Diffraction effects in length measurements by laser interferometry

TL;DR

This paper investigates how diffraction affects high-precision laser interferometry measurements, revealing wavelength variations caused by wavefront evolution and perturbations, which are crucial for accurate dimensional measurements.

Contribution

It demonstrates the origin of diffraction-induced wavelength variations in laser interferometry using combined X-ray and optical interferometers, highlighting wavefront evolution effects.

Findings

Wavelength variations up to 10^{-8}λ₀ observed across the beam.

Diffraction effects stem from wavefront evolution under paraxial propagation.

Wavefront and intensity-profile perturbations influence measurement accuracy.

Abstract

High-accuracy dimensional measurements by laser interferometers require corrections because of diffraction, which makes the effective fringe-period different from the wavelength of a plane (or spherical) wave $\lambda_0$. By using a combined X-ray and optical interferometer as a tool to investigate diffraction across a laser beam, we observed wavelength variations as large as $10^{-8}\lambda_0$. We show that they originate from the wavefront evolution under paraxial propagation in the presence of wavefront- and intensity-profile perturbations.