Transient biphotonic holographic grating in photoisomerizative azo materials

Wu, Pengfei; Wang, Li; Xu, Jing; Zou, B. S.; Gong, Xiong; Zhang, Guilan; Tang, Guiqian; Chen, Wenju

doi:10.1103/physrevb.57.3874

Cited by 36 publications

(26 citation statements)

References 31 publications

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“…The liquid crystalline structure of our polymer, with strong cooperative interactions among the molecules, can strengthen the influence of aggregation and reorientation processes with respect to amorphous polymers previously studied. [9][10][11][12] Those processes can give place to an increase of the diffracted light and to a relief grating as observed in our surface relief experiments. A similar mechanism has been proposed to explain some of the phenomena observed in gratings induced with coherent blue light.…”

Section: ͓S0003-6951͑00͒02436-0͔mentioning

confidence: 60%

“…They have explained it in terms of a spatial modulation of the isomer populations induced by the interference of the two He-Ne laser beams. [9][10][11] The growth of the diffraction efficiency observed in our experiments when the two He-Ne beams and the Xe lamp are present could be explained using the same model. When the Xe lamp is switched off, only cis to trans isomerization takes place in the illuminated areas and a reinforcement of the contrast between both populations would occur.…”

Section: ͓S0003-6951͑00͒02436-0͔mentioning

confidence: 66%

“…Another type of holographic storage has also been reported using coherent red light by means of biphotonic processes. [9][10][11][12] In these processes, a blue incoherent light is used to sensitize the azo chromophores in the red region and recording is performed with a coherent red source. This allows diode lasers to be used which is important for photonic applications.…”

Section: ͓S0003-6951͑00͒02436-0͔mentioning

confidence: 99%

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Biphotonic holographic gratings in azobenzene polyesters: Surface relief phenomena and polarization effects

Sánchez

Alcalá

Hvilsted

et al. 2000

Applied Physics Letters

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Biphotonic holographic gratings have been recorded in a side-chain azobenzene liquid crystalline polyester using a blue incoherent source and a He–Ne laser. Intensity gratings and the appearance of surface relief have been observed when two linearly polarized beams from a He–Ne laser are made to interfere on a film illuminated with blue light. Polarized holographic gratings are also created with two orthogonally circularly polarized He–Ne beams. All these gratings are stable in darkness but can be erased with blue light.

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Section: ͓S0003-6951͑00͒02436-0͔mentioning

confidence: 60%

Section: ͓S0003-6951͑00͒02436-0͔mentioning

confidence: 66%

Section: ͓S0003-6951͑00͒02436-0͔mentioning

confidence: 99%

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Biphotonic holographic gratings in azobenzene polyesters: Surface relief phenomena and polarization effects

Sánchez

Alcalá

Hvilsted

et al. 2000

Applied Physics Letters

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“…In some publications it was discussed that the absorbance of the Z-isomer at this wavelength is higher compared to that of the E-isomer. 13 The direction of the π-π* and the n-π* transition moment coincides with the long axis of the E-isomer. The decrease of absorbance in the range of the n-π* transition indicates the occurrence of Z-to-E isomerization.…”

Section: Uv-vis Spectroscopic Characterization Of Thementioning

confidence: 96%

Photoorientation of a Liquid-Crystalline Polyester with Azobenzene Side Groups: Effects of Irradiation with Linearly Polarized Red Light after Photochemical Pretreatment

