Dresden 2017 – wissenschaftliches Programm
HL 43.1: Vortrag
Dienstag, 21. März 2017, 14:00–14:15, TRE Ma
Scanning near-field optical microscopy with inline-homodyne detection — •Jens Brauer, Jinxin Zhan, Petra Groß, and Christoph Lienau — Carl von Ossietzky University, Oldenburg, Germany
Apertureless near-field optical microscopy is a good choice when it comes to optically investigating nanostructures with a size of only a few nanometer and is nowadays widely used in different geometries.
For most of the setups there remains the challenge of distinguishing the desired near-field signal from the very large optical background. To overcome this problem the tip-sample distance often is modulated at some tens of kilohertz and the detection signal is demodulated at higher harmonics. As Knoll & Keilmann  have shown theoretically the ratio of near-field to optical background improves with increasing demodulation frequency. However, also the signal amplitude at higher harmonics is decreasing dramatically. Therefore the use of interferometers, either in a homodyne or heterodyne detection scheme, is often used to amplify the near-field signal .
As a downside the contrast in the SNOM images critically depends on the stability of the interferometer. Here we present how to disentangle near field from background radiation in the 1st to 4th harmonic signal by measuring approach curves in an inherently stable in-line homodyne detection scheme and we give an outlook to ongoing spectroscopically resolved SNOM measurements.
 B. Knoll & F.Keilmann, Optics Communications, 182(4) (2000)
 Ocelic et al.,Applied Physics Letters, 89(10) (2006)