Detectability of unresolved particles in off-axis digital holographic microscopy

Area of Science:

• Optical microscopy
• Nanotechnology
• Biophysics

Background:

• Off-axis digital holographic microscopy (DHM) offers label-free 3D tracking of micro/nanoparticles.
• Contrast in DHM arises from refractive index differences (phase/absorption) and scattering.
• Existing DHM research prioritizes phase contrast and resolution, neglecting detection limits for unresolved particles.

Purpose of the Study:

• To quantify the limits of detection for nanosized particles using DHM.
• To investigate the influence of particle optical properties, microscope optics, and data processing on detection limits.
• To assess the utility of amplitude and phase contrast for unresolved particles.

Main Methods:

• Analysis of nanosized particles using off-axis DHM.
• Varying particle optical properties (refractive index, absorption, scattering).
• Modifying microscope optics (camera well depth, substrate) and data processing algorithms.

Main Results:

• DHM provides contrast for unresolved spheres in both amplitude and phase channels.
• Results align with Mie theory predictions for scattering cross-sections.
• Amplitude reconstructions are more effective than phase for low-index spheres.

Conclusions:

• DHM is a viable technique for detecting unresolved nanoparticles.
• Amplitude contrast is essential for detecting low-index particles in DHM.
• This work has implications for microbial detection, including extraterrestrial life detection.