Confocal Microscopy (CFM) | Free-Beam Setup
fundamentals
Confocal microscopy is the most common instrumental technique in
quantum optics to investigate semiconductor quantum dots, single mol-
ecules, color centers in diamond, photonic crystals, nanowires, quan-
tum 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 broaden-
ing, as well as in stronger optical signals, since the quantum efficiency
is improved due to less scattering and less non-radiative recombina-
tions. In addition, high magnetic fields can be used to extract informa-
tion about the energy levels.
A confocal microscope is able to increase the optical resolution com-
pared to conventional microscopes by rejecting out-of focus light (see
schematics below):
As in most of attocube’s low temperature microscopes, an image is
acquired by scanning the sample, while the probe, in this case the ob-
jective, remains fixed. This technique enables diffraction limited lateral
optical resolution, as well as 3D imaging with very good vertical resolu-
tion by scanning several thin sections at different focal planes through
the specimen. These advantages come at the price of lower collected
intensity, and hence longer integration times.
The shown schematics is usually referred to as ‘free-beam’ configura-
tion, which enables to add a number of filters to either the excitation,
the collection or the combined beam path. This enables sophisticated
spectroscopic as well as imaging techniques such as resonant fluores-
cence, Raman spectroscopy or polarization analysis. For further details
on our external optics head, please refer to page 126.
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.
4
1
5
01 ASC400 scan controller
ASC400
02 LDM600 laser source
03 LDM600 2nd detector
3
04 attoCFM I external optics head incl. optional filters
2
05 Optical top window
06 Free-beam based cryogenic LT-APO objective
6
07 Sample with xyz positioners and optional xy scanner
7
Y
X
Z
For details on attoCFM I
external optics head, see
also page 126
attoMICROSCOPY
Sophisticated Tools for Science
PAGE 85