# Digital Holographic Microscopy for 3D Imaging of Complex Fluids and Biological Systems

Written by: Grant England AP225 Fall, 2011

## Info

Title: Digital Holographic Microscopy for 3D Imaging of Complex Fluids and Biological Systems

Authors: Vinothan N. Manoharan

@Harvard: http://books.nap.edu/openbook.php?record_id=12821&page=5

## Summary

In this paper, a method for resolving three dimensional objects, at a timescale much faster than that achieved with confocal microscopy and for a much lower cost, is described. By using Fourier transformations and other mathematics, a three dimensional representation of a structure can be back-calculated by using the interference pattern generated by a laser shining through the sample. So, using this method coupled with a digital camera which can capture images at 30 fps, 3D reconstructions of particles in solution or other interesting materials can be created.

## Methods and Results

The above shows schematically how a point source can be resolved in three dimensions using the interference pattern collected by a camera. The top-right image shows the coherent superposition of several particles which could be used to calculate the locations and sizes of several particles in the sample.

The above shows some real data collected with the digital holographic microscope (DHM) for a single frame of a movie compared to the same image taken with a bright field microscope which does not give three dimensional information.

## Conclusions

Using a DHM to generate three dimensional representations of samples observed in a microscope provides several advantages over confocal microscopy in terms of cost and speed of capture that could lend it usefulness in observing processes with timescales which are currently unable to be observed using other three dimensional techniques. The drawback to such a method is, however, that there is a large computational cost to generate the three dimensional data from the two dimensional interference patterns. However, with the continuing increase in computer performance it seems that this technique will become more and more viable for scientific studies.