Experimental evidence of laser cooling of room temperature trans-stilbene upon excitation to the S-1 state

The room temperature photoinduced fluorescence decay of isolated trans-stil bene and trans-stilbene in the presence of 1 atm of Ar gas was measured as a function of the excitation laser frequency. Lifetimes were measured both to the blue and the red of the ground vibrational state of the ground elect ronic state (S-0) to the ground vibrational state of the S-1 state transiti on frequency omega(00). The lifetime was found to decrease on both sides of omega(00). The dependence of the decay rate on laser frequency in the pres ence of Ar gas is much weaker than for the isolated molecule. Both observat ions corroborate previous theoretical predictions of laser cooling of therm al trans-stilbene upon excitation at the omega(00) frequency. The experimen tal results are in good agreement with theoretical analysis. (C) 2000 Ameri can Institute of Physics. [S0021-9606(00)01809-2].