ULTRANARROW (C2H2)-C-13 SATURATED-ABSORPTION LINES AT 1.5 MU-M

The saturation spectroscopy of molecular transitions at 1.5 mum is rep orted. We show that it is possible, with a low-power laser diode, to o btain 2-MHz-wide acetylene saturated-absorption lines, and we give wha t is to our knowledge the first experimental estimation of (C2H2)-C-13 -saturation intensity. To our knowledge, these lines are the narrowest reported 1.5-mum frequency references and should be suitable for high -quality 1.5-mum laser frequency standards.