The nonlinear absorption properties of Ag nanoprism arrays synthesized by nanosphere lithography have been investigated by z-scan measurements. A picoseconds and low repetition rate laser source has been used to excite the electronic component of the nonlinear optical response without inducing thermal effects on the samples. Spectral effects in the nonlinear absorption response have been highlighted by performing measurements at different wavelengths, matching the laser wavelength with the dipolar and the quadrupolar surface plasmon resonances of the synthesized nanoarrays. The nonlinear absorption properties of the samples have been also investigated as a function of the polarization of the laser source and dichroism effects have been revealed.
Design of straight and S-bend optical channel waveguides based on silver ion implantation in SiO2 substrates is
presented. 3D Beam Propagation Method (BPM) calculations are used for the design of the waveguides based on step
index profiles produced from a sequential multiple ion implantation process. An analysis of modal optical confinement
was done by means of the Effective Index Method (EIM) for selecting the right dimensions of the channel waveguides.
Core index values between 1.4623-1.4662 are obtained, depending on the fluence, are considered. Depth and width for
the waveguides were chosen to provide single mode operation. Bending losses are determined as function of bending
radius, refractive index change (Δn), and wavelength.
In this work a study of the effects on the optical properties of channel waveguides in Nd:YAG crystals fabricated with
different proton implantations doses is presented. The channel structure was achieved by using an electroformed mask
with openings through which the protons were implanted. The optical properties studied included microphotographs, the
transversal modal distribution at visible wavelengths, the photoluminescence spectra and the laser emission. The laser
performance of the waveguides was obtained in a resonant cavity configuration with mirrors held onto the polished end
faces of the waveguides.
Optical waveguides have been obtained by silver ion implantation on fused silica substrates. First results of a
methodology oriented to design optical waveguides with silver nanoparticles in a dielectric matrix are presented.
Simulation of ion implantation is based on SRIM code and is correlated with a refractive index increase Δn calculated as
a function of the chemical composition. Effective refractive indices of the propagation modes are determined by prismcoupling
Gold nanoparticles (AuNPs) have proven to be powerful tools in various ultrafast photonic, plasmonic and nanomedical
applications. Numerous advances in the use of AuNPs include research on their interesting and remarkably fast changes
influenced by Surface Plasmon Resonance excitations. Within this work we report theoretical and experimental results
for the physical mechanisms that originate a nonlinearity of refractive index during different temporal regimes for a
high-purity silica matrix containing Au nanoparticles. The nanocomposites were prepared by ion implantation into a
silica matrix, followed by a thermal annealing. We used an optical Kerr gate with 80 fs pulses at 830 nm and a vectorial
self-diffraction technique with 26 ps and with 7 ns at 532 nm in order to investigate the magnitude and response time of
the resulting third order nonlinearity. In all cases we were able to measure and identify an electronic polarization
responsible for the nonlinear refraction. For the pico- and nano-second near resonance irradiations, a contribution of a
thermal effect could be stimulated and then the optical Kerr response enhanced. The presence of saturable absorption for
the pico- and nano-second experiments was measured. We observe that our samples behave like waveguides in the near
infrared spectrum and we estimate that they posses potential applications for all-optical switching devices.
We present the laser backwriting process on glass by laser ablation of metal targets, in order to fabricate waveguides on pyrex glasses. An horizontal position of the sample and the plate was found suitable to improve the effect of the plume in the sample with respect to the alternative vertical arrangement. We have analysed the longitudinal and transversal profiles, using a profilometer and have compared the results for the different laser sources used, speeds and metal targets. We have analyzed the refractive index profile of the samples obtained, in order to evaluate the change in the substrate due to the metal ablation. A cleaning of the surface and a heat treatment of the glass has been made in order to improve the results.
In this work we present experimental findings in the field of laser matter interaction on the topic of laser induced oxidation and crystalline structure change. It has been shown in the past few years that lasers can be used to induce both oxidization of metals as well changes the crystal in the crystalline structure of the metal oxide. Conventional theory has proven to be mildly successful in predicting these effects with a thermal model; drawing its influence from the traditional method of inducing material change by baking the metal. We reformed a scan of varying values of laser intensity and accumulated fluence. We will show evidence of an increase in the oxygen content in Ti and W thin films irradiated by a frequency doubled Nd:YAG laser source with a pulse duration of 4 ns and per pulse energies of 26 to 60 μJ (peak intensities of 1.7 x 107 to 3.8 x 107W/cm2). We will also show that other effects, that may include crystalline structure change, are also occurring.
We present the results of two different multi-pass designs for the amplification stage of a chirped pulse amplifier system. The first design is a typical one, where all of the beam paths that pass through the amplifying medium are in the same plane. The second one distributes the same number of passes in two planes, reducing the angle between the pump beam and the signal, thus increasing the overlap and the energy extraction efficiency.
