Lasers have not been widely used for full-field imaging and display applications, because the high coherence of conventional lasers causes artifacts such as speckle. Instead, low-coherence sources such as lamps and LEDs are typically used, even though they are not bright enough for high-speed imaging or wide-area projection. We have designed special type of lasers that have sufficient low spatial coherence to preclude speckle formation. Such lasers enable high-speed speckle-free full-field imaging and projection, with broad applications in biomedical imaging, laser projection and display, holography, lithography, and machine vision. In addition, we invented a fast and efficient method of switching the spatial coherence of a laser, and performed multimodality microscopy of a living tadpole heart, using the low spatial coherence illumination for structural image and high spatial coherence illumination to extract dynamic information of blood flow process. This new technique is now applied to clinical research to reveal the relationship between structure and function, which is fundamental to the study of biology.

Multimodal imaging of the heart of Xenopus embryo using a degenerate laser with tunable spatial coherence. (a) Top view of a large-area vertical external cavity surface emitting laser (VECSEL) with electrical contacts. (b) Speckle-free image with low-coherence illumination showing the tadpole heart with outlines of ventricle and conus ateriosus. (c) Speckled image under high-coherence illumination, from which the spatially resolved speckle-contrast is obtained in (d) to characterize blood flow.