Digital Holographic Microscopy for the Study of Nano-Fibers

16-05-2016 12:42

The advantages of digital holographic microscopy to record not only the intensity but also the optical phase are
employed. The experimental arrangement comprises a Mach-Zehnder type interferometer with a microscopic objective
of magnification 10_. The used camera is a 5 Mpixels Allied Vision Guppy Pro F-503 with a pixel pitch of 2.2 m. The
lateral magnification is set to about 20_ based on the standard MIL-STD-150A 1951 USAF resolution test target.
The dimensions of the aggregated natural cellulose nanowhisker fibers used are in the range of some hundreds of
nanometers, which are positioned in the front of the microscopic objective using a 3D translation stage in the object arm
of the holographic setup. The recorded off-axis holograms are refocused using the angular spectrum method. The
reconstructed complex field is used to calculate optical phase and intensity distributions of the object at different
reconstructions depths. The dimensions and orientation of the fibers can be evaluated from the optical field at different
depths. Then, the shape and textures along the aggregated natural cellulose nanowhisker fiber can be presented in 3D
space. The nano fiber found to have the dimensions of mean width 223 nm, depth 308 nm and length of 8.1 m. Further,
the mean local refractive index of the nano fibers can be calculated (n=1.501).