Laser frequency stabilization using an Fe-Ar hollow cathode discharge cell

Polarization spectroscopy of an Fe-Ar hollow cathode discharge cell was used to lock a frequency-doubled Ti:sapphire laser to the 372-nm5D4→5F5 transition of 56Fe. The discharge cell produced a density of 1018 m-3 ground-state 56Fe atoms at a temperature of 650 K, this density being comparable to a conventional oven at 1500 K. Saturated absorption spectroscopy and two schemes of polarization spectroscopy were compared with respect to signal-to-background ratio and the effect of velocity-changing collisions. The laser was locked within 0.2 MHz for hours by feedback of the dispersive polarization spectroscopy signal.