.1 to 2.5 MHz with a stability better than 0.2%. Important applications are velocity measurements in reversing flows, highly turbulent flows, two-phase flows, and boundary layers. The system described may also be used for vibration analysis. Experimental results are presented.

Application of a single-frequency unstable cavity to a CW HF laser

Abstract: Demonstrations of diffraction-limited performance from a CW diffusion-type HF chemical laser are reported. A novel type of edge-coupled nonconfocal unstable resonator consisting of a convex mirror and a diffraction grating is used. A new technique of coupling power out of an unstable resonator different from the edge coupling previously suggested by Siegman is also applied. This consists of coupling power out directly through the diffraction grating zero-order radiation. By this technique, a large fraction of the total power is concentrated within the diffraction-limited main lobe. Peak power levels of the order of 100 W have been achieved on a single line [ P_{2}(5) ] for flow conditions yielding approximately 1 kW in closed cavity measurements.

Self‐enhancement of LiNbO3 holograms

Abstract: Self‐enhancement (an increase in diffraction efficiency upon readout with a single laser beam) is reported for iron‐doped LiNbO3 holograms which have not been ``fixed'' (crystal heated to 100°C during or after recording). The rate of change for self‐enhancement was observed to be equal to and opposite in sign with the rate of erasure observed in the same crystal at the symmetrical Bragg angle.

Spectrograph calibration at soft X-ray wavelengths. I. From grating diffraction efficiency and plate response factors

Abstract: The sensitivity of a grazing incidence grating spectrograph has been derived from measurements of the absolute efficiency of the diffracting element, a Bausch and Lomb catalogue grating, and of the response of the recording emulsion, Ilford Q2 and Kodak Kodirex. Results are presented for wavelengths between 8 and 44 AA, obtained as K-line emissions from electron-bombarded targets, incident on the grating at an angle of 88 degrees .

Analysis of diffraction gratings by finite-difference coupling technique

Abstract: A general numerical technique for analyzing diffraction gratings of arbitrary groove shape as electromagnetic boundary-value problems is suggested. The method yields the scattered far-field modal amplitude without the necessity of initially computing the induced surface currents, which makes this technique very simple and convenient for analyzing the performance of diffraction gratings under normal and anomalous conditions. Some available computed results for rectangular gratings for the E-polarized case are compared with similar results in the literature and the adequacy and accuracy of the technique are demonstrated.

Scattering efficiency of high-periodicity dielectric gratings: Experiment

Abstract: The scattering efficiencies of embossed dielectric gratings, with grating period Λ shorter than the wavelength λ of the scattered light (Λ ∾ 0.6λ), were measured and compared with theory. The experimental and theoretical results were found to be in very good agreement.

Pulsed Writing of Solid State Holograms

Abstract: The pulsed writing of volume holograms in lithium niobate is reported, both with 200-nsec and 20-nsec duration pulses. This information is of particular interest in high capacity information storage applications since it indicates that writing times at least as short as 20-nsec are readily possible. A series of pulses was used in each case, and the diffraction efficiency was monitored using a He-Ne laser operating at 6328 A and aligned to its corresponding Bragg angle.

Holographic Optical Elements.

Abstract: : The significance of this research is the evaluation and characterization of possible recording materials for holographic optical elements. Seven recording materials were evaluated for use as holographic optical elements through measurement of holographic sensitometric and readout parameters and investigation of their environmental stability. The seven materials included four volume phase materials, bleached photographic emulsions, dichromated gelatin, photopolymer, and thick thermoplastics; and three thin phase materials, photoresist, iron oxide, and photoplastics. The holographic response of each material was characterized through measurements of exposure sensitivity, diffraction efficiency, signal-to-noise ratio, frequency response, and spectral variation of readout efficiency. Environmental stability was determined by monitoring the holographic parameters over a wide temperature and humidity range, under prolonged UV exposure, and by measuring the nondestructive readout intensity range. (Modified author abstract)

Angular Dispersion of Diffraction Gratings Used for Tuning Organic Dye Lasers

Abstract: The result given by Eq. (6) is valid only when the angle of incidence α is fixed as is the case in the original appli­ cation of Littrow's mounting in the grating spectrograph. It is important to note, however, that Eq. (6) does not hold for applications in which the angle of incidence does not remain constant, i.e., the tunable organic dye laser in which the grating is used to tune the wavelength of laser emission by changing the angle of incidence of the inter­ nal oscillator beam on the grating. Figure 2 shows a rap­ idly tunable organic dye laser in which the grating is Lit­ trow mounted, i.e., α = β, but the angle of incidence of the beam on the grating is changed rapidly by the intracavity rotating mirror to tune rapidly the wavelength of laser emission. When the angle of incidence is changing as in Fig. 2, the result obtained by differentiating the grating Eq. (1)