Quantitative thickness mapping of a freestanding thin liquid film by fusing digital holography and white light interferometry

Abstract

Quantitative measurement for thin-film thickness has been a widely studied issue, and, visualizing and characterizing for full-field thin-film evolution can provide effective data support for membrane science, polymer chemistry, biomaterials, applied Chemistry, etc. Interferometry was considered the most useful tool to measure film thickness in past decades. However, there were deficiencies in imaging speed and field of view for conventical interferometric measurement. In this paper, we proposed a fusion method to achieve full-field and quantitative analysis of the thin liquid film at nanoscale by using Digital Holography (DH) and White Light Interferometry (WLI) simultaneously. Compared with our previous holographic studies on thin film measurement, this new method can overcome the shortcomings of the holographic method related to registration and reconstruction. In addition, these parallel experiments can also provide a reference when we have to make a choice between DH and WLI. For the thickness reconstruction process, the entire life cycle registration is no longer required to obtain the thickness information. Moreover, the region where the thin film thickness is less than half the wavelength is now measurable. Thanks to the fusion processing, the film thickness calibration can be obtained without any background subtraction, in the meantime, the background hologram becomes not essential in the holographic recording process.