Cryogenic near-field microscope working at LN temperature

We have constructed a versatile low temperature scanning near-field optical microscope with the capability of near- field spectroscopy, operating at liquid nitrogen (LN) temperature. The compact low temperature scanning head was built on one piece of Marco with a unique linear nano-motor as the coarse approach. A tuning fork mechanism was adopted to detect and regulate the fiber tip-sample separation. The x-y scan can be performed either by the single tube scanner on triple tube scanner, depending on the application. A double shield dewar was used where the outer chamber was filled with LN. The core chamber was evacuated before cooling and then filled with cooled nitrogen gas, hence the working temperature can be controlled at around 80 K. A special designed coaxial double lens was used to introduce the illumination beam through a 200-micron fiber; the detected optical signal was transmitted via a fiber tip to a PMT or an APD. The performance test shows the stability of the new design. The resolution of shear force imaging and optical image of standard sample are shown.

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