In this work we report the performance of CW Nd:YAG waveguide lasers operating at 1064 nm at room temperature. The waveguides were fabricated by proton implantation and the main differences in the process of fabrication were the angle of implantation and the total dose implanted. The characterization of the waveguide refractive index profile induced by proton implantation and the main laser characteristics i.e. slope efficiency and threshold are presented. The results indicate that the optical properties of the waveguide in comparison with the bulk material are preserved after the implantation process and that this is a potential technique to develop compact and efficient lasers.
We report the study of the dynamics of the third-order nonlinear optical response of polydiacetylene micro-crystals. The material employed is the polydiacetylene know as poly-DCHD, and the micro-crystals were 100 nm in diameter contained in an aqueous suspension. Experimental results for transient changes in transmission measured by a time-resolved excite-probe technique, conducted with 100 fs pulses at 850 nm from a mode-locked Ti:sapphire laser are presented. A discussion of the role of the excitonic origin of the nonlinear response is also presented. (Abstract only available)
We present a wavelength-resolved study of the third-order nonlinearity of two derivatives of the 2-amino-1,2,3 triazole-quinone molecule. The substitution groups are a dialkylaminophenyl in one case, and ferrocene in the other, and both samples were prepared as chloroform solutions. The z-scan technique with a tunable 10 ps laser source was used to resolve the absorptive and refractive contributions to the nonlinearity at several wavelengths near resonance. In the case of the ferrocene derivative, the nonlinear response is attributed to the metal-ligand charge transfer that gives rise to the absorption spectrum features. The absorptive contribution changes from saturable to two-photon absorption going away from resonance, vanishing at λ=540 nm, while the nonlinear refractive index n2 remains finite. This is important for possible applications based on nonlinear refractive effects. For the dialkylaminophenyl derivative, a complex combination of saturable and induced absorption is observed at several wavelengths, becoming induced absorption closer to resonance and weak saturable absorption away from resonance. For both samples the nonlinear refractive index remains positive throughout the spectral range investigated.
In this work, we present a study of the third-order non linearities of two derivatives of the organic molecule 2- amino-1,2,3 triazole-quinone. The absorptive and refractive contributions to the nonlinearity were resolved using the z- scan technique with a 88ps pulse source at 532nm. For one of the materials, the open aperture z-scan result show a nonlinearity arising from a combination of two-photon and saturable absorption, and the closed aperture the signature of a negative n2.
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.
We report the study of the third-order optical nonlinearities of amorphous selenium, using picosecond pulses at 1.064 micrometer, from a mode-locked Nd:YAG laser. The Z-scan technique was used to resolve the absorptive and refractive contributions to the nonlinear response of the material, including their sign. The chosen wavelength lies to the lower photon energy side from the absorption edge for the material studied, the interaction is therefore nonresonant and electronic in origin. We measured an n2 equals -0.06 cm2GW-1, with negligible two-photon absorption. We discuss the influence of two photon absorption on the nonlinearity observed.
We report the observation of self-pulsing behavior in a linear cavity Er-doped fiber laser pumped by a 980 nm laser diode. Stable self-pulsing is observed for both continuous-wave and low frequency chopped pumping. By measuring the time evolution of the transmitted pump light, we were able to observe a long build-up time (around 5 ms) for lasing action to take place. While the self-pulsing behavior of similar lasers has been recently reported, the long laser build up times have not been reported before. A numerical model for the time and space dependance of the excited state populations of the Er-ions reproduces some of the observed features.
Recent experiments on optical bistability in amorphous Se an GexSe1-x chalcogenide thin films are presented. The results show a strong dependence on the energy density and on the sample composition. The faster responses are for pure selenium as the content of germanium is increased the material response is slower. A simple model is proposed in order to explain the observed results.
Polymeric composites containing microcrystals of 1:1 salts of tetracyano-p-quinodimethane, TCNQ, have been prepared. Re-crystallization of these organic one-dimensional semiconductors in-situ by either heat treatment or exposure to vapor yields uniform dispersions of crystallites of sub-optical dimensions. We report a strong dependence of the lowest energy electronic absorption band in the lithium and potassium TCNQ salt with crystallite size. The inter-molecular charge transfer band shows a shift of up to 0.5 eV between films where the crystallite size is a few microns and those where crystals cannot be observed optically. The non-linear refraction of a heat treated film containing TEA(direct sum)(TCNQ) (TEA(direct sum) - triethylammonium) is reported. (chi) (3) at 712 nm is 2.69 X 10-10 esu and is found to be a bleaching resonant non-linearity.