We report on the wavelength tuning and spectral properties of distributed feedback (DFB) diode lasers operated with a plane external cavity (XC) mirror positioned as close as possible to the diode-laser front facet. These lasers generate single-frequency near IR radiation at wavelengths of 1392, 1580, 1602, and 1653 nm. A piezoelectric variation of the XC length provided continuous single-frequency tuning to as high as 19 GHz. A further benefit of XC DFB lasers is a residual amplitude modulation per gigahertz tuning of less than 10<sup>−3</sup>. The XC feedback also suppresses residual side-mode oscillations to less than 60 dB. The laser’s total intensity noise is close to the shot noise limit. The laser linewidth (measured in a beat note experiment) is less than 90 kHz within an acquisition time of 40 ms. The advantageous properties of XC DFB lasers for molecular spectroscopy are demonstrated by recording <i>R</i>(3) 2ν<sub>3</sub> overtone spectra of methane by single-scan single-pass absorption or frequency-modulation spectroscopy.
© 2001 Optical Society of America
Christian K. Laue, Ralf Knappe, Klaus-Jochen Boller, and Richard Wallenstein, "Wavelength Tuning and Spectral Properties of Distributed Feedback Diode Lasers with a Short External Optical Cavity," Appl. Opt. 40, 3051-3059 (2001)