William E. Torruellas

Two photon absorption of di‐alkyl‐amino‐nitro‐stilbene side chain polymer

The two photon absorption spectrum has been measured in the 780–1600 nm range for a di‐alkyl‐amino‐nitro‐stilbene side‐chain polymer. A single two photon peak centered at 920 nm is observed with a peak two photon coefficient of 5.5 cm/GW. Bleaching via two photon absorption at this wavelength is investigated by measuring a refractive index change after an intensive exposure.

Two‐photon absorption and third‐harmonic generation of di‐alkyl‐amino‐nitro‐stilbene (DANS): A joint experimental and theoretical study

The one‐ and two‐photon optical absorption spectra as well as the frequency dependent third‐harmonic generation response of a side‐chain polymer containing 4‐dialkylamino‐ 4′‐nitro‐stilbene (DANS) as its side group have been measured over a wide range of frequency. A three‐state model, based on an intermediate neglect of differential overlap/multireference double‐configuration interaction description of the excited states, provides a coherent picture of the dynamic response of DANS, but fails in reproducing the red shift observed when going from the linear to the nonlinear absorption spectra; including vibronic coupling within the Franck–Condon approximation improves the fit.

All‐optical switching by spatial walkoff compensation and solitary‐wave locking

We demonstrate a novel approach to phase insensitive, all‐optical steering and switching based on an intensity‐induced change in the propagation direction of multidimensional spatial solitary waves in bulk, birefringent, quadratic nonlinear media. Our demonstration is based on second‐harmonic generation in a KTP crystal. Compensation for the lateral displacements due to walkoff in SHG is observed.

Measurement of the complex nonlinear refractive index of single crystal p‐toluene sulfonate at 1064 nm

Z‐scan at 1064 nm was used with single, 35 ps pulses to measure the nonlinear refraction and absorption in single crystal PTS (p‐toluene sulfonate). Detailed analysis of the Z‐scan data based on Δn=n2I+n3I2 and Δα=α2I+α3I2 yielded n2=5(±1)×10−12 cm2/W, α2=100(±20) cm/GW, n3=−5(±1)×10−21 cm4/W2 and α3=−5(±1) cm3/GW.2 The resulting two photon figure of merit T for PTS is marginal for high throughput, all‐optical waveguide switching at 1064 nm.

Two-dimensional solitons with second-order nonlinearities

We investigate the propagation of intense Gaussian beams in materials with quadratic nonlinearity. Excitation of (2 + 1) solitons is numerically predicted at finite phase mismatch and in the presence of linear walk-off between the fundamental and second-harmonic waves. The numerical results are interpreted in terms of the conserved quantities of the wave evolution, and the appropriate conditions for the experimental observation of the solitons are discussed.

Stationary trapping of light beams in bulk second-order nonlinear media

The mutual trapping of fundamental and second harmonic, continuous-wave light beams propagating in bulk second-order nonlinear media is studied. We find numerically families of stationary, radially symmetric solitary waves. The transverse profiles of the trapped beams, their scaling properties, and their stability under propagation are investigated as a function of the total power and the linear wavevector-mismatch between the waves. We show that at phase-matching mutually trapped solitary waves exist for any total wave power, whereas they exist only above a threshold power for both positive and negative phase-mismatches.

Second-order cascading as the origin of large third-order effects in organic single-crystal-core fibers

We have identified cascading of second-order nonlinear processes as the origin of previously reported, very large nonlinearities measured by self-phase-modulation experiments in organic single-crystal-core fibers of 4-(N,N-dimethylamino)-3-acetamidonitrobenzene.

Observation of mutual trapping and dragging of two-dimensional spatial solitary waves in a quadratic medium.

We report experimental evidence for trapping of two-dimensional (2 + 1) spatial solitary waves in a KTP crystal resulting from its second-order nonlinearity. In addition, dragging of the solitary beams is observed as a function of fundamental input intensity and of the relative phase difference between the fundamental and the second harmonic when beams at both frequencies are coherently launched.

Stable self-trapping and ring formation in polydiacetylene para -toluene sulfonate.

Summary form only given. We now report numerical simulations of beam propagation in polydiacetylene para-toluene sulfonate (PTS), using measured refractive index values, and demonstrate stable self-trapping and a new phenomenon in which a Gaussian input beam evolves into an expanding spatial ring and interpret these results in the context of the variational model of nonlinear Gaussian beam propagation. We also show preliminary experimental results suggesting the presence of ring formation.

Beam steering by chi((2)) trapping.

We show numerically the mutual dragging and locking together of intense fundamental and second-harmonic light beams propagating in second-order nonlinear media, and we discuss the potential applications of such effects for the steering of beams by spatial phase modulation of the input signals.