Line-scan Raman imaging method and apparatus for sample evaluation
Inventors
Chao, Kuanglin • Kim, Moon S. • Qin, Jianwei
Assignees
University of Maryland Baltimore • US Department of Agriculture USDA • University of Maryland College Park
Publication Number
US-9927364-B1
Publication Date
2018-03-27
Expiration Date
2033-11-01
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Abstract
A line-scan laser is directed to a sample so that a Raman-shifted light signal is emitted from the sample. An imaging spectrograph and associated camera and processor acquires the Raman-shifted light signal and processes the signal to thereby identify the composition of the sample.
Core Innovation
The invention disclosed is a method and apparatus for evaluating relatively large, especially dry powdered, particulate samples using a line-scan Raman imaging system. This system employs a line-scan laser beam emitted by a laser-emitting device, directed onto a sample via a beamsplitter, causing the sample to emit a Raman-shifted light signal. An imaging spectrograph and associated camera detect and disperse this signal to generate spectral data for each pixel of the laser-illuminated line on the sample. A processor then analyzes these spectra to identify the composition of the sample.
The background problem being addressed is the slow speed and small sample size limitations of prior art methods for detecting contamination in particulate food substances such as powders and granulated products. Contaminants like melamine and related chemicals (cyanuric acid, ammeline, and ammelide) may be present in food products and pose significant safety risks. Existing methods, including prior art using point-source lasers, are effective but time-consuming and limited in the volume of sample tested. There exists a need for a faster method that can test larger sample volumes while maintaining or improving accuracy.
The disclosed invention solves this problem by utilizing a line-scan laser system that reduces test times from hours to minutes and significantly increases the size of samples tested. The apparatus includes precise optical components such as a dichroic beamsplitter angled to ensure consistent alignment between the excitation laser line (Raman Plane) and the spectrograph input slit (Spectrograph Plane), enhancing signal quality regardless of sample height variation. The system produces hyperspectral Raman images, allowing chemical composition analysis and visualization of particulate samples with high spatial and spectral resolution.
Claims Coverage
The patent comprises three independent claims encompassing a method, an apparatus, and the system components for determining a sample composition using line-scan Raman imaging. Each independent claim includes various inventive features relating to the laser, beamsplitter, spectrograph, camera, and processing of Raman signals.
Method for determining sample composition using a continuous wave non-pulsed line-laser beam
The method involves emitting a continuous wave non-pulsed line-laser beam directed via a beamsplitter onto a sample, where the sample emits a Raman light signal. A Raman spectrograph with a long-pass filter receives and disperses the signal to generate spectral data. A camera connected to the spectrograph forms a spectrum for each pixel of the line-laser image, transmitting this to a processor to determine the sample composition based on Raman imaging.
Apparatus structured for line-scan Raman imaging to determine sample composition
The apparatus comprises a laser-emitting device generating a continuous wave non-pulsed line-laser beam, a beamsplitter positioned to deflect this beam onto a sample retention reservoir containing the sample, which emits a Raman-shifted light signal upon illumination. A Raman spectrograph with an attached long-pass filter receives and disperses the light signal. A camera forms spectra for each pixel of the line-laser image and transmits these to a processor for composition determination.
System configuration for line-laser beam excitation and Raman signal detection
The system includes a beamsplitter aligned to deflect the line-scan laser beam onto the sample so that Raman-shifted light is generated. The spectrograph's input slit is aligned in the same vertical plane as the excitation line defined by the line-laser beam, ensuring consistent signal collection. The processor communicates with the spectrograph and camera to analyze the Raman light signals and determine the sample composition.
The independent claims collectively cover the unique method, apparatus design with key optical configurations, and system arrangement that enable efficient, high-resolution line-scan Raman imaging for rapid and accurate determination of the composition of particulate samples.
Stated Advantages
Significantly reduces test times from hours to minutes compared to prior art methods.
Enables testing of much larger sample volumes of particulate materials.
Maintains or exceeds the accuracy and consistency of existing methods for contamination detection.
Improves signal quality and data reliability by aligning the Raman Plane with the spectrograph input slit through a beamsplitter angled at about 45°, minimizing effects of sample height variation.
High spatial and spectral resolution allow precise chemical imaging and contaminant identification.
Documented Applications
Detecting contamination in particulate-type food materials, including powders such as milk powder and milk substitutes.
Authentication of milk powder to detect adulterants like melamine and dicyandiamide mixed in the sample.
Food safety and quality applications that require visualization of chemical composition and spatial distribution of contaminants in particulate samples.
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