Investigation of temperature response of photopolymer material used for holographic sensor

Recently, functionalised photopolymer has emerged as a versatile recording material in the field of optical holography due to its novel characteristics and potential use in the development of holographic based sensors, and optical elements. This work describes the temperature response of a newly developed photopolymer, containing of a monomer N-isopropylacrylamide (NIPA) which under photopolymerisation forms a temperature sensitive polymer - Poly(N-isopropylacrylamide) (PNIPA). The photonic sensor was developed by holographic recording of volume phase transmission gratings in a self-processing NIPA-based polymer with a 532 nm laser beam. A 633 nm probe beam was used to monitor real time diffraction efficiency (DE) growth curve and the temperature dependent response of DE in the temperature range 22-50°C. It was observed that the DE increased with increasing temperature at 10°C min-1 and started to drop by reversing the temperature at 5°C min-1. It was also observed that the response depends on the rate of heating/cooling and the time spent at elevated temperature. The observed response to temperature could be used to design an indicator for packaging, showing that the content of the package has been exposed to a temperature that was above a predetermined temperature limit.