Zebger¹,

Rutloh²,

Hoffmann³

et al. 2003

Macromolecules

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In contrast to the conventional photoorientation process with blue light, an orientation of 4-cyano-4′-alkoxyazobenzene side groups parallel to the electric field vector of the incident light is generated upon irradiating films of a liquid-crystalline side-chain polymer with linearly polarized red light. The polyester is characterized by smectic and nematic phases g24S X26SA34N46i and a strong tendency to form J-aggregates. The process requires a photochemical pretreatment by irradiation with UV light or an exposure to visible light of high power density to produce a certain concentration of the Z-isomer, which destroys any initial orientational order and J-aggregates. The orientation process is cooperative, whereas the light-induced orientation of the photochromic moiety causes an ordering of the alkylene spacers and even of the main-chain segments into the same direction. The most probable mechanism of this two-step process is the angular-selective transformation of the bulky Z-isomers to the rodlike E-isomeric formed by the red light. The aligned E-azobenzene side groups become strongly J-aggregated. Very high values of dichroism of about 0.8 and birefringence of about 0.3 were generated as a result of this combination of the photoinduced orientation process and the thermotropic selforganization, which take place simultaneously under the irradiation conditions. The process results in a uniaxial prolate order of the film, whereas conventional photoorientation leads to a biaxial oblate order. These two different three-dimensional orders have been characterized by FTIR polarization spectroscopy and exhibit also varying intermediate thermal stabilities.

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“…Since a bR molecule can be recycled into a new photocycle after relaxation in to B state, the number of particles in the BM cycle is constant, i.e., M þ B ¼ B 0 , where B 0 represents the total concentration of bR. By a straightforward calculation, we can obtain [40] BðtÞ…”

Section: Photo-controlled Light Modulationmentioning

confidence: 99%

Nonlinear Optical Image Processing with Bacteriorhodopsin Polymer Films

Yelleswarapu

Kothapalli

et al. 2006

Molecular Crystals and Liquid Crystals

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Real-time medical image processing through nonlinear optical Fourier filtering and transient Fourier holography is demonstrated using bio-organic polymer films of Bacteriorhodopsin (bR). In nonlinear Fourier filtering, the photo-controlled light modulation characteristics of bR films are exploited for early detection of microcalcifications in analog (screen film) as well as digital mammograms. bR films are well known for light modulation between the two states: the initial stable B state with broad absorption band with maximum at 570 nm and the relatively long lived M state with absorption maximum at 412 nm. The spatial frequency information carried by a blue probe beam is selectively manipulated in the bR film by changing the position and intensity of a yellow control beam. In transient Fourier holography, photoisomerizative gratings are recorded and reconstructed in bR films. The laser output from an Ar-Kr ion is expanded and split into two beams. One of them, the object beam is Fourier transformed by a lens on to the bR film placed at the Fourier plane. The second beam (reference beam) overlaps the Fourier transform of the object beam on the bR film thereby recordi00000000ng a Fourier hologram. When the object beam is blocked, the reference beam performs the reconstruction of the recorded Fourier hologram. The filtered spectrum is inverse Fourier transformed on to the CCD camera. The image processing is based on the fact that the desired spatial frequency band is recorded with optimum diffraction efficiency and matching the reference beam intensity to their intensity in the Fourier spectrum. A novel feature of the technique is the ability to transient display selected spatial frequencies in the reconstructing process which enables the radiologist to study the features of interest in time scale. Both the techniques are This work is supported by National Cancer Institute, NIH grant 1R21CA89673-01A1. The high quality photographic images of the clinical mammograms were obtained from the University of Massachusetts Medical School, Worcester, MA. We thank Dr. Carl D'orsi and Prof. Andrew Karellas for providing them. We also thank Mr. Paul Foster of our Physics Department for providing phantom objects.

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Transient biphotonic holographic grating in photoisomerizative azo materials

Cited by 36 publications

References 31 publications

Biphotonic holographic gratings in azobenzene polyesters: Surface relief phenomena and polarization effects

Biphotonic holographic gratings in azobenzene polyesters: Surface relief phenomena and polarization effects

Photoorientation of a Liquid-Crystalline Polyester with Azobenzene Side Groups: Effects of Irradiation with Linearly Polarized Red Light after Photochemical Pretreatment

Nonlinear Optical Image Processing with Bacteriorhodopsin Polymer Films

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