Depth-scanning microscope vibration compensation via dynamic reference mirror
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Solution Overview
Problem
Depth-scanning interference microscopes, particularly white-light interference microscopes, are susceptible to measurement inaccuracies due to oscillations and vibrations, which current methods can only reliably compensate for single-frequency spurious oscillations, leaving higher-frequency harmonic or transient vibration components unaddressed.
Innovation Solution
The microscope employs a periodically moving reference mirror with a higher frequency than the image recording frequency, synchronized with a pulsed light source and image sensor operation, allowing for enhanced temporal and spatial resolution in distance measurements, and uses a frequency-selective filter to isolate monochromatic light interference signals for precise vibration compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a reference mirror oscillates periodically at a frequency matching the image recording frequency, then single-frequency vibrations can be compensated, but higher-frequency harmonic or transient vibration components cannot be reliably compensated
Solution Approach 1:
The reference mirror is moved dynamically with a frequency higher than the image recording frequency (e.g., 2x or higher), allowing the system to capture and compensate for higher-frequency vibration components that static or low-frequency reference systems cannot detect. This dynamic movement enables the reference beam to sample the optical path at multiple points during each vibration cycle.
Solution Approach 2:
The reference mirror performs periodic oscillation at a frequency synchronized with and higher than the image recording frequency. This periodic action creates multiple reference phases within each measurement cycle, enabling the system to distinguish and compensate for harmonic and transient vibrations that would be indistinguishable at lower frequencies.
2Measurement precision
If the reference mirror moves at a frequency higher than the image recording frequency, then temporal and spatial resolution in distance measurements is enhanced, but synchronization complexity between light source, reference mirror, and image sensor increases
Solution Approach 1:
The system employs feedback mechanisms where the actual position of the reference mirror is continuously monitored and used to adjust the phase and frequency of the light source modulation and image sensor triggering. This feedback loop ensures that even at higher frequencies, the synchronization between components remains precise, maintaining measurement accuracy while managing the increased complexity through active control.
Solution Approach 2:
The reference mirror's periodic movement is initiated and synchronized before the actual depth scanning measurement begins. This preliminary action establishes a known reference phase relationship between the mirror position, light source emission, and image sensor exposure, allowing the system to process higher-frequency movements without losing synchronization during the critical measurement phase.
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 enables reliable compensation for both mono-frequency and higher-frequency harmonic or transient vibrations, significantly improving measurement accuracy and resolution, particularly in sensitive white-light interference microscopes.
Implementation Method 1
a partial beam emanating from the light source and reflected by the measurement object, and a partial beam also emanating from the light source and reflected at the reference mirror, are superimposed and detected on an image sensor
Implementation Method 2
a partial beam emanating from the monochromatic light source and reflected by the measurement object, and a partial beam also emanating from the monochromatic light source and reflected at the reference mirror, are superimposed on a sensor
Data Source
Figure 1
Figure 2
AI summary
The invention relates to a depth-scanning microscope for determining a surface topography of a measurement object (1), comprising a light source (13) for illuminating the measurement object (1), wherein a partial beam originating from the light source (13) and reflected by the measurement object (1) is detected by an image sensor (23), and a monochromatic light source (24), wherein a partial beam originating from the monochromatic light source (24) and reflected by the measurement object (1) and a partial beam, likewise originating from the monochromatic light source (24) and reflected by a reference mirror (19), superpose on a photo sensor (26). The depth-scanning microscope also comprises an adjustment device for displacing at least parts of the microscope and/or measurement object for varying the length of the partial beams reflected by the measurement object (1). The microscope is characterized in that a drive (20) is provided for moving the reference mirror (19) along the optical axis thereof and hence for varying the path difference. The invention further relates to a method for operating such a depth-scanning microscope.