When ultrashort laser pulses are focused inside a glass at a high repetition rate, structural changes occur because of the heat accumulation from the train of laser pulses. This report describes phase measurement of the structural changes induced inside glass by phase-shifting digital holographic microscopy. Two-dimensional phase distribution across the structural change for static exposure is retrieved. By focusing femtosecond laser pulses at the interface between two glass substrates, melted materials can directly weld glass plates. Quantitative phase measurement of welded glass substrates revealed that the refractive index decreased in the laser-irradiated zone.
Multi-valued phase patterns were multiply recorded by retardagraphy in order to improve recording density and data
transfer rate. In the experiment, the phase pattern consists of four values were recorded on a polarization-sensitive
medium by focusing the recording beam, and three patterns were multiply recorded by shifting the focal point. The
recorded patterns could be independently reconstructed.
Multiple recording characteristics of polarization hologram was investigated for high density optical data storage.
Polarization and angular multiplexing was performed. Some polarization holograms were independently
recorded on the same position of a polarization-sensitive medium. The recorded images could be independently
reconstructed.
Photoinduced birefringence in the film made of our azobenzene copolymer was demonstrated using blue excitation
laser beams and observed by a red probe laser beam. The birefringence values was obtained by polarimeter. The
polarization state of the probe beam was changed by the photoinduced birefringent film when the polarization
state is not agreed with the polarization state of the excitation laser beam. Then, a polarization component
orthogonal to the polarization state of the incident probe beam was observed. Using the principle, an image
pattern was recorded in the film using one-beam.
Theoretical models for photoinduced birefringence and chiral structure formation in achiral azobenzene-containing materials were proposed considering phototriggered molecular reorientation via trans-cis-trans photoisomerization cycles of azobenzene. The photoisomerization cycles were expressed by two rate equations of the orientation distributions of trans- and cis-forms. Phototriggered molecular reorientation by illuminating linearly polarized light was verified theoretically. The photoinduced helical structure formation was simualted by elliptically polarized light. The molecular rotation angle was dependent on the sign of the ellipticity. The time evolution of the helical structure formation was consistent with the experimental result that reported by other papers.
A novel photoresponsive polymer containing bisazo chromophores have been synthesized for comparative study with
monoazo polymer. Since the bisazo structure has an extended Π-conjugation electronic system, it is expected to have
large intrinsic molecular birefringence that can realize large macroscopic photoinduced birefringence (ΔnPI) via
photoinduced molecular re-orientation process of bisazo molecules. As a result, it was found that the large value of ΔnPI
(0.17) could be obtained by using bisazo polymer at 514.5nm excitation with 1.0W/cm2.
In this paper, new azobenzene copolymers (PCDY and PPDY) with large photoinduced birefringence and good long-term stability of a recorded data have been introduced. The largest photoinduced value of 0.289 was obtained on the PCDY50 at 458 nm light irradiation. This value was brought about a result of molecular cooperative reorientation of cyanoazo and bisazobenzene moieties. It should be noted that the PCDY50 exhibited quite stable characteristics on the archival viewpoint. Furthermore, if we can optimize experimental conditions, more than 105 cycles of reversible data storage could be achieved. Making use of these superior characteristics of the PCDY50, an application for rewritable holographic memory and/or other optical addressable devices is anticipated.
With respect to the manufacturing of optical elements, facile and effective fabrication method is proposed. It is developed in connection with photo-induced surface relief (PSR)formation phenomenon that occurs on the azobenzene functionalized polymer film. Purely optically inscribed surface relief structures have been used as a plastic mold for manufacturing of its replica. At least a hundred times replication process has been achieved using thermosetting resin without any deterioration. This method has many merits not only from a technical viewpoint but also from a economical
efficiency. In this report,first the PSR phenomenon is explained and then several examples for optical component fabrication are demonstrated.
