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

Area of Science:

• Spectroscopy
• Laser Technology
• Optical Engineering

Background:

• Laser absorption spectrometry is a sensitive technique for detecting trace gases.
• Diode lasers offer tunable, narrow-linewidth light sources for absorption spectroscopy.
• Second harmonic detection enhances sensitivity by modulating the laser frequency.

Purpose of the Study:

• To compare the performance of different diode laser types for second harmonic detection of absorption lines.
• To evaluate noise levels and tuning ranges of various laser sources.
• To investigate spectral contamination from laser side modes.

Main Methods:

• Utilized AlGaAs and InGaAsP diode lasers, including short external cavity (SXC) and distributed feedback (DFB) configurations.
• Employed second harmonic detection at audio frequencies.
• Investigated noise levels and single-mode tuning ranges for each laser source.

Main Results:

• Achieved noise levels equivalent to line center absorptions of approximately 3 x 10(-6) with all tested laser sources.
• Obtained single-mode tuning ranges of 20-50 cm(-1) with both SXC and DFB laser sources.
• Identified and analyzed spectral contamination from suppressed laser side modes.

Conclusions:

• Various diode laser types demonstrate comparable sensitivity for absorption line detection.
• SXC and DFB lasers provide significant tuning ranges crucial for comprehensive spectral analysis.
• Understanding and mitigating laser side mode contamination is essential for accurate identification of weak absorption features.