Improving Spectral Quality Using Beam Collimation Control

Importance of the Topic

Controlling the beam collimation in UV-Vis-NIR spectroscopy is essential for obtaining high-quality spectral data when characterizing optical components such as filters, beam splitters, and coatings. Precise adjustment of the incident beam angle enhances measurement accuracy, reproducibility, and reliability, particularly for applications requiring steep filter edges or strict quality control.

Objectives and Study Overview

This work examines how varying the half cone angle of horizontal apertures in the Agilent Cary Universal Measurement Accessory (UMA) on the Cary 7000 spectrophotometer influences the edge steepness measurement of a high-quality beam splitter. The goal is to identify optimal beam collimation settings for improved data quality in transmission mode.

Applied Methodology

A Chroma Technology beam splitter was measured in transmission over the 780–800 nm region. The UMA provided interchangeable horizontal apertures with half cone angles from 0.25° to 3.0°. All spectra were recorded with a constant spectral bandwidth of 0.5 nm. Edge steepness was defined as the spectral width between two transmission points on the filter slope.

Used Instrumentation

Agilent Cary 7000 UV-Vis-NIR universal measurement spectrophotometer equipped with the Cary Universal Measurement Accessory, controlled by Cary WinUV software. The UMA offers three mounting positions: one for horizontal collimation control and two for vertical control. Horizontal aperture half cone angles and their corresponding f-numbers are: 0.25° (f/35), 0.50° (f/18), 0.75° (f/12), 1.0° (f/9), 2.0° (f/4), and 3.0° (f/3). Vertical apertures are used to adjust illuminated patch size.

Main Results and Discussion

Reducing the horizontal aperture half cone angle led to a sharper transition on the beam splitter edge. The smallest aperture (0.25°) produced the steepest spectral slope, indicating superior collimation and minimal angular spread. Larger apertures increased light throughput but degraded edge definition.

Benefits and Practical Applications

• Enhanced measurement precision and accuracy for edge steepness and other optical parameters
• Higher sample throughput and reduced analysis cost in QA/QC workflows
• Automated, unattended operation for comprehensive manufacturing testing
• Capability to measure absolute specular reflectance, transmission, and scattering over variable angles and polarizations

Future Trends and Potential Applications

Advances may include integration of dynamic aperture control with real-time feedback, AI-driven optimization of collimation settings, and miniaturized beam conditioning modules for portable spectrometers. Applications could expand to in situ monitoring of coatings, nanophotonic devices, and solar cell materials requiring precise optical characterization.

Conclusion

Precise control of beam collimation using the UMA on the Agilent Cary 7000 significantly improves edge steepness measurements of optical filters. The 0.25° horizontal aperture (f/35) delivered the highest spectral quality, demonstrating the value of high f-number optics for critical optics characterization and QA/QC processes.

References

Alwan W, Burt T. Improving Spectral Quality Using Beam Collimation Control. Agilent Technologies Technical Overview 2024.