Photon Counting via Signal Integration in Silicon Photomultipliers
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Solution Overview
Problem
Existing methods for counting photons using photomultipliers face challenges such as signal overlap, reduced signal height due to pulse shaping, and the need for complex corrections based on fluorescence lifetimes and sample-specific parameters.
Innovation Solution
The proposed method involves evaluating the integrated measurement signal over a long period using a semiconductor photomultiplier, particularly a silicon photomultiplier (SIPM), to determine the number of photons without relying on pulse shaping or threshold processing, thus avoiding signal overlap and simplifying corrections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If pulse shaping or threshold processing is used to count photons, then the counting process becomes simpler, but signal overlap occurs and measurement precision deteriorates
Solution Approach 1:
The patent extracts the essential information (total integrated signal area) from the raw photomultiplier output without applying traditional pulse shaping or threshold processing. By integrating the measurement signal over a long period and using the integral proportionality value, the method obtains accurate photon counts while avoiding the signal overlap problems that plague conventional threshold-based counting approaches.
Solution Approach 2:
The patent changes the evaluation parameter from instantaneous pulse height or threshold-exceeded events to the integrated area under the measurement signal curve. This parameter transformation allows the system to count photons based on total signal accumulation rather than discrete pulse detection, thereby eliminating signal overlap issues while maintaining operational simplicity.
2Reliability
If pulses are made shorter through high-pass filtering or capacitive tap to reduce overlap, then signal overlap is reduced, but signal level decreases
Solution Approach 1:
Instead of trying to shorten pulses to avoid overlap (the conventional approach), the patent inverts the strategy by integrating the signal over a long period. This allows the system to accommodate overlapping pulses by summing their contributions over time, thereby maintaining full signal levels while still achieving accurate photon counting through the integral proportionality relationship.
3Adaptability or versatility
If conventional pulse counting with threshold comparison is used, then the method is widely applicable, but saturation effect occurs and double-height pulses cannot be distinguished from single pulses
Solution Approach 1:
The patent replaces the mechanical threshold-comparison counting mechanism with an integration-based measurement system. Instead of comparing instantaneous signal values against a threshold and incrementing counters, the system integrates the measurement signal over time and determines photon counts from the accumulated area, using the integral proportionality value to convert signal area to photon number. This substitution eliminates saturation effects while preserving broad applicability.
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 accurate and efficient photon counting, independent of pulse distribution, and is suitable for confocal microscopy, enabling precise measurements with relatively inexpensive and robust photomultipliers.
Implementation Method 1
each detected photon produces an analog pulse
Implementation Method 2
The rapid rise is a consequence of the breakdown, during which the capacitance of the biased diode is discharged below the breakdown voltage
Data Source
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Figure 7
AI summary
The present invention relates to a method and a computing unit or microscopy system (500) for counting photons by means of a photomultiplier (511), wherein an incident photon produces a pulse in a raw signal produced by the photomultiplier (511), wherein a measurement signal is obtained from the raw signal by virtue of the raw signal being corrected by a noise signal and/or an offset, wherein the measurement signal is integrated over time in order to form an analog integrated measurement signal, wherein the number of photons that are incident in the photomultiplier (511) is established by virtue of a value of the analog integrated measurement signal being compared to an integral proportionality value, which corresponds to a certain number of photons that were incident in the photomultiplier.