Research On Improving Response Characteristics Of Photopolymer Polymer Holographic Sensors

Holographic sensor is a new kind of optical sensing device.The holographic grating is recorded in the photosensitive polymer material.The change of the fringe spacing and the refractive index of the polymer material is influenced by the environment,which leads to the peak wavelength shift of the grating diffraction spectrum.By quantifying the relationship between environmental factors and wavelength offset,holographic sensors can be developed.At the same time,the shift of the spectrum is accompanied by the color change of the diffraction image,so the holographic sensing has the ability of high visualization,that makes it become a novel sensing method which has attracted much attention in recent years.However,the slow response is the main disadvantage of polymer holographic sensors.This is due to the fact that the adsorption and permeation process of materials on gas molecules takes a long time.At the same time,the glass substrate restricts the adsorption capacity of the material,which limits the practical application of the holographic sensor.In this paper,we propose a novel method for preparing holographic sensing materials,develop a new devices,and realize the high sensitivity sensing response of sensors to organic gases.By removing the effect of the glass substrate,reduce the thickness of the sensing material,the experiment successfully improves the response speed of the sensor and reduces the minimum detection concentration of the organic gas.At the same time,in order to avoid the interference of the ambient temperature to the sensing performance,the temperature sensitivity of the holographic sensor is tested in detail,and the main factors of the wavelength offset are analyzed.The response characteristics of the temperature are improved by adding nanoparticles into the material,and the improvement of the holographic sensing performance is confirmed by the theoretical and experimental in detail.The results show that with the increase of temperature,although the thermal expansion occurs,the peak wavelength has a significant blue shift.Therefore,we tested the inducement of the temperature sensitive wavelength blue shift in detail.The thermal optic coefficient,average refractive index and linear thermal expansion were tested and expressed in theory,which kept a good agreement with the experimental results.In the process of organic gas sensing,ethanol is selected as the characteristic gas.The improvement of the response performance of the new double sensing material is analyzed in comparison with the traditional single surface sensing material.These experimental results provide an effective way to improve the response of holographic sensors and accelerate the development of holographic optical elements based on photosensitive polymers.