Two organometallic complexes, [(C2H5)4N]2[Cu(C3S5)2] and [(C4H9)4N]2[Cu(C3S5)2], abbreviated as ECDT and BCDT,
were synthesized. Then the materials were doped in polymethylmethacrylate (PMMA) with the doping concentration
1 % by weight (1wt. %) using a spin-coating method. Their third-order nonlinear optical properties were studied by the
Z-scan technique with 25 ps pulse duration at 1064 nm. The results revealed that the two materials exhibit
self-defocusing effect and two-photo absorption at 1064 nm, the nonlinear refraction coefficient n2 are as high as
-8.077×10-9, -4.564×10-9 esu, and the two-photon absorption coefficients β are 9.258×10-10, 9.851×10-10 m/W,
respectively. All the results suggest that these materials have potential for the application of optical devices.
We present a set of analytical formula on describing the diffraction field of the three dimensional (3D) triangular-meshbased
model. The advantage of the proposed method is that it can avoid using the numerical algorithm -- Fast Fourier
Transform, which leads to a depth-of-field limitation by the Whittaker-Shannon sampling theorem. We employ the
proposed method to generate the hologram of 3D texture model derived from the real scene or 3D design software. In
order to further increase the computation speed, we have rendered a real scene by employing the GPU platform. Our
homemade GPU algorithm performs hundreds of times faster than those of CPU. As we developed a general phase
adjustment technique for polygon-based algorithm, the holographic reconstructed scenes possess high performance.
We show, theoretically, that the combination of super-Gaussian filters and nonlinear gains can greatly control the self-frequency shift in ultrashort optical pulse. Typical examples are given for stabilizing the propagation of ultrashort optical pulse over a long distance. In particular, by comparing to the Gaussian filters, super-Gaussian filter is more effective in overcoming self-frequency shift in the presence of nonlinear gains.
We derive theoretical results on soliton interactions and timing jitter in soliton transmission systems by use of super-Gaussian filters of high order. It is shown that the soliton interactions and timing jitter can be effectively suppressed by filters of various orders. We get that the minimum value of two-soliton separation is maintained almost constant during propagation for different filter orders. The optimal filter for sliding frequency in suppressing soliton interaction is determined. We also show that the higher the filter order is, the better the improvement of the timing jitter is.
At pulse laser pumping, stimulated emissions are observed in ZnxMg1-xO epilayers. Among them, spectral blue shifts are
dependent on the Mg substitution concentration; and the highest lasing photon energy (in ZnO series materials even
reported) of 3.51 eV is observed. Furthermore, experimental results also show that by high concentration Mg
substitution, a red shift of the electron-hole plasma stimulated emission is reduced and its efficiency doesn't decrease
with the Mg substitution concentration. These results imply that the lasing frequency of ZnO series materials can be
modified by substitution. Secondly, lasing with low threshold in a closed micro-cavity filling with high scattering and
irregular structure gain medium is observed. Furthermore, the usual laser physics and random laser can't explain the
sharp bandwidth of lasing in sub-micron ZnO micro-crystals; a new concept of lasing needs to be proposed, which is
important to the develop in physics of carrier and lasing.
Narrow frequency sharp angular filters with integral times of quarter wavelength layer structure, which can be fabricated with commonly used coating machines and work in visible and near infrared, are designed. These filters possess not only a narrow frequency pass band but also a sharp angular pass breadth in visible and near infrared. The experimental result agrees with the theoretical calculations well. These dual functional filters have many potential applications.
On the basis of the optical thin film interference theory, a novel thin film multi-frequency filtering technology applied to CWDM filter, a comb-like filter, which is not applied to select single signal channel from the multi-channel, but to separate the multi-channel into two different sets of channels, is proposed in the article. According to the central wavelength and the width of pass-band of 8-channel CWDM system that were defined by the ITU-T, two kinds of thin-film filters for 8-channel CWDM system have been designed by the technology. A specific expression for these thin film structures has been described and the parameters of these structures have been analyzed and optimized. The transmission curves of the designed structures show that the design results are agreement with that of the theoretical calculation well. We can implement the function of the 8-channel CWDM using two above-mentioned thin-film filters, which make the CWDM system low-cost, simpleness and easy collimation. These thin film structures have the advantages of good stability, arbitrary wavelength spacing between the adjacent channels, perfect rectangular shape of the pass-band, less layers, low cost and easy encapsulation, which would make it more attractive to use in CWDM system and other fields.
Fiber optical Fabry-Perot (F-P) interferometric sensors have been used for the measurement of various physical parameters. A novel miniature asymmetric F-P interferometric cavity applied to fiber optical sensors is designed in this work; and its structure consists of fiber, complex metallic thin films, air or dielectric tunable layer, in which the reflectance of the cavity in response to phase thickness of the tunable layer can be approximated to saw wave function so it can improve the degree of linearity and the dynamic range of the sensors. The measurand to sense, which modulates the optical path of the tunable layer to change the reflectance of the structure, can be detected and demodulated. The response of the reflectance of the structure to the phase thickness of the tunable layer has been calculated and analyzed with optical thin film characteristic matrix method, and an expression for the response of this structure has been described. The design method to obtain optimal parameters of the F-P interferometric cavity has been concluded in this work. The result indicates that this miniature structure possess a high degree of linearity, sensitivity and dynamic range.
