Large third-order optical nonlinearity realized in symmetric nonpolar carotenoids

Abstract

We show that a very large enhancement of third-order optical nonlinearity ͑␥͒ of -conjugated molecules can be realized without a major redshift of the absorption spectrum that disturbs optical transparency in the visible region. By changing the number ͑n͒ of CϭC bonds of ␤ carotene ͑n =11͒ from 7 to 15, a remarkable 3.4-fold increase in the ␥ value was observed when n = 15 relative to that of ␤ carotene. This enhancement of ␥ mainly originates from three-photon resonance of a lowest optically allowed excited state. The controversial higher-lying essential state is not important for generating the large value of ␥.

Spectrally‐resolved transient grating signals from β‐carotene in benzene solution

“…As can be seen, when the TG signal of β-carotene is measured near the absorption edge (more correctly, when pumped at the isosbestic point), the experimental result is well reproduced using Eq. (1) [10][11][12]. However, in the impulsive limit the TG signal does not depend on the excitation wavelength, whereas the experimental results clearly show a strong excitation wavelength dependence (see Fig.…”

“…The rise constituent is less prominent on decreasing the excitation frequency. The coherent oscillations were clearly observed when the excitation wavelength is set to the isosbestic point (curve B) which is the excitation condition of our previous studies [10][11][12]. The coherent oscillations and slowly-varying background become weak when the excitation wavelength is on the longer wavelength side (curves C to D).…”

“…1. For comparison, in Table 1 we have also listed the parameters for β-carotene in THF which were obtained in our previous studies [10,12]. The homogeneous line width Γ that reflects the decay of the vibronic oscillations is slightly larger in the present case, but the parameters with the subscript B for the low-frequency Brownian mode are the same in both solvents.…”

Control of coherent vibronic oscillations in β‐carotene by ultrashort laser pulses

“…As discussed in our previous papers, it is necessary to introduce the S x state between S 1 and S 2 in considering the ultrafast phenomena of carotenoids [12,18,19,22,23]:…”

Third‐order optical nonlinearity of β‐carotene homologues

“…1). The β-carotene homologues are frequently used in the spectroscopic study of the polyenic structure [4][5][6][7], because they are chemically stable (compared to open-end carotenoids such as lycopene) and are soluble in most of all solvents (polyene hardly dissolves in most solvents). We investigate the third-order nonlinear optical property of a range of β-carotene homologues, which have different numbers (n) of conjugated C=C double bonds from n = 7 to 15, by using third-harmonic generation Maker fringe technique.…”