LiDAR Evaluation System: Measurement of Transmittance/Reflectance of Optical Materials

Importance of the Topic

LiDAR systems rely on optical materials for accurate distance and angle measurement. The transmittance and reflectance characteristics of sensor covers and optical components directly influence the performance of automotive, airborne, and satellite-based ranging technologies. Evaluating these optical properties across relevant wavelength ranges and incident angles is essential to ensure reliable object detection under varying operational conditions.

Objectives and Study Overview

This application note presents an evaluation of two sample types—a glass substrate with an infrared reflective film and an optical filter—using UV-VIS-NIR spectrophotometry. The study aims to characterize their angular and wavelength-dependent transmittance and reflectance to inform LiDAR system design and material selection.

Used Instrumentation

• Shimadzu SolidSpec™-3700i UV-VIS-NIR spectrophotometer
• Variable angle absolute reflectance measurement unit
• Large sample compartment (compatible with UV-2600i and UV-3600i Plus)
• Large polarizer set for measurements at incident angles ≥20°

Methodology

Measurements were performed over a wavelength range of 300–2000 nm. For reflectance, s- and p-polarized light components were recorded at incident angles of 10°, 20°, 40°, and 60°. Baseline correction used an empty integrating sphere. Transmittance was assessed at 20°, 40°, and 60° incident angles for the optical filter sample. Slit widths were automatically switched between 8 nm for UV-visible and 20 nm for near-infrared regions, with a scan interval of 1 nm and low scan speed.

Key Results and Discussion

• Glass substrate with IR reflective film:
  • High reflectance (above 80%) in the 1000–2000 nm near-infrared region
  • Low reflectance (below 10%) in the 300–800 nm UV-visible range
  • Minimal variation in reflectance across incident angles, indicating low angular dependence
  • Negligible differences between s- and p-polarized measurements, suggesting low polarization sensitivity
• Optical filter:
  • No transmission in the 350–500 nm visible range
  • Transmittance exhibited significant changes with increasing incident angle, demonstrating high angular dependence

Benefits and Practical Applications

• Provides critical data on material optical performance for LiDAR sensor covers and internal components
• Supports material selection and design optimization to maintain signal integrity across relevant wavelengths and angles
• Enables identification of low-polarization materials to ensure consistent LiDAR readings

Future Trends and Potential Applications

• Integration of advanced spectrophotometric techniques to cover extended wavelength ranges (e.g., SWIR and MWIR)
• Development of in situ angular-resolved measurements for real-time quality control in manufacturing
• Exploration of novel coating materials with bespoke angular and spectral responses for next-generation LiDAR systems

Conclusion

This study demonstrates the capability of UV-VIS-NIR spectrophotometry combined with variable angle reflectance measurement to characterize optical materials used in LiDAR systems. The distinct spectral and angular profiles of the samples underscore the importance of comprehensive optical evaluation for material selection and system performance assurance.

Reference

• No references provided in the source document.