Volume polarization holographic recording in thick phenanthrenequinone-doped poly(methyl methacrylate) photopolymer

Volume polarization holographic recording in phenanthrenequinone-doped poly (methyl methacrylate) photopolymer is obtained. Photoinduced birefringence in a 2 mm thick sample is measured by a phase-modulated ellipsometry. The birefringence induced in this material by linearly polarized beam at 514 nm reaches 1.2×10(-5). In addition, ability for recording volume polarization grating using two different polarization configurations is demonstrated and compared. The experimental results show that the diffraction efficiency of the hologram reaches to ～40% by using two orthogonal circularly polarized beams.     

Study on the mechanism of dark enhancement in phenanthrenequinone-doped poly(methyl methacrylate) photopolymer for holographic recording

The dark enhancements with various exposure energies are studied in thick PQ/PMMA photopolymer. Considered the weak molecules diffusion of PQ component and the grating detuning, a new mechanism of dark reaction is proposed to explain the dark enhancement. Moreover, the influences of dark reaction on Bragg angular selectivity and grating recording are analyzed. The results are beneficial to the practical holography application.     

Two-dimensional higher-diffraction-order optical beam splitter based on phenanthrenequinone-doped poly(methyl methacrylate) photopolymer

A two-dimensional optical beam splitter has been realized that uses the higher diffraction orders of a refractive-index grating. Gratings were recorded experimentally with light from a semiconductor laser incident at a small angle on phenanthrenequinone-doped poly(methyl methacrylate) photopolymer. The incident signal beam, which was made up of three different wavelengths (632.8, 532.0, and 488.0 nm), was split by the grating into multiple output beams with nearly equal size and separation. Results are given for when the sample grating was placed behind, in front of, and in the focal plane of a Fourier lens. The properties of higher-order-diffraction images have been discussed. The discussion shows that a two-dimensional higher-diffraction-order optical beam splitter provides a practical method for splitting a signal beam.     

Phenanthrenequinone-doped poly(methyl methacrylate) photopolymer bulk for volume holographic data storage

We present the design and fabrication of a phenanthrenequinone-doped poly(methyl methacrylate) photopolymer material. Large blocks of samples were made, and the material showed negligible shrinkage after optical exposures. We recorded and reconstructed 250 holograms at a single spot, using a 1-cm(3) block.     

Photochemical kinetics for holographic grating formation in phenanthrenequinone doped poly (methyl methacrylate) photopolymer

The photochemical kinetics of phenanthrenequinone (PQ) doped poly (methyl methacrylate) photopolymer in holographic recording was studied theoretically and experimentally. The diffusion of PQ molecules during holographic recording was negligible because of its small diffusion coefficient at room temperature. A photochemical reaction kinetics model of PQ/PMMA was established. The analytical expressions for the temporal variations of transmittance and diffraction efficiency were derived. By fitting the experimental curves, some parameters related with the polymer components were obtained by the proposed model, which can be used to analyze the photochemical process and will be helpful to the optimization of material preparation.     

Real-time holographic reflection gratings in volume media of azo-dye-doped poly(methyl methacrylate)

Real-time formation of holographic reflection gratings is experimentally demonstrated in thick media of Disperse Red 1- (DR-1) doped poly(methyl methacrylate) at a nonresonant wavelength (647 nm). Our diffraction efficiencies of 30% and 23% are achieved for reflection gratings inscribed by spatial modulation of intensity and polarization, respectively, and are believed to be the highest achieved for a dye-doped polymer. In addition to the recording of amplitude and phase, the polarization state is also recorded and reconstructed.     

High-efficiency holographic volume index gratings in DR1-dye-doped poly(methyl methacrylate)

Holographic volume index gratings with high diffraction efficiency (greater than 80%) are recorded in a thick sample of Disperse Red 1-doped poly(methyl methacrylate) with red light (647 nm), which is far away from the absorption peak (488 nm) of the material. Measurements of photoinduced birefringence and polarization holography recording confirm that the azo-dye reorientation mechanism is responsible for the grating formation. Energy coupling between the two writing beams is observed even when the incident beams have equal intensity.     

Sm(DBM)3Phen-doped poly(methyl methacrylate) for three-dimensional multilayered optical memory

We report on the formation of submicrometer voids within Sm(DBM)3Phen-doped poly(methyl methacrylate) (PMMA) under multiphoton absorption excited by an infrared laser beam. An ultrashort-pulsed laser beam with a pulse width of 200 fs at a wavelength of 800 nm is focused into doped PMMA. The large changes in refractive index and the fluorescence associated with a void allow conventional optical microscopy and reflection-type confocal microscopy to be used as detection methods. Voids can be arranged in a three-dimensional multilayered structure for high-density optical data storage.     

