Microscope Autofocus Using Grid Pattern Backscatter Analysis
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Solution Overview
Problem
Existing autofocus systems in microscopy struggle with accurately determining the focus plane in samples with multiple interfaces, leading to incorrect focus determination due to additional backscattered light from planes at different axial positions, and often require iterative and time-consuming processes or reduced capture range to suppress such signals.
Innovation Solution
A method using a multi-element autofocus detector, such as a camera, to project and analyze a reference pattern backscattered from multiple interfaces, allowing for the isolation and analysis of the reference surface's contribution to determine the focus deviation, enabling robust and fast focusing even with complex samples by analyzing the spatial distribution of light intensity across the detector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a single-spot reference pattern is used in active autofocus systems, then the focusing speed is improved, but the system becomes vulnerable to false signals from additional interfaces in complex samples
Solution Approach 1:
The reference pattern is divided into multiple spots arranged in a grid pattern, with each spot providing an independent measurement of focus deviation. This segmentation allows the system to distinguish between signals from different interfaces by analyzing the spatial distribution of backscattered light, thereby maintaining fast focusing while improving reliability in complex samples.
Solution Approach 2:
The patent transitions from a single-point measurement to a multi-point spatial distribution measurement. By projecting a grid of reference spots and analyzing their backscattered light across different spatial positions, the system gains an additional dimension of information that enables discrimination between multiple interfaces and accurate focus determination.
2Reliability
If the focal length is reduced and numerical aperture increased to suppress backscatter from out-of-focus interfaces, then the reliability of focus determination is improved, but the capture range of the autofocus system is reduced
Solution Approach 1:
Instead of relying on a single measurement point, the system uses multiple reference spots distributed across the field of view. Each spot provides information about focus deviation at its specific location, allowing the system to suppress out-of-focus signals through spatial analysis while maintaining a large capture range because the grid pattern can accommodate interfaces at various axial positions.
Solution Approach 2:
The grid pattern of reference spots acts as an intermediary that mediates between the objective and the interfaces. By analyzing the spatial distribution of backscattered light from multiple spots, the system can identify which spots correspond to in-focus interfaces and which to out-of-focus interfaces, enabling accurate focus determination without sacrificing capture range.
3Ease of manufacture
If iterative image-based autofocus is used, then the cost is reduced, but the focusing process becomes slow due to repeated image acquisition and analysis
Solution Approach 1:
The system performs preliminary action by projecting the reference pattern and capturing the backscattered light in a single step. The grid pattern is designed to provide immediate information about focus deviation direction and magnitude, eliminating the need for iterative image acquisition and analysis while maintaining cost-effectiveness through the use of existing camera detectors.
Solution Approach 2:
The patent replaces the mechanical iterative adjustment process with an optical measurement approach. Instead of repeatedly acquiring images and mechanically adjusting focus based on image analysis, the system uses a reference pattern projection and single-shot detection to directly determine focus deviation, significantly reducing focusing time while keeping the system cost-effective.
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 allows for reliable and rapid autofocus determination with a large capture range, avoiding the limitations of iterative processes and maintaining accuracy even with multiple interfaces, by isolating the reference surface's contribution and suppressing other interface signals, thus enabling precise and efficient focus adjustment.
Implementation Method 1
a known reference pattern is projected through the microscope objective towards the sample. Reference patterns are simple in structure; most often a single spot is used, but other structures like grid or line structures may also be used. The dedicated detector typically comprises a single detector element or a small number of detector elements, e.g. photodiodes, which receive light backscattered through the microscope objective from a reference surface within or near the sample.
Data Source
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AI summary
A method for autofocusing a microscope at a correct autofocus position in a sample (60) comprises the steps: -Generating a reference pattern by an autofocus light device (20, 21, 22, 23; 20, 21, 22), -Projecting the reference pattern towards a sample (61), whereby the reference pattern is backscattered by at least two interfaces (70, 71, 72) being located at or close to the sample (61), -Projecting the backscattered reference pattern towards a detector (26, 6) which provides spatial resolution, -Obtaining a superposition of a number of detection patterns (80, 81, 82), each detection pattern related to one of the interfaces (70, 71, 72), on the detector (26, 16), -Analyzing the superposition of detection patterns (80, 81, 82) to identify at least one autofocus detection pattern (80, 81) related to at least one of the interfaces (70, 71, 72), and -Analyzing the at least one autofocus detection pattern (80, 81) to current focus position from the correct focus position.