Chiral helical polymethylphenylethylcarbodiimides (Poly-PhEMCDI) and polymethylcyclohexylethylcarbodiimides (Poly-ChEMCDI) have been synthesized by insertion polymerization of corresponding monomeric carbodiimide using copper complex as initiator. Their circular dichroism, optical rotation power induced by ordered rigid main chain helical structure in solution and casting films were obtained and molecular weight dependent circular dichroism were studied. Primary results about Second Harmonic Generation (SHG) of casting films of polycarbodiimides prepared by different solvents were measured and chloroform was the best solvent to prepare casting films with preferential orientation of molecular helical structure. Polycarbodiimides can form lyotropic liquid crystal in chloroform, THF solution etc.
Chiral helix materials have large optical rotatory power, and therefore, their application has been caught much attention for optical elements and/or optical switching devices. Among such helical polymers, chiral poly-lactic acid can be easily synthesized without racemization. However, the film formation of poly-lactic acid for optical application is difficult because of the high crystallinity. We synthesized the chiral oligo-L-lactic acid with the definite degree of polymerization by using GPC fractionation technique and found that the optical rotatory power reached to a saturated constant value even in the octamer. Such oligomers whose repeating units are less than 14 are liquid state at ambient temperature. These results indicate that the helical structure has stably existed even in the low molecular weight oligomers. The oligo-L-lactic acid could be oriented in liquid crystalline cell and by electro-poling treatment. The orientation structure was discussed from ORD spectra and SHG measurement.
KEYWORDS: Near field scanning optical microscopy, Near field optics, Polarization, Near field, Polymers, Optical fibers, Polymer thin films, Optical microscopes, Optical lithography, Optics manufacturing
Regarding the characterization of the spatial distribution and the polarization condition of optical field emitted from a probe tip of scanning near-field optical microscope (SNOM), simple and effective evaluation technique is developed. It is realized in connection with the detailed knowledge of photo-induced surface relief formation phenomenon that occurs on the azobenzene functionalized polymer film. Since there was no easy method of evaluating a SNOM probe so far, this could be one of the promising techniques much more convenient than conventional methods. In this report, first the PSR phenomenon is explained and then several examples for the probe evaluation are demonstrated in far- and near-field condition. Furthermore, a trial for nano-patterning and ultra-high density rewritable data storage is performed via scanning near-field optical lithography.
We synthesized some novel rigid NLO-active maleimide copolymers bearing DR-1 moieties (PMPD, PHSD, and PHND). All copolymers exhibited high Tgs and good solubilities for common solvents and excellent film-forming properties. Dependence of film thickness on the d33 value for the poled copolymers induced by corona poling was investigated and it was demonstrated that from less than thickness of 0.3 micrometers decrease of the thickness gives rise to remarkable increase in the d33 value. The poled copolymers exhibited large d33 value for PMPD, 290 X 10-9 esu for PHSD and 350 X 10-9 esu as well as large r33 values. The d33 values of the poled copolymers were kept constant even after standing 1000 h at 80 degrees C, although a small decrease was observed at a very initial state. Further, the d33 values did not change up to ca. 123 degrees C upon heating at the rate of 10 degrees C/min in all cases.
In order to improve third-order nonlinear optical properties of polydiacetylenes (PDAs), we have been investigating modification of PDA structures. From the point of view of PDA molecular design, three series of monomers for ladder- type PDAs were prepared. Oligoyne monomers having more than five conjugated acetylenes gave polymers which showed broad bands at longer wavelength than their excitonic absorption bands. This implies production of (pi) -conjugated ladder polymer having two PDA backbones linked by acetylenic groups in each repeating unit. From monomers with two butadiynes connected by an alkylene group, ladder-type PDAs were obtained when the carbon number of the alkylene group is more than four. However, monomers with two butadiynes connected by an arylene group gave only single-chain PDAs. From the point of view of PDA morphological engineering, PDA microcrystal water dispersions were applied to evaluate nonlinear optical susceptibilities by z-scan method together with PDA thin films. High-density microcrystal deposited film prepared by layer-by-layer deposition technique showed more than three orders of magnitude enhanced (chi) (3) than the dispersion state. Polycrystalline thin films compose of ladder-type PDAs were also found to have large (chi) (3). The quite large nonlinear refractive index of -41 cm2/GW was attained just near excitonic absorption maximum for one of the polymers.
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