Sphere imagers featuring specific wavelength recognition and wide-angle imaging are required to meet the fast development of modern technology. However, it is still challenging to deposit high-quality photosensitive layers on sphere substrates from low-cost solution processes. Here we report spray-coated quasi-two-dimensional phenylethylammonium/formamidinium lead halide (PEA2FAn-1PbnX3n+1) perovskite hemispherical photodetectors. The crystallization speed is manipulated by perovskite compositions, and the film thickness can be controlled by spray-coating cycles and solution concentration from tens of nanometers to hundreds of micrometers with a fast velocity of 1.28 × 10−4 cm3 s−1. The lens-free hemispherical photodetectors allow light response at a wide incident angle of 180°. Simultaneously, the wavelength selective response from visible to the near-infrared range is achieved with full width at half maximums (FWHMs) of ~20 nm, comparable to single-crystal devices. Wide-angle and wavelength-selective imaging are also demonstrated, which can find potential applications in intelligent recognition and intraoperative navigated surgery.
We developed a self-powered broadband perovskite/silicon hybrid photodetector based on a novel heterostructure of Si/SnO2/MAPbI3/MoO3. The insertion of SnO2 and MoO3 was effective in reducing the recombination of photogenerated carriers. By optimizing the thickness of the SnO2 layer, the detection capabilities of the hybrid photodetectors were significantly improved. The best-performing photodetector had a 40 nm SnO2 layer, showing a detectivity of 2.23 × 1012 Jones with a responsivity of 50.9 mA W−1 at 815 nm and a photocurrent/dark current ratio of 3.37 × 104 under zero bias. Furthermore, the photodetectors were sensitive to broadband irradiation from 300 to 1150 nm.
This paper reviews theoretical studies on stochastic processes in gyrotrons. Three different types of stochasticity related to high-power gyrotron operation are considered. First, stochasticity in electron residual energies may develop at the resonator exit for some values of operating parameters and complicate the operation of depressed collectors. Second, stochastic radio-frequency oscillations can set in after the electron beam current is raised above certain threshold values. Third, the high-frequency field structure can exhibit spatio-temporal chaos if the cavity diameter is increased too much to minimize Ohmic losses. In high-power gyrotrons the third type of stochasticity is most important, but there are applications in which the two other types should also be taken into account and could even be utilized.
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