Synthesis of several C60-(antenna)x conjugates was performed to demonstrate high flexibility in the design of organic nonlinear optical (NLO) nanostructures showing broadband characteristics with capability to absorb light over a wide range of wavelengths. It was achieved by covalent attachment of a hybrid combination of two types of light-harvesting fluorescent antenna chromophores on a C60 cage. Ultrafast photoresponsive intramolecular Föster resonance energy-transfer among antenna units and shared excited energy-accepting C60 cage is proposed as a plausible mechanism to enhance the broadband NLO ability. Characterization of the branched triad C60(>DPAF-C18)(>CPAF-C2M) and the tetrad C60(>DPAF-C18)(>CPAF-C2M)2 was carried out by various spectroscopic techniques. These compounds showed approximately equal extinction coefficients of optical absorption over 400‒550 nm that corresponds to near-IR two-photon based excitation wavelengths at 780‒1100 nm. These nanomaterials may be utilized in NLO coatings for achieving efficient light-transmittance reduction at the same NIR wavelengths.
Recently there are many reports on the nonlinear optical (NLO) and electronics properties of semiconducting binary
nanocrystals such as CdSe, PbS and CdS. In the spectral regime where the photon energy (ħω) is less than the bandgap
(Eg), two photon absorption and two-photon-absorption-associated processes are dominant mechanisms. When ħω > Eg,
however, saturable absorption due to band filling mechanism plays an important role. However, very few results related
to optoelectronics properties on ternary nanocrystals are reported. Here, we present large NLO properties of ternary
nanocrystals such as AgInS2 quantum dots (QDs) and AgInSe2 nanorods (NRs) studied by femtosecond laser pulse at 780 nm. By employing Z-scan and transient absorption techniques, the third-order susceptibility of AgInS2 QDs and
AgInSe2 NRs has been measured to be as large as 10-8 esu. The origin of NLO properties in AgInS2 QDs is due to two
photon absorption. While the NLO behavior of AgInSe2 NRs is mainly contributed by saturation in the nonlinear
absorption and optical Kerr nonlinearity with a recovery time determined to be a few ten picoseconds.
Recently, ultrafast nonlinear optical responses of single-wall carbon nanotubes (SWCNTs) in suspensions and in films have been investigated intensively. Transient photobleaching has been observed with femtosecond laser pulses at photon energies of 0.8 ~ 1.1 eV (wavelengths = 1100 ~ 1550 nm), resonant with the lowest interband transitions of semiconducting SWCNTs. Here, we report both absorptive and refractive nonlinearities in a film of multiwalled carbon nanotubes (MWCNTs) grown mainly along the direction perpendicular to the surface of quartz substrate. Such MWCNT films are prepared by a method of plasma enhanced chemical vapor deposition. By employing Z-scans with 180-fs laser pulses at wavelengths ranging from 720 to 1550 nm, we have observed that both absorptive and refractive nonlinearities are of negative. More importantly, the degenerate pump-probe measurement reveals an ultrafast recovery time of ~ 1 ps. In addition, we also present a demonstration that the ultrafast nonlinear optical properties can be manipulated by a hybrid system in which MWCNTs are coated with ZnO nanoparticles. At wavelengths of interest, it is known that ZnO possesses three-photon (or four-photon) absorption, which is of positive sign and can be used to balance off the negative nonlinearity of MWCNTs.
We have developed a deep ultraviolet (DUV) lithography technique for fabricating super dense silicon based photonic crystals. Binary mask is used to create nano scale patterns of very high density. Based on the simulation, photonic crystals with both square and triangular lattice of air cylinders are designed and fabricated to work in communication frequency range (λ within 1.3 to 1.55μm) on amorphous silicon. In order to pattern circular hole we designed different kind of polygons on the mask and layout pattern was under sized at constant pitch. Bottom anti reflection coating (BARC) recipe was developed to improve circularity of the pattern and reduce interhole spacing.
