R. Rangel-Rojo

Large near-resonance third-order nonlinearity in an azobenzene-functionalized polymer film

The third-order nonlinear optical response of a thin film containing the azobenzene dye Disperse Red 1 was studied using the z-scan technique with tunable picosecond pulses. A nonlinear refractive index of −5.0 cm2/GW, corresponding to a Re χ(3)=−3.0×10−15 m2/V2 (2.1×10−7 esu), has been measured at 570 nm. The observed nonlinearity is attributed to the change in refractive index induced by the trans-cis transition in the dye molecule.

Image formation by linear and nonlinear digital scanned light-sheet fluorescence microscopy with Gaussian and Bessel beam profiles

We present the implementation of a combined digital scanned light-sheet microscope (DSLM) able to work in the linear and nonlinear regimes under either Gaussian or Bessel beam excitation schemes. A complete characterization of the setup is performed and a comparison of the performance of each DSLM imaging modality is presented using in vivo Caenorhabditis elegans samples. We found that the use of Bessel beam nonlinear excitation results in better image contrast over a wider field of view.

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.

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.

Wavelength dependence of the third-order nonlinear optical properties of a polythiophene/selenophene derivative film

The third-order nonlinear optical properties of a hybrid polymer film containing substituted thiophene rings copolymerized with unsubstituted selenophene were measured using the Z-scan technique. Large, resonantly enhanced third-order nonlinearities were found at wavelengths on the low-energy side of the absorption band. In contrast to the results on a similar copolymer film incorporating only thiophene, a strong two-photon absorption appeared in the near infrared. The imaginary part of the third-order susceptibility can be adequately explained as saturation of an exciton band, while the origin of the large negative real part is unknown.

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.

Saturation in the near-resonance nonlinearities in a triazole-quinone derivative

Abstract In this work, we present a study of the third-order nonlinearities of a novel organic material, a derivative of the 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 88 ps pulse source at 532 nm. The open aperture z -scan results show a nonlinearity arising from a combination of induced and saturable absorption, and the closed aperture the signature of a negative n 2 . The irradiance dependence of the closed aperture signal reveals a saturating nonlinearity which even decreases at high irradiances. A three-level model is used to explain the observed irradiance dependence of the nonlinearity.

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.

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.

Refractive Third-order Nonlinearity in Vanadium-oxide Phthalocyanine Micro-crystals

We report a study on the resonant third-order nonlinear optical response of vanadyl-phthalocyanine micro-crystals. The refractive and absorptive contributions to the nonlinear response at several wavelengths across resonance were determined by employing the z-scan technique with a tunable picosecond pulsed laser source. The samples studied were cyclohexane suspensions of vanadium-oxide phthalocyanine micro-crystals 40 nm in diameter. These micro-crystals represent an interesting alternative for the production of solid state samples of good optical quality through relatively simple techniques. Experimental results show that for wavelengths above 610 nm, the sample presents saturation of absorption, while for shorter wavelengths, induced absorption is found. Around 610 nm however, the absorptive contribution to the nonlinearity vanishes while a finite refractive contribution remains. This wavelength region is therefore potentially useful for all-optical switching applications.