Nonlinear spectroscopy of oxygen isotopes using an AlGaAs diode laser at 777 nm

An investigation of the transitions starting from the metastable (180-μs lifetime) 3s5S level, using an AlGaAs diode laser mounted in an extended cavity configuration, is reported. The very-low-intensity noise of the diode laser allowed the detection of oxygen in direct absorption using very low total pressures (down to 10 mtorr) and a short (approximately 2-cm) interaction length. The saturation dip could be observed with a good SNR by retroreflecting the laser beam back through the cell at a small angle. Derivative saturation spectra could be obtained introducing 10-kHz modulation on the cavity length by means of the piezoelectric transducer. The typical spectrum of an enriched sample is shown for the 5S2-5P3 fine structure component at 777.1 nm. Besides the individual resonances of 16O and 18O, the spectra show that the five hyperfine components of the lower level are fully resolved for 17O, allowing this structure to be determined on a state different from the ground state. This gives a preliminary value for the magnetic coupling constant of A = 74.3 (2) MHz.