Wide-Spectrum Microscope with a Long Working Distance Aspherical Objective Based on Obscuration Constraint.

Weibo Wang,Jian Liu,Chao Wang,Jiubin Tan

doi:10.3390/s16111886

Weibo Wang, Jian Liu + Show 2 more

Open Access

https://doi.org/10.3390/s16111886

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Abstract

We present an approach for an initial configuration design based on obscuration constraint and on-axis Taylor series expansion to realize the design of long working distance microscope (numerical aperture (NA) = 0.13 and working distance (WD) = 525 mm) with a low obscuration aspherical Schwarzschild objective in wide-spectrum imaging (λ = 400–900 nm). Experiments of the testing on the resolution target and inspection on United States Air Force (USAF) resolution chart and a line charge-coupled device (CCD) (pixel size of 14 μm × 56 μm) with different wavelength light sources (λ = 480 nm, 550 nm, 660 nm, 850 nm) were implemented to verify the validity of the proposed method.

Highlights

The typical working distance (WD) of an objective depends on the numerical aperture (NA) and ranges from tens or hundreds of micrometers to approximately 30 mm
We present an approach for the the initial initialconfiguration configuration design of an aspherical
The primary and secondary mirrors are denoted by polar coordinates (ρ, θ) and (r, u) with origin points at O and I, respectively

Summary

Introduction

The typical working distance (WD) of an objective depends on the numerical aperture (NA) and ranges from tens or hundreds of micrometers to approximately 30 mm. The design of an objective with a working distance of hundreds of millimeters and a relatively larger NA is quite difficult, because the aberration will grow proportionally with respect to the size of pupil apertures. Such an optical microscope objective is somewhat irreplaceable when high lateral imaging resolution and sensitive axial position detection are concurrently needed. When measuring over large areas using subaperture stitching, such as imaging a multiwindow wide-spectrum detector, a long working distance to satisfy mechanical clearance requirements and relatively high NA objectives to inspect structures with suitable lateral resolution are needed.

Methods

Modulation

Experiment

Conclusions