INHERENT SAMPLE HEATING AND TEMPERATURE CALIBRATION IN EXCITED-STATE ABSORPTION (ESA) MEASUREMENTS BETWEEN ROOM-TEMPERATURE AND 77-KELVIN

Laser pulses of high intensities are usually required for recording ex cited state absorption (ESA) spectra of molecules in solution. Followi ng the optical excitation non-radiative relaxation processes in the ch romophores can lead to a remarkable and unintentional heating of the o verall excited sample volume, especially at low temperatures. This tem perature rise and its spatial distribution is investigated experimenta lly and compared to model calculations. The temperature of the excited sample volume was monitored by the temperature sensitive fluorescence of 4-methylumbelliferone (4-MU; synonymous with 7-hydroxy-4-methylcou marine). A maximal temperature rise of several degrees was observed ex perimentally. Although the model was based on simple assumptions the a greement between theoretical results and experimental data proved to b e satisfying.