We use cookies to distinguish you from other users and to provide you with a better experience on our websites. Close this message to accept cookies or find out how to manage your cookie settings.
We use cookies to distinguish you from other users and to provide you with a better experience on our websites. Close this message to accept cookies or find out how to manage your cookie settings.
X/γ-rays have many potential applications in laboratory astrophysics and particle physics. Although several methods have been proposed for generating electron, positron, and X/γ-photon beams with angular momentum (AM), the generation of ultra-intense brilliant γ-rays is still challenging. Here, we present an all-optical scheme to generate a high-energy γ-photon beam with large beam angular momentum (BAM), small divergence, and high brilliance. In the first stage, a circularly polarized laser pulse with intensity of 1022 W/cm2 irradiates a micro-channel target, drags out electrons from the channel wall, and accelerates them to high energies via the longitudinal electric fields. During the process, the laser transfers its spin angular momentum (SAM) to the electrons’ orbital angular momentum (OAM). In the second stage, the drive pulse is reflected by the attached fan-foil and a vortex laser pulse is thus formed. In the third stage, the energetic electrons collide head-on with the reflected vortex pulse and transfer their AM to the γ-photons via nonlinear Compton scattering. Three-dimensional particle-in-cell simulations show that the peak brilliance of the γ-ray beam is 
$\sim 1{0}^{22}$ photons·s–1·mm–2·mrad–2 per 0.1% bandwidth at 1 MeV with a peak instantaneous power of 25 TW and averaged BAM of 
$1{0}^6\hslash$/photon. The AM conversion efficiency from laser to the γ-photons is unprecedentedly 0.67%.
A miniature dual-band bandpass filter with interlocked stepped-impedance resonators (SIRs) is presented in this paper, which was designed for the student design competition held in European Microwave Week 2019. This bandpass filter is required to have two concurrent passbands, namely, the first passband at 900–1000 MHz and the second passband at 1427–1518 MHz bands, which cover six designated bands in sub-6 GHz range of fifth generation (5G) New Radio Access Technology. Three stopbands are required at 500–850, 1050–1350, and 1600–2000 MHz, respectively. To achieve the best figure of merit, an interlocked configuration of two SIRs is proposed. One advantage is that the impedance ratio of the inter-locked SIR can be controlled to have two passbands at the required frequencies. Second, the coupling section of the interlocked SIR gives three transmission zeros distributed to every stopbands such that the stopband suppression are dramatically enhanced. The measured results show that the passband insertion losses are 2.16 dB at the first passband and 1.33 dB at the second passband, and the return losses are greater than 10 dB. The stopband suppression at the transmission zeros are greater than 38 dB. The circuit is very compact as 41.40 × 19.96 mm2, equivalent to $0.25 \times 0.12\,\lambda _g^2$
.
