Study On The Environmental Response Characteristics Of Holographic Sensor In Acrylamide Photopolymer

During recent years,holographic sensor has attracted many attentions due to its high sensitivity,high signal-to-noise ratio and high dynamic range optical core components.Diffraction colors and intensity of holographic image was used to monitor environmental conditions.Compared with other photopolymer materials,poly(vinyl alcohol)-acrylamide(PVA/AA)is an ideal material for holographic sensor with its high diffraction efficiency,fast response,low cost and flexibility preparation process.The PVA/AA photopolymer has received many researches on its good performance,however its application for holographic sensing is lack of quantitative experimental results.Consequently it is a significant investigation for experimental data supplement and sensing characteristics research.In this paper,with the preparation of PVA/AA materials and analyzing the principle of holographic sensor,environment humidity and alcohol organic vapor response characteristics are measured in detail at transmission and reflection geometries.These studies provided significant experimental foundations for holographic sensing development in actual application.The results show that osmosis progress of analyte molecules caused decrease of modulation depth and average refractive index,and increase of fringe spacing.The decrease of average refractive index leads to blue shift while the increase of fringe spacing caused by material swelling leads to red shift.This competition mechanism between two models is proposed to explore the wavelength shift mechanism.Obvious red shift of diffraction spectrum peak was observed in humidity response,the maximum red shift is about 60 nm.Meanwhile the blue shift was found for the first time in alcohol response,the maximum blue shift is about 5nm.Due to the elastic retractive force of crosslinking structure,hysteresis of swelling process obviously compared to the decrease of average refractive index and the red shift occurs after the blue shift.After adding Y nano-zeolites,the maximum change of wavelength shift close to 10 nm for blue shift and 90 nm for red shift,the optimized concentration is 0.3wt%.The addition of nanoparticles can effectively delay the reduction trend of diffraction efficiency,improve the sensitivity and widen the detection range of holographic gratings.Increasing the slanted angle reduces the peak wavelength shift.The reversibility of the spectrum shows that the sensor is achieved for confirming repeatability in practical applications.Synthesizing the advantages of holographic properties,obvious red shift can be a representative method for environmental monitory,and the blue shift provide a novel identification method for low concentration and refractive index vapors.Reflection gratings suit for low concentration vapor with its high sensitivity,on the contrary,transmission gratings suit for high concentration vapor.In conclusion,PVA/AA material has good research and application values,so the holographic sensor provide a novel,simple,quick and intuitive sensing strategy for environmental factors.