Frequency-locking of a CW dye laser to the center of the sodium D lines by a Faraday filter

Single-mode CW oscillations at the center of the sodium
D
lines have been achieved by inserting a Faraday filter in an argon-laser-pumped dye laser cavity. The oscillations at the D
1
and D
2
lines can be selected by choosing adequate values of the sodium temperature and the magnetic field strength. Experimentally obtained conditions to get the single-mode oscillations at the center of the
D
lines are compared with the theoretically calculated feature of the Faraday filter, and a relatively good agreement has been found. The shifts of oscillation frequencies due to the magnetic field are also discussed.