Photomultiplier Tube Voltage Segmentation for Dynamic Protection
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Solution Overview
Problem
Confocal microscopes face damage risks due to high light intensities during dynamic sample processes, leading to slow protective cutoffs that impair image capture and reduce PMT lifespan, especially in methods like FRAP, FLIP, and FLAP, where high light intensities are used for bleaching or activating molecules.
Innovation Solution
A switch that rapidly adjusts the voltage between the photocathode and the first dynode, allowing for pixel-accurate control of electron multiplication, enabling immediate protection against overloads by short-circuiting or reversing polarity, thus preventing ion feedback and maintaining high voltage sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective cutoff of the high voltage is implemented to protect the PMT from damage due to high light intensities, then the PMT is protected from damage, but the response time is in the millisecond range which is too slow compared to the pixel dwell time of a few microseconds
Solution Approach 1:
The high voltage supply is segmented into multiple independent voltage sources: a main high voltage source and a separate first voltage source for the first acceleration stage. This segmentation allows the first stage to be controlled independently with fast switching to protect the PMT, while the main high voltage can be maintained or adjusted separately.
Solution Approach 2:
The switch for the first acceleration stage is activated in advance when the target spot enters a given region before actual damage can occur. This preliminary action prevents ion feedback and photocathode damage before they can happen, rather than waiting for damage indicators to appear.
2Reliability
If the high voltage is switched off to protect the PMT, then damage is prevented, but the PMT is switched on again after a long delay so that subsequent sample regions may not be captured
Solution Approach 1:
By segmenting the voltage supply into independent stages, only the first acceleration stage needs to be switched off for protection, while the main high voltage and other stages remain active. This allows the PMT to be protected during bright regions and immediately ready to capture subsequent regions without prolonged delays.
Solution Approach 2:
The voltage configuration is made dynamic through the switch that can rapidly change the state of the first acceleration stage. The switch responds dynamically to the position of the target spot, activating protection only when needed in bright regions while maintaining normal operation in other regions.
3Productivity
If high light intensities are used for bleaching or activating molecules in methods like FRAP, FLIP, and FLAP, then dynamic sample processes can be measured, but the PMT is at high risk of damage due to ion feedback and high photoelectron current densities
Solution Approach 1:
Different voltage conditions are applied locally depending on the region being scanned. In bright regions where bleaching occurs, the first acceleration stage is switched off to protect the PMT. In other regions, normal voltage conditions are maintained for optimal detection sensitivity.
Solution Approach 2:
The switch acts as an intermediary between the high light intensity bleaching process and the PMT detector. It mediates protection by blocking the harmful photoelectron current during bright regions while allowing normal detection in other regions, enabling both bleaching and safe detection.
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 provides fast and spatially dependent protection for the PMT, ensuring accurate image capture and extending its lifespan by preventing damage from high light intensities, allowing for precise bleaching and imaging with minimal delay.
Implementation Method 1
a photomultiplier (photomultiplier tube or PMT) which has a photocathode, a plurality of dynodes and an anode... light entering the photomultiplier causes an avalanche of secondary electrons
Implementation Method 2
By applying respective electric voltages to the dynodes of a PMT, light entering the photomultiplier causes an avalanche of secondary electrons which can be measured with high accuracy
Data Source
AI summary
A switch which reduces the voltage between the photocathode and the first dynode in the activated switching state compared to the deactivated switching state and a control unit which is adapted to move a target spot, which can be illuminated by means of the light source, over a scanning field by means of a deflecting unit. The control unit activates the switch when the target spot enters a given region of the scanning field and deactivates the switch when the target spot exits the region.