A novel single-shot femtosecond spectroscopy technique permits real-time examination of irreversible decomposition in energetic solids. In a single laser shot, measurements at 400 different temporal delays are recorded to cover a total temporal range of more than 10 ps in 30 fs steps. This is accomplished by using two crossed echelon optics to separate a single probe pulse into 400 spatially and temporally separate probe pulses. Dielectric breakdown of silica glass and of 1,3,3-trinitroazetidine (TNAZ) was observed to occur on the time scale of the 50-fs pump pulse duration.