Polarization-Switched Microscope Focusing for Fast Axial Scanning
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Solution Overview
Problem
Existing focusing devices for microscopes face limitations in achieving fast and accurate axial scanning, particularly for applications like MINFLUX microscopy, due to mechanical inaccuracies, high costs, and wavelength dependence, which are not suitable for real-time iterative scanning and multicolor applications.
Innovation Solution
A focusing device using a polarization switching element and a polarization-dependent focusing element, such as a telescope, to axially displace the focus without mechanical movement, enabling fast switching rates up to 5 kHz and robust, affordable components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If mechanical actuators (motors or piezoelectric elements) are used to move the objective or sample carrier for focusing, then the focusing device is simple in structure and low cost, but the focusing speed is limited and inaccuracies occur due to inertia and resonance
Solution Approach 1:
The patent replaces the mechanical actuator system with an optical system consisting of a polarization switching element and polarization-dependent focusing element. The polarization switching element electrically switches between different polarization states, and the polarization-dependent focusing element (such as a birefringent crystal or polarizing beam splitter arrangement) redirects the light beam through different optical paths with different focal lengths, achieving fast focus positioning without mechanical movement, thereby eliminating inertia and resonance issues while maintaining high precision.
2Speed
If AOM-based varifocal lenses or deformable mirrors are used for fast axial scanning, then focusing speed is improved, but the devices are expensive, technically challenging, and easily damaged
Solution Approach 1:
The patent employs relatively simple and robust optical components (polarization switching element and polarization-dependent focusing element) that are less fragile and more reliable than AOM-based varifocal lenses or deformable mirrors. These components are commercially available, easier to maintain, and less susceptible to damage, thereby improving device reliability while maintaining fast scanning capability.
3Speed
If AOM-based focusing devices are used, then fast axial scanning is achieved, but beam displacement is strongly wavelength dependent which is disadvantageous for multicolor applications
Solution Approach 1:
The patent uses a polarization-dependent focusing element whose optical path difference and focal length variation are determined by the birefringence properties of the material and the polarization state of the light, rather than by acoustic frequency or mechanical position. This approach makes the beam displacement largely independent of wavelength, enabling multicolor applications while maintaining fast axial scanning capability.
4Adaptability or versatility
If iterative MINFLUX microscopy requires non-periodic axial scans, then application flexibility is improved, but AOM-based solutions become technically challenging and expensive
Solution Approach 1:
The patent employs a polarization switching element that can be electrically controlled to switch between different polarization states dynamically. This allows the system to adapt to different scanning patterns (periodic or non-periodic) in real-time by changing the polarization state, providing application flexibility without requiring complex acoustic signal generation or mechanical positioning systems.
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
Enables accurate and fast axial scanning suitable for MINFLUX microscopy, avoiding mechanical limitations and reducing costs, with switching rates sufficient for real-time iterative scanning and multicolor applications.
Implementation Method 1
a first polarization switching element, particularly a Pockels cell, configured to rotate a polarization of a linearly polarized light beam around a first optical axis from a first polarization direction to a second polarization direction upon receiving a switching signal
Implementation Method 2
a polarizing beam splitter configured to selectively guide the light beam along a first light path and a second light path dependent on the polarization of the light beam
Implementation Method 3
a focusing element configured to axially displace a main focus of the light beam between a first axial position and a second axial position
Data Source
Figure 1A~1B
Figure 2A~2C
Figure 3A~3B
AI summary
The invention relates to a focusing device (1) for a microscope (100) comprising a first polarization switching element (3) configured to rotate a polarization of a linearly polarized light beam (L) around a first optical axis (A) from a first polarization direction (Pl) to a second polarization direction (P2) upon receiving a switching signal, and a focusing element (4) configured to axially displace a main focus (MF) of the light beam (L) generated by a microscope objective lens (121) between a first axial position and a second axial position dependent on the polarization of the light beam (L). The invention further relates to a focusing system (2) comprising at least two of the focusing devices (1), a microscope (100) using the focusing device (1) and a method for imaging and/or localizing molecules (M) or particles (P) in a sample (S).