Diode laser cavity ring down spectroscopy

We recently demonstrated how in cativy ring down spectroscopy (CRDS) a CW single frequency dye laser may be conveniently employed in place of the pulsed laser of standard CRDS. Here we extend this result to external cavity tunable diode lasers. Compact spectroscopic devices with extreme sensitivity (2 × 10⁻¹⁰/cm) become a reality. To demonstrate the instrumental resolution we obtained high quality NO₂ spectra in a supersonic slit jet, with a residual Doppler width of about 250 MHz.