Photothermal imaging device and system
Inventors
Li, Zhongming • Hartland, Gregory • Kuno, Masaru Ken
Assignees
Publication Number
US-11592391-B2
Publication Date
2023-02-28
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 a mid-infrared photothermal heterodyne imaging (MIR-PHI) system and method that surpasses the traditional mid-infrared (MIR) imaging diffraction limit and enables the use of visible photodiodes as detectors. Photothermal imaging systems utilitize a mid-IR 'pump' laser and a visible or near-infrared 'probe' laser. The absorption of mid-IR light by the sample generates a localized temperature increase, which causes a thermal lens effect, altering the refractive index in the medium around the sample.
By scanning the sample and detecting modulations in the probe beam caused by these localized changes, the system achieves high sensitivity and spatial resolution below the diffraction limit of conventional MIR imaging. The system's design allows the use of widely available, reliable, and cost-effective visible or near-IR photodiode detectors instead of traditional MIR detectors, which are typically expensive, less reliable, and require inconvenient cooling systems. Counter-propagating geometry, utilizing separate optical paths for pump and probe, is used to enhance both spatial resolution and imaging contrast.
The core problem addressed is that conventional MIR imaging systems suffer from limited spatial resolution due to the Abbe diffraction limit and rely on cumbersome, expensive MIR detectors. Existing approaches such as scanning probe microscopy and solid-immersion lens techniques introduce complex and sophisticated instrumental integration yet do not resolve the detector sensitivity issue. The disclosed MIR-PHI system provides improved spatial resolution and avoids the need for traditional MIR detectors, serving as a sensitive, affordable, and broadly applicable tool for submicron-scale imaging, especially in biological and other chemical analysis applications.
Claims Coverage
There are two independent claims, each with inventive features that define the method and system for submicron-resolution MIR photothermal heterodyne imaging.
Submicron resolution MIR photothermal heterodyne imaging using pump and probe beams with non-intersecting pathways
The method involves: 1. Illuminating a region of the sample with a focused mid-infrared pump beam generated by a first light source, absorbed by the sample. 2. Illuminating the same region with a probe beam of a different wavelength generated by a second light source. 3. Focusing the pump beam with a reflective objective and the probe beam with a refractive objective onto the region of the sample. 4. Collecting part of the probe beam from the sample with a detector. 5. Analyzing the collected probe light to construct a signal indicative of infrared absorption with submicron spatial resolution. 6. Ensuring the pump and probe beams travel along separate, non-intersecting pathways toward the region of the sample.
System for detecting MIR absorption with submicron resolution utilizing separate reflective and refractive objectives and non-intersecting pump and probe beam pathways
The system comprises: - A first light source to deliver a focused MIR pump beam absorbed by the sample; - A second light source to deliver a probe beam to the sample; - A reflective objective focusing the pump beam and a refractive objective focusing the probe beam onto the sample region; - A detector to collect and measure the probe beam coming from the sample; - A signal processing device generating, from probe light collected by the detector, a signal indicative of MIR absorption with submicron spatial resolution; - Arrangement of the first and second light sources such that the pump and probe beams travel on separate, non-intersecting pathways toward the sample.
The claims broadly cover both the methods and systems for achieving mid-infrared photothermal imaging with submicron resolution through dual light sources (mid-IR and visible/near-IR), specialized objectives, separate beam pathways, and signal analysis based on probe beam collection.
Stated Advantages
Overcomes the diffraction limit of traditional MIR imaging and achieves submicron spatial resolution.
Enables use of visible or near-IR photodiodes as detectors, which are more sensitive, affordable, reliable, and do not require inconvenient cooling systems like traditional MIR detectors.
Allows for high sensitivity and high acquisition speed in imaging applications.
Retains the spectroscopic potential of mid-IR absorption for chemical identification without sample staining or labeling.
Provides a robust, widely applicable, and cost-effective imaging tool suitable for biological systems and submicron-scale applications.
Documented Applications
Imaging of biological systems with submicron-scale spatial resolution.
Analysis and chemical identification of complex structures, such as single live cells and individual protein complexes.
Investigation of nano-scale structures that are not accessible with conventional MIR imaging techniques.
Potential for medical imaging, including pushing MIR imaging to the subcellular level.
Spectroscopic applications, including mid-IR mapping of absorption spectra for material characterization.
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