In this paper, a kind of absorptive thin film, for the first time, was used in laser welding of SiO2, Si and LiNbO3. This absorptive thin film of three-layer metal-dielectric-metal structure is designed for further reducing the high reflectance of the Nd:YAG laser beam in the surface of the tin layer that is utilized as solder between the transparent parent materials. The actual absorption exceeds 99%. This combination of absorber and solder transformed the laser energy into heat effectively and decreased the minimum necessary incident laser power transmitting through the transparent parent materials. As a result, the damage of the parent materials, which is suffered from laser transmission, is avoided; on the other hand, the laser power is of full utilization and saved.
Based on the optical thin film interference theory, a novel thin film multi-half-wave multi-frequency filtering technology applied to DWDM interleaver, a comb-like filter, is proposed in this report. A flexible on-demand design of arbitrary frequency spacing can be easily obtained by this thchnology. The parameters of this thin film structure have been analyzed and optimized, and a specific expression for these thin film structure has been described. 50G-spaced and 100G-spaced DWDM interleavers with flat-top passband consisting of less than 30 layers have been designed and fabricated. The process of fabrication is also discussed in this paper. These thin film interleavers have the advantages of good stability, arbitrary wavelength spacing between the adjacent channels, rectangular shape of the pass-band, less layers, low cost, and easy encapsulation, which would make it more attractive to use in DWDM system. The above-mentioned technology exhibits the flexibility in design and the advantages of thin film coating, which will have more applications besides interleaver.
The ultrafast emission of nanodiamond powder has been detected with ultrafast fluorescence spectroscopy. The ultrafast emission spectrum has been deconvoluted by the Monte-Carlo method and the results show 2 fast decays as 60ps and 350ps, with weighting about 80 percent and 20 percent of the whole emission intensity respectively. Such fast emission has not been detected under the same experimental condition for the samples of pure and defected bulk diamonds. The reason for such ultrafast process has been discussed.
A laser microbeam system has been set up for microsurgery on cell. The relations of laser wavelength, pulse duration and pulse energy to punching effects and self-healing are studied. The experimental results demonstrate that picosecond pulse laser microbeam offers many advantages in cell microsurgery. The mechanism of punching by picosecond microbeam is high field puncture instead of heat effect, and is irrelevant to cell kinds and colors. The diameter and depth of microsurgery can therefore be easily controlled by adjusting the laser pulse energy. The diameter of the minimum aperture is about 0.1 micrometers , much smaller than the theoretical limit ((lambda) /2) for optical microscope due to self- focusing effect. With ultrashort pulse laser microbeam, we can easily cut off any part of a cell. An example is that eight nuclei in the center of unicellular parasite Pneumocystis Carinii can be destroyed one by one by ultrashort pulse laser microbeam without cell wall injury. The holes can also be punched by ultrashort pulse laser microbeam from cell wall to cell nucleus. In a fraction of a second to several seconds after punching, the hole on cell wall or cell membrane can self-heal. Exogenous DNA can be introduced into the cell before its self- healing.
Both theoretical and experimental studies are presented on chromophore excited-state coupling in linker-free allophycocyanin (APC), one of the antenna phycobiliproteins in algal photosynthesis. A three-site-coupling model has been introduced to describe the exciton interaction mechanism amoung the excited (beta) chromophore in APC, and the exciton energy splitting is estimated. Picosecond polarized fluorescence experiments both on monomeric and trimeric APC isolated from alga Spirulina platensis have been performed. The experimental results show that APC monomer and trimer exhibit remarkedly different spectropic characteristics, and satisfy the suggestion of strong excited- state coupling among chromophores in APC.
Single ps pulse spectroscopic techniques have been employed to investigate excited-state dynamics of R-phycoerythrin (R-PE) isolated from two red algae Polysiphonia urceolata and Porphyra yezoensis, respectively, at various excitation photon densities in a range of 8 X 1014 $AP 1 X 1017 photons/cm2. The fluorescence quantum yields of the R-PE from the two algae are found to decrease in logarithm with increasing of excitation intensity due to S1-S1 exciton collision. A fast component in addition to a slow one recorded at low excitation density and a large initial anisotropy are observed at higher excitation density. Different dynamical characteristics of exciton collision between the cases of Polysiphonia urceolata and Porphyra yezoensis are shown and proposed to be owing to different numbers of excited pigments available and chromophore architectrue in R-PE from different biological sources.
Theoretical descriptions of excitation energy transfer between chromophores in allophycocyanin are presented, including bilateral energy transfer paths between chromophores, and are expressed, based on Foster interaction mechanism, as Pauli master equations. Group analysis in C3 symmetry is performed to carry out analytic expressions for fluorescence decays which is generally of triexponential with effects of chromophore coupling and exciton splitting taken account. It is pointed out that the time constant of each decay component contains mixed information of different energy transfer paths, and therefore show its dependence on subtle configuration of chromophores, probably related to site heterogeneity and thus to inhomogeneous broadening previously observed.
Experimental demonstration of optical pulse slicing and pulse shaping by pumping a large core, liquid-filled waveguide with picosecond radiation are reported. Steepening of the optical pulses to the extend that the peak of an input pulse catches up and overpasses the rising edge is observed, which results in the pulse shape with a 'negative-like' rising edge. Significant pulsewidth reduction by over 20 fold is obtained. Based on the experimental results, a new mechanism of self trapping of picosecond radiation in a waveguide structure is proposed, which is shown to agree well with our experimental results.
The dynamics of the carrier recombination in a-Si:H/a-SiN3:H multilayers has been investigated with picosecond photoluminescence spectroscopy. The thermalization of photogenerated carriers is a direct hopping process. The decay time cutoff, the mobility edge and the bandtail width vary non-monotonously with a turning point near x=O.85, which is attributed to the changes of the build-in field and the multilayer structure with nitrogen content.
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