2500-Channel single-shot areal profilometer using hyperspectral interferometry with a pinhole array

Tobias V Reichold,Pablo D Ruiz,Jonathan M Huntley

doi:10.1016/j.optlaseng.2019.05.015

Tobias V Reichold, Pablo D Ruiz + Show 1 more

Open Access

https://doi.org/10.1016/j.optlaseng.2019.05.015

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Journal: Optics and Lasers in Engineering	Publication Date: May 25, 2019
Citations: 9	License type: cc-by

Affiliation: Loughborough University

Abstract

Surface profilometry techniques such as coherent scanning interferometry or focus variation require long scan times and are thus vulnerable to environmental disturbance. Hyperspectral interferometry (HSI) overcomes the problem by recording all the spatial and spectral information necessary to reconstruct a 2D surface height map in a single shot. In this paper, we present a new HSI system that uses a pinhole array to provide the necessary gaps for the spectral information. It is capable of measuring 2500 independent points, twice the previous maximum number, with a maximum unambiguous depth range of ∼825 µm and a larger maximum surface tilt angle of 33.3 mrad. The use of phase information allows height to be measured to a precision of ∼6 nm, an order of magnitude improvement on previous HSI systems.

Highlights

A wide range of contact and non-contact techniques exist to measure absolute surface profiles and roughness
Optical surface profilers based on coherence scanning interferometry (CSI) or focus variation avoid some of the problems of contacting instruments, and as a result are finding widespread industrial application [4]
Provided the pinhole size is comparable to the spot size, the pinhole array (PHA)-Hyperspectral interferometry (HSI) shares many of the same design considerations as the microlens array (MLA)-HSI

Summary

Introduction

A wide range of contact and non-contact techniques exist to measure absolute surface profiles and roughness. Contact tools such as drag stylus profilers or atomic force microscopy can make measurements irrespective of material composition, are able to cope with modest surface discontinuities and provide axial resolutions down to a few picometers [1]. With scanning times per line as long as several minutes, measurements are vulnerable to environmental disturbances such as temperature and humidity changes or ambient vibrations [3]. Single shot measurement approaches are required to remove environmental sensitivities, such as the system proposed by Schwider and Zhou in which a broadband Fizeau interferometer and grating spectrometer were used to measure absolute 1D line profiles [6]

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