Bidirectional phase sensitivity in holographic phototransient microscopy
Abstract
Mid-infrared photothermal microscopy combines the chemical specificity of infrared absorption with the spatial resolution of visible-light detection, but practical implementations face a persistent trade-off between forward-scattering (FWS) and backward-scattering (BWS) detection geometries. FWS provides quantitative, shape-independent phase contrast but requires two-sided optical access that is difficult to achieve in aqueous or thick samples. BWS offers convenient single-sided access, but its signals are strongly distorted by depth-dependent interference for micron-scale objects. Here we present a bidirectional femtosecond mid-infrared pump-probe holographic microscope capable of switching between FWS and BWS geometries within a single instrument, and use it to introduce and validate a new imaging modality, internal forward scattering (IFS). IFS exploits the back-reflection generated at the top surface of the mid-infrared-transparent sample substrate as an internally generated forward-scattering illumination wave, isolated from the directly backscattered field via temporal coherence gating. Using polystyrene beads on CaF2 substrates in air, water, and a refractive-index-matched glycerol-water mixture, we show that IFS reproduces the signal magnitudes and temporal dynamics of true FWS measurements while retaining the mechanical simplicity and single-sided accessibility of BWS. These results establish IFS as a practical, quantitative alternative to conventional FWS and BWS geometries for photothermal, and more broadly quantitative phase, imaging, with direct relevance to single-sided imaging of biological or solvent-contained specimens.
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BibTeX
@misc{robertson2026bidirectional,
title = {{Bidirectional phase sensitivity in holographic phototransient microscopy}},
author = {Emmanuel Kotu Robertson and Dennis van de Lockand and Matz Liebel},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2607.03170},
eprint = {2607.03170},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.03170},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Bidirectional phase sensitivity in holographic phototransient microscopy
AU - Emmanuel Kotu Robertson
AU - Dennis van de Lockand
AU - Matz Liebel
PY - 2026
DA - 2026/09/21
PB - arXiv
DO - 10.48550/arxiv.2607.03170
UR - https://arxiv.org/abs/2607.03170
AB - Mid-infrared photothermal microscopy combines the chemical specificity of infrared absorption with the spatial resolution of visible-light detection, but practical implementations face a persistent trade-off between forward-scattering (FWS) and backward-scattering (BWS) detection geometries. FWS provides quantitative, shape-independent phase contrast but requires two-sided optical access that is difficult to achieve in aqueous or thick samples. BWS offers convenient single-sided access, but its signals are strongly distorted by depth-dependent interference for micron-scale objects. Here we present a bidirectional femtosecond mid-infrared pump-probe holographic microscope capable of switching between FWS and BWS geometries within a single instrument, and use it to introduce and validate a new imaging modality, internal forward scattering (IFS). IFS exploits the back-reflection generated at the top surface of the mid-infrared-transparent sample substrate as an internally generated forward-scattering illumination wave, isolated from the directly backscattered field via temporal coherence gating. Using polystyrene beads on CaF2 substrates in air, water, and a refractive-index-matched glycerol-water mixture, we show that IFS reproduces the signal magnitudes and temporal dynamics of true FWS measurements while retaining the mechanical simplicity and single-sided accessibility of BWS. These results establish IFS as a practical, quantitative alternative to conventional FWS and BWS geometries for photothermal, and more broadly quantitative phase, imaging, with direct relevance to single-sided imaging of biological or solvent-contained specimens.
ER -