Truncated-Correlation Photothermal Coherence Tomography Axial Resolution
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Solution Overview
Problem
Current thermal-diffusion-wave imaging techniques face limitations in energy localization and axial resolution due to the loss of frequency modes and coherence, especially in complex subsurface structures like biological specimens, leading to poor efficiency and signal-to-noise ratio (SNR), which hinders three-dimensional visualization.
Innovation Solution
The implementation of truncated-correlation photothermal coherence tomography (TC-PCT) using a chirped-pulse sequence with time-evolving filtering, where a truncated chirped waveform is cross-correlated with time-dependent photothermal signal data to achieve high energy localization and axial resolution beyond conventional thermographic modalities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional thermal-diffusion-wave imaging techniques are used, then the imaging process is simple, but energy localization and axial resolution are poor due to loss of frequency modes and coherence
Solution Approach 1:
The patent applies preliminary action by pre-coding the excitation signal with a pseudo-random binary sequence (PRBS) before applying it to the sample. This pre-coding enables subsequent cross-correlation processing to achieve energy localization and improve axial resolution. The PRBS sequence is generated in advance and stored, allowing the system to process thermal diffusion wave signals with high resolution without requiring complex real-time processing.
Solution Approach 2:
The patent uses cross-correlation processing as an intermediary between the raw thermal diffusion wave signals and the final image reconstruction. The cross-correlation operation with the pre-stored PRBS sequence acts as a mediator that extracts localized energy information from the dispersed thermal signals, achieving both improved axial resolution and signal-to-noise ratio without direct complex processing of the raw data.
2Reliability
If matched filtering with pulse compression is used, then signal-to-noise ratio is improved, but frequency mode loss and coherence degradation still occur outside the completeness bandwidth
Solution Approach 1:
The patent applies dynamics by using a time-evolving filtering approach where the effective bandwidth adapts to the time-dependent frequency content of the thermal diffusion wave signals. The cross-correlation processing with PRBS dynamically captures frequency modes across different time delays, allowing the system to maintain high signal-to-noise ratio while preserving frequency information that would otherwise be lost in fixed-bandwidth matched filtering approaches.
3Measurement precision
If chirped-pulse thermal-diffusion-wave radar is used, then depth profiling capability is improved, but axial resolution control and three-dimensional visualization are hindered by limited frequency bandwidth
Solution Approach 1:
The patent applies periodic action by using periodic PRBS sequences for excitation and cross-correlation processing. The periodic nature of the PRBS sequence enables repeated measurement cycles with consistent frequency sampling, improving depth profiling capability while maintaining adaptability to different frequency contents through multiple measurement passes. This periodic approach allows the system to build up comprehensive frequency information over time, overcoming the limitations of single-shot chirped-pulse methods.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
TC-PCT provides axially resolved layer-by-layer imaging with improved SNR and depth profiling capabilities, enabling three-dimensional visualization of subsurface features in materials with intricate structures, significantly enhancing the axial and lateral resolution compared to traditional methods.
Implementation Method 1
exciting a sample with the chirped delivery of incident laser pulses and detecting photothermal radiation emitted from the sample
Implementation Method 2
detecting photothermal radiation emitted from the sample with an infrared camera
Data Source
AI summary
Photothermal imaging systems and methods are disclosed that employ truncated-correlation photothermal coherence tomography (TC-PCT). According to the example methods disclosed herein, photothermal radiation is detected with an infrared camera while exciting a sample with the chirped delivery of incident laser pulses (where the pulses have a fixed width), and time-dependent photothermal signal data is obtained from the infrared camera and processed using a time-evolving filtering method employing cross-correlation truncation. The cross-correlation truncation method results in pulse-compression-linewidth-limited depth-resolved images with axial and lateral resolution well beyond the well-known thermal-diffusion-length-limited, depth-integrated nature of conventional thermographic and thermophotonic modalities. As a consequence, an axially resolved layer-by-layer photothermal image sequence can be obtained, capable of reconstructing three-dimensional visualizations (tomograms) of photothermal features in wide classes of materials. Additional embodiments are disclosed in which the aforementioned systems and methods are adapted to photo-acoustic and acousto-thermal imaging.