System spectrum conversion from white light interferogram.

Risto Montonen,Peter Lehmann,Ivan Kassamakov,Anton Nolvi,Stanislav Tereschenko,Peter Kühnhold,Edward Hæggström

doi:10.1364/oe.25.012090

Risto Montonen, Peter Lehmann + Show 5 more

Open Access

https://doi.org/10.1364/oe.25.012090

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Journal: Optics Express	Publication Date: May 15, 2017
Citations: 1	License type: cc-by

Affiliation: University of Helsinki, University of Kassel

Abstract

Capability to simulate the coherence function is important when tuning an interference microscope in an effort to reduce sidelobes in interference signals. The coherence function cannot directly be derived from the light source spectrum since the microscope's effective spectrum is affected by e.g. spatial coherence effects. We show this by comparing the true system spectrum measured using a spectrometer against the effective system spectrum obtained by Fourier analysis of the interference data. The results show that a modulation function that describes the scattering-induced spatial coherence dampening in the system is needed to correct the observed difference between these two spectra. The validity of this modulation function is further verified by quantifying the arithmetic mean roughness of two specified roughness standards. By providing a spectral transfer function for scattering, our method can simulate a sample specific coherence function, and thus shows promise to increase the quality of interference microscope images.

Highlights

Scanning white light interferometry (SWLI) allows topographic characterization of materials with nanometer axial resolution and lateral resolution beyond the diffraction limit [1]
The results show that a modulation function that describes the scattering-induced spatial coherence dampening in the system is needed to correct the observed difference between these two spectra
SWLI imaging is done in Michelson, Mirau, or Linnik configuration where the sample is illuminated by a broad band light source and where interferograms are acquired by moving the sample by a piezoelectric actuator [2]

Summary

Introduction

Scanning white light interferometry (SWLI) allows topographic characterization of materials with nanometer axial resolution and lateral resolution beyond the diffraction limit [1]. A hybrid white light source constructed from several LEDs with different central wavelengths can reduce these sidelobes [3,5,6]. In this approach the LED currents are tuned individually to tailor a hybrid light spectrum that produces nearly a sidelobe-free coherence function. The coherence function [2] cannot be directly simulated from the hybrid light spectrum since the coherence function is affected by the imaging system’s transfer function. This transfer function comprises the spectral responsivity of the imaging components and the spatial coherence effects in the system [7]

Methods

Results

Discussion

Conclusion