Multi-pass Interferometer Retroreflector Array for Picometer Resolution
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Solution Overview
Problem
Interferometers face limitations in achieving picometer-level sensitivity for displacement and surface irregularity measurements, necessitating improved sensitivity and compact form factors for various applications.
Innovation Solution
The design incorporates a single retroreflector at the target plane and multiple retroreflectors at the reference plane, allowing the measurement beam to make multiple passes, with one retroreflector acting as a terminal reflector to ensure the output beam is coaxial with the input, enhancing sensitivity and resolution while maintaining a compact form factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple retroreflectors are used at the reference plane to enable multiple passes, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The reference plane retroreflector array is segmented into multiple retroreflectors of different sizes (e.g., full-size, half-size, quarter-size retroreflectors) arranged in a hierarchical pattern. This segmentation allows the measurement beam to make multiple passes through the interferometer by reflecting between the target retroreflector and the segmented reference retroreflectors, thereby achieving picometer-level sensitivity while organizing the complexity through a systematic segmented structure
Solution Approach 2:
The retroreflectors are arranged in a nested configuration where smaller retroreflectors are positioned within the optical path defined by larger retroreflectors. This nesting pattern creates multiple reflection paths where the beam sequentially interacts with retroreflectors of decreasing size, enabling multiple passes without requiring completely separate optical paths for each pass, thus improving precision while containing device complexity
2Measurement precision
If multiple retroreflectors are arranged at the reference plane, then sensitivity is improved, but the form factor increases
Solution Approach 1:
The multiple retroreflectors are arranged in a two-dimensional array pattern on the reference plane rather than spreading them out in one dimension. This dimensional arrangement allows the measurement beam to access multiple retroreflectors through angular deviations while maintaining a compact overall footprint, thereby achieving high sensitivity without proportionally increasing the device's form factor
Solution Approach 2:
Different regions of the reference plane are assigned retroreflectors with specific local properties (different sizes and positions) optimized for their specific function in the multiple-pass sequence. This local quality differentiation allows each retroreflector to contribute specifically to certain passes, achieving high sensitivity while minimizing the total area required by optimizing the spatial distribution of each component
3Ease of operation
If a terminal retroreflector is positioned to reflect the beam back on itself, then ease of operation is improved, but device complexity increases
Solution Approach 1:
The terminal retroreflector is positioned asymmetrically within the array of reference retroreflectors and has a specific size and orientation that creates a unique optical path. This asymmetric positioning causes the measurement beam to reflect back on itself in a coaxial manner after completing multiple passes, simplifying operation and alignment while the asymmetry itself becomes part of the designed optical path rather than adding arbitrary complexity
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 enables interferometers to operate in the picometer stability regime, providing high-resolution measurements suitable for applications like lithography and telescope devices, and allows for use in space applications where size and weight are critical.
Implementation Method 1
a single retroreflector arranged at a target plane of the interferometer and a plurality of retroreflectors arranged at a reference plane of the interferometer
Implementation Method 2
the measurement beam provided to the interferometer makes a plurality of passes between the single retroreflector and the plurality of retroreflectors
Implementation Method 3
One of the plurality of retroreflectors is positioned as a terminal retroreflector that reflects the measurement beam back on itself such that an output of the interferometer is coaxial to an input of the interferometer
Data Source
AI summary
An interferometer is provided that includes a single retroreflector arranged at a target plane and a plurality of retroreflectors arranged at a reference plane of the interferometer. The single retroreflector and the plurality of retroreflectors are positioned such that a measurement beam provided to the interferometer makes a plurality of passes between the single retroreflector and the plurality of retroreflectors. One of the plurality of retroreflectors is positioned as a terminal retroreflector that reflects the measurement beam back on itself such that an output of the interferometer is coaxial with an input to the interferometer.