Development of kinetic analysis system in pump–probe measurement based on femtosecond chromium: forsterite laser and its application to S1–S0 relaxation dynamics of azulene

Ultrafast transient absorption measurement system with cavity-dumped chromium:forsterite (Cr:F) laser as a light source was developed. The second harmonic of the Cr:F laser can cover the immeasurable region of the titanium:sapphire laser which is nowadays the most popular light source for the ultrafast spectroscopy. The second harmonic of the Cr:F laser was tunable from 620 to 640 nm and the shortest pulse duration attained in the present condition was ∼25 fs. The sensitivity of this laser to ultrafast spectroscopy was evaluated by the measurement of S0 and S1 state dynamics of azulene. In spite of extremely small molar extinction coefficient of the S1←S0 transition, i.e. 300 M−1 cm−1, the ultrafast dynamics of azulene after photo-excitation to S1 state was clearly observed with high S/N ratio and ≤30 fs time resolution. Although the small molar extinction coefficient value of 300 M−1 cm−1, pump-and-probe measurement clearly resolved the multi-exponential recovery profile with a very weak oscillation of 160 cm−1.