Acrylic Light-induced Polymerization Characteristics And Real-time Measurement Study

Holographically constructed optical components made of the photopolymerizable composite materials mixed with liquid crystal are very promising in many fields. To optimize the performance of HPDLCs, many studies have been carried out. Although, some feature properties for optical grating of holographic polymer dispersed liquid crystal (HPDLC) has been demonstrated, the general performances as optical device still need to be improved further. Papers have been published dealing experimentally and theoretically with the dynamical processes during the formation of phase grating in HPDLC. Phase separation between LC and polymer induced by photopolymerization plays a most important role in the HPDLCs performance. To study the photopolymerization we propose a theory for monitoring the variation in real time of refractive index in laser-induced polymerization in a thin layer of acrylate composite, based on the curing intensity dependent photopolymerization, and its influence on guassian beam wave front distortion. Different intermittent curing methods were conducted for pulsed laser induced photopolymerization reactions in TMPTA acrylic system. Two methods of curing were compared, named grouped pulses impingement (GPI) and consecutively pulsed curing (CPC), we have conducted aspects of researches as the following:1. Absolute variation process of the refractive index of curable chemical composite in laser-induced photopolymerization was modeled. According to the results, we use the theory from Matrix Optics to establish a method for detecting the real-time photopolymerization. Data rate of more than 20Hz made this system suitable for real time measurement with a systematic resolution of±0.3%.2. Continuous and pulsed lasers were taken, respectively as the curing sources to cure the TMPTA acrylic system. The precision of 0.1% change in refractive index was clearly resolved. Meanwhile application of the method to the photopolymerization for acrylate composite was also presented. The results showed the post curing effect was phenomenal.3. In GPI, a prominent light diffraction effect was observed in the post curing process, whereas absent in the CPC procedure. We believed there must be an unexpected structure shaped during the procedure.4. Simulations based on Fresnel diffraction theory were performed to model the diffraction in GPI curing, and the result was in good agreement with the experimental observations, which demonstrated that a condensed but limited sized core of polymeric structure was ascribed to the cause of the light diffraction.