Biomedical Engineering Reference
In-Depth Information
Fig. 9.10.
Setup for a microscope (speckle) interferometer. Light source: frequency
doubled cw Nd:YAG laser (
λ
= 532 nm); SMF: single-mode fibers for object illumi-
nation and reference wave; the illumination of the sample can be performed optional
with incident light or in transmission; AP: aperture for regulation of the speckle size
and suppression of scattered light
schematic setup for a microscopic (speckle) interferometer. The object is im-
aged by a microscope lens on a CCD sensor. The coherent object illumination
is performed either in transmission or with incident light by single mode opti-
cal fibers. The speckle size (or in the case of smooth waves disturbing scattered
light due to transparent specimens) is regulated by an additional aperture AP
that is positioned behind the microscope lens. The detection of optical path
length changes affected by micro changes of the sample can be performed by
a spatial phase shifting method as described in Sect. 9.2.2. Therefore, the ref-
erence wave is generated by an optical single mode fiber placed in the plane
of AP that is positioned with an off-set from the optical axis of the interfer-
ometer to produce a nearly constant phase gradient between object wave and
reference wave.
Figure 9.11 shows results obtained by a microscope (speckle) interfer-
ometer setup in combination with a
10 magnification microscope lens. In
Fig. 9.11a the white light image of an USAF 1951 test chart is depicted.
Figure 9.11b shows the corresponding speckle image effected by illumina-
tion with coherent laser light (
λ
= 532 nm) with a lateral resolution of
7.8
×
m. In Fig. 9.11c-f results from displacement measurements on a dyed
probe of an intestine carcinoma which was tilted in the experiment are de-
picted. Figure 9.11c shows the white light image of the investigated area.
The correlation fringe pattern, the corresponding phase difference distribu-
tion, and the filtered phase difference fringes are presented in Fig. 9.11d-f.
µ
