Study of β‐carotene by time and wavenumber domain coherent anti‐stokes Raman scattering techniques

Dephasing of vibrations of all‐trans‐β‐carotene in cyclohexane was studied by resonance CARS in the wavenumber domain, using scanning CARS, and also in the time domain, by interferometric CARS (I‐CARS) applying temporally incoherent light from non‐transform limited broadband lasers. The ground‐state vibrations (1002, 1153, 1188, 1210 and 1522 cm−1) are predominantly homogeneously broadened and have dephasing times ranging from 0.6 to 0.7 ps. For broadband wavenumbers in the long‐wavelength wing of the absorption band and a Stokes laser intensity exceeding 0.5 GW cm−2, the CARS signal saturates and decreases above 1 GW cm−2. The decrease in the CARS signal is accompanied by the appearance of additional Raman lines. Taking into account all these Raman lines (solvent lines and two additional very broad lines), the features of the I‐CARS can be explained with the same parameters as for scanning CARS. Consideration of these additional lines is essential. Using excitation wavenumbers within the absorption band, power broadening of the 1522 cm−1 line is observed. In some experiments, diffraction by a laser‐induced grating strongly competes with I‐CARS.