Optical Design of a Large-Angle Spectral Confocal Sensor for Liquid Surface Tension Measurement

Area of Science:

• Optics and Photonics
• Surface Science
• Metrology

Background:

• Surface tension measurement relies on accurate droplet profile determination via the Young-Laplace equation.
• Spectral confocal sensors offer high-precision, non-contact droplet surface profiling.
• Existing sensors have limitations in angular measurement, affecting accuracy at large inclinations.

Purpose of the Study:

• To design a large-angle spectral confocal sensor for enhanced droplet surface tension measurement.
• To overcome the angular measurement limitations of current spectral confocal sensors.
• To improve the accuracy of surface tension measurements for droplets with varied surface profiles.

Main Methods:

• Theoretical analysis of linear axial dispersion in dispersive objective lenses.
• Design of a front-end dispersive objective lens using positive and negative lenses.
• Development of an astigmatism-free Czerny-Turner spectrometer for the back-end.
• Optical simulation, optimization, and tolerance analysis using Zemax.

Main Results:

• The designed system achieves 1.5 mm axial dispersion over 430-700 nm.
• Maximum allowable object angle is ±40° with a theoretical resolution of 3 μm.
• High measurement accuracy is maintained across a wide angular range.

Conclusions:

• The proposed large-angle spectral confocal sensor significantly enhances measurement accuracy for droplet profiles at large inclination angles.
• This advancement facilitates precise surface tension measurements in challenging conditions.
• The sensor design overcomes limitations of previous systems, broadening applications in surface science and metrology.