Abstract
Scattering-type scanning near-field optical microscopy has allowed for investigation of light-matter interaction of a large variety of samples with excellent spatial resolution. Light incident on a metallic probe experiences an amplitude and phase change on scattering, which is dependent on optical sample properties. We implement phase-shifting interferometry to extract amplitude and phase information from an interferometric near-field scattering system, and compare recorded optical images with theoretical predictions. The results demonstrate our ability to measure, with nanoscale resolution, amplitude and phase distributions of optical fields on sample surfaces. The here-introduced phase-shifting method is considerably simpler than heterodyne methods and less sensitive to errors than the two-step homodyne method.
Highlights
Scattering-type scanning near-field optical microscopy combines the resolution of atomic force microscopy with the chemical sensitivity of optical spectroscopy
It has been shown that infomation about the local optical field can be used to determine the distribution of a sample’s complex-valued dielectric function with spatial resolution of a few tens of nanometers[1, 2, 3]
We present an alternative method of amplitude and phase recovery for Scattering-type scanning near-field optical microscopy (sSNOM), drawing from the field of phase-shifting interferometry (PSI), which has been used for several decades in optical testing, and which has the potential to mitigate these issues[17]
Summary
Scattering-type scanning near-field optical microscopy (sSNOM) combines the resolution of atomic force microscopy with the chemical sensitivity of optical spectroscopy. One method of background suppression involves the modulation of the tip-sample separation, which is usually accomplished by vibrating an AFM cantilever at its resonance This creates an optical modulation of the collected light, which is demodulated at higher harmonics of the tip vibration frequency[12, 13, 14, 3]. The latter makes it possible to simultaneously recover amplitude and phase of the scattered light[16, 15] Another method for recovery of this information is pseudoheterodyning, in which a small modulation of the reference beam is introduced, along with demodulation techniques similar to heterodyning[5]. Extensive work has already been published on suppression of common interferometric errors, which may plausibly be applied to SNOM applications
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