Light Detection Device Dark Current Noise Discrimination
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Solution Overview
Problem
Photometers and charged particle beam apparatuses face challenges in accurately detecting small amounts of light due to the inability to correctly discriminate dark current pulses from floor noises, leading to incorrect base voltage determination and impaired light detection accuracy.
Innovation Solution
A light amount detection device is developed, incorporating a photomultiplier tube, preamplifier, A/D converter, base voltage calculation part, base correction processing, and threshold value processing to differentiate dark current pulses from floor noises, allowing for accurate base voltage calculation and enhanced light detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If dark current pulses are not distinguished from floor noises, then processing is simpler, but base voltage accuracy deteriorates, impairing light detection precision
Solution Approach 1:
The patent introduces a second threshold value as an intermediary mechanism between the raw signal and the base voltage calculation. This intermediary threshold specifically targets dark current pulses, filtering them out before base voltage determination. The added processing step is minimal but effectively resolves the accuracy issue without significantly increasing system complexity.
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
The device enhances the accuracy of light detection by correctly determining the base voltage and distinguishing dark current pulses from noise, thereby improving the signal-to-noise ratio and precision of light measurement.
Implementation Method 1
a photomultiplier tube that detects incident light to convert the incident light into a current
Implementation Method 2
converts a weak secondary electron generated from a surface of the sample into light by using a scintillator
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
For a detection signal that has been detected by the photomultiplier tube 2, has been amplified by the preamplifier 5, and has been converted into a digital signal, a time average value of signal components, each of which has a voltage lower than a predetermined base threshold value, is calculated as a base voltage. Base correction processing that offsets the detection signal in such a manner that the base voltage becomes 0 is performed. A signal that has been subjected to the base correction processing is subjected to threshold value processing that calculates a signal component having a voltage higher than a predetermined signal detection threshold value, and to base correction processing in a non-incident state in which light is not incident on the photomultiplier tube 2. An output signal thereof is subjected to dark current calculation processing that calculates a signal component having a voltage higher than a predetermined signal detection threshold value. The light emission signal amount is calculated by subtracting, from the signal component of the detection light obtained by the threshold value processing, a time average value of the signal components of the dark current obtained by the dark current calculation processing. As the result, discriminating the dark current pulse from floor noises enables to enhance the accuracy of the base voltage, and thus to enhance the accuracy of light detection.