Common-path interferometer for digital holographic Doppler spectroscopy of living biological tissues

Common-path interferometers have the advantage of producing ultrastable interferometric fringes compared with conventional interferometers, such as Michelson or Mach-Zehnder that are sensitive to environmental instabilities. Isolating interferometric measurements from mechanical disturbances is important in biodynamic imaging because Doppler spectroscopy of intracellular dynamics requires extreme stability for phase-sensitive interferometric detection to capture fluctuation frequencies down to 10 mHz.

The aim of this study was to demonstrate that Doppler spectra produced from a common-path interferometer using a grating and a spatial filter (SF) are comparable to, and more stable than, spectra from conventional biodynamic imaging.

A common-path interferometer using a holographic diffraction grating and an SF was employed with a low-coherence source. Simulations evaluated the spatial resolution. DLD-1 (human colon adenocarcinoma) spheroids were used as living target tissue samples. Power spectra under external vibrations and drug-response spectrograms were compared between common-path and Fourier-domain holographic systems.

The common-path holography configuration shows enhanced interferometric stability against mechanical vibrations through common-mode rejection while maintaining sensitivity to Doppler frequency fluctuations caused by intracellular motions.

A common-path interferometer using a grating and an SF can provide enhanced interferometric stability in tissue-dynamics spectroscopy for drug screening assays.