Bidirectional Phase Sensitivity in Holographic Phototransient Microscopy.
- 1Department of Physics and Astronomy, Vrije Universiteit Amsterdam, De Boelelaan 1100, Amsterdam 1081 HZ, The Netherlands.
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, which 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 micrometer-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
@article{robertson2026bidirectional,
title = {{Bidirectional Phase Sensitivity in Holographic Phototransient Microscopy.}},
author = {Emmanuel Kotu Robertson and Dennis van de Lockand and Matz Liebel},
journal = {ACS photonics},
year = {2026},
month = oct,
doi = {10.1021/acsphotonics.6c01684},
url = {https://europepmc.org/article/MED/42997715},
note = {CC BY},
}
RIS
TY - JOUR
TI - Bidirectional Phase Sensitivity in Holographic Phototransient Microscopy.
AU - Emmanuel Kotu Robertson
AU - Dennis van de Lockand
AU - Matz Liebel
PY - 2026
DA - 2026/10/15
JO - ACS photonics
DO - 10.1021/acsphotonics.6c01684
UR - https://europepmc.org/article/MED/42997715
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, which 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 micrometer-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.
SN - 2330-4022
ER -