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Common Spectroscopic and Imaging Detection Techniques
Published in Helmut H. Telle, Ángel González Ureña, Laser Spectroscopy and Laser Imaging, 2018
Helmut H. Telle, Ángel González Ureña
Essentially, this register is nothing more than a chain of MOS pixel capacitors through which the signal charge is transferred. Within each of these gain pixels, one of the normally three phase electrodes is replaced with two electrodes. The first is held at a fixed potential while the second is set to a much higher voltage of 40–60 V when clocked. The large voltage potential difference between the fixed and clocked electrodes is sufficient for some electrons to cause the so-called “impact ionization” while being transferred, and thus generating additional electrons. In a certain way, the process is similar to the electron multiplication in an avalanche diode. Overall, the multiplication factor (i.e., the statistical average increase in electron number) per chain pixel is small—normally of the order of MP ≅ 0.010–0.015. However, since in common, practical devices, the number of multiplying elements is large (of the order of n = 500 or more), one would find for those numbers an overall register gain up to GEM = (1 + MP)n ≈ 150–1700. Thus, EMCCDs are useful for very low-light signal applications and can be sensitive down to the single-photon level. It should be noted that the gain function can be switched off by suitably adjusting the voltage of the clocked gain electrode; then the EMCCD operates as a standard CCD. For some further details on EMCCD functionality, see, e.g., “Fundamentals of EMCCD—A Tutorial” (EMCCD Forum 2005).
Introductory Concepts
Published in Dragica Vasileska, Stephen M. Goodnick, Gerhard Klimeck, Computational Electronics, 2017
Dragica Vasileska, Stephen M. Goodnick, Gerhard Klimeck
Two-terminal devices: Avalanche diode (avalanche breakdown diode)DIACDiode (rectifier diode)Gunn diodeIMPATT diodeLaser diodeLEDPhotocellPIN diodeSchottky diodeSolar cellTunnel diodeVCSELVECSELZener diode
Airborne and Spaceborne Laser Profilers and Scanners
Published in Jie Shan, Charles K. Toth, Topographic Laser Ranging and Scanning, 2017
Gordon Petrie, Charles K. Toth
The SLICER (Scanning Lidar Imager of Canopies by Echo Recovery) is yet another airborne laser scanner that was developed by NASA in the mid-1990s. The system was based on the ATLAS (Airborne Topographic Laser Altimeter System), an earlier airborne laser profiler that had been built by NASA. The ATLAS was first modified into the SLICER through the installation of a more powerful laser and the addition of a waveform digi-tizer. The rangefinder in the SLICER uses a Q-switched, diode-pumped Nd:YAG laser that outputs a short-duration (4 ns) pulse at the wavelength (λ) of 1064 nm. The scanning mechanism comprises a simple oscillating mirror that is rotated rapidly to the successive positions of a set of fixed scan angles using a computer-controlled galvanometer. Usually, five fixed angular positions are used for each cross-track scan, so only a very narrow scan width is achieved. The detector used in the receiver is a silicon avalanche diode that converts the energy received from the reflected pulse into an output analogue voltage. The waveform digitizer is an analogue-to-digital (A/D) converter that samples and records the output voltage values in digital form. The on-board position and orientation system utilizes twin Ashtech Z-12 dual-frequency GPS receivers. The first of these provides the required positional data, while the second set provides the time reference for the recorded data stream. The IMU is a Litton LTN-92 unit based on a laser ring gyro.
A comparison of three surface roughness characterization techniques: photogrammetry, pin profiler, and smartphone-based LiDAR
Published in International Journal of Digital Earth, 2022
Zohreh Alijani, Julien Meloche, Alexander McLaren, John Lindsay, Alexandre Roy, Aaron Berg
LiDAR technology was added to iPhone 12 Pro and iPad Pro (4th generation) for the first time in 2020. The iPhone 12 Pro has three RGB 12 MP rear cameras and a LiDAR sensor. The LiDAR sensor on the iPhone 12 Pro measures the distance to surrounding objects up to 5 m away. These sensors create accurate high-resolution models of small objects with a side length > 10 cm with an absolute accuracy of ± 1 cm (Luetzenburg, Kroon, and Bjørk 2021). Although the type of Apple’s LiDAR seems to be a trade secret, some researchers reported that these sensors may be based on a single-photon avalanche diode (SPAD) coupled with a laser light source (Tontini, Gasparini, and Perenzoni 2020; Murtiyoso et al. 2021). However, it is more likely that the sensor is a solid-state LiDAR (SSL) (Wang et al. 2022) which, in contrast to traditional LiDAR systems with a mechanical rotator that can often be bulky in size, avoids the use of large mechanical parts to ensure higher scalability and reliability (García-Gómez et al. 2020). Therefore, the SSL sensors have recently drawn attention in both academic and industry circles. More information about the SSL sensors can be found at Li et al. (2022). In the current study, all profiles were scanned using the iPhone 12 Pro LiDAR scanner at a distance of 0.3 m from the surface, measured using a rod, placed on the top of the flume, to facilitate a consistent scan and to reduce human error (Figure 1(b)). Generated point clouds were exported in LAS (LASer) format after scanning all profiles.
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
Four-frame GOI based on proximity-focused MCPII was first demonstrated in 1988 by Young et al. [7], four separate two-dimensional images with each frame having a 120-ps gate width were obtained by using four gated proximity-focused MCPIIs which share an avalanche diode-based pulse module, the relative interframe times between channels were selected by the relative lengths of the cables between each tube and the module. However, both the interframe time and gate width are hard to be varied, therefore, it is most suitable for applications where the interframe time and gate width are fixed. A beam-splitter system has also been constructed which produces a separate image for each tube from a single scene, however, the space frame of the beam-splitter is large and the optical path length is not equal. Murphy et al. designed a splitting system that provides for equal path length and equal intensity splitting in each arm while being compact [8]. However, both these image splitting systems are based on semi-transparent beamsplitters, and their spectral response depends on the characteristics of the mirror.
A compact time-to-amplitude converter for single-photon time-of-flight measurement
Published in Journal of Modern Optics, 2021
Zhiqiang Ma, Yue Xu, Sihui Zhu, Zhong Wu
Recently, light detection and ranging (LiDAR) technique based on single-photon avalanche diode (SPAD) detectors have gained more and more attention in time-correlated measurement applications such as autonomous self-driving vehicles, Raman spectroscopy, fluorescence lifetime imaging, and three-dimensional (3-D) vision systems [1–5]. In LiDAR systems, the photon time-of-flight (TOF) measurement principle is typically used to determine the distance of the target [6–8]. The direct TOF (d-TOF) technique relies on the delay measure between the time of laser pulse emission and the time of arrival of the first photon reflected by the target to calculate the photon flight-time. Compared with indirect TOF (i-TOF) measurement, it is more suitable for long-distance applications due to the high response sensitivity and strong ability to suppress the high ambient illumination [8,9].