Polarization and Spectral Interferometric Techniques for Quantitative Phase Microscopy - Biomedical Optical Phase Microscopy and Nanoscopy - page 282

previously with the resolution target, although the beam now passes through the liquid
culture medium, which in general is a source of instability in temporal measurement of
phase through cell samples. This is evidence of superior suppression of ambient fluctuations
by the common-path geometry of DIC microscopy. The dynamics of a second
cardiomyocyte are shown in Figure 14.5D , registering four periodic beating events in 10 s
with an average duration of 0.4 s.
The relatively rare pulsatile events seen for the first cardiomyocyte are consistent with
stochastic contractions often observed in freshly isolated ventricular cardiomyocytes,
whereas the regular events in the second cardiomyocyte are of the same frequency as
contraction cycles observed in “pacing cells,” which is a type of specialized cardiomyocyte
readily identified in culture [25] . The observation of similar durations of the events in
Figure 14.5C (0.5 s) and Figure 14.5D (0.4 s) are consistent with this explanation.
In this section, we have demonstrated that polarization diversity can be used to provide
highly stable measurements of cell samples. A fiber-optic SD-DIC microscope for imaging
both reflective surfaces and live cells was presented and applied to monitoring dynamics at
selected sample sites. SD-DIC offers a high-sensitivity means to quantitatively decouple
OPL gradient and intensity in a single measurement. As a point-scanning system, the SD-
DIC achieves enhanced OPL gradient resolution at the expense of acquisition speed. Using
existing technologies, the system can be adapted to achieve sub-Hz frame rates for two-
dimensional imaging and greater than 50 kHz acquisition rates for single-point
measurements. Hence, wide-field imaging using SD-DIC is most suited for high-resolution,
low-speed characterization, such as surface profiling or observation of relatively slow
dynamics (on the order of a few seconds) of live biological specimens, while fast dynamics
below 0.1 ms can be monitored for selected locations.
14.4 Spectral Multiplexing by RGB Color Channels
As described earlier, light sources with continuous, broad bandwidths can be exploited to
provide drastic improvement of phase measurement resolution. The concept of exploiting
the spectral domain can also be leveraged with sources that have multiple discrete
bandwidths. We now show how color cameras can be incorporated to facilitate spectral
multiplexing that introduces new functionalities to conventional quantitative phase
measurements.
The spectral channels of commercial RGB cameras can be used not only for color imaging
applications but also for multiplexing of independent information through the use of
spectral encoding. With careful consideration of illumination and detection schemes, the
three color channels of an RGB camera can be used to multiplex both phase and
fluorescence information about biological samples with minimal crosstalk between color