Immersion white light scanning interferometry using elastic polymer path length compensation

Abstract

Improvements have been made to a commercial Linnik microscope in order to perform measurements in water for studying structures of transparent and non-transparent samples. One of the main goals of the present work is to study pollutants in colloidal layers immersed in liquid. The second reason to work in liquid is to increase the lateral resolution. The challenges to overcome include achieving stability in the complex Linnik design as well as the difficulty of balancing the optical distance of the two arms of the interferometer to obtain the interference fringes. The main problem is the path length compensation in the mirror arm which needs a complex mechanical design to allow a high enough number of degrees of freedom for to correct alignment of the optical elements. In our system, the reference mirror arm is mounted horizontally, making liquid immersion tricky. In this work, we have investigated alternative solutions based on non-liquid elastic polymers placed between the end of the objective and the reference mirror using sodium polyacrylate (SPA) beads and PDMS (polydimethylsiloxane) slabs, with a refractive index very close to that of water. The results of the performance tests of the modified system are presented and demonstrated. The new design provides a workable system that is ready for the future study of colloidal and other samples directly in water.

Characterization of Functional Materials Using Coherence Scanning Interferometry and Environmental Chambers

“…Results on etched squares in Si (6 μm wide, 2.5 um deep) measured with a ×20 water immersion Linnik system (NA = 0.5, λ eff = 450 nm, working distance of 3.5 mm) and an aggregate layer of 1 g/L alumina measured with a ×40 water immersion Linnik system (NA = 0.8, λ eff = 450 nm). (a) & (d) height images, (c) & (f) line profiles from (a) & (d), and (b) & (e) 3D images . Reproduced with permission from H. Mukhtar, P. Montgomery, F. Anstotz, R. Barillon, A. Rubin Immersion white light scanning interferometry using elastic polymer path length compensation.…”

“…A water-based compensator, sodium polyacrilate (SPA), was used in the reference beam arm due to the difficulty of using liquid water in the horizontal position of the reference arm. 9 SPA was chosen because of its specific characteristics of being a nonliquid elastic polymer and the stability in its form at a maximum temperature of 25 °C. The refractive index of SPA is close to that of water, with a value of 1.335 as measured by an Abbe refractometer.…”

“…The second one uses the automatic control of the deposition of microdroplets to measure the drying properties of liquid polymers. The final one uses an immersion system for studying changes in colloidal layers immersed in water in the presence of heavy metals with an application in the study of pollution of the environment …”

“…The final one uses an immersion system for studying changes in colloidal layers immersed in water in the presence of heavy metals with an application in the study of pollution of the environment. 9 …”

Lateral resolution enhanced interference microscopy using virtual annular apertures

“…In contrast, in interference microscopy resolution enhancement techniques are rarely applied till now. Nevertheless, techniques such as microsphere-assistance or immersion systems known from conventional microscopic imaging are being used in interference microscopy too [4][5][6][7][8][9]. However, due to the complex composition of signals additional options for resolution enhancement exist in interference microscopy.…”