We present the first demonstration of a waveguide-integrated dielectric laser accelerator. This structure and associated grating coupler are designed using a gradient-based inverse design approach. A waveguide is directly interfaced with an accelerator structure which is patterned with sub-wavelength features to produce near-fields phase-matched to electrons travelling through a 250 nm gap in the structure. We have experimentally demonstrated these waveguide-integrated accelerators by showing acceleration of subrelativistic electrons of initial energy 83.5 keV. We observe a maximum energy modulation of 1.19 keV over 30 μm. These results represent a significant step toward scalable and integrable on-chip dielectric laser accelerators for applications in ultrafast, medical, and high-energy technologies.
Particle accelerators are central to applications ranging from high-energy physics to medical treatments. However, the cost and size of conventional accelerators operating in radio-frequencies is prohibitive for widespread proliferation. Operating at optical and near-infrared frequencies, dielectric laser accelerators (DLAs) leverage the high damage threshold of dielectric materials, advances in nanofabrication techniques, and femtosecond pulsed lasers to produce miniaturized laser-driven accelerators. Previous demonstrations of dielectric laser acceleration have utilized free-space lasers directly incident on the accelerating structure. While this is acceptable for proof-of-principle, for DLAs to become a mature technology, it is necessary to integrate the accelerators on-chip to increase scalability and robustness of the system.
Here we demonstrate the first waveguide-integrated dielectric laser accelerator. In this scheme, a grating coupler is used to couple light from femtosecond pulsed laser to a 30 μm wide waveguide, fabricated on a silicon-on-insulator platform. The waveguide is then directly interfaced with an accelerating structure that is patterned with sub-wavelength features to produce near-fields phase-matched to electrons travelling through a vacuum-channel in the device. Both the input grating coupler and accelerator structure have been designed using the inverse design optimization approach.
We have experimentally demonstrated these waveguide-integrated accelerators by showing acceleration of subrelativistic electrons of initial energy 83.5 keV. We observe a maximum energy modulation of 1.19 keV over 30 μm. These results represent a significant step toward scalable and integrable on-chip DLAs for applications in ultrafast, medical, and high-energy technologies.
Luminescent coupling effects are considered crucial for the performance of multijunction solar cells. We report a novel approach based on small signal measurement, which can directly measure the luminescent coupling efficiency of a multijunction solar cell with different voltage bias. In addition, this method demonstrated the light and voltage dependence of the coupling efficiency, and can potentially lead to a deeper understanding of luminescent coupling effects as well as more effective design of multijunction solar cells.
For solar cells composed of direct bandgap semiconductors such as GaAs, the performance can be significantly improved by utilizing photon recycling and luminescence coupling effects. Accurate modeling with those effects may offer insightful guidance in designing such devices. Previous research has demonstrated different numerical models on photon recycling and luminescent coupling. However, most of those works are based on complicated theoretical derivation and idealized assumptions, which made them hard to implement. In addition, very few works provide method to model both photon recycling and luminescent coupling effects. In this paper, we demonstrate an easy-to-implement but accurate numerical model to simulate those effects in multijunction solar cells. Our numerical model can be incorporated into commonly used equivalent circuit model with high accuracy. The simulation results were compared with experimental data and exhibit good consistency. Our numerical simulation is based on a self-consistent optical-electrical model that includes non-ideal losses in both the single junction and the tandem device. Based on the numerical analysis, we modified the two-diode circuit model by introducing additional current-control-current sources to represent the effects of both photon recycling and luminescence coupling. The effects of photon recycling on the diode equation have been investigated based on detailed-balanced model, accounting for internal optical losses. We also showed the practical limit of performance enhancement of photon recycling and luminescent coupling effects. This work will potentially facilitate the accurate simulation of solar cell with non-ideal effects, and provide more efficient tools for multijunction solar cell design and optimization.
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