Fig. 1.
Comparison between D-FFOCT setup versus iSR D-FFOCT. Fig.1a illustrates a classic D-FFOCT setup with a spatially incoherent source (mounted LED, Thorlabs, λ0 = 810 nm, Δλ = 25 nm) illuminating a Linnik interferometer using a Köhler illumination. The incoming field, in yellow, is split by a non-polarizing beam splitter (NPBS, BS014, Thorlabs, Newport, NJ, USA) cube into a reference arm and a sample arm. In the reference arm, an objective focuses the light on a mirror, placed at the image focal plane (FPI ref) of the reference objective (Obj. ref). The back reflected field is sketched in red. In the sample arm, an identical microscope objective (Obj. Sam) focuses the light onto a sample, laid on a coverslip (CoverSlip Sam) for the inverted microscope, at its image focal plane (FPI Sam). The backscattered light is illustrated in green. The objective (Obj. Sam) also collects the out-of-focus light (pictured in blue) reflected by the specular top surface of the coverslip (CoverSlip Sam). The two beams are recombined by the NPBS and focused on a camera by intermediary of a tube lens L3. In iSR FFOCT, the reference arm is blocked so that only the two beams from the sample arm reach the camera and can interfere. The microscope objectives are 30X, 1.05 NA silicon oil Olympus objectives, and the tube lens an achromatic doublet of focal length 300 mm. Fig.1b illustrates the iSR D-FFOCT configuration showing the imperfect overlap of these two beams occurring on the camera. Camera Im. P means camera image plane and CoverSlip Conj. P stands for the plane conjugated to the coverslip surface.