Raman Probe End Optics Beam Steering
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Solution Overview
Problem
Longer probe lengths in Raman spectroscopy face challenges with beam alignment and vignetting due to beam divergence and mechanical stress, particularly when using multimode optical fibers, leading to inefficient focusing and reduced spectral collection.
Innovation Solution
Incorporating two intermediate lenses between the probe head and the focusing objective within the end optic tube to maintain beam centering and improve numerical aperture, minimizing vignetting and optimizing beam filling at the focus point, even with probe tilting or bending.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If longer end optic tubes are used to increase probe length for various applications, then the probe can reach deeper into sample vessels and provide greater versatility, but beam divergence causes the optical path to overfill the focus lens aperture resulting in vignetting and reduced measurement precision
Solution Approach 1:
The patent introduces a beam steering mirror as an intermediary component positioned within the end optic tube. This mirror redirects the diverging beam path to properly fill the focus lens aperture without overfilling, thereby maintaining beam alignment precision throughout the length of the probe. The mirror acts as a mediator between the diverging beam from the probe head and the focusing objective, correcting the optical path to eliminate vignetting while preserving the ability to use longer probe lengths for deep sample vessel access
2Length of moving object
If longer end optic tubes are used to increase probe length, then the probe can access deeper samples, but mechanical stress causes misalignment of the beam path and reduces reliability
Solution Approach 1:
The beam steering mirror serves as a compensatory intermediary that actively corrects for mechanical stress-induced misalignments. By positioning the mirror within the end optic tube, it can redirect the beam path to maintain proper alignment at the focus lens even when the probe experiences bending or stress during insertion into sample vessels. This intermediary component provides a degree of passive alignment compensation that maintains reliability throughout the probe's operational range
3Device complexity
If the beam path is allowed to diverge naturally from the probe head, then the optical system is simpler, but the focus lens is overfilled causing vignetting and loss of information
Solution Approach 1:
The beam steering mirror introduces a controlled complexity to the optical system that prevents information loss. By redirecting the diverging beam to properly fill the focus lens aperture, the mirror ensures that maximum light collection efficiency is achieved without vignetting. The added component is justified by the significant improvement in spectral collection efficiency and the elimination of beam truncation losses that would occur with natural divergence
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
The solution effectively reduces vignetting and maintains efficient beam focusing across longer probe lengths, ensuring high numerical aperture and improved light collection without overfilling or underfilling the focus lens, thus enhancing the quality of Raman spectroscopic measurements.
Implementation Method 1
a collimating lens having an aperture for collimating and focusing a counter-propagating excitation and collection beam
Implementation Method 2
Incorporating two intermediate lenses between the probe head and the focusing objective within the end optic tube to maintain beam centering and improve numerical aperture
Data Source
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AI summary
In one aspect of the present disclosure, improved end optics are disclosed that maximize the numerical aperture focused at a sample point (sample focus 720) while minimizing unwanted artifacts such as vignetting. The configurations also maintain centering of the excitation/collection beam on the objective (focus lenes 202) if the probe tilts or bends. The disclosed configurations are particularly suited to probes wherein the excitation and/or collection paths between the probe and the laser/analyzer are coupled through multimode fibers, such as in Raman and other forms of laser spectroscopy. The disclosure includes the insertion of one or more additional lenses (e.g. lenses 702, 704) between the probe head and the focusing objective at the probe tip.