Plasmon coupling interactions and inhibition of nonlinear absorption in a complex system with Ag and Pt nanoparticles in silica.

The optical response exhibited by a complex hybrid system integrated by Pt ultrasmall fluorescent particles and plasmonic Ag nanoparticles is reported. The system was synthesized by coimplantation of Ag and Pt ions into a silica matrix followed by a proper thermal annealing. The energies and fluences were chosen in order to overlap the spatial regions of the Ag and Pt ion distributions below the silica surface. Optical absorption and emission spectroscopies show that the complex nanostructures exhibit an important plasmonic response, together with photoluminescence excited at 355 nm, which is enhanced when compared to the reference sample with only Pt particles. Off-resonance nonlinear transmission and Z-scan measurements were undertaken using ultrafast pulses. High-irradiance excitation at 1064 nm with picosecond pulses shows that the Pt or Ag nanoparticles exhibit a two-photon absorption effect, while the complex system shows the absence of any nonlinear absorption. Similar observations were made using femtosecond pulses at 800 nm wavelength. This inhibition of the two-photon absorption effect and enhancement in the emission of the complex hybrid samples by the synergic participation of Ag and Pt particles can be explained as a result of a plasmon coupling via the near-field interaction between plasmonic and emitting sources.

Polarization dependence of second harmonic generation from plasmonic nanoprism arrays.

The second order nonlinear optical response of gold nanoprisms arrays is investigated by means of second harmonic generation (SHG) experiments and simulations. The polarization dependence of the nonlinear response exhibits a 6-fold symmetry, attributed to the local field enhancement through the excitation of the surface plasmon resonances in bow-tie nanoantennas forming the arrays. Experiments show that for polarization of the input light producing excitation of the plasmonic resonances in the bow-tie nanoantennas, the SHG signal is enhanced; this despite the fact that the linear absorption spectrum is not dependent on polarization. The results are confirmed by electrodynamic simulations which demonstrate that SHG is also determined by the local field distribution in the nanoarrays. Moreover, the maximum of SHG intensity is observed at slightly off-resonance excitation, as implemented in the experiments, showing a close relation between the polarization dependence and the structure of the material, additionally revealing the importance of the presence of non-normal electric field components as under focused beam and oblique illumination.

Third-order nonlinear optical properties of a multi-layer Al2O3/ZnO for nonlinear optical waveguides.

This is a report of a study of the nonlinear optical properties of samples based on multiple Al2O3/ZnO bilayers fabricated by atomic layer deposition (ALD) in silica. The multi-layer configuration for samples consists of alternated layers of constant thickness of Al2O3 (Δx) and ZnO (Δy) nanolaminates with a total thickness of ∼ 500 nm. The physical properties of the samples were characterized by means of TEM, spectrophotometry and variable angle spectroscopic ellipsometry. The absorptive and refractive contributions to the nonlinearity of the samples were studied by means of z-scan technique using a 100 fs at 800 nm. The nonlinear parameters, ß and n2, are studied using different values of the layers thickness, Δx and Δy, in the nanolaminated stack. The possible applications in optical signal processing system are discussed by means of the figures of merit W and T.

Nonlinear optical response of platinum nanoparticles and platinum ions embedded in sapphire.

We report on the fabrication of sapphire samples containing platinum nanoparticles (Pt-NPs) and platinum ions (Pt-ions) and the investigation of their third-order nonlinear (NL) optical properties. The presence of Pt-NPs was confirmed by electronic microscopy and by the linear absorption spectrum that shows a localized surface plasmon band centered at 290 nm. A sample without NPs but containing Pt-ions was also studied. The absorptive and refractive contributions to the nonlinearity were studied using the z-scan technique with 100 fs pulses at 800nm. The experiments revealed a NL refractive index, +3.8×10-13 < n2 < +1.3×10-12cm2/W and NL absorption coefficient (ß < 9.3 cm/GW). The results show enhancement of about five orders of magnitude with respect to the NL refractive index of sapphire.

Collective optical Kerr effect exhibited by an integrated configuration of silicon quantum dots and gold nanoparticles embedded in ion-implanted silica.