We report the optical limiting response of carbon nanoparticle colloids in different organic solvents. The carbon nanoparticles were prepared by Nd:YAG laser ablation of carbon target immersed in ethanol. Optical limiting properties towards 532 and 1064 nm wavelengths were measured with a 7-ns pulsed Nd:YAG laser. Strong optical limiting effect was detected for the carbon nanoparticle colloids within a solvent having low thermal conductivity. The limiting effect at 532 nm is stronger than that at 1064 nm. Possible mechanisms of optical limiting were discussed.
The refractive nonlinearity is measured in several nonlinear optical crystals using the Z-scan technique with femtosecond pulses at 780-nm wavelength. The crystals studied include KTiOPO4, KTiOAsO4 (beta) BaB2O4, LiB3O5 and LiNbO3:MgO, which are extensively used for ultrashort- pulse second-harmonic generation and optical parametric oscillation. The nonlinear refractive index n2 in these crystals is determined to be in the range from 10-16 to 10-15 cm2/W. No two-photon absorption is observed. The experimental results are compared with two-parabolic band model for the bound electronic Kerr nonlinearity. It is found that the measured n2 values in (beta) BaB2O4 and LiB3O5 are one order of magnitude smaller than those of LiNbO3:MgO, KtiOAsO4,KtiOPO4, which is in agreement with the theoretical prediction.
Wide applications of lasers have stimulated a great interest in development of optical limiting devices. These devices can be used to protect optical sensor form laser-induced damage because their transmission is high when they are exposed to low-power laser light, and their transmission becomes low when irradiated by intense laser beams. Here we report such a device based on nonlinear optical effects in two neutral nickel complexes with multi-sulfur 1,2 dithiolene ligands, 1 and 2. The limiting device consisted of a focusing setup and a 1-mm-thick cell, which contained a benzene solution of one of the complexes. THe limiting properties were investigated by both nanosecond and picosecond laser pulses. At 532 nm, the limiting thresholds of complexes 1 and 2 measured by the picosecond laser pulses. At 532 nm, the limiting threshold of complexes 1 and 2 measured by the picosecond laser pluses with a focusing geometry were determined to be approximately 0.3 J/cm2. The linear absorption spectra of the to complexes also indicated that their limiting response should cover the visible and near-IR region. All these result show their limiting performance is superior to the limiting effecting C60. Picosecond time-resolved pump-probe and Z-scan experiments revealed that the observed limiting effects should originate from excited-state absorption and refraction.
Optical limiting effects in cubane-like metal clusters dissolved in dichlormethane have been studied by measurements of nonlinear transmissions, nonlinear scattering, and pump-probe. The nonlinear transmission measurements show that there are strong optical limiting effects in these two cluster solutions; and the silver- containing cluster has larger limiting properties than the other. The nonlinear scattering results indicate that nonlinear scattering is responsible for the limiting action in both clusters. And the pump-probe experiments show that the nonlinear scattering is thermal in origin.
We present our investigation of two-photon absorption and self-focusing in second-harmonic-generation crystals on a picosecond 532-nm-wavelength beam using the z-scan technique. By measuring the crystal transmittance as a function of the crystal position with respect to the focus, the two-photon absorption coefficients were determined to be 0.041 plus or minus 0.008, 0.10 plus or minus 0.02, and 0.24 plus or minus 0.06 cm/GW for KTPA, KTA, and LiNbO3, respectively. With inserting an aperture in front of the detector that recorded the transmitted laser pulse energy, self-focusing effects manifested themselves in the z scans on the three crystals at input irradiances of higher than a few GW/cm2. The quantitative data confirm that the optical Kerr nonlinearity should be responsible for the observed self-focusing and n2 equals (4.6 plus or minus 0.9), 3.6 plus or minus 0.7), and 5.3 plus or minus 1.0) multiplied by 10-6 cm2GW in KTP, KTA and LiNbO3, respectively. The microscopic origin of the measured n2 can be understood in terms of bound electronic effects. The theoretical predictions are in agreement with our measurements. Finally, effects of the observed refractive nonlinearity on laser-induced damage are discussed.
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