Adjustable Collimating Lens for Fizeau Interferometer Chromatic Compensation
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Solution Overview
Problem
Fizeau interferometers face issues with chromatic focus shift and non-common path errors when using light sources of different wavelengths than the design wavelength, leading to defocusing and errors in test results due to aberrations in the transmission sphere.
Innovation Solution
Adjusting the power of the test beam by making the collimating lens position in the optical train adjustable along the optical axis, allowing for alignment of rays perpendicular to the reference surface, thereby correcting chromatic focus shifts and accommodating various wavelengths and focal lengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a transmission sphere designed for a specific wavelength (e.g., 633 nm) is used at a different wavelength (e.g., 658 nm), then the interferometer can operate with high-power solid-state lasers, but chromatic focus shift and aberrations are introduced into the transmitted wavefront
Solution Approach 1:
The patent changes the optical power parameter of the collimating lens to compensate for chromatic focus shift. By adjusting the lens power, the system maintains accurate wavefront transmission across different wavelengths, resolving the contradiction between wavelength versatility and wavefront accuracy
Solution Approach 2:
The patent introduces an adjustable collimating lens that can dynamically change its optical power. This dynamic adjustment capability allows the system to adapt to different wavelengths while maintaining precision, resolving the contradiction between fixed design parameters and wavelength variability
2Adaptability or versatility
If the collimating lens position is fixed, then the optical path is stable, but the system cannot accommodate different wavelengths or focal lengths
Solution Approach 1:
The patent makes the collimating lens position adjustable along the optical axis, transforming a fixed system into a dynamic one. This allows accommodation of different wavelengths and focal lengths while adding minimal complexity through a simple linear adjustment mechanism
Solution Approach 2:
The adjustable collimating lens mechanism serves multiple functions: it compensates for chromatic focus shift, accommodates different wavelengths, and adjusts for various focal lengths. This multi-functionality resolves the contradiction between versatility and complexity by using a single adjustment mechanism for multiple purposes
3Measurement precision
If the test beam power is increased to improve signal strength, then measurement sensitivity improves, but chromatic focus shift and non-common path errors increase
Solution Approach 1:
The patent applies preliminary correction by adjusting the collimating lens power before the test beam enters the transmission sphere. This pre-compensation prevents chromatic focus shift and non-common path errors from occurring, allowing high beam power to be used without introducing harmful aberrations
Solution Approach 2:
The system performs preliminary alignment and power adjustment of the collimating lens to ensure optimal beam conditions before illumination. This preliminary action ensures that even at high power levels, the beam remains properly focused and free from chromatic aberrations
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 solution enables the use of different wavelengths and focal lengths in Fizeau interferometers, eliminating chromatic focus shift and non-common path errors, allowing for accurate optical testing without the need for repositioning the reference surface, thus improving measurement quality.
Implementation Method 1
Adjusting the power of the test beam by making the position of the collimating lens relative to the beam expander adjustable along the optical axis
Implementation Method 2
The most significant aberration that results from such a mismatch in wavelengths is a change in the optical power (also called chromatic focus shift)
Implementation Method 3
Fizeau interferometers for optical testing of spherical surfaces
Data Source
AI summary
The focus of the collimating lens in the optical train of a Fizeau interferometer is adjusted to change the power of the test beam illuminating the transmission sphere. As a result, the rays can be made sufficiently perpendicular to the reference surface to eliminate the chromatic focus shift and non-common path errors produced by a light source of wavelength different from the design wavelength of the transmission sphere. By making the position of the collimating lens relative to the beam expander adjustable along the optical axis over some small range, illumination sources of various wavelength can be used in the same interferometer.