Operating characteristics of a tunable diode laser absorption spectrometer using short-external-cavity and DFB laser diodes.

Second harmonic detection at audio frequencies of isolated absorption lines with a laser absorption spectrometer employing AlGaAs and InGaAsP diode lasers, short external cavity (SXC) AlGaAs and InGaAsP diode lasers, and InGaAsP distributed feedback (DFB) diode lasers was investigated and compared. Noise levels equivalent to line center absorptions of ~3 x 10(-6) were achieved with each source. Single mode tuning ranges of 20-50 cm(-1) were obtained with both the SXC and DFB sources. The contamination of absorption spectra by suppressed laser side modes was identified and investigated as it relates to the identification of weak lines in the presence of strong lines.