LASER COOLING IN THE CONDENSED-PHASE BY FREQUENCY UP-CONVERSION

Frequency up-conversion has been observed in fluid solutions of the la ser dye, rhodamine 101, when excited at 1.96 eV into the low energy ab sorption tail 0.15 eV from the 0-0 band origin. The emission intensity is temperature dependent and is demonstrated to be an excellent measu rement of the temperature of the sample. We show for the first time ho w intense laser irradiation in this spectral region leads to the remov al of thermal energy by the frequency up-conversion process, and thus lowers the temperature of the sample. A decrease in temperature at a r ate of 0.7 K h(-1) is demonstrated for a sample with a 3 J K-1 heat ca pacity, when irradiated with 350 mW of laser light at 1.96 eV.