Optically Tunable Diffraction Efficiency in Reflection Grating Written in Photomobile Polymers

In this work, we report the fabrication and optical characterization of a one-dimensional reflection holographic volume phase grating recorded in a recently developed holographic photomobile composite polymer mixture. The reflection grating recorded on the photomobile material was a periodic one-dimensional arrangement of hard polymeric walls and viscous regions. The reflection notch was located in the near-infrared region of the electromagnetic spectrum. The transmission efficiency of the grating was modulated by an external CW laser light source operating at λ = 532 nm. The transmission efficiency increased with the increase in the power of the external laser source, and in the range of the used power values, the phenomenon was completely reversible. At the highest power levels, a 48% increase in the diffraction efficiency was achieved. The increase in the diffraction efficiency was related to the growth of the refractive-index contrast of the grating. In particular, under illumination, the viscous material escaped from the irradiated area. This feature explains the experimentally observed changes in the values of the grating’s refractive index

Light-Induced Dynamic Holography

Holographic photomobile polymers (H-PMP) are a novel class of photomobile materials in which holograms can be optically recorded. They can be used in a large variety of applications, including optical switches and color selectors. In this work, we show one of the most important properties of the photomobile film, which is the photophobicity of the unpolymerized parts of the photomobile mixture. In order to investigate this property, we recorded a transmission phase grating on an H-PMP film, and used a different experimental technique to measure the diffraction efficiency, surface tension, and mixture properties. The results allowed for a better understanding of the mechanism of the light-controlled bending observed in these compounds

Light amplification by dye-doped holographic polymer dispersed liquid crystals

(selected for June 7, 2004 issue of Virtual Journal of Nanoscale Science & Technology) In this letter we report a “one-step” fabrication technique of an optical active organic photonic band gap (PBG) structure allowing the onset of the amplification spontaneous emission effect and narrowing of the corresponding band. This result has been achieved through the addition of the dye rhodamine 6G to a standard holographic polymer dispersed liquid crystal pre-polymer mixture. The effects of the dye addition on the optical properties of the polymerized PBG structure have been analyzed. The spectra emitted by this optically active periodic structure have been studied as a function of the excitation energy

Polymer-Based High Diffraction Efficiency and High Resolution Volume Holographic Transmission Gratings

We report on the optical characterization of very high-efficiency and high-resolution holographic volume phase transmission gratings. The gratings are recorded in a new photo-polymerizable mixture made by epoxy-resin and multi-acrylate. The epoxy-resin used is known to make tenacious acrylate-based films. The holographic mixture contains two photo-initiators, the synergic effect of which enables a reliable photo-polymerization process in the visible region of the electromagnetic spectrum. The recorded holograms are mechanically stable, show long-term temporal stability and very high values of diffraction efficiency, coupled with good angular selectivity due to a relatively narrow band of wavelengths. We measured the intensity of the transmitted beam and calculated the intensity of the diffracted beam at different wavelengths, deriving the refractive index modulation and the grating pitch by fitting the experimental data with a slightly modified theoretical approach. These kind of mixtures can be used in several fields of application, such as chemical or bio-sensors, high resolution optical sensors, high-density optical data storage, encryption and security