Yaohui Geng

Holographic humidity response of slanted gratings in moisture-absorbing acrylamide photopolymer

Holographic humidity response is characterized in detail using transmission and reflection geometry in moisture-absorbing acrylamide photopolymer. The diffraction spectrum and its temporal evolution at various relative humidity are measured and analyzed. The quantitative relations between relative humidity and holographic properties of slanted gratings are determined. The responsibility of holographic gratings for various relative humidity is observed by the spectrum response of gratings. The extracted humidity constants reflect the applicability of reflection and transmission gratings at different humidity regions. The humidity reversibility experiment is achieved for confirming repeatability of the sensor. These experiments provide a probability for improving the applicability of a holographic humidity sensor. Finally, the extended diffusion model is derived by introducing the expansion coefficient to describe the dynamic swelling process. This work can accelerate development of the holographic sensor and provide a novel strategy for exploring the swelling mechanism of photopolymer.

Enhancement of spectrum strength in holographic sensing in nanozeolites dispersed acrylamide photopolymer.

Holographic sensing of organic vapor is characterized at transmission and reflection geometries in ZSM-5 nanozeolites dispersed acrylamide photopolymer. Nano-zeolites as absorption medium are dispersed into the polymer to enhance the absorptivity to organic vapor. Obvious enhancements of spectrum strength are observed during the sensing process. Two primary factors causing the enhancement, absorption of nanozeolites and photopolymerization induced by broadband white light, are analyzed experimentally. Significant increment provides a quick and intuitive identification strategy for holographic sensing. Accompanying with the wavelength blue-shift, the shrinkage of sample is measured quantitatively under homogeneous white light. It is further demonstrated that the significance of nanozeolites absorption. Finally a theoretical model with mutual diffusion is used to simulate the swelling process. This study provides significant foundation for the application of holographic sensor.

Two-way shift of wavelength in holographic sensing of organic vapor in nanozeolites dispersed acrylamide photopolymer.

Holographic sensing of alcohol organic vapor is characterized in detail at transmission and reflection geometries in Y nanozeolites dispersed acrylamide photopolymer. The two-way shift of the diffraction spectrum and its temporal evolution with various vapor concentrations are measured. Obvious blueshifts of diffraction spectrum peaks are observed and analyzed in two recording geometries. The competition mechanism between decreasing the average refractive index and swelling the grating fringe space is proposed for exploring the wavelength shift mechanism. In the reflection grating, as organic vapor increases, the redshift after the blueshift of the wavelength peaks are observed clearly. We further demonstrate the significance of this competition mechanism. In the low concentration region, at transmission <700  ppm and reflection <400  ppm in nanozeolites dispersed polymer, the blueshift of the wavelength is a significant factor in identifying an organic vapor with a low refractive index. These experimental results provide a probability for improving the applicability of a holographic sensor. This work can accelerate the development of the holographic sensing strategy and provide a novel identification method for organic vapor.

Improvement of holographic sensing response in substrate-free acrylamide photopolymer

A novel substrate-free acrylamide photopolymer was proposed to improve holographic sensing characterization. The diffraction spectrum response of reflection volume grating recorded in the medium was characterized for exploring the improvement of sensitivity. The compared result indicated that the response rate and sensitivity were evidently improved by absorption of double surface in substrate-free polymer. The thickness of the sample as a significant factor was discussed in detail experimentally. During the sensing process, the inhibition concentration and concentration constant of organic vapor were extracted to evaluate the significance of sample thickness. Simultaneously, optimization of thickness could be considered as an effective approach to improve the response rate of holographic sensing. The reversibility of a novel holographic sensor with double surface was demonstrated by recovery measurement. The swelling ratio indicated that the peak wavelength shift was attributed to the expansion of binder induced by absorption of organic vapor. Theoretically, the sensing physical mechanism and the dynamic swelling process were analyzed and simulated using a diffusional model with nonlocal response. These experimental results provide an effective strategy for improving the response of a holographic sensor and accelerate the development of the holographic optical element based on photopolymer.