A novel shock tube reactor was used to pulse heat a gaseous mixture of He, FN3, and Bi(CH3)3along a 40 cm optical path between two highly reflective mirrors. Production of NF(a1&Dgr;) by dissociation of the azide was found to occur in a ‘‘delayed avalanche’’ approximately 50 &mgr;s after shock reflection, and weak lasing at 470 nm was observed that is assignable to electronic transitions in the BiF(A–X, &Dgr;v=3) band.