The study of the third-order optical nonlinear response exhibited by a composite containing gold nanoparticles and silicon quantum dots nucleated by ion implantation in a high-purity silica matrix is presented. The nanocomposites were explored as an integrated configuration containing two different ion-implanted distributions. The time-resolved optical Kerr gate and z-scan techniques were conducted using 80 fs pulses at a 825 nm wavelength; while the nanosecond response was investigated by a vectorial two-wave mixing method at 532 nm with 1 ns pulses. An ultrafast purely electronic nonlinearity was associated to the optical Kerr effect for the femtosecond experiments, while a thermal effect was identified as the main mechanism responsible for the nonlinear optical refraction induced by nanosecond pulses. Comparative experimental tests for examining the contribution of the Au and Si distributions to the total third-order optical response were carried out. We consider that the additional defects generated by consecutive ion irradiations in the preparation of ion-implanted samples do not notably modify the off-resonance electronic optical nonlinearities; but they do result in an important change for near-resonant nanosecond third-order optical phenomena exhibited by the closely spaced nanoparticle distributions.

Nanoparticle containing channel waveguides produced by a multi-energy masked ion-implantation process.

We present the fabrication and characterization of channel waveguides based on composites containing silver nanoparticles. The substrate employed is silica and the nanoparticles were produced by a masked ion-implantation technique. Multiple implantation processes were made at different energies in order to produce waveguides with an appropriate width. We also present results for the characterization of the waveguiding properties of the devices produced.

Optical Kerr phase shift in a nanostructured nickel-doped zinc oxide thin solid film.

The optical Kerr effect exhibited by a nickel doped zinc oxide thin solid film was explored with femto- and pico-second pulses using the z-scan method. The samples were prepared by the ultrasonic spray pyrolysis technique. Opposite signs for the value of the nonlinear refractive index were observed in the two experiments. Self-defocusing together with a two-photon absorption process was observed with 120 ps pulses at 1064 nm, while a dominantly self-focusing effect accompanied by saturated absorption was found for 80 fs pulses at 825 nm. Regarding the nanostructured morphology of the resulting film, we attribute the difference in the two ultrafast optical responses to the different physical mechanism responsible of energy transfer generated by multiphoton processes under electronic and thermal effects.

Ultrafast nonlinear optical response of photoconductive ZnO films with fluorine nanoparticles.

The absorptive and refractive third order nonlinear optical properties exhibited by a ZnO thin solid film with fluorine nanoparticles were studied with picosecond and femtosecond pulses using different techniques. We were able to evaluate the photoconductivity of the material and the quenching of the induced birefringence observed in the presence of two-photon absorption. The samples were prepared by a chemical spray deposition technique. In order to investigate the different contributions of the third order nonlinearities of the film, we analyzed the vectorial self-diffraction effect and the optical Kerr transmittance observed in the sample. A dominantly absorptive nonlinearity was measured at a 532 nm wavelength with 50 ps pulses, while nonlinear refraction was found to be negligible in this regime. On the other side, a pure electronic refractive third order nonlinearity without the contribution of nonlinear absorption was detected at 830 nm with 80 fs pulse duration. A quasi-instantaneous optical response and a strong enhancement in the ultrafast nonlinear refraction with the inhibition of the picosecond two-photon absorption mechanism were measured for the case of the femtosecond excitation.

Ultrafast optical phase modulation with metallic nanoparticles in ion-implanted bilayer silica.

The nonlinear optical response of metallic-nanoparticle-containing composites was studied with picosecond and femtosecond pulses. Two different types of nanocomposites were prepared by an ion-implantation process, one containing Au nanoparticles (NPs) and the other Ag NPs. In order to measure the optical nonlinearities, we used a picosecond self-diffraction experiment and the femtosecond time-resolved optical Kerr gate technique. In both cases, electronic polarization and saturated absorption were identified as the physical mechanisms responsible for the picosecond third-order nonlinear response for a near-resonant 532 nm excitation. In contrast, a purely electronic nonlinearity was detected at 830 nm with non-resonant 80 fs pulses. Regarding the nonlinear optical refractive behavior, the Au nanocomposite presented a self-defocusing effect, while the Ag one presented the opposite, that is, a self-focusing response. But, when evaluating the simultaneous contributions when the samples are tested as a multilayer sample (silica-Au NPs-silica-Ag NPs-silica), we were able to obtain optical phase modulation of ultra-short laser pulses, as a result of a significant optical Kerr effect present in these nanocomposites. This allowed us to implement an ultrafast all-optical phase modulator device by using a combination of two different metallic ion-implanted silica samples. This control of the optical phase is a consequence of the separate excitation of the nonlinear refracting phenomena exhibited by the separate Au and Ag nanocomposites.

Inhibition of the two-photon absorption response exhibited by a bilayer TiO2 film with embedded Au nanoparticles.

