Photothermal Speckle Detection for Non-Contact Material Sensing
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Solution Overview
Problem
Existing non-contact sensing techniques for target materials face challenges such as difficulty, expense, and noise associated with detecting long-wavelength infrared light, complexity in interpreting scattering spectra, limited spatial resolution, and sensitivity issues.
Innovation Solution
A method and device using a pump and probe light source to generate a speckle pattern, where the pump light is modulated to irradiate a target specimen, and the changes in the speckle pattern's position and intensity are detected and analyzed to determine absorption spectra and thermal diffusivity without direct detection of IR radiation or thermal cameras, utilizing visible or SWIR wavelengths for improved sensitivity and resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If long-wavelength infrared (LWIR) detection is used to sense target materials, then the ability to detect thermal emission is improved, but sensor noise increases and requires cryogenic temperatures to reduce noise
Solution Approach 1:
The patent uses a visible or SWIR probe wavelength as an intermediary to indirectly detect the thermal effects caused by IR pump absorption. Instead of directly detecting LWIR thermal emission with noisy sensors, the system uses a probe beam whose speckle pattern changes in response to thermal expansion and refractive index changes induced by the pump beam, thereby mediating the detection process to avoid direct LWIR detection noise
Solution Approach 2:
The patent replaces the thermal radiation detection mechanism (which requires cryogenic sensors) with an optical interference mechanism. By using coherent probe light to create speckle patterns that respond to thermal changes, the system substitutes mechanical/thermal detection with optical detection, allowing room-temperature operation with high sensitivity
2Loss of information
If infrared radiometry is used to measure thermal emission changes, then material absorption information can be obtained, but the complexity of interpreting scattering spectra increases and spatial resolution is limited
Solution Approach 1:
The patent utilizes changes in the optical properties (effective 'color' response) of the material through thermal effects. The probe beam's speckle pattern changes in response to thermal expansion and refractive index changes, providing material-specific optical response signatures that are easier to interpret than scattering spectra while preserving absorption information
3Measurement precision
If traditional infrared sensing techniques are used, then thermal emission can be detected, but spatial resolution and signal-to-noise ratio are limited
Solution Approach 1:
The patent adds the dimension of coherent optical interference to the detection process. By using coherent probe light to generate speckle patterns, the system exploits the spatial coherence and interference effects to achieve higher spatial resolution beyond the diffraction limit of traditional infrared sensors, while the correlation analysis extracts thermal emission information from the speckle dynamics
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
This approach enables high-sensitivity, non-contact detection of target materials with improved spatial resolution and reduced noise, allowing for remote sensing and identification of materials based on absorption spectra and thermal properties without the need for cryogenic temperatures or expensive LWIR detectors.
Implementation Method 1
a pump light source configured to be modulated at a pump modulation and to irradiate a target specimen
Implementation Method 2
a probe light source arranged to generate a speckle pattern from the target specimen
Implementation Method 3
locations of constructive interference in an intensity pattern produced as a result of a diffuse reflection of coherent light
Implementation Method 4
a sensor configured to detect changes in at least one of position and intensity of one or more speckle lobes... having correlation with the pump modulation
Implementation Method 5
a correlator that is configured to perform a frequency analysis to determine correlation of the changes in at least one of position and intensity of the one or more speckle lobes with a frequency of the pump modulation
Implementation Method 6
The processor can be configured to determine an absorption spectrum of the target specimen based on the changes in at least one of position and intensity of the one or more speckle lobes correlated with the pump modulation. The processor can also be configured to determine a thermal diffusivity of the target specimen
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
A device (100), and corresponding method, includes a pump light source (102) configured to be modulated at a pump modulation and to irradiate a target specimen (112). The device also includes a probe light source (106) arranged to generate a speckle pattern (114) from the target specimen, as well as a sensor (110)configured to detect changes in at least one of position and intensity of one or more speckle lobes of the speckle pattern having correlation with the pump modulation. The device and method are used for non-contact monitoring and remote sensing of surfaces, gases, liquids, particles, and other target materials by analyzing speckle pattern changes as a function of pump light irradiation. Advantages can include much higher sensitivity than existing methods; the ability to use visible probe wavelengths for uncooled, low-cost visible detectors with high spatial resolution; and the ability to obtain target material properties without detecting infrared light.