Frequency-modulation spectroscopy provides ultrasensitive absorption measurements. The technique is especially adaptable to diode lasers, which can be modulated easily, and has been used extensively in the near-infrared and infrared spectral regions. The availability of blue diode lasers now means that the accessible wavelength region can be increased. We successfully demonstrate wavelength-modulation spectroscopy and two-tone frequency-modulation spectroscopy for the weak second resonance line of potassium at 404.8 nm and for the transition at 405.8 nm in lead, starting from the thermally populated 6p23P2 metastable level. Information on the modulation parameters is obtained with a fitting procedure. Experimental signal-to-noise ratios at different absorption levels are compared with theoretical signal-to-noise ratios and show good agreement. Detection sensitivities of 2 × 10-6 and 5 × 10-6 for wavelength and two-tone frequency-modulation spectroscopy, respectively, for a 120-Hz bandwidth are demonstrated.
© 2000 Optical Society of America
Original Manuscript: October 28, 1999
Revised Manuscript: April 21, 2000
Published: July 20, 2000
Ulf Gustafsson, Gabriel Somesfalean, Janis Alnis, and Sune Svanberg, "Frequency-modulation spectroscopy with blue diode lasers," Appl. Opt. 39, 3774-3780 (2000)