Search results for "Diffraction efficiency"
showing 10 items of 64 documents
Holographic recording in amorphous chalcogenide thin films
2007
Abstract Holographic recording by He–Ne laser (line 632.8 nm) light in amorphous As 0.55 Se 0.45 thin films for different film thickness and grating period was studied. A strong dependence of the diffraction efficiency of the gratings on the readout light wavelength (650 nm, 805 nm and 1150 nm) was observed. A decrease in diffraction efficiency for longer wavelengths is explained by a decrease in the photoinduced changes of refractive index. It is shown that high efficiency gratings can be recorded in As 0.55 Se 0.45 films with a thickness of ∼1 μm.
Surface relief grating recording in azo polymer films
2013
In this work holographic recording of surface relief grating in organic Poly(Disperse Red 1 – methacrylate) thin films was studied. In this compound azo dye is chemically bonded to monomers making mass transport very efficient in the presence of optical field gradient. Sample preparation was performed using different solvents and coating methods. In the obtained samples holographic recording was performed by solid-state diode pump laser with 532 nm wavelength. Polarization grating and surface relief grating formation was studied by diode laser with 660 nm wavelength. Diffraction efficiency's dependence on read-out laser beam polarization state was investigated. The depth of surface relief g…
Asymmetric transmission of terahertz radiation through a double grating.
2013
We report on experimental evidence of unidirectional transmission of terahertz waves through a pair of metallic gratings with different periods. The gratings are optimized for a broadband transmission in one direction, accompanied with a high extinction rate in the opposite direction. In contrast to previous studies, we show that the zero-order nonreciprocity cannot be achieved. Nonetheless, we confirm that the structure can be used successfully as an asymmetric filter.
Holographic properties of azobenzene oligomers with differently bonded chromophore groups
2007
Holographic properties of two types (I and II, specified in the text) of azobenzene oligomers (ABO) have been experimentally studied in the spectral region of low absorption at 633 nm. In the case of type I ABO the chromophore groups were covalently bonded to either tolyl-polyurethane or hexamethylene-polyurethane matrix. In the case of type II ABO azobenzene chromophores were dispersed in polystyrene matrix, and their concentration was varied from 0.005 to 0.200 mol/l. Samples were in the form of 10 µm thick films. In both cases the diffraction efficiency exposure time dependences were measured for the holographic grating period of 2 (m at 633 nm. The diffraction efficiency of more than 2%…
Wavelength tuning of femtosecond pulses generated in nonlinear crystals by using diffractive lenses
2010
We demonstrate that diffractive lenses (DLs) can be used as a simple method to tune the central wavelength of femtosecond pulses generated from second-order nonlinear optical processes in birefringent crystals. The wavelength tunability is achieved by changing the relative distance between the nonlinear crystal and the DL, which acts in a focusing configuration. Besides the many practical applications of the so-generated pulses, the proposed method might be extended to other wavelength ranges by demonstrated similar effects on other nonlinear processes, such as high-order harmonic generation.
Effect of reflections on phase hologram recording in amorphous As-S-Se films
2002
Experimental and theoretical studies of phase hologram recording in amorphous As-S-Se films with slightly wedge-shaped thickness profile are presented. It is shown that Fabry-Perot resonator effect caused by the interference of multiply reflected light beams inside the sample strongly changes the values of diffraction efficiency and its growth rate as well as the exposure time dependences of diffraction efficiency and transmissivity making them site-dependent and sample-dependent. Absorptivity and recording light intensity inside the sample are also significantly changed. The obtained results can be used to explain the holographic and optical experiments also in other materials with Fabry-P…
<title>Amorphous As-S-Se films for holographic recording</title>
2003
The amorphous As40S15Se45 films as recording media for optical holography were studied. The results on research of transmission and Bragg grating holographic recording and readout conditions are presented. The recording of transmission holographic gratings was performed by He-Ne (0.6328 μm) or Kr+ (0.6764 μm) laser beam, while the readout of the diffraction efficiency was made at Bragg angle using He-Ne (0.6328 and 1.15 μm) or diode (0.805 μm) laser lines. It is shown that self-enhancement of Bragg grating reflectors is possible. The influence of thin film interference conditions on holographic recording parameters is demonstrated.© (2003) COPYRIGHT SPIE--The International Society for Optic…
<title>Bragg and asymmetric-relief reflection gratings in As-S-Se thin films</title>
2005
Bragg and asymmetric-relief gratings and their formation in the amorphous As-S-Se films are discussed. Due to the high refractive index and its photoinduced change, the films are useful in holography. The thickness of the As0.4S0.15Se0.45 and As0.4S0.3Se0.3 films used in the Bragg gratings is optimized. The dependence of the dimaction efficiency of the asymmetric-relief gratings on the conditions of recording, chemical treating, and reading out (polarization and angle) is studied.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
Modeling of the photorefractive nonlinear response in Sn_2P_2S_6 crystals
2007
We develop a theory of the photorefractive nonlinear response for Sn2P2S6 crystals. The theory incorporates two types of charge carrier (optically active and passive), provides explicit expressions for the characteristic buildup-relaxation rates and gain factors, explains naturally a big variety of accumulated experimental data, and facilitates characterization-optimization of this important nonlinear material.
Generation of accelerating beams using nano-scale metallic circular gratings
2014
Spatially accelerating beams that are solutions to the Maxwell equations may propagate along incomplete circular trajectories, after which diffraction broadening takes over and the beams spread out. In this paper we report on numerical simulations that show the conversion of a high-numerical-aperture focused beam into a nonparaxial shape-preserving accelerating beam having a beam-width near the diffraction limit. Beam shaping is induced by a diffractive optical element that consists of a non-planar sub-wavelength grating enabling a Bessel signature.