Investigation into optimizing laser speckle contrast imaging illumination

Abstract

The primary purpose of this work is to optimize the illumination parameters used for laser speckle imaging and investigate how spatial modulation of the light used for illumination can enhance the sampling volume. An in-line illumination scheme is detailed that removes the need to manually position a side mounted coherent light source, instead utilizing a polarizing beam splitter (PBS) and linear polarizer to illuminate the sample plane through the same objective used to collect the backscattered light. This method ensures repeated, robust interrogation of the sample plane and allows for control over the light intensity using the polarizing elements. Spatial modulation of the illumination beam was then investigated as a method to increase the depth-penetration of LSCI. The premise was to use a focused beam of light, as opposed to a traditional wide-field beam, and illuminate the sample at various distances from the detector increasing the probability scattered photons sample deeper volumes. Single and two-point source configurations were used to image a microfluidic phantom with added static scattering layers to simulate different vessel depths. Varying the distance between the source and the detector, the camera field of view (FOV), we showed that it is possible to collect information from submerged vessels using a non-full field approach. This led to the design and implementation of an in-line, DMD-based illumination scheme that allows the projection and modulation of spatially complex illumination schemes.