Diffraction efficiency

About: Diffraction efficiency is a research topic. Over the lifetime, 10320 publications have been published within this topic receiving 158298 citations.

Surface plasmon enhanced diffraction for label-free biosensing.

Abstract: Surface plasmon enhanced evanescent field at a (noble) metal/dielectric interface can be employed to enhance the diffraction efficiency of surface grating structure composed of biomolecules. Based on a Kretschmann configuration, we realized a diffraction biosensor to monitor the dynamic interaction of biological molecules in a label-free way. It was demonstrated by the binding of an anti-biotin antibody to the biotin-functionalized region of a periodically patterned surface, which generated significant optical contrast to diffract the surface plasmon field. With the aid of the synchronic surface plasmon resonance signal, a quadratic dependence of diffraction signal on the amount of bound antibody was found, which coincides with the theoretical expectation. Time-dependent measurements were conducted to estimate the density of biotin thiols on the functional region.

Polarization dependence of holographic grating recording in azobenzene-functionalized polymers monitored by visible and infrared light.

Abstract: The holographic grating recording process in thin films of amorphous azobenzene-functionalized polymers has been widely reported in the literature. In spite of the many reports, little is known about the mechanisms responsible for different temporal behaviors of the diffraction efficiency during long recording times. Here, we report on experimental studies of the diffraction efficiency changes during the holographic diffraction grating recording process in photochromic polymer. The gratings were inscribed for four different polarization combinations of the recording beams: s-s, p-p, s-p and right to left circular polarization (RCP-LCP) employing the degenerate two-wave mixing technique. The grating recording process was simultaneously monitored by three different wavelengths: 514.5 nm (writing) and 632.8 and 904 nm (reading). The temporal evolution of the diffraction efficiency (for all polarization configurations and for each wavelengths) was precisely fitted within the model, which assumes simultaneous formation of the absorption grating and three coupling phase gratings shifted by 0 or π with respect to each other. Two of the phase gratings originate from the refractive index grating changes in the bulk (volume) of a material and the third one from the surface relief modulation. The model enabled us to extract relevant parameters for each grating such as the build-up time constant, its final amplitude, and the phase shifts between phase gratings. Performed studies and the discussion of results revealed the main differences in the diffraction grating formation process for s-s, p-p, s-p, and RCP-LCP polarization configurations.

Computational spectrometer based on a broadband diffractive optic.

Abstract: We describe a simple, compact, low-cost spectrometer comprised of a broadband diffractive optic and a sensor array. The diffractive optic is designed to disperse incident collimated light onto the sensor array in a prescribed manner defined by its spatial-spectral point-spread function. By applying a novel nonlinear optimization method, we show that it is possible to reconstruct the unknown spectrum from the measured image on the sensor array. We experimentally reconstructed numerous spectra with resolution as small as ~1nm and bandwidths as large as 450nm. Furthermore, we readily resolved two spatially overlapping but spectrally distinct objects. The spectral resolution is determined by dispersion of the diffractive optic via a spectral correlation function, while the bandwidth is limited primarily by the quantum efficiency of the sensor array. Using simulations, we present a spectral extraction of solar radiation from 300nm to 2500nm with a resolution of ~0.11nm. Moreover, our technique utilizes almost all the incident photons owing to the high transmission efficiency of the broadband diffractive optic, which allows for fast spectroscopy with dim illumination. Due to its simple construction with no moving parts, our technique could have important applications in portable, low-cost spectroscopy.

Holographic characteristics of a 1-mm-thick photopolymer to be used in holographic memories.

Abstract: Poly(vinyl alcohol-acrylamide) photopolymers are materials of interest in the field of digital information storage (holographic memories). We analyzed the behavior of a 1-mm-thick photopolymer. Using a standard holographic setup, we recorded unslanted diffraction gratings. The material has high angular selectivity (0.4°), good sensitivity (88 mJ/cm2), and small losses caused by absorption and scattering of light. It also has a high maximum diffraction efficiency (70%). A significant induction period was seen in the material. The authors hypothesize that, during most of this induction period, polymerization does in fact take place but is not reflected in the appearance of the diffracted light until a certain threshold value of exposure is reached.

Encoding amplitude and phase information onto a binary phase-only spatial light modulator.

Abstract: We report what to our knowledge is a new technique for encoding both amplitude and phase information onto a single binary-valued spatial light modulator. In our approach, we spatially modulate the diffraction efficiency of the filter. Light that is not diffracted into the first order is sent into the zero order, effectively allowing amplitude modulation of either the first-order or zero-order diffracted light. This technique has applications in both optical pattern recognition and image processing. Experimental results are included.