One-dimensional rainbow technique using Fourier domain filtering

Area of Science:

• Optical Physics
• Fluid Dynamics
• Analytical Chemistry

Background:

• Rainbow refractometry measures droplet size and refractive index simultaneously.
• Accurate refractive index measurement relies on precise angular calibration of the rainbow scattering angle.

Purpose of the Study:

• To propose a novel optical design for one-dimensional rainbow refractometry.
• To enhance the accuracy of angular calibration for droplet analysis.
• To simultaneously measure the refractive index and size of n-heptane droplets.

Main Methods:

• Implemented a one-dimensional spatial filter in the Fourier domain for optical design.
• Developed a simple calibration method to correlate CCD pixel data with scattering angle.
• Applied both standard and global one-dimensional rainbow techniques using the new design.

Main Results:

• The proposed optical design accurately determines the relationship between scattering angle and CCD pixels.
• The method successfully measures the refractive index and size of n-heptane droplets.
• Perpendicularly incident light selection aligns with classical rainbow refractometry inversion algorithms.

Conclusions:

• The novel optical design offers accurate angular calibration for rainbow refractometry.
• This technique provides a reliable method for simultaneous measurement of droplet size and refractive index.
• The approach is validated by successful application to n-heptane droplets.