Spatially Offset Raman Probe with Asymmetric Apertures
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Solution Overview
Problem
Conventional remote Raman probes face challenges in achieving efficient spatially offset excitation and collection while maintaining a compact design, leading to interference from container or window materials that introduce unwanted background signatures, affecting signal quality.
Innovation Solution
The design incorporates a first lens to collimate the excitation beam into a smaller aperture and a second lens to collimate the collection beam into a larger aperture, with a blocking element, such as a mirror or bandpass filter, to separate and reject unwanted light from the container or window, allowing coaxial excitation and collection paths while maintaining signal purity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If spatially offset excitation and collection paths are used to reduce background interference, then signal purity is improved, but device complexity and probe size increase
Solution Approach 1:
The patent applies asymmetry by using different aperture sizes for excitation and collection paths. The collection aperture is made significantly larger than the excitation aperture, creating an asymmetric optical configuration that enables spatial offset functionality while maintaining a compact coaxial probe design. This asymmetric aperture arrangement allows the collection path to gather Raman scattered light from a larger spatial region while the smaller excitation aperture limits the area where background interference occurs, thereby achieving signal purity improvement without requiring complex probe configurations.
2Device complexity
If a common objective lens is used for both excitation and collection, then device complexity is reduced, but background interference from the objective and container increases
Solution Approach 1:
The patent applies local quality by creating spatial differentiation within the optical paths. By using asymmetric apertures where the collection aperture is larger than the excitation aperture, the system enables different functional zones: the smaller excitation aperture limits background generation at the objective, while the larger collection aperture captures Raman signal from a broader region. This local spatial quality differentiation allows the common objective to serve both functions while minimizing its contribution to background interference.
Solution Approach 2:
The patent applies parameter changes by varying the aperture sizes in the optical system. Specifically, the collection aperture is designed to be at least two times greater than the excitation aperture. This parameter change enables the system to maintain a simple common objective configuration while controlling background interference through aperture geometry rather than requiring separate objectives or complex spatial offset mechanisms.
3Quantity of substance
If the collection aperture is made larger to improve signal collection, then signal strength increases, but background noise from container and objective increases
Solution Approach 1:
The patent resolves this contradiction through asymmetric aperture design where the collection aperture is made significantly larger than the excitation aperture. This asymmetry allows the collection path to gather Raman scattered light from a large spatial region (improving signal strength) while the smaller excitation aperture confines the area where background interference is generated. The key insight is that Raman scattered light travels in all directions, so a larger collection aperture can capture signals from regions away from the objective without proportionally increasing background noise from the objective and container.
Data Source
AI summary
An optical measurement probe for capturing a spectral response through an intervening material emitting unwanted background radiation includes: a first lens configured to receive light and collimate the light into a collimated excitation beam defining a first aperture; an objective element for focusing the collimated excitation beam to a point or region in a sample through the intervening material, wherein the objective element also receives light scattered by the sample and the intervening material and collimates the scattered light into a collimated collection beam defining a second aperture; and a blocking element within the collimated collection beam for removing the light scattered by the intervening material from the collimated collection beam received from the sample, wherein the second aperture defined by the collimated collection beam is at least two times greater than the first aperture defined by the collimated excitation beam.