Precise wavelength calibration in continuous-wave cavity ringdown spectroscopy based on the HITRAN database.

We describe the wavelength calibration method of a narrowband laser diode in continuous-wave (CW) cavity ringdown spectroscopy (CRDS). The method uses known spectral lines as wavelength markers to calibrate and refine the wavelength-current relation of laser diodes, and their spectral positions are taken directly from the HITRAN 2004 database. We built a compact CW CRDS apparatus with a 1.517 microm (approximately 6594 cm-1) distributed feedback (DFB) laser diode as the light source and a 25 cm long glass ceramic as the cavity in which to demonstrate the method. A wavelength precision of approximately 0.8 x 10(-3) cm-1 was obtained by comparing the HITRAN 2004 database, which was approximately four times more precise than that of the conventional method.