Question

Biomedical Optical Microscopy: What is the image artifact caused by the high spatial coherence of a laser light? What can you do to create a uniform illumination field from the laser?

Answer 1

Spatial coherence of lasers allows the laser to be focused to a tight spot and allows it to stay narrow along long distances, which means that the light waves emitted by the laser are all synchronised with each other. But this causes the formation of optical artifact called Speckle. These are intensity patterns caused due to mutual interference of a variety of wave fronts. these patterns occurs mainly on rough surfaces or object with large number of scattering particles such as tissues. This can be prevented by using the following modifications:

1. Illumination of the sample with different angles.
2. Using laser sources which differs in wavelength by only a small value.