Improving Spectral Quality Using Beam Collimation Control

Importance of the Topic

Precise control of beam collimation is critical in UV-Vis-NIR spectroscopy when characterizing optical components such as edge filters and beam splitters. Variations in the angle of incidence (AOI) can distort spectral features, making it difficult to assess filter performance. By optimizing beam collimation, laboratories can achieve higher spectral accuracy, sharper filter edges and more reliable quality control data.

Objectives and Study Overview

This study evaluated how different horizontal apertures in the Agilent Cary Universal Measurement Accessory (UMA) affect spectral edge steepness for a high-quality beam splitter. The goal was to identify the aperture setting that yields the sharpest transition region between 780 and 800 nm, thereby demonstrating improved data quality through beam collimation control.

Methodology and Instrumentation

The Agilent Cary 7000 Universal Measurement Spectrophotometer (UMS) equipped with the UMA was operated in transmission mode at a fixed spectral bandwidth of 0.5 nm. Horizontal apertures with half-cone angles of 0.25°, 0.50°, 0.75°, 1.0°, 2.0° and 3.0° (corresponding to f-numbers f/35 to f/3) were tested. Vertical apertures were held constant to maintain a uniform beam height on the sample.

• Cary 7000 UMS
• Cary Universal Measurement Accessory (UMA)
• Agilent Cary WinUV software
• Horizontal apertures: 0.25°, 0.50°, 0.75°, 1.0°, 2.0°, 3.0°

Main Results and Discussion

As the horizontal aperture half-cone angle decreased, the measured edge steepness became significantly sharper. The 0.25° aperture (f/35) produced the steepest transition, improving the filter’s qualification by clearly defining the transmission cutoff. Wider apertures (e.g., 3.0°, f/3) yielded broader transition regions, reducing the ability to discern fine spectral features.

Benefits and Practical Applications

Controlling beam collimation with high f-number apertures offers:

• Improved measurement precision and accuracy for optical filters
• Faster QA/QC throughput due to reduced re-measurements
• Lower risk of shipping out-of-spec products in manufacturing
• Automated unattended analyses of reflectance, transmission and scattering at various AOI and polarizations

Future Trends and Opportunities

Further developments may include dynamic aperture adjustment during scans, integration with advanced polarimetric modules and expanded solid-sample accessories. These enhancements can enable real-time collimation optimization for advanced coatings, thin films and emerging photonic materials.

Conclusion

Precise beam collimation control in the Agilent Cary 7000 UMS with UMA significantly improves spectral edge steepness measurements. The 0.25° horizontal aperture delivers the highest data quality, making it the preferred setting for critical filter characterization and rigorous QA/QC workflows.

Reference

Alwan, W. and Burt, T. "Improving Spectral Quality Using Beam Collimation Control," Agilent Technologies, Inc., Application Note 5994-7224EN, May 2024.