A new wavelength locking method for tunable diode lasers based on a photoacoustic (PA) detection unit is presented. A wavelength modulated laser is repeatedly tuned over an absorption line of a small molecule in the gaseous phase and the generated PA signal is recorded. In the phase variation curve of the recorded PA signal, there is a 180-deg phase reversal around the peak of the absorption line, and the corresponding inflection point is a characteristic wavelength feature to be used for wavelength locking. An automated algorithm has been developed, which has <2 s execution time if the optical absorption coefficient at the peak of the absorption line is at least 2 × 10 ¢5 cm¢1. With this algorithm, the wavelength of a near-infrared distributed feedback diode laser can be locked with an absolute accuracy of 60 fm (i.e., relative accuracy of 4 × 10¢8) or better even at atmospheric sample gas pressure. As there is no need to stabilize the gas pressure or temperature or the concentration of the light absorbing component and the PA detection unit can be easily integrated into various experimental setups, the proposed method has the potential to be applicable even under demanding industrial or field conditions.
- Distributed feedback diode laser
- Photoacoustic spectroscopy
- Wavelength locking
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics