The image shows fast object detection and data analysis of high-power high-repetition-rate laserplasma experiment using neural networks. In the petawatt, Hz laser system at the Center for Advanced Laser Applications, Munich, object detection networks are used to rapidly process and visualize various diagnostic data from each frame of the laser’s output images, including electron energy spectra, plasma wave, and laser damage.
Helical laser beams, due to their unique ?eld structure, are ideal optical drivers for producing monoenergetic, pellet-like electron bunches. In contrast to regular laser beams, their ?eld structure close to the axis of the beam is dominated by longitudinal electric and magnetic ?elds. The bunches are generated as a result of two synergetic e?ects that take place when such a beam is re?ected o? a mirror: the longitudinal electric ?eld accelerates electrons after extracting them from the mirror surface; while the magnetic ?eld con?nes them into the central region, allowing for acceleration within the laser over a long duration.
The cover image illustrates the photonic quasicrystal fiber (PQF), which is also named quasiperiodic photonic crystal fiber. The five insets surrounding the PQF end-face provide a simultaneous display of three typical structures and two representative potential applications of PQF. The three white-circled insets (top-left, right, and bottom-left) represent the Stampfli-type, Penrose-type, and Sunflower-type structures, respectively. The two blue-circled insets (left and bottom-right) show applications of the supercontinuum generation and orbital angular momentum mode propagation, respectively.
By harnessing Tamm plasmon coupling, spintronics THz radiation not only achieved a 264% enhancement but guaranteed nearly lossless (~4%) THz transmission. This approach provides the compatible optical structure design and the low energy consumption for ultrafast opto-spintronics devices.
A snapshot full-polarization hyperspectral imaging method based on convolutional neural network (CNN) reconstruction is proposed. In the imaging system, a quarter-wave plate is combined with a liquid crystal tunable filter to encode full-polarization information. Meanwhile, the liquid crystal tunable filter flexibly selects spectral bands of interest. Finally, a CMOS detector captures the total light intensity image after full-polarization encoding. In the reconstructed model, a two-layer CNN reconstructs four full-polarization images from one full-polarization encoded image. The cover image shows the main components of both the full-polarization hyperspectral imaging system and the CNN reconstruction model.
Free-electron light sources feature extraordinary luminosity, directionality, and coherence, which has enabled significant scientific progress in fields i
Free-electron light sources feature extraordinary luminosity, directionality, and coherence, which has enabled significant scientific progress in fields including physics, chemistry, and biology. The next generation of light sources has aimed at compact radiation sources driven by free electrons, with the advantages of reduction in both space and cost. With the rapid development of ultra-intense and ultrashort lasers, great effort has been devoted to the quest for compact free-electron lasers (FELs). This review focuses on the current efforts and advancements in the development of compact FELs, with a particular emphasis on two notable paths: the development of compact accelerators and the construction of micro undulators based on innovative materials/structures or optical modulation of electrons. In addition, the physical essence of inverse Compton scattering is discussed, which offers remarkable capability to develop an optical undulator with a spatial period that matches the optical wavelength. Recent scientific developments and future directions for miniaturized and integrated free-electron coherent light sources are also reviewed. In the future, the prospect of generating ultrashort electron pulses will provide fascinating means of producing superradiant radiation, promising high brilliance and coherence even on a micro scale using optical micro undulators.show less
We show that a III-V semiconductor vertical external-cavity surface-emitting laser (VECSEL) can be engineered to generate light with a customizable spatio
We show that a III-V semiconductor vertical external-cavity surface-emitting laser (VECSEL) can be engineered to generate light with a customizable spatiotemporal structure. Temporal control is achieved through the emission of temporal localized structures (TLSs), a particular mode-locking regime that allows individual addressing of the pulses traveling back and forth in the cavity. The spatial profile control relies on a degenerate external cavity, and it is implemented due to an absorptive mask deposited onto the gain mirror that limits the positive net gain within two circular spots in the transverse section of the VECSEL. We show that each spot emits spatially uncorrelated TLSs. Hence, the spatiotemporal structure of the light emitted can be shaped by individually addressing the pulses emitted by each spot. Because the maximum number of pulses circulating in the cavity and the number of positive net-gain spots in the VECSEL can be increased straightforwardly, this result is a proof of concept of a laser platform capable of handling light states of scalable complexity. We discuss applications to three-dimensional all-optical buffers and to multiplexing of frequency combs that share the same laser cavity.show less
Optical metasurfaces are two-dimensional ultrathin devices based on single-layer or multilayer arrays of subwavelength nanostructures. They can achieve pr
Optical metasurfaces are two-dimensional ultrathin devices based on single-layer or multilayer arrays of subwavelength nanostructures. They can achieve precise control of phase, amplitude, and polarization on the subwavelength scale. In this paper, a substrate-free all-silicon coded grating is designed, which can realize the phase control of the outgoing beam after the
The ability to amplify optical signals is of paramount importance in photonic integrated circuits (PICs). Recently, lithium niobate on insulator (LNOI) ha
