Two-fiber spectroscopic probe with improved scattered light rejection.

Area of Science:

• Spectroscopy
• Optical Engineering
• Analytical Chemistry

Background:

• In situ spectroscopic measurements require specialized probes for efficient signal collection.
• Scattered excitation light can interfere with desired spectroscopic signals (fluorescence, phosphorescence, Raman).
• Existing angled fiber probes may suffer from back reflections and suboptimal light cone overlap.

Purpose of the Study:

• To modify an existing angled two-fiber probe design for enhanced in situ spectroscopic measurements.
• To improve the rejection of scattered excitation light.
• To maintain or improve the efficiency of collecting the desired spectroscopic signal.

Main Methods:

• Modified the probe axis to an off-normal configuration.
• Optimized the overlap of excitation and collection fiber light cones at the sample-window interface.
• Utilized sapphire windows for spectroscopic analysis.
• Conducted laser-induced fluorescence measurements on phenol solutions and sand samples.

Main Results:

• Achieved improved rejection of scattered excitation light.
• Maintained efficient collection of the desired spectroscopic signal.
• Observed up to a 90-fold improvement in the fluorescence/scattered light ratio.
• Demonstrated enhanced performance with phenol and sand samples.

Conclusions:

• The off-normal angled two-fiber probe design effectively minimizes back reflection.
• The modified probe design maximizes light cone overlap for superior signal collection.
• This improved probe design offers significant advantages for in situ spectroscopic analysis, particularly in reducing spectral interference.