Frequency stabilization to a molecular line of a diode-pumped Er–Yb laser at 1533-nm wavelength

Two identical diode-pumped bulk Er:Yb:glass lasers, operating at 1533-nm wavelength, have been locked independently to the P(13) vibrational–rotational line of an acetylene molecule. A long-term frequency stability over a 4-h period of better than 1.5 MHz and a short-term laser linewidth narrower than 50 kHz have been obtained by measurement of the beat note between the two lasers.