Quantum-Limited EUV Coherent Diffraction Imaging
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Solution Overview
Problem
Current coherent diffraction imaging (CDI) techniques in the extended ultraviolet (EUV) and x-ray range are limited by the slow readout rate of EUV sensitive charge-coupled device (CCD) detectors, leading to slow imaging and wasted photon flux due to limited frame rates and high exposure times.
Innovation Solution
Implementing CMOS active pixel detectors for coherent diffraction imaging, which allows for high-speed data acquisition by thresholding and preprocessing raw data to enhance noiseless photon detection and reconstruction, enabling continuous scanning and improved image fidelity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If EUV sensitive CCD detectors are used for coherent diffraction imaging, then quantum-limited sensitivity is achieved, but the readout rate is limited to a few frames per second
Solution Approach 1:
The patent replaces the mechanical/electronic readout mechanism of CCD detectors with a computational approach. By using single-photon counting CMOS detectors and implementing photon counting with thresholding, the system achieves high-speed readout while maintaining quantum-limited sensitivity. The substitution of the detector readout mechanism enables frame rates of hundreds to thousands of frames per second while preserving the ability to detect individual photons.
2Measurement precision
If CCD detectors with limited frame rates are used, then quantum-limited sensitivity is maintained, but photon flux is wasted due to high exposure times
Solution Approach 1:
The patent implements continuous high-speed photon detection by using CMOS detectors with frame rates of hundreds to thousands of frames per second. This continuous operation eliminates the idle time between exposures that causes photon flux waste in CCD-based systems. The high frame rate allows the detector to continuously capture photons as they arrive, maximizing photon utilization while maintaining quantum-limited sensitivity through single-photon counting capability.
3Measurement precision
If high exposure times are used to accumulate sufficient photons, then image quality is improved, but the readout rate decreases to a few frames per second
Solution Approach 1:
The patent employs periodic photon accumulation through high-speed frame capture followed by computational integration. Instead of using long continuous exposures, the system captures many short-duration frames at high frame rates and accumulates photon counts computationally. This periodic sampling approach maintains high readout rates while achieving the necessary photon statistics for high-quality images through post-acquisition data integration.
4Productivity
If CMOS detectors are used for high-speed readout, then frame rates increase to hundreds or thousands of frames per second, but fixed pattern noise from amplifier gain fluctuations occurs
Solution Approach 1:
The patent implements feedback through routine pixel-by-pixel calibration and background subtraction to correct for fixed pattern noise. By measuring and storing the gain characteristics of each pixel during calibration, the system can compensate for amplifier gain fluctuations in real-time during imaging. This feedback mechanism eliminates fixed pattern noise while preserving the high frame rate capability of CMOS detectors, enabling reliable single-photon counting at speeds of hundreds to thousands of frames per second.
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 enables high-speed quantum-limited CDI with increased frame rates and efficient photon utilization, overcoming the limitations of CCD detectors and achieving high-resolution imaging in the EUV and x-ray range.
Implementation Method 1
the fundamental sensitivity mechanism—photon absorption in silicon—is identical between the two types of imagers
Implementation Method 2
measuring diffraction patterns from the object (from reflection, transmission, or a combination) with a detector
Data Source
AI summary
Apparatus and methods for coherent diffraction imaging. This is accomplished by acquiring data in a CDI setup with a CMOS or similar detector. The object is illuminated with coherent light such as EUV light which may be pulsed. This generates diffraction patterns which are collected by the detector, either in frames or continuously (by recording the scan position during collection). Pixels in the CDI data are thresholded and set to zero photons if the pixel is below the threshold level. Pixels above the threshold may be set to a value indicating one photon, or multiple thresholds may be used to set pixels values to one photon, two photons, etc. In addition, multiple threshold values may be used to detect different photon energies for illumination at multiple wavelengths.