Electron detection with CdTe and GaAs sensors using the charge integrating hybrid pixel detector JUNGFRAU

Speed, dynamic range, and radiation hardness make hybrid pixel detectors suitable image detectors for diffraction experiments. At synchrotrons and X-ray free electron lasers they are ubiquitous. However, for electron microscopy their spatial resolution is limited by multiple scattering in the sensor layer. In this paper we examine the use of two high Z sensor materials: CdTe and GaAs, as a way to mitigate this problem. The sensors were bonded to a JUNGFRAU readout chip which is a charge integrating hybrid pixel detector developed for use at X-ray free electron lasers. Using in-pixel gain switching, it can detect single particles down to 2 keV while maintaining a dynamic range of 120 MeV/pixel/frame. The characteristics of JUNGFRAU, besides being a capable detector, make it a good tool for sensor characterization since we can measure dark current and energy deposition per pixel. The high Z material shows better spatial resolution than silicon at 200 and 300 keV, however, their practical use with integrating detectors is still limited by material defects.

Statistics of the Optical Phase of a Gain-Switched Semiconductor Laser for Fast Quantum Randomness Generation

The statistics of the optical phase of the light emitted by a semiconductor laser diode when subject to periodic modulation of the applied bias current are theoretically analyzed. Numerical simulations of the stochastic rate equations describing the previous system are performed to describe the temporal dependence of the phase statistics. These simulations are performed by considering two cases corresponding to random and deterministic initial conditions. In contrast to the Gaussian character of the phase that has been assumed in previous works, we show that the phase is not distributed as a Gaussian during the initial stages of evolution. We characterize the time it takes the phase to become Gaussian by calculating the dynamical evolution of the kurtosis coefficient of the phase. We show that, under the typical gain-switching with square-wave modulation used for quantum random number generation, quantity is in the ns time scale; that corresponds to the time it takes the system to lose the memory of the distribution of the initial conditions. We compare the standard deviation of the phase obtained with random and deterministic initial conditions to show that their differences become more important as the modulation speed is increased.

Robust Dual-Channel Disturbance Rejection Attitude Control for a Quadrotor UAV: Theory and Experiment

In this paper, a robust dual-channel disturbance rejection control based on an inner-outer loop control framework is proposed for the attitude control of the quadrotor under modeling uncertainties and unknown disturbances. In the outer loop, a tracking differentiator is introduced to obtain smooth tracking signals and their derivatives. In addition, an outer loop controller is developed with the tracking signals set as the desired signals. In the inner loop, a robust dual-channel disturbance rejection controller based on a sliding mode observer is constructed, which contains an inner disturbance rejection channel (IDRC) and an outer disturbance rejection channel (ODRC). In the IDRC, a disturbance rejection compensator is designed to obtain the disturbance compensation values and to compensate a part of the lumped disturbances in the attitude dynamic model. In the ODRC, an inner loop controller with variable-gain switching terms and constant-gain switching terms is designed, whose switching terms are used to compensate the remaining part of the lumped disturbances in the attitude dynamic model. By using the proposed control scheme, the robustness is guaranteed, and the chattering phenomenon caused by the variable-gain switching terms is greatly reduced. The stability of the proposed scheme is analyzed by using the Lyapunov theory. Finally, the effectiveness is tested by the platform experiments.