Pulse interaction induced systematic errors in dual comb spectroscopy.

Area of Science:

• Spectroscopy
• Nonlinear Optics
• Physical Chemistry

Background:

• Dual comb spectroscopy (DCS) is a powerful technique for molecular gas analysis.
• Systematic errors can compromise the accuracy of DCS measurements.
• Common fiber propagation of dual comb pulses is a potential source of error.

Purpose of the Study:

• To investigate the origin and impact of systematic errors in DCS caused by common fiber propagation.
• To identify the physical mechanisms responsible for these spectral distortions.
• To quantify the magnitude of errors under varying experimental conditions.

Main Methods:

• Simulations of dual comb interferograms using a generalized nonlinear Schrödinger equation.
• Analysis of spectral distortions, line shapes, and retrieved concentrations.
• Modeling of self-phase modulation and cross-phase modulation effects.

Main Results:

• Two primary error mechanisms identified: self-phase modulation (SPM) and cross-phase modulation (XPM).
• SPM alters spectral content, affecting baseline and absorption features, leading to line intensity errors.
• XPM modifies inter-pulse delay, causing sampling errors and asymmetric spectral line distortions.
• Simulations accurately replicate experimental error magnitudes (0.1% at 10 mW/10 m, increasing with power and fiber length).

Conclusions:

• Common fiber propagation in DCS introduces significant systematic errors.
• SPM and XPM are key contributors to spectral line shape and intensity inaccuracies.
• Understanding these errors is crucial for accurate molecular gas concentration retrieval using DCS.