Photothermal imaging device and system
Inventors
Li, Zhongming • Hartland, Gregory • Kuno, Masaru Ken
Assignees
Publication Number
US-12228503-B2
Publication Date
2025-02-18
Expiration Date
2037-04-05
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Abstract
Mid-infrared photothermal heterodyne imaging (MIR-PHI) techniques described herein overcome the diffraction limit of traditional MIR imaging and uses visible photodiodes as detectors. MIR-PHI experiments are shown that achieve high sensitivity, sub-diffraction limit spatial resolution, and high acquisition speed. Sensitive, affordable, and widely applicable, photothermal imaging techniques described herein can serve as a useful imaging tool for biological systems and other submicron-scale applications.
Core Innovation
The invention describes mid-infrared photothermal heterodyne imaging (MIR-PHI) techniques that overcome the diffraction limit of traditional MIR imaging and allow the use of visible photodiodes as detectors. By using a combination of a mid-IR "pump" laser and a visible or near-IR "probe" laser, the MIR-PHI system enables sensitive detection of mid-IR absorption with spatial resolution well below the Abbe diffraction limit applicable to the MIR pump beam.
The core problem addressed is the limited spatial resolution and the high cost, scarcity, and operational inconvenience of traditional mid-IR detectors in existing MIR imaging systems. Existing techniques are limited by the Abbe diffraction limit and require sophisticated, expensive, or difficult-to-operate detectors, making submicron-scale imaging with MIR light infeasible in conventional systems.
The described MIR-PHI system operates by using the MIR pump beam to locally heat a sample, forming a thermal lens effect, which is then interrogated by a tightly focused probe beam of shorter wavelength. This approach enables spatial resolution determined by the probe wavelength, allowing the use of standard, sensitive, affordable visible or near-IR detectors. The system can achieve submicron spatial resolution, high acquisition speed, and is adaptable for hyperspectral imaging and spectroscopic analysis using mid-IR absorption.
Claims Coverage
The patent contains several independent claims that encompass inventive features related to methods and systems for mid-infrared photothermal heterodyne imaging with enhanced spatial resolution and affordable detection.
Detecting infrared absorption using a mid-IR pump and shorter-wavelength probe beam
A method includes illuminating a sample region with a pump beam generated by a first light source (mid-IR), and a probe beam generated by a second light source (visible or near-IR), where the probe has a wavelength shorter than the pump and a Gaussian beam width less than 2.33 micrometers. A detector collects part of the probe beam from the sample, and the collected light is analyzed to construct a signal indicative of infrared absorption by the sample region.
Method for multispectral detection using a tunable mid-IR pump
A method involves illuminating a sample region with a pump beam from a tunable mid-infrared source at multiple wavelengths, using a probe beam with a wavelength shorter than the pump, and collecting the probe beam from the region. A signal based on the probe beam is generated to indicate the amount of IR light absorbed at each wavelength. The steps are repeated for various wavelengths, allowing spectroscopic analysis.
System for detecting infrared absorption using a tunable mid-IR pump and a focused visible probe
A system includes: - A first light source that illuminates the sample with a tunable mid-IR pump beam (covering multiple wavelengths). - A second light source delivering a probe beam of shorter wavelength and Gaussian beam width less than 2.33 micrometers. - A detector collecting at least a portion of the probe beam from the sample region. - A signal processing device generating a signal indicative of the mid-IR absorption at different pump wavelengths.
The inventive features focus on methods and systems that allow mid-IR absorption imaging with submicron spatial resolution using visible or near-IR detectors, making use of a combination of mid-IR pump and much shorter wavelength probe beams for enhanced sensitivity and affordable detection.
Stated Advantages
Overcomes the diffraction limit of traditional mid-IR imaging, achieving submicron spatial resolution.
Enables the use of sensitive, affordable, and widely available visible/near-IR photodiodes as detectors instead of expensive or scarce mid-IR detectors.
Provides high sensitivity and high acquisition speed for imaging.
Remains applicable to a broad range of materials since most compounds absorb mid-IR light.
Allows label-free imaging and chemical identification without requiring stains or exogenous markers.
Potentially enables robust imaging of biological systems at the subcellular or submicron scale.
Maintains spectroscopic selectivity of mid-IR absorption while improving acquisition practicality.
Documented Applications
Imaging biological systems at the submicron or subcellular level using mid-IR photothermal heterodyne imaging.
Spectroscopic analysis and identification of chemical composition through mid-IR absorption spectrum mapping at high spatial resolution.
Visualizing single particles or nano-scale objects, such as polystyrene beads, in various media including water and glycerin.
Use of mid-IR imaging for potential medical imaging applications such as tracking biological activity and providing a diagnosis tool.
Construction of contrast-enhanced images in different solvents by tuning the pump wavelength to maximize analyte versus solvent absorbance.
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