The ability to amplify optical signals is of paramount importance in photonic integrated circuits (PICs). Recently, lithium niobate on insulator (LNOI) has attracted increasing interest as an emerging PIC platform. However, the shortage of efficient active devices on the LNOI platform limits the development of optical amplification. Here, we report an efficient waveguide amplifier based on erbium and ytterbium co-doped LNOI by using electron beam lithography and an inductively coupled plasma reactive ion etching process. We have demonstrated that signal amplification emerges at a low pump power of 0.1 mW, and the net internal gain in the communication band is 16.52 dB/cm under pumping of a 974 nm continuous laser. Benefiting from the efficient pumping facilitated by energy transfer between ytterbium and erbium ions, an internal conversion efficiency of 10% has been achieved, which is currently the most efficient waveguide amplifier under unidirectional pumping reported on the LNOI platform, to our knowledge. This work proposes an efficient active device for LNOI integrated optical systems that may become an important fundamental component of future lithium niobate photonic integration platforms.show less
AlGaN-based light-emitting diodes (LEDs) on offcut substrates enhance radiative emission via forming carrier localization centers in multiple quantum wells (MQWs). This study introduces carrier
AlGaN-based light-emitting diodes (LEDs) on offcut substrates enhance radiative emission via forming carrier localization centers in multiple quantum wells (MQWs). This study introduces carrier transport barrier concept, accessing its impact on the quantum efficiency of LEDs grown on different offcut sapphire. A significantly enhanced internal quantum efficiency (IQE) of 83.1% is obtained from MQWs on the 1° offcut sapphire, almost twice that of the controlled 0.2° offcut sample. Yet, 1° offcut LEDs have higher turn-on voltage and weaker electroluminescence than 0.2° ones. Theoretical calculations demonstrate the existence of a potential barrier on the current path around the step-induced Ga-rich stripes. Ga-rich stripes reduce the turn-on voltage but restrict sufficient driving current, impacting LED performance.show less
Indoor organic and perovskite photovoltaics (PVs) have been attracting intense interest in recent years. Theoretical limit of indoor PVs has been calculated based on the detailed balance method
Indoor organic and perovskite photovoltaics (PVs) have been attracting intense interest in recent years. Theoretical limit of indoor PVs has been calculated based on the detailed balance method brought by Shockley-Queisser (known as SQ). However, realistic losses of the organic and perovskite PVs under indoor illumination are to be understood for further efficiency improvement. In this work, the efficiency limit of indoor PVs is calculated to 55.33% under the indoor illumination (2700 K, 1000 lux) when the bandgap (Eg) of the semiconductor is 1.77 eV. The efficiency limit was obtained on the basis of assumptions of 100% photovoltaic external quantum efficiency (EQEPV) when E ≥ Eg, no nonradiative recombination, and no resistance losses. In reality, the maximum EQEPV reported in the literature is 0.80 - 0.90. The proportion of radiative recombination in realistic devices is only 10-5 - 10-2, which causes the open-circuit voltage loss (ΔVloss) of 0.12 - 0.3 V. Fill factor (FF) of the indoor PVs is sensitive to the shunt resistance (Rsh). These realistic losses of EQEPV, nonradiative recombination and resistance cause the large efficiency gap between the realistic values (excellent perovskite indoor PV: 32.4%; superior organic indoor PV: 30.2%) and theoretical limit of 55.33%. In reality, it is feasible to reach the efficiency of 47.4% at 1.77 eV for organic and perovskite photovoltaics under indoor light (1000 lux, 2700 K) with VOC = 1.299 V, JSC = 125.33 μA/cm2, and FF = 0.903, when EQEPV = 0.9, EQEEL = 10-1, Rs = 0.5 Ω cm2 and Rsh = 104 kΩ cm2.show less
The pandemic of respiratory diseases enlightened people that monitoring respiration has promising prospect in averting many fatalities by tracking the development of diseases. However, the respo
The pandemic of respiratory diseases enlightened people that monitoring respiration has promising prospect in averting many fatalities by tracking the development of diseases. However, the response speed of current optical fiber sensors is still insufficient to meet the requirements of high-frequency respiratory detection during respiratory failure. Here, a scheme for fast and stable tachypnea monitor is proposed utilizing water-soluble C<sub>60</sub>-Lys ion compound as functional material for the tracking of humidity change in the progression of breath. The polarization of C<sub>60</sub>-Lys can be tuned by the ambient relative humidity change and an apparent refractive index alteration can be detected due to the small size effect. In our experiments, C<sub>60</sub>-Lys is conformally and uniformly deposited on the surface of a tilted fiber Bragg grating (TFBG) to fabricate an ultra-fast response, high-sensitivity, and long-term stable optical fiber humidity sensor. A RH detecting sensitivity of 0.080 dB/% RH and the equilibrium response time and recovery time of 1.85 s and 1.58 s is observed respectively. Besides, a linear relation is detected between the resonance intensity of the TFBG and the environment RH. In practical breath monitoring experiment, the instantaneous response time and recovery time are measured as 40 ms and 41 ms respectively during a 1.5 Hz fast breath process. Furthermore, an excellent time stability and high repeatability are exhibited in experiments conducted over a range of 7 days.show less
In this work we compare different methods to implement a triplicator, a phase grating that generates three equi-intense diffraction orders. The design with optimal efficiency features a continuo
In this work we compare different methods to implement a triplicator, a phase grating that generates three equi-intense diffraction orders. The design with optimal efficiency features a continuous phase profile, which cannot be easily reproduced, typically affected by quantization. We compare its performance with binary and sinusoidal phase profiles. We also analyze the effect of quantizing the phase levels. Finally, a random approach is adopted to eliminate the additional harmonic orders. In all cases a liquid-crystal on silicon spatial light modulator (LCOS-SLM) is employed to experimentally verify and compare the different approaches.show less