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X-Ray and Computed Tomography
Published in Ravishankar Chityala, Sridevi Pudipeddi, Image Processing and Acquisition using Python, 2020
Ravishankar Chityala, Sridevi Pudipeddi
The input phosphor is made of cesium iodide (CsI) and is vapor deposited to form a needlelike structure that prevents diffusion of light and hence improves resolution. It also has greater packing density and hence higher conversion efficiency, even with smaller thickness (needed for good spatial resolution). A photocathode emits electrons when light photons are incident on it. The anode accelerates the electrons. The higher the acceleration the better is the conversion of electrons to light photons at the output phosphor. The input phosphor is curved, so that electrons travel the same length toward the output phosphor. The output fluorescent screen is silver-activated zinc-cadmium sulfide. The output can be viewed using a series of lenses on a TV or it can be recorded on a film.
Optical Methods of Single Molecule Detection and Applications in Biosensors
Published in George K. Knopf, Amarjeet S. Bassi, Smart Biosensor Technology, 2018
Anna Shahmuradyan, Ulrich J. Krull
The PMT consists of a photocathode, a series of dynodes, and an anode all assembled in a vacuum tube. Negative potential is applied across the tube, with the highest potential being at the photocathode. The potential decreases across the dynodes, reaching zero at the anode (77). The photocathode is a thin film of metal and releases an electron as a photon strikes the surface (photoelectric effect). Due to the difference in the potentials, the ejected electron is accelerated toward the first dynode. The subsequent impact with the surface causes ejection of 5–20 additional secondary electrons (77). These secondary electrons are then accelerated toward the next dynode, causing further ejection of electrons upon impact with the electrode surface. This process repeats, causing the formation of a current pulse that reaches the anode, and the current pulse is proportional to the light intensity (77).
Advances in CMOS SSPM Detectors
Published in Krzysztof Iniewski, Biological and Medical Sensor Technologies, 2017
James F. Christian, Kanai S. Shah, Michael R. Squillante
PMTs are excellent low-light, high-bandwidth, large-area photodetectors. They are vacuum tubes that convert incident light into an electrical signal, and the Photomultiplier Handbook [11] describes the fundamental principles and operating considerations. In a PMT, visible light photons are converted into electrons by the photoelectric effect in the “photocathode” of the device. These photoelectrons are accelerated in an electric field such that they create additional electrons by secondary emission upon impact with “dynodes.” Figure 13.2 shows a simplistic illustration of a PMT detecting and amplifying an incident light signal. In brief, the photocathode converts the incident light signal to an electrical signal, based on the photoelectric effect. The electrons, represented by straight arrows in the figure, are accelerated into the dynodes where they generate additional current. Finally, the total charge signal strikes the anode and is readout with subsequent electronics. In the figure, open circles at the dynodes represent the “equivalent” of holes, which is simply current from the power supply. The figure illustrates two separate paths for the charge, the electron path in the vacuum and the current path for the power supply.
Assessment of the effective parameters for the enhancement of light-harvesting power in the photoelectrochemical microbial fuel cell
Published in Environmental Technology, 2023
Elahe Fallah Talooki, Mohsen Ghorbani, Mostafa Rahimnejad, Mohammad Soleimani Lashkenari
However, in reality, MFCs performance is relatively poor and before the MFC technology can gain a major share of the energy markets, some limiting factors can have a serious impact on the overall performance [5]. There are definitely two unique hurdles to overcome. Those are, the high cost and another is relatively low overall performance. In this regard, improvement of performance has been the mainstream in MFC development. One approach to overcome this low power hurdle is the use of solar energy in MFC structure which is considered the ultimate long-term treatment for environmental and energy crises, so the use of the photo-assisted MFC, which incorporates the use of sunlight into MFC technology for multiple energy conversions is introduced to improve MFC performance [6–9]. When a photocathode in cathode chamber is irradiated by light with an energy equal to or greater than its bandgap energy, photo-excited electrons and holes are generated. The photoelectrons can reduce contaminants like Cr(VI).
A four-channel ICCD framing camera with nanosecond temporal resolution and high spatial resolution
Published in Journal of Modern Optics, 2021
Yuman Fang, Minrui Zhang, Junfeng Wang, Lehui Guo, Xueling Liu, Yu Lu, Jinshou Tian
The image intensifier operates by focusing an image onto a photocathode coated on the input window. The incident light drives the photocathode to launch photoelectrons proportional to the intensity of the light. Then, these photoelectrons are accelerated by an applied electric field and enter the microchannel plate (MCP). In the MCP, the photoelectrons collide with the channel walls to release secondary electrons, which produces a multiplication effect of many orders of magnitude. After exiting the MCP, the electrons are accelerated by an electric field again, this time impacting against the phosphor screen. The phosphor emits light, producing an output image that can be viewed by the CCD [13].