Abstract
In this work, we present an alternative optical method to determine the probe-sample separation distance in a scanning near-field optical microscope. The experimental method is based in a Lloyd’s mirror interferometer and offers a measurement precision deviation of ∼100 nm using digital image processing and numerical analysis. The technique can also be strategically combined with the characterization of piezoelectric actuators and stability evaluation of the optical system. It also opens the possibility for the development of an automatic approximation control system valid for probe-sample distances from 5 to 500 μm.
Highlights
Optical metrology has demonstrated over the last decades its efficacy in measuring various physical properties with high precision, contactless and ultra-fast speeds.[1,2] accurate distance measurements can be achieved with very high precision by using interferometric techniques.[3]
The first one corresponds to the characterization of the elongation of a piezoelectric actuator used for approximation in the Scanning near-field optical microscopy (SNOM)
Piezoelectric actuator characterization The characterization of a piezoelectric actuator is helpful if the parameters are unknown a priori, e.g. when the detailed characteristics of a piezo are not available from the manufacturer, or if the piezo is already discontinued from the market
Summary
Optical metrology has demonstrated over the last decades its efficacy in measuring various physical properties with high precision, contactless and ultra-fast speeds.[1,2] accurate distance measurements can be achieved with very high precision by using interferometric techniques.[3]. A collision between the optical fiber and the sample usually destroys the conical shape of the tip, making it useless for SNOM measurements, and requiring a tip replacement Bearing these reasons in mind, we propose an alternative optical method able to determine the probe-sample separation in SNOMs without adding new elements into the setup, i.e. using the same optical elements that already constitute the microscope. The developed approach provides a visual and safe alternative to approximate the optical fiber tip to ∼ 5 μm above the sample in a fast and controllable way, with a measurement precision deviation of ∼100 nm This technique opens the possibility for the development of an automatic approximation control system which may notify the user the probe-sample separation in real time, for distances between 5 and 500 μm; a feature that is not available in current SNOM systems. The interference pattern can be used as a quality indicator of the probe
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