Signal-to-noise ratio improvement of low-temperature passive near-field optical microscope using a tip-height modulation method

We have recently developed a low-temperature scattering-type scanning near-field optical microscope (s-SNOM). The system mainly contains a highly sensitive long-wavelength infrared confocal microscope and a crystal tuning fork-based atomic force microscope. In this work, a sample-height modulation is replaced by a tip-height modulation. The acquisition time is reduced from 10 s to 3 s after improving the signal-to-noise ratio of the near-field signal. We carry out the near-field detection on a self-Joule heated NiCr wire deposited on SiO
2
. The resource of the near-field signals has been analyzed as the thermally excited evanescent wave due to fluctuating electrons.