can be changed by expanding and contracting the piezo actuator at a particular
frequency, thereby applying a periodic stress to the quartz to produce birefringence.
During CPL measurements, left- and right-handed circularly polarized fluorescence
emitted by the sample is converted to linearly polarized light synchronously with the
PEM frequency. This is transmitted through the polarizer and then detected. When a
sample exhibits CPL, an alternating current (AC) signal is produced as shown in
Fig. 14.4b, and its amplitude corresponds to the CPL signal intensity. The direct
current (DC) component corresponds to the normal fluorescence spectrum.
We next describe the JASCO CPL-300 circularly polarized luminescence spectrophotometer (Fig. 14.5), as an example.
(a)
Quartz
Piezo actuator
DC component
Fluorescence intensity
AC component
CPL signal
Time
Light intensity
(b)
20 µsec
(50 kHz)
Fig. 14.4 Phase-sensitive detection of CPL using PEM. (a) Appearance of PEM. (b) Time-domain
signal of CPL and fluorescence
Light source
PMT
Ex monochromator
Em monochromator
Sample chamber
Fig. 14.5 External view of CPL-300
14 Principles and Applications of Circularly Polarized Luminescence. . .
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