attoMICROSCOPY
PAGE 104
Confocal Microscopy (CFM) - free-beam setup
fundamentals
Confocal microscopy is the most common
instrumental technique in quantum optics
to investigate semiconductor quantum
dots, single molecules, color centers in
diamond, photonic crystals, nanowires,
quantum wells, 2D layered materials
(graphene, chalcogenides) and many more.
Often, the quantum nature of light emission requires cryogenic temperatures for
the samples under investigation. Low temperatures also result in sharper spectral
lines due to decreased thermal broadening, as well as in stronger optical signals,
since the quantum efficiency is improved
due to less scattering and less non-radiative recombinations. In addition, high
magnetic fields can be used to extract
information about the energy levels.
A confocal microscope is able to increase
the optical resolution compared to conventional microscopes by rejecting
out-of focus light (see schematics below):
1. The sample is illuminated with a focused
beam, which restricts the excitation to a
small region on the sample both in lateral
as well as vertical direction.
2. The use of a blocking pinhole in the conjugate plane eliminates any out-of-focus
information in the collection path.
As in most of attocube’s low temperature
microscopes, an image is acquired by
scanning the sample, while the probe,
in this case the objective, remains fixed.
This technique enables diffraction limited
lateral optical resolution, as well as 3D imaging with very good vertical resolution by
scanning several thin sections at different
f