In this paper, the optical nonlinearity and multiplex holographic storage using azo side-chain polymer are studied by degenerate four-wave mixing and polarized light pump- probe method with a Ne-Ne laser. The He-Ne laser wavelength is located in the tail of absorption peak of sample. This material shows high diffraction efficiency of gratin and information storage capability in the case of weak absorption. The diffraction of grating is up to the order of 10-2. The effect of polarization beams on grating is studied. The diffraction efficiency of grating is least in the case that the polarization of readout beam is orthogonal to that of both writing beams. An angle multiplex holographic storage in the sample is performed and information can be stored for long-term in room temperature. The information readout of multiple holographic storage in the samples can be controlled by the polarization of readout beam. The diffraction deficiency of grating versus temperature of sample is studied. It is demonstrated that the higher temperature under the melt-temperature the sample has, the larger diffraction efficiency and faster relaxation grating has. The grating is completely erased by increasing temperature over the melting-temperature of the sample. Reading the grating with a circular polarized light is not able to erase the grating. When two recording beams are turned off, great parts of the grating remains for a long- term beside few part of the grating degrades. The results show that the azo side-chain polymer is a good information storage material.
Nanometer-scale holes and words were reproducibly create don a typical organic charge transfer compound, Triethylammonium Bis-7,7,8,8-tetracyanoquinodimethanide (TEA(TCNQ(2) single crystal, using scanning tunneling microscope in ambient conditions by applying a pulse voltage across the tunneling gap. The decomposition products of TEA(TCNQ)2 single crystal were investigated with mass spectroscopy by applying a pulse to the crystal in a vacuum tube. TEA was the sole product being detected. A micro-Raman Spectroscopy was used to fabricate and characterize the sample using a He-Ne laser. A dots array was written by a focused beam and in situ Raman spectra showed the same was decomposited. The most possible mechanism of holes formation appears to be TEA(TCNQ)2 decomposition and TEA evaporation by heating effect of STM current. Comparing data storage in TEA(TCNQ)2 single crystal with a market-sell CD-R disk, the writing threshold value of TEA(TCNQ)2 is much smaller than that of the CD-R disk. This kind of organic conductor may be a promising material for the STM-based high density storage and popular optical storage techniques.
Optical nonlinearity and multiplex holographic storage using azo side-chain polymer are studied by using degenerate four- wave mixing and polarized pump-probe laser method. The He-Ne excitation laser wavelength is located at the tail end of the absorption peak of the sample. This material shows high grating diffraction efficiency and promises information storage capability using weak absorption. The diffraction efficiency of the grating is up to the order of 10-2. The effect of input beam polarization planes on grating is studied. The diffraction grating efficiency is lowest when the polarization of the redout beam is orthogonal to that of both writing beams. An angle multiplex holographic storage study is also performed in the sample. Information can be stored for a long time at room temperature. The information readout of this multiplex holographic storage system can be controlled by the polarization state of the readout beam. Dependence of grating diffraction efficiency on the sample temperature is studied. It is demonstrated that the higher the temperature under the melting temperature of the sample, the higher the diffraction efficiency and the faster the relaxation time of the grating. The grating is completely erased by increasing the temperature over the melting temperature of the sample. Reading the grating with a circularly polarized light does not erase the grating. When two recording beams are turned off, a large part of the grating remains for a long time and only a small part of the grating degrades. The results show that the azo side-chain polymer is a good information storage material. The anisotropic optical nonlinear refractive index of the sample is also measured. The relationship of the nonlinear refractive index of the samples, the different ratios of azo functional groups in the polymers, and the temperature of the sample are also studied. The highest nonlinear refractive index is up to the order of 10-2. The optical nonlinearity of the samples increase with increasing sample temperature. No anisotropic nonlinearity appears when the temperature of the sample is over the melting temperature of the sample. The anisotropic nonlinearity levels of three samples with different azo side-group ratios in the polymer are compared.
Third-order nonlinearity and polarization holographic storage in acceptor-donor azo dye-doped PMMA films are studied by using nonresonant degenerate four-wave mixing with a He-Ne laser. The samples exhibit reasonably large third-order susceptibility and strong polarization sensitivity, and the highest third-order nonlinear susceptibility is up to the order of 10-3 esu. The relationship between optical nonlinearity and 'push' and 'pull' electron ability in polar azo molecules is studied, and further effect from a push- electron group attached to azobenzene ring on third-order nonlinearity of the samples is explored. Third-order nonlinearity of the sample is found to be proportional to the push-pull electron ability of polar azo molecules. Attaching a side group with push-electron ability to the azobenzene ring increases third-order nonlinearity (dipole moment) of the material. Polarization holographic storage properties in azo dye-doped PMMA films are also studied. The samples show strong polarization sensitivity and real-time information storage properties. The polarization hologram in the sample results from a birefringent grating formed by photoinduced reorientation of polar azo molecules. The optical phase conjugation signal consists of both fast and slow parts when two recording beams are turned off. They respond to the processes of four-wave mixing and holographic grating. It is demonstrated that nonresonant nonlinearity of samples mainly results from photoinduced anisotropy of polar azo chromophores. The advantages of nonresonant nonlinearity and its applications are discussed.
