Nanometer-precision surface metrology of millimeter-size stepped objects using full-cascade-linked synthetic-wavelength digital holography using a line-by-line full-mode-extracted optical frequency comb

TL;DR

This paper introduces a novel full-cascade-linked synthetic-wavelength digital holography technique that achieves nanometer-precision surface measurements of millimeter-sized stepped objects by utilizing a broad range of synthetic wavelengths derived from an optical frequency comb.

Contribution

It presents a new method combining full-cascade-linked synthetic wavelengths with digital holography for high-precision surface metrology of large stepped objects.

Findings

Achieved 6.1 nm axial uncertainty in surface measurement.

Covered an axial range up to 14.85 mm.

Utilized 300 modes of optical frequency comb for synthetic wavelength generation.

Abstract

Digital holography (DH) is a powerful tool for surface profilometry of objects with sub-wavelength precision. In this article, we demonstrate full-cascade-linked synthetic-wavelength DH (FCL-SW-DH) for nanometer-precision surface metrology of millimeter-size stepped objects. 300 modes of optical frequency comb (OFC) with different wavelengths are sequentially extracted at a step of mode spacing from a 10GHz-spacing, 3.72THz-spanning electro-optic modulator OFC (EOM-OFC). The resulting 299 synthetic wavelengths and a single optical wavelength are used to generate a fine-step wide-range cascade link covering within a wavelength range of 1.54 um to 29.7 mm. We determine the 0.1000mm-stepped surface with axial uncertainty of 6.1 nm within the maximum axial range of 14.85 mm.