Optics & Photonics News

Cell Identification with
3-D Holographic 3-D Holographic 3-D Holographic
Inkyu Moon, Mehdi Daneshpanah, Arun Anand and Bahram Javidi
Recent developments in 3-D computational optical imaging have
ushered in a new era for biological research. Techniques in 3-D
holographic microscopy integrated with numerical processing
are enabling researchers to obtain rich, quantitative information
about the structure of cells and microorganisms in noninvasive,
real-time conditions.

igital holography is in many ways similar to classic holography, except that opto-
electronic sensors are used instead of photographic film. ;is allows for numerical
processing of holographic data for a host of applications in biomedicine, public
health and environmental monitoring. ;is technique has been adapted to microscopy, and it
is widely used in the three-dimensional (3-D) visualization of biological specimens.

;e essence of holographic imaging lies in the fact that, when coherent light propagates through a semi-transparent object, its amplitude and phase get modulated due to light-matter interaction. As a result, the outgoing wavefront carries information about the entire 3-D structure of the object.

With digital holographic microscopy (DHM), one can indirectly record information about the phase and amplitude of the object’s wavefront and thus numerically reconstruct sectional images of biological specimens at di;erent depths from only a single holographic sampling. DHM is therefore commonly categorized as a form of 3-D optical-computational microscopy.

At its core, DHM includes an optical interferometer, which is used to form an interference pattern between the Fresnel di;raction of cells or microorganisms and a reference wavefront. ;e intensity distribution of this interference pattern is digitized using an optoelectronic image sensor array (e.g., CCD or CMOS camera), and the result is a digital hologram in which the information about the 3-D structure of a biological specimen is encoded. An inverse Fresnel transform can be used to decode the digital hologram and to reconstruct the specimen’s characteristic phase and amplitude modulation information. DHM does not require mechanical scanning and thus o;ers an advantage over laser scanning and confocal 3-D microscopy methods, which commonly require beam steering in the transverse plane and/or mechanical translation of the specimen along the optical axis in order to bring di;erent planes of the specimen into focus.