Abstract

Identifying microbes in real time has a great significance in biological, medical, and environmental research and applications. New techniques are needed to develop a practical method for continuously monitoring the growth, motion, and content of microbes. The holographic filtering technique has been used for this purpose. However, since living microbes are mainly phase objects, varying in size and shape and also moving randomly, it is difficult to recognize them by holographic filtering that is based on their bodies. In our research we found that when a divergent laser beam passes through a culture of microbes, the dynamic-speckle graphs or patterns that are produced are unique to that particular culture. Information related to microbe size, orientation, concentration, and motion is transferred into these speckle graphs. We use the graphs as recognition targets to make an averaged holographic matched spatial filter (MSF). Theoretical analysis and experimental results have shown that MSF, combined with digital information processing, has many advantages over previous techniques. Our experiments support the hypothesis that it will eventually be possible to identify microbes in real time.

© 1990 Optical Society of America