Ultrafast rise of translational temperature after photoexcitation to electronic excited state in solution: Transient lens study of Ni2+ aqueous solution

An increase of the translational temperature after photoexcitation to the electronically excited state of Ni2+ in aqueous solution is detected using a time-resolved transient lens method from the picosecond to millisecond time scale. Besides a large lens signal due to the volume expansion of water in the submicrosecond time range, two other lens signals are observed at an initial part of the signal. During the pump laser pulse, a convex lens signal is observed, which is attributed to the optical Kerr lens signal. After the pulse, a concave lens is created, which remains a nearly constant amplitude until the density lens signal appears. The signal is attributed to the temperature lens signal, which originates from the heat energy by the nonradiative transition of the excited state. It is found that the signal rises within 3 ps after the photoexcitation, which indicates that the temperature rise is very fast. After the fast rise, another slower dynamics (500 ps) is observed and the deactivation processes of Ni2+ in aqueous solution are discussed based on these results. (C) 1996 American Institute of Physics.