Biomedical Engineering Reference
In-Depth Information
In this section, we introduce a new optical polarization technique for obtaining dynamic
quantitative phase measurements with high precision and a low degree of phase noise. The
method, termed dual-interference channel quantitative phase microscopy (DQPM), is based
on a novel dual-polarization channel interferometric setup that is capable of simultaneous
acquisition of two phase-shifted interferograms of the same sample. These interferograms
are then digitally processed to produce the phase profile of the sample. Since the two
interferograms are acquired at the same time, this approach eliminates most of the common
phase noise in the final phase image. Additionally, due to the simultaneous nature of the
acquisition, one can capture rapid cell phenomena with subnanometer temporal resolution,
limited only by the speed of the digital camera used.
Ikeda et al.
[7]
have suggested an alternative dynamic QPM method which is based on the
acquisition of a single interferogram. This method is able to avoid the temporal phase noise
between successive frames, but since only one interferogram is acquired, common phase
noise due to the sample is not eliminated. Various attempts for simultaneous phase imaging
have been reported in the optical testing field
[8
12]
. However, these methods have not
been implemented for biologically relevant applications.
The DQPM system is shown in
Figure 14.1
, which includes a Mach
Zehnder
interferometer-based off-axis digital holographic microscopy setup, followed by an image-
splitting system. A HeNe laser, linearly polarized at 45
, is split into sample and reference
beams by beamsplitter BS
1
. The sample arm contains the sample, and microscope objective
(MO) forms a 4 f configuration with lens L
2
, as does lens L
1
in the reference arm.
Beamsplitter BS
2
combines the sample and reference beams, and the interference pattern of
interest appears one focal length from lens L
2
. This interference pattern is spatially
restricted by an aperture to half of the digital camera sensor size and imaged through the 4 f
image-splitting system shown in
Figure 14.1B
, onto the digital camera. This 4 f image-
splitting system includes two identical lenses, L
3
and L
4
, creating a 1:1 image of the
aperture plane on the camera. A Wollaston prism is positioned between these two lenses,
BS
1
M
M
L
3
L
4
/4
Wave plate
λ
Aperture
Aperture
L
1
Digital
camera
4 f Image-
splitting
system
Sample
Digital
camera
MO
M
BS
2
Wollaston
prism
HeNe laser
L
2
M
(A)
(B)
Figure 14.1
The DQPM system: dual-channel, single exposure interferometer for obtaining phase profiles of
live dynamic biological cells. (A) The entire interferometer. (B) The 4 f image-splitting system.
Source: From Ref.
[13]
.
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