The near-range lidars for hard target and atmosphere detection should follow to the quick motion/activity of the measurement target. The transmitting optical power will be lowered for safety in the human activity space. And the lidar should increase the pulse repetition frequency to get the enough signal-to-noise ratio. The high-speed, high-resolution and high-repetition photon counting is desired for the near-range lidar. It is not a single photon counting at a certain delay time, but a multi-channel scaler with a deep memory for a series of delay times, that is, ranging data acquisition for lidar application. In this chapter, the mini-lidar for near-range observation is discussed. The targets are dust, gas, and atmosphere (aerosols). The activity monitoring of the atmosphere within a few hundred meters is the purpose of this mini-lidar. To follow and visualize the rapid motion of the target, high-speed and high-resolution photon counters (multi-channel scalers) were developed. The observation range can be easily adjustable depending on the lidar setup. The system can visualize the rapid motion of target with the high-resolution of 0.15 m (BIN width of 1 ns) and the minimum summation time of 0.2 s.
Part of the book: Photon Counting
Now, Hydrogen gas is of particular interest as new energy source and dangerous material in nuclear facility. Fuel cell is started to use in home power generation system in 2008 and fuel cell vehicle (FCV) is commercialized from 2014 in Japan. On contrary, the Great East Japan Earthquake revealed the fear of hydrogen explosion on Fukushima Nuclear Power plant in 2011. Contact type hydrogen sensors induce changes on the gas flow, and the actual concentration cannot be known. It is hard to get the gas concentration distribution in hydrogen leakage area. We focused on optical remote sensing for the hydrogen detection. Raman scattering detection was accomplished for the hydrogen gas with a compact Diode Pumped Solid State (DPSS) laser-based Raman lidar. The quantitative measurement was conducted on the hydrogen gas concentration of 1 - 100% and the detectable distance of <50 m. Next, a LED-based mini Raman lidar was developed with the same optical design as the former one in viewpoints of its robust operation and usability in the nuclear facility. The high-speed photon counter was developed to follow the high repetition frequency of LED pulse of >500 kHz, and the quantitative measurements of hydrogen concentration were conducted on lab-experiment and at outdoor.
Part of the book: Ionizing Radiation Effects and Applications