Video-rate mid-infrared photothermal imaging by single-pulse photothermal detection per pixel

Abstract

By optically sensing absorption-induced photothermal effect, mid-infrared (IR) photothermal (MIP) microscope enables super-resolution IR imaging of biological systems in water. However, the speed of current sample-scanning MIP system is limited to milliseconds per pixel, which is insufficient for capturing living dynamics. By detecting the transient photothermal signal induced by a single IR pulse through fast digitization, we report a laser-scanning MIP microscope that increases the imaging speed by three orders of magnitude. To realize single-pulse photothermal detection, we use synchronized galvo scanning of both mid-IR and probe beams to achieve an imaging line rate of more than 2 kilohertz. With video-rate speed, we observed the dynamics of various biomolecules in living organisms at multiple scales. Furthermore, by using hyperspectral imaging, we chemically dissected the layered ultrastructure of fungal cell wall. Last, with a uniform field of view more than 200 by 200 square micrometer, we mapped fat storage in free-moving Caenorhabditis elegans and live embryos.

Mid-infrared single-photon upconversion spectroscopy enabled by nonlocal wavelength-to-time mapping

“…It is proved that the measurement of the quantum correlation is fully justified to obtain the information carried by MIR photons, although the MIR photons are not directly detected. The second-order Glauber correlation function G (2) (t h , t up ) is defined as where E j (+) (t j ) = ∫ dω j a(ω j )exp( −iω j t j ) , (j = up, h) is the positive frequency components of the field at the single-photon detector for upconverted photons and heralding photons, respectively, and a(ω j ) is the annihilation operators at the frequency ω j .…”

“…After propagation in the 10-km SMF, different spectral components of the heralding photons arrive at the superconducting nanowire single-photon detector (SNSPD; Photon Technology Co. Ltd.) in sequence to trigger coincidence measurement with the upconverted MIR signal photons. Although the time stretching discussed here is not physically interpreted by the concept of wavepacket broadening for either heralding or signal path individually, the first-order correlation function G (1) (τ) remains unchanged as the dispersion is introduced, and the G (2) (τ) function does represent being broadened by the group dispersion medium in the temporal domain (42,43). Let S(ω) be the spectral function of the sample; the existing quantum correlation between the upconverted MIR photons and the time-stretched heralding photons can then be evaluated with…”

“…Mid-infrared (MIR) spectroscopy plays a crucial role in biological (1,2) and materials research (3), pharmaceutical sciences (4), molecular dynamics (5), art conservation (6), and environmental monitoring (7,8) as a vital instrument for investigating the structure of substances. The most common method of analyzing MIR spectra is Fourier transform infrared (FTIR) spectroscopy (9)(10)(11).…”

Monitoring Phenotype Heterogeneity at the Single-Cell Level within Bacillus Populations Producing Poly-3-hydroxybutyrate by Label-Free Super-resolution Infrared Imaging

“…Although O-PTIR measurements discussed here were acquired from dry samples, which might be an issue for online monitoring of bioprocesses, previous studies have shown that infrared measurements acquired through mid-infrared absorption-induced photothermal effect can also be performed on living cells in aqueous samples. 39,40 More recently, Yin et al reported a novel imaging technique operating with similar working principles of O-PTIR imaging that enables to acquire infrared chemical maps from aqueous solutions at video-rate speed, which opens up opportunities to monitor the dynamics of biological processes in real time. 40 Ultimately, we highlight that O-PTIR spectroscopy can also be coupled with fluorescence and Raman spectroscopies to acquire spectral data from the same sample location at the same high spatial resolution, 30,31,41 expanding the range of applications of this emerging technique to various fields of research including characterization of materials, online measurements at the industrial scale, as well as in vivo measurements.…”

Dual-Hyperspectral Optical Pump–Probe Microscopy with Single-Nanosecond Time Resolution

“…Indeed, methods like mid-infrared (MIR) photothermal heterodyne imaging − and MIR photothermal microscopy − essentially fall under the category of PPM techniques, where the pump is a MIR laser pulse vibrationally resonant with the materials. These methods cover long delay time windows from hundreds of nanoseconds to a few microseconds (μs) and offer submicrometer spatial resolution at MIR wavelengths.…”