Rotating Diffuser Laser Speckle Reduction
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Solution Overview
Problem
High coherence of infrared lasers causes speckle, which negatively affects the signal-to-noise ratio in spectroscopy and microscopy by reducing optical power during speckle reduction techniques, making it challenging to achieve effective speckle reduction without compromising signal quality.
Innovation Solution
A two-step speckle reduction approach using a rotating Infragold® diffuser to temporally average the laser beam, followed by coupling it into a multi-mode optical fiber, which significantly reduces speckle contrast while maintaining high optical throughput, and exploiting the temperature-dependent changes in speckle patterns for sensitive chemical detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If speckle reduction techniques are applied to reduce speckle contrast, then speckle contrast is reduced, but optical power is reduced
Solution Approach 1:
The patent employs a rotating diffuser that dynamically changes the illumination wavefront over time. The diffuser rotates at a controlled speed to temporally average the speckle pattern, reducing speckle contrast while maintaining continuous illumination and preserving optical power throughput.
Solution Approach 2:
The rotating diffuser creates periodic modulation of the illumination pattern. By rotating the diffuser at specific speeds, the system achieves temporal averaging of the speckle pattern, reducing contrast while maintaining the periodic delivery of full optical power to the sample.
2Illumination intensity
If laser coherence is maintained for high brightness, then brightness is improved, but speckle is generated
Solution Approach 1:
The system maintains laser coherence for high brightness by using a rotating diffuser that dynamically modulates the coherent beam. The rotation creates temporal averaging that reduces speckle while preserving the underlying laser brightness and coherence properties during illumination.
Solution Approach 2:
The rotating diffuser acts as an intermediary between the coherent laser source and the sample. It modulates the coherent beam to reduce speckle generation while allowing the full brightness of the laser to reach the sample through the diffused illumination pattern.
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 method provides a sensitive and cost-effective means for detecting trace amounts of chemicals by leveraging temperature-induced changes in speckle patterns, offering improved sensitivity and reduced costs compared to prior art techniques, with tailored applications for various configurations.
Implementation Method 1
A two-step speckle reduction approach using a rotating Infragold® diffuser to temporally average the laser beam
Implementation Method 2
followed by coupling it into a multi-mode optical fiber, which significantly reduces speckle contrast while maintaining high optical throughput
Implementation Method 3
Heating the speckle-inducing substrate causes it to expand and the resulting speckle to change
Implementation Method 4
The amount of speckle change is proportional to the increase in temperature, which is in turn proportional to the infrared (IR) absorption spectrum of the analyte to detect
Data Source
AI summary
A photo-thermal speckle spectroscopy device having an infrared laser, a visible laser, a foam, and a camera. The infrared and visible lasers are focused on the foam, which causes the visible laser to scatter. A camera records the speckle pattern, which shifts when the IR laser is turned on. The related method of photo-thermal speckle spectroscopy is also disclosed.