[NT-MDT: Molecular Devices and Tools for NanoTechnology]

SNOM probes

SNOM head with non optical tip-sample distance control

NT is supplying the optical fiber with the following characteristics:

Type - single mode optical fiber coated by aluminum
Cut of frequency of radiation at the wave length of 500nm
Wave length ~ 0.5um
Optical fiber tip aperture ~ 50-100nm
Optical fiber diameter - 100um
R curv - 50-100nm
Angle of fiber - 7-13 degrees
Maximum optical input power - 5-6 mW
Maximum optical output power - 5 uW
optical efficiency 1-3·10^-3 for 100 nm aperture
optical efficiency 1-3·10^-4 for 30 nm aperture
The probes are prepared by chemical etching method. This method gives the optical efficiency 10^-2 - 10^-4 times better than those obtained by mechanical pulling.

The advantages of SNOM probes produced by the method of
chemical etching

1. Core of optical fiber reaches probe's aperture it leads to:
a) more effective transformation of the HE11 mode of one-mode optical fiber to the TE11 mode of cylindrical metal waveguide. Into the mechanically stretched fiber core stops to contain radiation into the center of the fiber and it spreads in extrasized waveguide that leads to the running in the highest modes. In probe based on chemically etched fiber this disadvantage is absent. It provides increasing of the transmission coefficient of optical radiation through SNOM probe.

b) better localization of optical radiation in the area of probe narrowing and, consequently, in decreasing of ohmic loss on the plates of metal waveguide, i.e. in lower heating. It's experimentally got that it is possible to use higher-intensity radiation in such probe than in the probe based on mechanically stretched fiber.

2. The probe is faster because extraneous mechanical stress, arisen during stretching is absent.