Movable fiber probe for gas-phase laser-induced breakdown spectroscopy

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Optical Engineering

Background:

• Laser-induced breakdown spectroscopy (LIBS) is a powerful analytical technique.
• Fully fiber-coupled LIBS systems are desirable for remote sensing applications.
• Understanding the impact of fiber optic components on LIBS plasma is crucial for system optimization.

Purpose of the Study:

• To evaluate a movable, fiber-coupled probe for gas-phase LIBS.
• To investigate the effect of delivery fiber curvature on plasma characteristics and LIBS spectra.
• To assess the feasibility of remote, fully fiber-coupled gas-phase LIBS measurements.

Main Methods:

• A movable probe was designed to fiber-couple beam delivery and signal collection for gas-phase LIBS.
• LIBS measurements were performed on methane-air mixtures with varying equivalence ratios using straight and curved delivery fibers.
• Spectroscopic analysis of LIBS data, including hydrogen emission line ratios, was conducted.

Main Results:

• Decreasing fiber radius of curvature reduced transmission efficiency and spark formation probability.
• Minimal differences in LIBS measurements were observed between straight and curved fibers when output energy and beam spot size were maintained.
• Using the Balmer series H(alpha)/H(beta) ratio significantly reduced data scatter and improved linearity.
• A linear variation of the H/N elemental ratio with equivalence ratio was confirmed.

Conclusions:

• A flexible, fully fiber-coupled probe is feasible for remote gas-phase LIBS analysis.
• Optimized fiber coupling and specific spectral line ratios enhance measurement accuracy and reliability.
• This approach facilitates remote monitoring of fuel-air ratios in various applications.