Holographic characterization of epoxy resins at 351.1 nm (original) (raw)

Characterisation of Epoxy Resins for Microstereolithographic Rapid Prototyping

International Journal of Advanced Manufacturing Technology, 1999

Two epoxy resins are investigated using non-degenerate fourwave mixing. The materials assessed are optimised for use with a UV argon-ion laser. The holographic gratings were written at a wavelength of = 351.1 nm for an irradiance range 0.5-3.0 W/cm 2 and read at = 632.8 nm in order to compare the reactivity, curing speed, shrinkage and resolution of the resins. These experiments were carried out to prove the suitability of the photopolymerisation systems for use with a new microstereolithographic technique. This new technique exploits a spatial light modulator to create 3D components using a completely planer, layer-by-layer, process of exposure which is described herein. With this procedure it is possible to build components with dimensions in the range of 50 mm to 50 m, and feature sizes as small as 5 m with a resolution of 1 m.

Photopolymerization of an Epoxy Resin: Conversion and Temperature Dependence of its Refractive Index

Macromolecular Chemistry and Physics, 2016

Obtaining photocomposite materials with predefi ned optical properties requires a good knowledge of the refractive index evolution of the photopolymerizable media. In this aim, relationships between refractive index and conversion in the course of an epoxy resin photopolymerization are fi rst established due to real time refractometric and infrared spectroscopic techniques. Refractive index value increases with conversion as long as the photocured material is not in glassy state. A shift of the relationship toward lowest refractive index values is observed when the reaction temperature increases. Second, the fi nal photocured materials previously obtained are characterized. It is highlighted that the higher the photocuring temperature, the higher the epoxy conversion but the lower the material density at room temperature. This unusual result can be explained by the evolution of the material thermo-optic coeffi cient, d n /d T. Indeed, the higher the conversion, the lower this coeffi cient.

Optical and holographic characteristics of photopolymer layers

2009

In the present work the optical and holographic characteristics of acrylamide-based photopolymer layers are studied. For the first time the refractive index change of a liquid acrylamide photopolymer due to exposure at 532 nm is obtained using a critical angle laser micro-refractometer. The 30 µm thick solid photopolymer films are prepared by casting on glass substrates. Bragg holographic gratings with spatial frequencies of 710 mm -1 , 1050 mm -1 and 1600 mm -1 are recorded using a diode laser operating at 532 nm wavelength. The diffraction efficiency dependence on the exposure energy is investigated. The obtained results are compared with the Stetson holographic recording method, where two gratings are simultaneously recorded in the same location with spatial frequencies 2020 mm -1 and 3670 mm -1 , using a totally reflected reference wave from the airphotopolymer interface. Despite the fact that in the second method the two gratings share the same dynamic range, higher diffraction efficiencies are observed.

Photopolymerization model for holographic gratings formation in photopolymers

Applied Physics B-lasers and Optics, 2003

This work describes the study of free-radical homopolymerization kinetics for a system based on acrylamide, triethanolamine, and methylene blue on a polyvinylalcohol matrix, by analyzing temporal variations of the diffraction efficiency. Due to the high viscosity of the material, it has been demonstrated that diffusion processes at the time of recording are negligible. So, the modulation index has been related to the parameters of the system’s components, giving as a result, a method that can be used to estimate the chain-length of the polymer, the kinetic rate constants and absorption-scattering parameters. Depending on the termination step, two models of homopolymerization has been proposed – a bimolecular model (bimolecular termination) and a radicalic model (primary radical termination). Using these methods it was possible to compare the results obtained for the kinetic parameters of the photopolymerization process when the intensity and the concentration of each component were changed. Thus, holography can be used as holographic method to analyze the photopolymerization processes.