We use two different synthesis approaches for the preparation of TiO(2) films in order to study their resulting third order optical nonlinearity, and its modification by the inclusion of Au nanoparticles in one of the samples. An ultrasonic spray pyrolysis method was used for preparing a TiO(2) film in which we found two-photon absorption as a dominant nonlinear effect for 532 nm and 26 ps pulses; and a purely electronic nonlinearity at 830 nm for 80 fs pulses. A strong optical Kerr effect and the inhibition of the nonlinear optical absorption in 532 nm can be obtained for the first sample if Au nanoparticles embedded in a second TiO(2) film prepared by a sol-gel technique are added to it. We used an optical Kerr gate, z-scan, a multi-wave mixing experiment and an input-output transmittance experiment for measuring the optical nonlinearities.

Modification of the nonlinear optical absorption and optical Kerr response exhibited by nc-Si embedded in a silicon-nitride film.

We studied the absorptive and refractive nonlinearities at 532 nm and 26 ps pulses for silicon-nitride films containing silicon nanoclusters (nc-Si) prepared by remote plasma-enhanced chemical vapor deposition (RPECVD). Using a self-diffraction technique, we measured for the as-grown sample beta=7.7x10(-9)m/W, n(2)=1.8x10(-16)m(2)/W, and /chi(3)1111/ = 4.6x10(-10)esu; meanwhile, when the sample was exposed to an annealing process at 1000 degrees C during one hour in a nitrogen atmosphere, we obtained beta=-5x10(-10)m/W, n2=9x10(-17)m(2)/W, and /chi(3)1111/=1.1x10(-10)esu. A pure electronic nonlinear refraction was identified and a large threshold ablation of 41 J/cm(-2) was found for our films. By fitting nonlinear optical transmittance measurements, we were able to estimate that the annealed sample exhibits a response time close to 1 fs. We report an enhancement in the photoluminescence (PL) signal after the annealing process, as well as a red-shift due to an increment in size of the nc-Si during the thermal process.

Thermo-optic effect and optical third order nonlinearity in nc-Si embedded in a silicon-nitride film.

Using a self-diffraction experiment with 7ns pulses at 532nm we studied a silicon nitride film containing silicon nanoclusters (nc-Si) of 3.1+/-0.37 nm mean size. The sample was prepared by remote plasma-enhanced chemical vapor deposition (RPECVD), and we found that its nonlinearity consists of a combination of electronic and thermal contributions. By varying the repetition rate of the laser, we discriminated the responsible mechanisms for the nonlinear response. Using this procedure we determined a total /chi((3))1111/ = 3.3x10(-10)esu, n2 = 2.7x10(-16) m(2)/W, beta = 1x10(-9) m/W and dn/dT =1x10(-4) degrees C(-1) for our sample. We also show results for the optical Kerr effect using 80 fs pulses at 820 nm. The purely electronic nonlinearity measured is characterized by /chi((3))1111/=9.5 x10(-11) esu.

Optical channel waveguides by proton and carbon implantation in Nd:YAG crystals.

In this work the formation of optical channel waveguides in Nd:YAG crystals by either proton or carbon implantation is reported. The channel waveguides were obtained by a single implantation process through an electroformed mask of nickel-cobalt alloy. Experimental measurements of the optical properties of these waveguides are presented.

Photon pair-state preparation with tailored spectral properties by spontaneous four-wave mixing in photonic-crystal fiber.

We study theoretically the generation of photon pairs by spontaneous four-wave mixing (SFWM) in photonic crystal optical fiber. We show that it is possible to engineer two-photon states with specific spectral correlation ("entanglement") properties suitable for quantum information processing applications. We focus on the case exhibiting no spectral correlations in the two-photon component of the state, which we call factorability, and which allows heralding of single-photon pure-state wave packets without the need for spectral post filtering. We show that spontaneous four wave mixing exhibits a remarkable flexibility, permitting a wider class of two-photon states, including ultra-broadband, highly-anticorrelated states.

Laser emission in proton-implanted Nd:YAG channel waveguides.

The performance of lasers based on channel waveguides produced by proton implantation in Nd:YAG crystals through an electroformed mask is reported. The fabrication method used can produce several waveguide lasers in the crystal by a single implantation process with very good optical performance. The analysis and comparison of the main laser emission features, as well as the propagation losses of these waveguides, by using different output couplers in the laser cavity is also presented.

Planar waveguide lasers by proton implantation in Nd:YAG crystals.

The performance of CW Nd:YAG waveguide lasers operating at 1.06 microm at room temperature is described. 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.