Dark diffusional enhancement of holographic multiplexed gratings in phenanthrenequinone doped poly（methyl methacrylate） photopolymer

In this paper, we experimentally investigate the dark diffusional enhancement of the optimized multiplexed grating in the phenanthrenequinone doped poly (methyl methacrylate) (PQ-PMMA) photopolymer. The possibility of improving the holographic characteristics of the material through the dark enhancement is demonstrated. The optimal preillumination exposure and the optimal time interval between exposures are extracted to obtain the optimized diffraction efficiency, and their values are 3.4×10³ mJ/cm² and 2 min, respectively. The dark enhancement of the multiplexed grating is presented as an effective method to improve the response region and the dynamic range and to prevent saturation of the material. The dependence of the phenanthrenequinone concentration on the increment of the refractive index modulation is quantitatively studied, which provides a significant basis for improving the homogeneity in the multiplexed gratings using a quantitative strategy. Finally, a simple experimental procedure using the dark enhancement is introduced to improve the homogeneity of the diffraction efficiency and to avoid the complex schedule exposure.     

Highly concentrated phenanthrenequinone-doped poly (MMA-co-ACMO) for volume holography

Novel composite materials are synthesized by incorporating N-acryloylmorpholine(ACMO) in highly concentrated phenanthrenequinone(PQ) doped poly(methyl methacrylate)(PMMA). The photosensitizer concentration of PQ was increased from 0.7 wt. % to 1.8 wt. %. The doping of ACMO component results in a higher diffraction efficiency and photosensitivity than a typical PQ/PMMA system. The enhanced performance of the material may stem from the ACMO molecules, which might open a new route for improving the holographic performance of the PQ/PMMA photopolymer.     

Laser processing of poly(methyl methacrylate) Lambertian diffusers

Matrix-assisted pulsed laser deposition was used to deposit poly(methyl methacrylate) on silicon wafers and sodium silicate glass slides for the purpose of making optical diffusers. After deposition, the reflectance of the coated substrates was measured as a function of scattering angle. We found that the angular dependence of the reflectance could be described as the sum of two functions. First, a Gaussian describes the specular reflection of the underlying substrate that has been broadened by passage through the film. Second, a cosine function describes the reflectance contribution from the film itself. We found that by increasing the thickness of the deposited film that we could eliminate the specular reflection to obtain Lambertian diffusers. Since we can control the surface roughness by adjusting the ratio of the two matrices in laser processing, this deposition technique offers the possibility of producing a wide range of diffusers of different types.     

IR laser ablation of doped poly(methyl methacrylate)

We investigate the TEA CO₂ laser ablation of films of poly(methyl methacrylate), PMMA, with average M_W 2.5, 120 and 996 kDa doped with photosensitive compounds iodo-naphthalene (NapI) and iodo-phenanthrene (PhenI) by examining the induced morphological and physicochemical modifications. The films casted on CaF₂ substrates were irradiated with a pulsed CO₂ laser (10P(20) line at 10.59 μm) in resonance with vibrational modes of PMMA and of the dopants at fluences up to 6 J/cm². Laser induced fluorescence probing of photoproducts in a pump and probe configuration is carried out at 266 nm. Formation of naphthalene (NapH) and phenanthrene (PhenH) is observed in NapI and PhenI doped PMMA, respectively, with relatively higher yields in high M_W polymer, in similarity with results obtained previously upon irradiation in the UV at 248 nm. Above threshold, formation of photoproducts is nearly complete after 200 ms. As established via optical microscopy, bubbles are formed in the irradiated areas with sizes that depend on polymer M_W and filaments are observed to be ejected out of the irradiated volume in the samples made with high M_W polymer. The implications of these results for the mechanisms of polymer IR laser ablation are discussed and compared with UV range studies.     

High-repetition-rate femtosecond laser micromachining of poly(methyl methacrylate)

Investigations are performed to explore high-repetition-rate femtosecond laser ablation effects on the physical and chemical properties of poly(methyl methacrylate)(PMMA). A scanning electron microscopy(SEM) is used to characterize the morphology change in the laser-ablated regions. The infrared and Raman spectroscopy reveals that the fundamental structure of the PMMA is altered after laser ablation. We demonstrate the cumulative heating is much greater during high-repetition-rate femtosecond laser ablation, supporting a photothermal depolymerization mechanism during the ablation process.     

Fabrication and characterization of poly(methyl methacrylate) photopolymer doped with 9,10-phenanthrenequinone (PQ) based derivatives for volume holographic data storage

We present our studies on the photopolymer of poly(methyl methacrylate) (PMMA) doped with 9,10-phenanthrenequinone based derivatives for volume holographic storage. By introducing different functional groups on the side-chain of 9,10-phenanthrenequinone molecule, the holographic characteristics of the material can be modified. The photoreaction involved with the holographic recording in the samples was investigated by measuring UV-Vis absorption spectrum and mass spectrum. The experimental results show that the similar behaviors were exhibited in these photopolymers. It is found that phase hologram recording in our PQ derivatives doped PMMA photopolymer involves a structure change of the quinone based molecule, which induces a strong change of the refractive index. Experimental characterizations on holographic data storage, including material sensitivity, dynamic range (M#) and bit-error-rate have been performed. We found that, by selecting appropriate functional groups, an improvement in sensitivity and M# for holographic data storage can be achieved.     

