ThermoMicroscopes Aurora-2, User Manual

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Aurora-2 User’s Manual
C H A P T E R
Chapter 1
Theory of Operation
NSOM T
HEORY
Historically, the limiting factor in optical microscopy has been the diffraction limit of light.
Attempts to image features approximately the size of a wavelength of light met with frus-
tration because of diffraction. As far back as the 1930’s, a theoretical solution to this
problem was suggested.
1
However, it was not until the early 1980’s that the electronic
control and feedback capability existed to realize this solution.
2
If the aperture exposing
the sample is kept very small—on the order of 50 nm—and the aperture is kept close to the
sample surface—generally less than 20 nm—the diffraction problems can be avoided. It
was not until the development of scanning probe microscopes, however, that technology
existed to maintain such close tip-sample spacing while a tip was being scanned over a
sample.
NSOM T
IPS
The light source in an NSOM system is launched into an optical fiber. The end of the fiber
is “pulled down” to a diameter of 50 nm. The fiber is then coated with aluminum, approx-
imately 100 nm thick. The fiber becomes a “light funnel” directing light onto the sample.
Photodetectors are placed behind the sample (transmission mode) or beside the tip (reflec-
tion mode) to collect light emitted from the sample. A laser is used as a light source and is
coupled into the back side of the NSOM fiber-optic probe.
1. E.H. Synge: A Suggested Model for Extending Micro-
scopic Resolution into the Ultramicroscopic Region. Phil.
Mag. 6, 356-362 (1928).
2. D.W. Pohl, W. Denk, and M. Lanz: Optical Stethoscopy:
Image Recording with Resolution 1/20. Appl. Phys. Lett. 44,
No. 7, 651-653 (1984).