Excitation Laser Selection in the AIRsight Infrared Raman Microscope ―An Evaluation of UV-Degraded Plastics―

Importance of the Topic

Effective analysis of UV-degraded plastics is critical for quality control, material recycling, and environmental monitoring. Fluorescence interference often limits Raman spectroscopy applications, so having selectable excitation lasers and photo-bleaching options enhances analytical reliability.

Objectives and Study Overview

This study evaluates the performance of 532 nm and 785 nm excitation lasers in the AIRsight infrared Raman microscope when measuring UV-exposed plastics (polyamide (PA), polyethylene (PE), and ABS). The aim is to compare fluorescence suppression, spectral clarity, and the impact of photo-bleaching on signal quality.

Methodology and Used Instrumentation

The following measurement conditions were applied:

• Instrument: IRTracer-100 with AIRsight infrared Raman microscope
• Excitation wavelengths: 532 nm and 785 nm lasers
• Accumulations: 10; Exposure time: 5 s per scan
• Objective lens: 50×; Detector: CCD
• Photo-bleaching times up to 180 s for fluorescence reduction

Additional fluorescence characterization used a Shimadzu RF-6000 spectrofluorometer under dual excitation (532 nm, 380 nm).

Main Results and Discussion

• For unirradiated PA, 532 nm excitation produced a raised baseline due to fluorescence, while 785 nm yielded flat baselines and clear Raman peaks.
• UV-irradiated PA spectra showed similar trends: strong fluorescence at 532 nm obscured signals, but 785 nm retained peak resolution.
• PE measurements exhibited minimal fluorescence at both wavelengths when unirradiated; after UV exposure, both lasers showed baseline elevation, which was effectively reduced by 180 s photo-bleaching.
• ABS samples emitted strong fluorescence under 532 nm regardless of UV treatment; 785 nm minimized fluorescence influence. Spectrofluorometry confirmed high-intensity emission at 532 nm excitation and a red-shifted peak after UV degradation.

Benefits and Practical Applications of the Method

• Dual-laser configuration enables tailored excitation to sample fluorescence properties.
• 785 nm excitation reduces baseline interference and improves detection of weak Raman signals.
• Photo-bleaching provides an additional tool to control fluorescence without changing hardware.
• The approach supports polymer degradation studies, quality assurance in manufacturing, and research on material aging.

Future Trends and Possibilities for Use

• Integration of time-resolved Raman to further separate Raman scattering from fluorescence.
• Development of adaptive laser selection driven by real-time spectral feedback and machine learning.
• Expansion to additional wavelength options (e.g., 1064 nm) for even lower fluorescence backgrounds.
• Field-portable Raman systems combining multi-laser modules for on-site polymer and environmental monitoring.

Conclusion

The dual-laser AIRsight infrared Raman microscope effectively addresses fluorescence challenges in analyzing UV-degraded plastics. Using a 785 nm laser and optional photo-bleaching significantly improves spectral clarity across PA, PE, and ABS samples, offering a versatile tool for polymer research and industrial quality control.

References

1. Sobue K. Excitation Laser Selection in the AIRsight Infrared Raman Microscope. Shimadzu Application News 01-00586-EN, First Edition: Sep. 2023.
2. Shimadzu Application News 01-00001. Evaluation of UV-Degraded Plastics.