Femtosecond, Frequency-Agile, Phase-Sensitive-Detected, Multi-Wave-Mixing Nonlinear Optical Spectroscopy Applied to π-Electron Photonic Materials

Abstract

Degenerate four-wave mixing (DFWM) spectroscopy is modified to exploit femtosecond pulses, phase-sensitive-detection, frequency (wavelength) agility, two-color (nearly degenerate multiwave mixing) radiation, and improved signal-to-noise capabilities that can be realized through a combination of new solid state lasers, nonlinear optical components, and novel design concepts. The resulting time-resolved nonlinear optical techniques permit “instantaneous” optical nonlinearities, such as two-photon absorption cross sections, to be accurately measured over the spectral range from 450 to 2500 nm (and with significantly greater effort from 225 to 5000 nm). The power of the new techniques is illustrated by their application to the definition of Hg two-photon resonances of C60 and C70 as well as to the characterization of optical nonlinearities in two linear chromophores of putative utility for sensor protection and electrooptic modulation. Explicitly, these measurements provide accurate determination of both transition energies and transition moments (matrix elements connecting the two photon levels). Results are compared to those previously reported in the literature illustrating the advantages and problems associated with particular measurement techniques. All of the molecules studied are found to exhibit two-photon absorption coefficients comparable to that of GaAs, the most studied putative sensor protection material (based on utilization of electronic optical nonlinearity). Femtosecond pulse techniques are shown, in all cases, to be necessary to avoid complications arising from excited-state absorption and relaxation phenomena. The importance of phase-sensitive detection in identifying complications from overlapping transitions is illustrated.

Tunable resonance hyper-Raman spectroscopy of second-order nonlinear optical chromophores

“…[1][2][3] Another is the molecular first hyperpolarizability ͑␤͒, usually measured through either electric field induced second harmonic generation ͑EFISH͒ 4 -6 or hyper-Rayleigh scattering ͑HRS͒. The most direct of these is two-photon absorption ͑TPA͒.…”

Experimental GVD engineering in slow light slot photonic crystal waveguides

“…In the same time, a material filling the slot with the same refractive index used in these experiments encounters a ≈ 107.0 enhancement. So, even with modest group indices corresponding to acceptable losses through long propagation lengths for practial applications (700 μm, here), the enhancement experienced by the slot material in ultra-small effective areas is very promising regarding highly nonlinear liquids and polymers with low refractive indices at λ = 1550 nm exhibiting ultra-fast response 44 45 46 . For instance, in the lower ng obtained experimentally ( n g ≈ 5.72), representing the best waveguide in terms of transmission, the expected slowdown enhancement would be of .…”

Theory-Guided Design of Organic Electro-Optic Materials and Devices

“…The ubiquitous femtosecond phase relaxation times of π-electron chromophores raise the possibility of terahertz bandwidth in device applications [1][2][3][4]. This potential has been demonstrated in all-optical switching and optical rectification [1,2], terahertz generation and detection [3], and in femtosecond pulse experiments [4].…”

“…The ubiquitous femtosecond phase relaxation times of π-electron chromophores raise the possibility of terahertz bandwidth in device applications [1][2][3][4]. This potential has been demonstrated in all-optical switching and optical rectification [1,2], terahertz generation and detection [3], and in femtosecond pulse experiments [4]. However, more frequently, device bandwidth will be defined by the properties of other materials such as the resistivity of electrode materials (e.g., metals or doped silicon) used in devices such as Mach Zehnder modulators [5,6].…”