Configurational-conformational statistics of stereoirregular poly(methyl methacrylate)s

The mean-square radius of gyration of poly(methyl methacrylate) (PMMA) with Bemoullian statistics was theoretically investigated utilizing the method of periodic condition. The dependent curve of the characteristic ratio of mean-square end-to-end distance on periodic microstructure length increases monotonously with the length and goes gradually to its asymptotic value for atactic PMMA chains (P _m = 0.5). Conformational energies E _α ～1.3 kcal mol^?1 and E _β ～-0.6 kcal mol^?1 of the two-state scheme are acceptable, from which the derived meansquare end-to-end distance and mean-square radius of gyration conform to the experimental data. The ratio ?S²?/χ of atactic PMMA (P _m = 0.2) as a function of the degree of polymerization χ first increases with increasing chain length, then passes through a maximum at χ = 30, and finally decreases to its asymptotic value, which is in reasonable agreement with the experimental measurements reported elsewhere. The ratio ?S²?/χ as a function of stereochemical composition indicates that theoretical and experimental data are in accord for isotactic and atactic PMMA, but small-angle neutron scattering (SANS) measurements are higher than the calculated values for syndiotactic PMMA.     

Low-energy librational excitations in vitreous poly(methyl methacrylate)

The infrared (IR) and Raman spectra of vitreous poly(methyl methacrylate) (PMMA) are measured and investigated in the frequency range 10–150 cm^?1. A comparison of the results obtained from IR and Raman spectroscopic measurements permits the assignment of the low-frequency anomaly (boson peak) observed in the spectra to librational vibrations occurring in a segment of the main chain that is comparable in length to the statistical chain segment. It is demonstrated that coherent librational excitations are associated with the relaxation processes proceeding in the polymers.     

Cobalt iron-oxide nanoparticle modified poly(methyl methacrylate) nanodielectrics

In this paper, we report the dielectric properties of composite systems (nanodielectrics) made of small amounts of mono dispersed magnetic nanoparticles embedded in a polymer matrix. It is observed from the transmission electron microscope images that the matrix polymeric material is confined in approximately 100 nm size cages between particle clusters. The particle clusters are composed of separated spherical particles which comprise unconnected networks in the matrix. The dielectric relaxation and breakdown characteristics of the matrix polymeric material are altered with the addition of nanometer size cobalt iron-oxide particles. The dielectric breakdown measurements performed at 77 K showed that these nanodielectrics are potentially useful as an electrical insulation material for cryogenic high voltage applications. Finally, structural and dielectric properties of nanocomposite dielectrics are discussed to present plausible reasons for the observed low effective dielectric permittivity values in the present and similar nanodielectric systems. It is concluded that polymeric nanoparticle composites would have low dielectric permittivity regardless of the permittivity of nanoparticles are when the particles are coordinated with a low dielectric permittivity surfactant.     

Synthesis of photosensitive poly(methyl methacrylate-co-glycidyl methacrylate) for optical waveguide devices

Photosensitive poly(MMA-co-GMA) for optical waveguide was synthesized, and the refractive index of the polymer film was tuned in the range of 1.481–1.588 at 1550 nm by mixing with bis-phenol-A epoxy resin. The film, which was made by spinning coated the poly(MMA-co-GMA) with photo initiator, had good UV light lithograph sensitivity, high glass transition temperature (T _g : 153°C, after crosslinking) and good thermal stabilities (T _d : up to 324°C, after crosslinking). The optical waveguides with very smooth top surface were fabricated from the resulting polymer by direct UV exposure and chemical development. For waveguides with cladding, the propagation losses of the channel waveguides were measured to be below 3 dB/cm at 1550 nm.     

Structural modification of poly(methyl methacrylate) by proton irradiation

A general survey is presented on the structural modification of poly(methyl methacrylate) (PMMA) by proton implantation. The implanted PMMA films were characterized by FT-IR attenuated total reflection (FT-IR ATR), Raman, Rutherford backscattering spectroscopy (RBS), gel permeation chromatography (GPC) and surface profiling. The ion fluence of 350 keV protons ranged from 2×10¹⁴ to 1×10¹⁵ ions/cm². The IR and Raman spectra showed the reduction of peaks from the pendant group of PMMA. The change of absorption and composition was observed by UV–VIS and RBS, respectively. These results showed that the pendant group is readily decomposed and eliminated by proton irradiation. The change of molecular weight distribution was also measured by GPC and G-value of scission was estimated to be 0.67.