POPULATION LENS IN THERMAL LENS SPECTROSCOPY .2. PROBE WAVELENGTH DEPENDENCE AND A NEW METHOD FOR SUBTRACTING THE TRANSIENT ABSORPTION FROM THE THERMAL LENS SIGNAL

Existences of three distinct origins of an observed thermal lens signal (TL(ex) signal) are demonstrated; these origins are classified into thermal lens, population lens (PL), and transient absorption (TA). In order to measure the contribution of TA in the TL(ex) signal quantitatively, a new method of TL detection is proposed. The validity of this method is demonstrated for quinoxaline and C60. By combining this method and the time-resolved TL signal, general existence of PL due to the ground-state depletion and the creation of the excited triplet state in the TL signal is clearly shown in several typical aromatic molecules. This finding indicates that the effect of PL cannot be neglected even when TA is negligibly weak in the TL(ex) signal at the probe light wavelength.