Influence of laser spot size at diffuser plane on the longitudinal spatial coherence function of optical coherence microscopy system

TL;DR

This study examines how the size of the laser spot at the diffuser plane affects the longitudinal spatial coherence and axial resolution in optical coherence microscopy, demonstrating optimized resolution with specific spot sizes.

Contribution

It reveals the relationship between diffuser spot size and axial resolution in PTS, enabling high-resolution imaging without complex optical corrections.

Findings

Maximum axial resolution of ~13 microns at 3.5 mm spot size

Resolution confirmed by gauge block experiments

Potential for high-resolution imaging with simple setup

Abstract

Coherence properties and wavelength of light sources are indispensable for optical coherence microscopy/tomography as they greatly influence the signal to noise ratio, axial resolution, and penetration depth of the system. In the present letter, we investigated the longitudinal spatial coherence properties of the pseudo-thermal light source (PTS) as a function of spot size at the diffuser plane, which is controlled by translating microscope objective lens towards or away from the diffuser plane. The axial resolution of PTS is found to be maximum ~ 13 microns for the beam spot size of 3.5 mm at the diffuser plane. The change in the axial resolution of the system as the spot size is increased at the diffuser plane is further confirmed by performing experiments on standard gauge blocks of height difference of 15 microns. Thus, by appropriately choosing the beam spot size at the diffuser plane, any monochromatic laser light source depending on the biological window can be utilized to obtain high axial-resolution with large penetration depth and speckle-free tomographic images of multilayered biological specimens irrespective of the source temporal coherence length. In addition, PTS could be an attractive alternative light source for achieving high axial-resolution without needing chromatic aberration corrected optics and dispersion-compensation mechanism, unlike conventional setups.