Knowledge Bank

A 50 cm absorption pathlength, 40 MHz sub-Doppler linewidths, 5 K rotational temperatures. $1017/cm3$ number density, and detection limits of $5\times 107$ moleculas/cm/quantum state for direct absorption: these are the advantages of spectroscopy in a slit supersonic expansion. A system is described which includes a 200-1000 usec duration, 60 Hz repetition rate pulsed valve with a 4 cm long by 75 pa wide slit nozzle and multipass optics. Examples are presented from the near-IR $(2-4\mu m)$ spectra of hydrocarbons and van der Walls complexes.