Fluorolog-3 v. 2.2 (12 Jul 2002)
Glossary
16-2
tector signal is ratioed to the reference signal, which provides 90%
of the corrected excitation scan. To obtain a completely correct scan,
the excitation scan acquired in the manner described above is multi-
plied by correction factors. A set of excitation correction factors is
included on the software disks.
Correction factors
Compensates for the wavelength-dependent components of the sys-
tem, like the xenon lamp, gratings, and signal detector. Emission and
excitation correction factors are included with the software and are
titled
xcorrect.spt
and
mcorrect.spt
.
Cut-on filter
Optical component that passes light of a higher wavelength.
Cut-off filter
Optical component that passes light of a lower wavelength.
Dark counts
Inherent background signal of the photomultiplier when high voltage
is applied. Cooling the detector decreases the dark counts.
Demodulation
(less modulation) Usually refers to the demodulated emission rela-
tive to the excitation.
Demodulation factor
Can be calculated using the following equation:
m
f
f
x
x
=
AC
DC
AC
DC
/
/
where AC
f
is the amplitude of the emission voltage, DC
f
is the exci-
tation offset voltage, AC
x
is the amplitude of the excitation voltage,
and DC
x
is the offset of the emission voltage.
Emission scan
Shows the spectral distribution of light emitted by the sample. Dur-
ing an emission scan, the excitation spectrometer remains at a fixed
wavelength while the emission spectrometer scans a selected region.
Energy transfer
The transfer of the excited energy from a donor to an acceptor. The
transfer occurs without the appearance of a photon and is primarily a
result of dipole-dipole interactions between the donor and acceptor.
Excitation scan
Shows the spectral distribution of light absorbed by the sample. To
acquire an excitation scan, the excitation spectrum scans a selected
spectral region while the emission spectrum remains at a fixed wave-
length.
Extrinsic fluorescence
Inherent fluorescence of probes used to study non-fluorescent mole-
cules.
Flash lamp
A lamp that provides pulsed-light output used to excite a sample.
Can be either “free running” or “gated.”
Fluorescence
The emission of light or other electromagnetic radiation during the
transition of electrons from the excited singlet state to the ground
state. Fluorescence typically occurs within about ~10
–9
s.
Fluorescence lifetime
The average length of time that a molecule remains in the excited
state before returning to the ground state.
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