Dispersion of the first hyperpolarizability of a strongly charge-transfer chromophore investigated by tunable wavelength hyper-Rayleigh scattering

Abstract

Two-photon resonant hyperpolarizability of an H-shaped molecule studied by wavelength-tunable hyper-Rayleigh scattering J. Chem. Phys. 133, 244503 (2010); 10.1063/1.3506421Resonant Raman spectra and first molecular hyperpolarizabilities of strongly charge-transfer molecules Hyper-Rayleigh scattering and frequency dependence of the first molecular hyperpolarizability of a strong charge-transfer chromophoreThe first hyperpolarizability ͑␤͒ of a strongly charge-transfer ͑azulenic-barbituric͒ chromophore is measured by hyper-Rayleigh scattering ͑HRS͒ experiment using 11 excitation wavelengths, ranging from 900 nm to 1907 nm. The measured wavelength-dependence of the ␤ value is used to investigate the dispersion relation of the first hyperpolarizability of the charge-transfer chromophore. When excited by the 1064 nm wavelength laser radiation, the experimental HRS spectrum shows a two-photon resonance ͑TPR͒ peak, which does not coincide with the maximum of the linear absorption spectrum. The wavelength dependence of the first hyperpolarizability cannot be explained by an undamped or damped two level model. However, incorporating vibrational motion in the damped two-level model results in a good fit between theoretical and experimentally measured ␤, especially in the vicinity of TPR region.

Highly sensitive setup for tunable wavelength hyper-Rayleigh scattering with parallel detection and calibration data for various solvents

“…DR1 is a classical donor-acceptor system with an azostilbene-derived structure, which belonged for a long time to the best nonlinear optical molecules [75], and which is still one of the most commonly used chromophores for fabricating NLO materials. Currently, DR1 is also very often used as an external reference standard for HRS [9,13,14,18,76]. Although both EFISHG and HRS measurements at a single wavelength have been performed on DR1 [77,78], the dispersion of its first hyperpolarizability has never been examined.…”

“…Also, once a reliable static value β 0 is obtained, it is important for applications to determine the (resonant) value for a specific NLO process at a given working wavelength (for instance, β for the EO effect at the telecommunication wavelengths of 1300 or 1500 nm). Because the wavelength-dependence of the first hyperpolarizability β is still not well-understood [10,[14][15][16][17][18][19][20][21][22][23], it is necessary to determine this dispersion behavior experimentally by wavelength-dependent HRS measurements. The HRS technique is based on incoherent second harmonic generation (SHG) by the randomly oriented molecules in a liquid solution, and is by far more straightforward to interpret than the previously often applied electric-field induced second harmonic generation (EFISHG) technique [24,25], where the (necessarily dipolar) molecules are aligned by use of an externally applied static electric field.…”

“…In pioneering papers by Wang and co-workers [14,17,19,27] and more recently also by Shoute et al [10,[20][21][22], the resonance effect on the first hyperpolarizability was observed by performing HRS measurements at a number of different wavelengths. However, these measurements are generally characterized by a very low signal-to-noise (S/N) ratio, which was attributed to the noise of the detector and to intensity fluctuations of the incoming laser pulses [19].…”

“…However, these measurements are generally characterized by a very low signal-to-noise (S/N) ratio, which was attributed to the noise of the detector and to intensity fluctuations of the incoming laser pulses [19]. Moreover, because the signal from the pure solvent [28] (and in reference [14] even the one from para-nitroaniline (pNA)) could not be detected at longer wavelengths, two different reference standards (pNA and Disperse Red 1 (DR1)) had to be used for external calibration in different wavelength regions, almost inevitably leading to systematic errors as a priori the strong β dispersion of the reference standards themselves is unknown. The large scatter in their results makes it impossible to decide between the various possible β dispersion models [16,20,21,[29][30][31], which often exhibit subtle differences in the resonance region with however strong effects on the static value β 0 [32].…”

Careful measurement of first hyperpolarizability spectrum by hyper-Rayleigh scattering (HRS)

“…Subsequently, Kelly suggests that the Kramers-Kronig relations between the real and the imaginary part of a complex polarizability can be used to calculate the first hyperpolarizability spectrum from the absorption spectrum [4]. Based on these two methods, several push-pull chromophores have been studied [3][4][5][6][7]. However, there are also some details to be investigated.…”