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 100x. The used camera is a 5 Mpixels Allied Vision Guppy Pro F-503 with a pixel pitch of 2.2 μm. The lateral magnification is set to about 200x 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 μm. Further, the mean local refractive index of the nano fibers can be calculated (n=1.501).

Date Published: 13 May 2013
PDF: 7 pages
Proc. SPIE 8788, Optical Measurement Systems for Industrial Inspection VIII, 87883F (13 May 2013); doi: 10.1117/12.2020579

Published in SPIE Proceedings Vol. 8788:
Optical Measurement Systems for Industrial Inspection VIII
Peter H. Lehmann; Wolfgang Osten; Armando Albertazzi, Editor(s)