Experimental evidence of laser cooling of room temperature trans-stilbene upon excitation to the S1 state

The room temperature photoinduced fluorescence decay of isolated trans-stilbene 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 electronic state ${\mathrm{(S}}_0)$ to the ground vibrational state of the $S_1$ state transition 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 presence of Ar gas is much weaker than for the isolated molecule. Both observations corroborate previous theoretical predictions of laser cooling of thermal trans-stilbene upon excitation at the ${\omega }_{00}$ frequency. The experimental results are in good agreement with theoretical analysis.