Method for a deflection-type refractometer measuring the fringe shift by using linear Fresnel zone plates.

Area of Science:

• Optics and Photonics
• Metrology and Measurement Science

Background:

• Conventional differential refractometers face limitations in measurement range, resolution, zero balancing, and monitoring analysis.
• Addressing these limitations is crucial for advancing refractive index measurement techniques.

Purpose of the Study:

• To design and evaluate a novel deflection-type refractometer.
• To overcome the limitations of conventional differential refractometers using Fresnel diffraction patterns.

Main Methods:

• The refractometer employs a coherent light source, a linear Fresnel zone plate, a measuring cell, and an image capture device.
• Fringe deflection in the Fresnel diffraction pattern is measured to determine refractive index differences.
• Distance measurements with nanometer accuracy are achieved using local frequency and fringe shift methods.

Main Results:

• The developed refractometer demonstrates a highly extended measurement range of at least ±0.4 RIU.
• A precision of the order of 2×10^-4 RIU was achieved.
• The technique's uncertainty is limited by the CCD camera's pixel position detection accuracy.

Conclusions:

• The deflection-type refractometer based on Fresnel diffraction offers significant improvements over conventional methods.
• This design provides an extended measurement range and high precision for refractive index analysis.
• The study validates the feasibility of using diffraction pattern analysis for advanced refractometry.