Michelson Interferometer Rotating Path Length Variation for Layer Thickness
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for determining geometric values, such as layer thicknesses and surface curvatures, in transparent or diffusive objects are complex and require intricate optical arrangements, making them cumbersome and difficult to adjust.
Innovation Solution
A Michelson interferometer with two reference arms of different optical lengths, where a rotating path length variation element changes the optical path length in a sequential manner, allowing for the separation of interference signals from the front and rear sides of a layer without the need for precise adjustment of optical components, and using different wavelengths for layer thickness and topography measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional methods with intricate optical arrangements are used to determine geometric values, then measurement accuracy can be achieved, but the device complexity and difficulty of adjustment increase significantly
Solution Approach 1:
The reference arm is segmented into multiple reference arms (first reference arm and second reference arm) with different optical path lengths. This segmentation allows simultaneous measurement of different depth ranges without requiring complex adjustment mechanisms, as each reference arm is optimized for specific measurement zones.
Solution Approach 2:
A dynamic path length adjustment mechanism is introduced in the reference arm, allowing real-time variation of optical path length. This dynamic adjustment enables the system to adapt to different measurement requirements without changing the overall optical arrangement, thereby maintaining measurement precision while reducing device complexity.
2Productivity
If multiple reference arms with different optical path lengths are used, then measurement time is reduced and simultaneous measurements are enabled, but the device complexity increases
Solution Approach 1:
The multiple reference arms are designed with a universal structure where each arm serves multiple functions: one reference arm measures the front surface while another measures the rear surface, and both can operate simultaneously. This multi-functionality increases measurement productivity without proportionally increasing device complexity, as the additional arms follow the same structural design pattern.
3Device complexity
If a single reference arm is used, then the device structure is simpler, but measurement time increases due to the need for staggered measurements
Solution Approach 1:
The single reference arm is segmented into multiple parallel reference arms with different fixed optical path lengths. This segmentation enables simultaneous measurement of different depth ranges (front surface and rear surface), dramatically reducing measurement time while maintaining relatively simple device structure through modular design.
4Measurement precision
If the optical path length in the reference arm is varied to match measurement lengths, then accurate geometric value determination is achieved, but the adjustment process becomes cumbersome and time-consuming
Solution Approach 1:
A dynamic path length adjustment mechanism is implemented in the reference arm, allowing electronic or automated control of optical path length variation. This dynamic adjustment replaces manual cumbersome adjustments, maintaining measurement precision while significantly improving ease of operation through automated control.
Solution Approach 2:
The optical path length parameter in the reference arm is made variable through controlled adjustment mechanisms. By changing this parameter dynamically rather than through fixed manual setup, the system achieves accurate geometric value determination while simplifying the operation process.
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 approach simplifies the determination of geometric values by enabling robust and interference-free measurements with high sensitivity, allowing for accurate layer thickness and topography analysis, even with weakly reflecting surfaces, and reduces measurement time by avoiding the need for staggered measurements.
Implementation Method 1
An interference phenomenon occurs in the detector arm of the Michelson interferometer whenever the delay time of a radiation in the measurement arm is equal to a radiation delay time in the reference arm
Data Source
AI summary
A Michelson-interferometer which has two reference arms and a short coherence length is used for the method and apparatus for measurement of geometric values on transparent or diffuse objects (19). The basic optical delay times of the reference arms (11, 12) are chosen in such a manner that they result in an optical delay time difference corresponding to a layer thickness, as a geometric value. The at least two reference arm beams (33a, 35a) are passed to a single rotating path-length variation element (23), with a mutual spatial offset angle (dw). A delay-time change, which is dependent on the rotation angle, of the reference arm beams is produced as a function of a rotation angle caused by rotation, in order to allow a delay-time change caused by the path-length variation element (23) to be applied successively to the basic optical delay times in the reference arms (11, 12). A topography as a further geometric value is obtained by projection of a light-intensity structure onto a surface to be measured, and by measurement of its image.