Characteristics of DuPont photopolymers for slanted holographic grating formations

Journal of the Optical Society of America B, 2004

The characteristic parameters of DuPont OmniDex613 photopolymers including the shrinkage factor, diffusion coefficient, and nonlocal response length are studied for slanted holographic gratings recorded at the UV wavelength of 363.8 nm by application of the rigorous coupled-wave analysis in conjunction with an angularselectivity measurement, a real-time diffraction-monitoring technique, and a nonlocal diffusion model. Both small (Ͻ20 deg) and large (Ͼ40 deg) slant-angle gratings are presented. Depending on the exposure intensity, the recording shrinkage factor of the photopolymer varies from ϳ2.75% to ϳ4.20%. Furthermore, the effects of postbaking conditions on the refractive-index modulations and the shifts of Bragg angles for slanted holographic gratings are also investigated systematically. It is found that the postbaking processing can not only increase the refractive-index modulations from ⌬n 1 ϳ 0.013 to ϳ0.028 for a small slant-angle grating and from ⌬n 1 ϳ 0.011 to ϳ0.022 for a large slant-angle grating, but can also compensate the recording shrinkage.

Hologram recording in polyvinyl alcohol/acrylamide photopolymers by means of pulsed laser exposure

Applied Optics, 2002

The variation in transmittance produced when a photopolymer is irradiated with a pulsed laser is analyzed and experimental results obtained when diffraction gratings are stored using pulsed exposure are presented. In either case, the influence of the energy of the irradiation pulse, the number of pulses, and the pulse repetition rate were studied. The photopolymer used was an acrylamide͞polyvinyl alcohol dry film with a yellow eosin-thiethanol-amine mixture as a photoinitiator system. The recording of the gratings was performed by use of a holographic copying process. The samples were exposed and holograms recorded with a collimated beam from a frequency-doubled Nd:YAG ͑532 nm͒ Q-switched laser. Our initial results show that it is possible to obtain diffraction gratings with a diffraction efficiency of 60% and a refractive index modulation up to 2.8 ϫ 10 Ϫ3 . The energetic sensitivities achieved are close to those obtained with the same material and continuous irradiation without a preprocessing of the gratings.

Photopolymères pour mémoire holographiques

2007

Data flow and its storage is one of the immediate requirements in present information age. There is a huge demand for a suitable storage media for immediate use and for data archive. Photopolymers are one of the most interesting materials with great storage potentials at extremely low cost. Photopolymers are attractive optical recording materials for holography, optical image multiplexing, holographic Contents Abstract iii Résumé iv Contents v List of figure viii List of Tables xiii Chapter 1. Introduction (IV) Poly vinyl alcohol (PVA) 1.5 Photopolymerization process (A) Photophysical process (B) Photochemical process The initiation. The propagation. Termination. 1.6 Monomer Diffusion 1.7 Holographic recording 1.8 Kogelnik's two-wave coupled wave theory 1.9 Outline of the thesis v References 35 Chapter 2. Acrylamide based photopolymers for red region volume holographic recording. 38 2.1. Introduction. 38 2.2 Preparation of photopolymer films. 39 2.2.1 Optimization of the photosensitizer. 42 2.3 Holographic recording : Experimental setup. 44 2.4 Experimental results. 46 2.4.1 Angular Selectivity. 49 2.5 Conclusion. 52 References. 53 Chapter 3. Photopolymers for green region volume phase holographic recording. 54 3.1 Introduction. 54 I. Transmission volume phase gratings. 55 3.2 Rose Bengal photopolymer. 55 3.3 Erythrosin B photopolymer. 71 3.4 Eosin photopolymer. 84 3.5 Acridine Orange photopolymer. 92 3.6 Effect of BSA in Photopolymer. II. Reflection volume phase gratings. 3.7 Reflection experimental setup. 3.8 RB photopolymer for reflection holographic gratings recording. 3.8.1. Effect of photosensitizer. 3.8.2 Sensitivity. 3.8.3 Shrinkage. 3.8.4 Effect of the exposure time on the diffraction efficiency. 3.9 Acridine orange for reflection geometry. 3.10 Conclusion. References Chapter 4. Novel dyes for blue wavelength volume transmission grating recording.