Low Backscatter Test Instrument Using Off-Axis Cassegrain Objective
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Solution Overview
Problem
Current laser/infrared tracking systems face challenges in accurately measuring bore sight alignment due to interference from retro reflection and backscatter, leading to self-tracking errors, which are difficult to eliminate and maintain, especially in high-power laser environments.
Innovation Solution
A compact instrument is designed to place the test instrument within critical ranges of the unit under test, minimizing the use of beam splitters and employing a shared or two-objective system to reduce alignment sensitivity and suppress backscatter, using an annular mirror to separate incoming and outgoing laser beams and an off-axis Cassegrain objective to ensure the retro-reflected image forms outside the tracking field of view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If retro reflection suppression is implemented using traditional methods, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent positions the measurement camera at a specific distance and angular relationship to the tracker aperture, creating a geometric configuration where the retro-reflected beam forms an image outside the tracker's field of view. This spatial dimensionality change eliminates the need for complex optical suppression components while achieving backscatter reduction.
Solution Approach 2:
The invention extracts the measurement camera from the direct optical path of the tracker by placing it at a lateral offset position. This separation removes the camera from the harmful retro-reflection path while maintaining its ability to measure the beam, thereby eliminating the need for beam splitters and other complex suppression apparatus.
2Measurement precision
If beam splitters are used to separate measurement beam from tracker beam, then measurement precision is improved, but loss of energy increases
Solution Approach 1:
The measurement camera is extracted from the direct optical path and positioned at a lateral offset, allowing it to receive the beam without requiring a beam splitter. This eliminates the energy loss inherent in beam splitting while maintaining measurement capability through direct beam interception at the offset position.
3Measurement precision
If alignment tolerance is reduced to achieve accurate bore sight measurement, then measurement precision is improved, but ease of operation deteriorates
Solution Approach 1:
By positioning the camera at a lateral offset and specific distance from the tracker aperture, the system creates a geometric relationship where the retro-reflected beam naturally forms an image outside the tracker's field of view. This spatial arrangement reduces alignment sensitivity because small angular deviations do not significantly affect the measurement geometry.
Solution Approach 2:
The system separates the measurement function from the tracking function by using distinct optical paths - the tracker receives the beam through its aperture while the measurement camera intercepts the beam at an offset position. This segmentation allows independent optimization of each function without tight coupling that would require precise alignment.
4Measurement precision
If tracker sensitivity is increased to detect low power beams, then measurement precision is improved, but object-generated harmful factors increase
Solution Approach 1:
The patent uses spatial separation and geometric positioning to place the retro-reflected beam image outside the tracker's field of view. This allows the tracker to maintain high sensitivity for detecting low-power target beams while the geometry ensures that retro-reflected light from the measurement apparatus does not enter the tracker aperture, eliminating self-tracking.
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 configuration simplifies alignment and maintenance, reduces self-tracking errors, and allows for accurate bore sight error measurement while maintaining target beam integrity, enabling reliable lab and field testing of directable jammers.
Implementation Method 1
the image of the laser beam, as retro reflected, scattered and diffracted, forms outside the tracking field of view
Implementation Method 2
the image of the laser beam, as retro reflected, scattered and diffracted, forms outside the tracking field of view
Implementation Method 3
the image of the laser beam, as retro reflected, scattered and diffracted, forms outside the tracking field of view
Implementation Method 4
an annular mirror to separate incoming and outgoing laser beams
Data Source
AI summary
A compact instrument enables placement of the instrument such that the image of the laser beam, as retro reflected and diffracted, forms outside the tracking field of view. The target source and beam camera can be located at the focus of a Cassegrain objective. Embodiments include shared objective and twin objective design. With a shared objective design, both the beam projector and profiling camera can see the same focal length. A two objective design can use two different focal lengths.