One-shot recording of the instantaneous change in the refractive index of bulk semiconductors exposed to pulsed radiation by a Fabry-Perot-like interferometer.

An interferometer, directly coupling a single-mode fiber with a bulk semiconductor, was used to one-shot record the instantaneous change in the refractive index of bulk semiconductors. A practical contrast level can be achieved in the interferometer with different types of polished bulk materials several hundred micrometers in thickness. The temporal resolution was approximately 50 ps and can be improved by using thinner materials or higher bandwidth detection. This interferometer can also be used to study the fast recording technology based on pulsed radiation-induced changes in optical characteristics.

Development of an all-optical framing camera and its application on the Z-pinch.

An all-optical framing camera has been developed which measures the spatial profile of photons flux by utilizing a laser beam to probe the refractive index change in an indium phosphide semiconductor. This framing camera acquires two frames with the time resolution of about 1.5 ns and the inter frame separation time of about 13 ns by angularly multiplexing the probe beam on to the semiconductor. The spatial resolution of this camera has been estimated to be about 140 µm and the spectral response of this camera has also been theoretically investigated in 5 eV-100 KeV range. This camera has been applied in investigating the imploding dynamics of the molybdenum planar wire array Z-pinch on the 1-MA "QiangGuang-1" facility. This framing camera can provide an alternative scheme for high energy density physics experiments.

High resolution, high efficiency liquid scintillator capillary array for gamma imaging.

We fabricated a liquid scintillator capillary array (LSCA) for gamma imaging with the aim of developing a one-dimensional detector system utilizing a streak camera for high temporal and spatial resolution pulsed gamma radiation detection. The detector's performance was studied in a simulation and via an experiment. The maximum efficiency of the LSCA's emission was at a wavelength of 420 nm. To establish a high fidelity representation of the detector's edge spread function and modulation transfer function (MTF), a slanted edge algorithm was introduced to calculate the edge spread function of the discrete sampling array's image screen. The simulation results showed that the spatial resolution of the LSCA was better for 14 MeV neutrons than for 1.25 MeV gamma radiation. The experimental results show that in comparison with a 6-mm-thick LaBr3 image plate, the LSCA had a higher temporal and spatial resolution when used as a gamma detector. The spatial resolution was 1.1 lp/mm (MTF = 0.1) for the LSCA. In addition, when an ultra-violet streak camera was coupled with the LSCA, it had a comparable sensitivity to that of a 6-mm-thick LaBr3 image plate.

Interferometric method for quantitatively testing the RadOptic effect in bulk semiconductors.

For the quantitative investigation of MeV-photon-induced changes in the refractive indices of bulk semiconductors, a model was established to describe the evolution of the excess carrier density, including the generation and recombination processes. The two key parameters of the evolution model, namely, the summed injection intensity and the gamma intensity curve, were obtained via dose measurements and gamma pulse monitoring, respectively. An interferometric method of measuring instantaneous changes in the refractive index and obtaining real-time measurements of the excess carrier density in bulk materials was successfully implemented. The probe beam was transmitted through a single-mode fiber to form double-beam interference in a slab geometry. Two bulk samples, one consisting of intrinsic GaAs and one of intrinsic ZnO, were tested. The recombination time constant of the intrinsic GaAs sample was found to be approximately 0.6 ns and did not vary distinctly with the photon energy, whereas the ZnO sample's recombination behavior consisted of two components. The short component was evident when short and intense pulses were incident, whereas the long component dominated under long and relatively weak pulses. The method reported in this work can be used to study the excess carrier dynamics induced by pulsed gamma radiation and to investigate the mechanisms of refractive index modulation under pulsed gamma conditions; thus, it is expected to be beneficial for guiding the development of RadOptic systems based on bulk materials.