Four-wave mixing spectroscopy is presented as a convenient and effective optical method for the study of excited-state optical storage properties and nonlinear mechanisms in a dye-doped polymer film. The dynamic processes of optical storage properties and the efficiency of the diffraction grating are discussed. Backward-scattering four-wave mixing and forward-scattering four-wave mixing optical configurations are presented. A simple energy-level model is used to explain the excited-state optical storage mechanism, resulting from photo-induced excited-state population grating and trans-cis isomer grating.
Optical power limiting of Fullerenes/PMMA has been studied based on a time-resolved single-beam technique. A nanosecond/picosecond Nd:YAG laser system with pulse width of 8-ns, repetition frequency of 10 Hz and wavelength of 532-nm was employed. Temporal profile of pulse beam is Gaussian profile. When the peak power density of incident laser pulse Pin is 180 WM/cm2, the incident and the transmitted laser pulses versus time are measured using a 4402 Boxcar of 0.4 ns time resolution. The experimental results have shown that, at high irradiance the transient transmitted power density increases nonlinearly and limits to less than 30 MW/cm2. In our experiment, the switching speed of the optical power limiter is less than 5 ns. The measured results can be fitted on the excited state absorption theory. Theoretical results are shown that the excited state absorption saturation occurred at higher peak power.
The optical limiting of Q-switched Nd:YAG radiation oat 532 nm is performed using Fullerenes-toluene solution contained in a cell with a random rough surface. One of the inside surface of K9 glass was roughened. At low incident fluences the random rough surface windows index matches with fullerenes solution, so optical limiting behavior in fullerenes-toluene solution is based on excited state absorption. At high incident fluences thermally induced index change causes a sufficient index mismatch at the random rough surface and leads to significant scattering. Additional limiting due to scattering occurs. The limiter of excited state absorption/random surface scattering is superior to the limiter of purely excited state absorption.
The optical limiting response and excited-state absorption properties of a novel organic polymer (poly(5-2-methythio-4- methyl-5-pyrimidinyl)-2,4-pentadine-1-ol)-p-toluene sulfinate) in chloroform solvent have been investigated and its solutions almost have no absorption in visible spectral range. A Nd:YAG laser source with 8-ns/21-ps pulse width and 532-nm wavelength was employed. The pulse-width-dependent measurements indicated that the optical limiting mechanism is excited state absorption along with nonresonant two photon absorption. The open aperture Z-scan was also performed to measure the molecular excited state absorption coefficient. The nanosecond optical limiting behavior of the various concentration solution samples with nominal transmissions of 87%, 56% and 26% have been measured as a function of the beam fluence. The theoretical fitting result of excited state cross section can be fitted on the mode that excited-state absorption is the predominant mechanism causing the observed optical limiting behavior.
Nonresonant photoinduced birefringence of an acceptor-donor azo dye doped in polymethyl methacrylate film was studied by degenerate four-wave mixing and Z-scan methods with a He-Ne laser. The sample has appreciable large third-order nonlinear susceptibility and polarization sensitivity. The nonlinear mechanism of the material originates from photoinduced birefringence of polar azo molecule.
Azo dye polymeric film were widely studied for real-time polarization holography and optical storage by degenerate four-wave mixing in the resonant absorption spectrum of the sample in the few past years. In this paper, we will report the experimental results of four-wave mixing based on excited-state absorption in ethyl orange doped in polyvinyl alcohol film. A He-Ne laser was used as the four-wave mixing source, and the excited light was an Ar+ beam. To explain the experimental results, a simplex four-level model of azo molecule polymeric system is built up. The dynamic process of phase conjugation signal by excited-state four- wave mixing is calculated through solving the rate equation of population in the excited-state. The theoretical analyses agree with the experimental results well. The excited-state optical storage mechanism of sample is discussed.
We report experimental results of the nonresonant third-order nonlinear properties of an acceptor-donor azo dye doped in polymethyl methacrylate (PMMA) thin films by degenerate four-wave mixing with a He-Ne laser, which have appreciable nonresonant third-order nonlinearity, (chi) (3) being approximately 4 X 10-4 esu. The OPC signal has strong sensitivity with the polarization of the three incident beams, and the self- refracted phase conjugation by the coupled two counter-propagation beams was studied. In conclusion, nonresonant third-order nonlinear mechanism is demonstrated to be a result of photoinduced birefringence of the azo molecules. The real-time polarization storage properties of the azo dye were used in the interferometry to measure the shape variation of the object.