Standoff trace chemical sensing via manipulation of excited electronic state lifetimes.

We present a technique for standoff trace chemical sensing that is based on the dependence of excited electronic state lifetimes on the amount of internal vibrational energy. The feasibility of the technique is demonstrated using N,N-dimethylisopropylamine (DMIPA). Time-resolved measurements show that the lifetime of the S1 state in DMIPA exponentially decreases with the amount of vibrational energy. This property is employed to acquire molecular spectral signatures. Two laser pulses are used: one ionizes the molecule through the S1 state; the other alters the S1 state lifetime by depositing energy into vibrations. Reduction of the S1 state lifetime decreases ionization efficiency that is observed by probing the laser-induced plasma with microwave radiation.