Microspectroscopy Autofocus via Astigmatic Beam Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Microspectroscopy devices with high numerical aperture objective lenses face challenges in maintaining focus during long-term continuous measurements due to thermal expansion, making real-time defocus correction difficult, especially when analyzing large biopolymers like DNA passing through a nanopore.
Innovation Solution
A defocus-sensing beam with astigmatism is used to detect the amount and direction of defocus in real-time, enabling high-speed real-time autofocusing by analyzing the blur of the spot image, which allows for continuous and accurate focus adjustment without interrupting the measurement process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high numerical aperture objective lens is used to observe weak Raman scattering light with high sensitivity and high resolution, then the depth of field becomes submicron and maintaining the distance between the sample and the objective lens stably for a long time becomes difficult due to thermal expansion, but using mechanical fixing alone cannot maintain focus during long-term continuous measurement
Solution Approach 1:
The patent implements an autofocus system that continuously monitors the focus state by analyzing the spot image formed by a defocus-sensing beam on a photodetector. When defocus occurs due to thermal expansion or sample drift, the system detects the blurred spot image and automatically adjusts the objective lens position to restore sharp focus, enabling long-term stable measurement without manual intervention
Solution Approach 2:
The patent replaces manual mechanical focusing with an automated optical feedback system. Instead of relying on mechanical precision and operator skill to maintain focus, the system uses optical sensing (defocus-sensing beam) and automated control to detect and correct focus drift in real-time, substituting mechanical stability requirements with active optical compensation
2Measurement precision
If normal focusing is performed by shifting the distance between the sample and the objective lens back and forth to acquire through-focus images, then the image can be measured, but this process is time consuming and is not suitable for real-time auto focus in continuous measurement
Solution Approach 1:
The patent pre-arranges a defocus-sensing beam path that allows immediate detection of focus state without requiring through-focus scanning. The sensing beam is continuously directed through the objective lens and focused onto a photodetector, enabling real-time focus monitoring and instantaneous correction, eliminating the time-consuming back-and-forth scanning process
Solution Approach 2:
The patent extracts the focus detection function from the main measurement process by using a separate defocus-sensing beam. This dedicated sensing beam independently monitors focus status without interfering with the Raman measurement, allowing simultaneous measurement and focus correction without time loss
3Loss of information
If one excitation light beam is focused on one spot on a sample substrate to observe the light emission image on the spot, then the occurrence of defocus can be detected but it is difficult to detect the direction of defocus
Solution Approach 1:
The patent introduces astigmatism into the defocus-sensing beam path using a cylindrical lens, creating asymmetric spot images on the photodetector. When the beam is in focus, the spot is circular; when defocused, the spot becomes elliptical with the major axis orientation indicating the direction of defocus. This asymmetric transformation enables both detection and directional information extraction
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 long-term continuous analysis of large polymers, such as DNA, and allows for multi-point measurements with improved sensitivity and resolution by detecting defocus and tilt of the sample substrate, facilitating base sequence determination and maintaining focus during prolonged measurements.
Implementation Method 1
one excitation light beam is focused on one spot on a sample substrate by an objective lens to observe the light emission image on the spot
Implementation Method 2
A defocus-sensing beam having defocus or astigmatism is incident on the objective lens. Since the blur of the spot image of such a defocus-sensing beam is different depending on the direction of defocus, it becomes possible to detect the amount and direction of defocus in real time
Implementation Method 3
a device for analyzing a biopolymer by irradiating the biopolymer passing through a nanopore with light to generate Raman scattering light, and measuring the light
Implementation Method 4
The present invention is particularly useful for applications requiring long-term continuous measurement such as determination of the DNA base sequence based on the Raman microspectroscopy, etc.
Data Source
AI summary
With a microspectroscopy device provided with an objective lens with a high numerical aperture, a defocus arises from thermal drift, etc., necessitating auto-focusing. Conventional auto-focus based on through-focus image acquisition takes time, and thus, it cannot be applied to continuous measurement over a long time wherein high-speed sampling is carried out. The present invention addresses this problem by having a defocus-sensing beam that has either defocus or astigmatism fall incident on the objective lens. Since how the image of the spot of the beam for defocus sensing blurs differs depending on the orientation of the defocus, real-time detection of the amount and orientation of defocus becomes possible, and high-speed realtime auto-focus becomes possible.