Interference Objective Lens Thermal Expansion Compensation
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Solution Overview
Problem
Conventional light-interference measuring apparatuses face challenges in maintaining high precision measurements due to environmental temperature changes, which cause shifts in the focal plane and refractive index of interference objective lenses, leading to decreased brightness of interference fringes.
Innovation Solution
An interference objective lens unit with a first holder made of material having a low linear expansion coefficient and a second holder with a higher linear expansion coefficient, which adjusts the optical path differences between the reference and measuring optical paths to maintain phase congruence, even when the focal point shifts with temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the beam splitter position is set to achieve phase congruence between reference light and object light, then interference fringes can be seen in clear contrast, but when environmental temperature changes, the focal plane and reflecting plane become unconjugated, causing phase difference and decreased brightness of interference fringes
Solution Approach 1:
The patent applies thermal expansion by using a holder made of material with a specific linear expansion coefficient that differs from the objective lens material. When temperature changes occur, the holder expands or contracts at a different rate than the objective lens, thereby compensating for the focal plane shift and maintaining phase congruence between the reference light and object light, ensuring stable interference fringe brightness.
Solution Approach 2:
The patent changes the physical parameter of the holder material by selecting a material with a specific linear expansion coefficient that is different from the objective lens material. This parameter change allows the holder to compensate for temperature-induced focal plane shifts, maintaining the optical path difference correction and phase congruence under varying temperature conditions.
2Ease of manufacture
If holders made of the same material are used for both objective lens and reference mirror, then manufacturing is simplified, but temperature changes cause focal plane shifts and optical path difference errors
Solution Approach 1:
The patent applies local quality by using different materials for the holder and objective lens, where the holder material has a specific linear expansion coefficient different from the objective lens material. This localized material differentiation allows the holder to compensate for temperature-induced focal plane shifts, maintaining optical path difference accuracy while enabling precise measurement.
3Ease of operation
If the focal plane is kept fixed relative to the beam splitter, then consistent imaging plane is achieved, but temperature changes cause the focal plane to shift, requiring cumbersome re-adjustment of optical element positions
Solution Approach 1:
The patent uses thermal expansion of the holder material to automatically compensate for temperature-induced focal plane shifts. The holder, made of material with a different linear expansion coefficient than the objective lens, expands or contracts with temperature changes in a way that maintains the focal plane position relative to the beam splitter, eliminating the need for manual re-adjustment and ensuring operational ease and reliability.
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 ensures high-precision measurements without decreasing the brightness of interference fringes, as the optical path differences are corrected, maintaining the phase congruence between reference and object light, even with temperature fluctuations.
Implementation Method 1
a first holder that holds the objective lens and that is formed by material having a first linear expansion coefficient; and a second holder that holds the reference mirror and is provided at the outer face-side of the first holder, the second holder that is formed by material having a second linear expansion coefficient which is different from the first linear expansion coefficient
Data Source
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AI summary
Disclosed is an interference objective lens unit, comprising: an objective lens (30) ; a beam splitter (21) that splits the light transmitted through the objective lens (30) into a reference optical path in which a reference mirror is provided and a measuring optical path in which the measuring object (W) is placed, and that superposes the split lights to output interference light; a first holder (34) that holds the objective lens and that is formed by material having a first linear expansion coefficient; and a second holder (35) that holds the reference mirror and that is formed by material having a second linear expansion coefficient different from the first linear expansion coefficient, wherein when a usage environment temperature changes, a difference in the linear expansion coefficients between the first holder and the second holder corrects an optical path difference between the reference optical path and the measuring optical path.