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Integrated-photonics microchips now enable a range of advancedfunctionalities for high-coherence applications such as data transmission,highly optimized physical sensors, and harnessing quantum states, but withcost, efficiency, and portability much beyond tabletop experiments. Throughhigh-volume semiconductor processing built around advanced materials thereexists an opportunity for integrated devices to impact applications cuttingacross disciplines of basic science and technology. Here we show how tosynthesize the absolute frequency of a lightwave signal, using integratedphotonics to implement lasers, system interconnects, and nonlinear frequencycomb generation. The laser frequency output of our synthesizer is programmed bya microwave clock across 4 THz near 1550 nm with 1 Hz resolution andtraceability to the SI second. This is accomplished with a heterogeneouslyintegrated III/V-Si tunable laser, which is guided by dualdissipative-Kerr-soliton frequency combs fabricated on silicon chips. Throughout-of-loop measurements of the phase-coherent, microwave-to-optical link, weverify that the fractional-frequency instability of the integrated photonicssynthesizer matches the $7.0*10^{-13}$ reference-clock instability for a 1second acquisition, and constrain any synthesis error to $7.7*10^{-15}$ whilestepping the synthesizer across the telecommunication C band. Any applicationof an optical frequency source would be enabled by the precision opticalsynthesis presented here. Building on the ubiquitous capability in themicrowave domain, our results demonstrate a first path to synthesis withintegrated photonics, leveraging low-cost, low-power, and compact features thatwill be critical for its widespread use.

Free-electron beams are versatile probes of microscopic structure and composition.sup.1,2, and have revolutionized atomic-scale imaging in several fields, from solid-state physics to structural biology.sup.3. Over the past decade, the manipulation and interaction of electrons with optical fields have enabled considerable progress in imaging methods.sup.4, near-field electron acceleration.sup.5,6, and four-dimensional microscopy techniques with high temporal and spatial resolution.sup.7. However, electron beams typically couple only weakly to optical excitations, and emerging applications in electron control and sensing.sup.8-11 require large enhancements using tailored fields and interactions. Here we couple a free-electron beam to a travelling-wave resonant cavity mode. The enhanced interaction with the optical whispering-gallery modes of dielectric microresonators induces a strong phase modulation on co-propagating electrons, which leads to a spectral broadening of 700 electronvolts, corresponding to the absorption and emission of hundreds of photons. By mapping the near-field interaction with ultrashort electron pulses in space and time, we trace the lifetime of the the microresonator following a femtosecond excitation and observe the spectral response of the cavity. The natural matching of free electrons to these quintessential optical modes could enable the application of integrated photonics technology in electron microscopy, with broad implications for attosecond structuring, probing quantum emitters and possible electron-light entanglement. The coupling between light and relativistic free electrons is enhanced through phase matching of electrons with optical whispering-gallery modes in dielectric microspheres and through extended modal lifetimes., Author(s): Ofer Kfir [sup.1] , Hugo Lourenço-Martins [sup.1] , Gero Storeck [sup.1] , Murat Sivis [sup.1] , Tyler R. Harvey [sup.1] , Tobias J. Kippenberg [sup.2] , Armin Feist [sup.1] [...]

Coherent ranging, also known as frequency-modulated continuous-wave (FMCW) laser-based light detection and ranging (lidar).sup.1 is used for long-range three-dimensional distance and velocimetry in autonomous driving.sup.2,3. FMCW lidar maps distance to frequency.sup.4,5 using frequency-chirped waveforms and simultaneously measures the Doppler shift of the reflected laser light, similar to sonar or radar.sup.6,7 and coherent detection prevents interference from sunlight and other lidar systems. However, coherent ranging has a lower acquisition speed and requires precisely chirped.sup.8 and highly coherent.sup.5 laser sources, hindering widespread use of the lidar system and impeding parallelization, compared to modern time-of-flight ranging systems that use arrays of individual lasers. Here we demonstrate a massively parallel coherent lidar scheme using an ultra-low-loss photonic chip-based soliton microcomb.sup.9. By fast chirping of the pump laser in the soliton existence range.sup.10 of a microcomb with amplitudes of up to several gigahertz and a sweep rate of up to ten megahertz, a rapid frequency change occurs in the underlying carrier waveform of the soliton pulse stream, but the pulse-to-pulse repetition rate of the soliton pulse stream is retained. As a result, the chirp from a single narrow-linewidth pump laser is transferred to all spectral comb teeth of the soliton at once, thus enabling parallelism in the FMCW lidar. Using this approach we generate 30 distinct channels, demonstrating both parallel distance and velocity measurements at an equivalent rate of three megapixels per second, with the potential to improve sampling rates beyond 150 megapixels per second and to increase the image refresh rate of the FMCW lidar by up to two orders of magnitude without deterioration of eye safety. This approach, when combined with photonic phase arrays.sup.11 based on nanophotonic gratings.sup.12, provides a technological basis for compact, massively parallel and ultrahigh-frame-rate coherent lidar systems. A massively parallel coherent light detection and ranging (lidar) scheme using a soliton microcomb--a light source that emits a wide spectrum of sharp lines with equally spaced frequencies--is described., Author(s): Johann Riemensberger [sup.1] , Anton Lukashchuk [sup.1] , Maxim Karpov [sup.1] , Wenle Weng [sup.1] , Erwan Lucas [sup.1] , Junqiu Liu [sup.1] , Tobias J. Kippenberg [sup.1] Author [...]

Author(s): Pablo Marin-Palomo [1]; Juned N. Kemal [1]; Maxim Karpov [2]; Arne Kordts [2]; Joerg Pfeifle [1, 2]; Martin H. P. Pfeiffer [2]; Philipp Trocha [1]; Stefan Wolf [1]; Victor [...]

In the 1970s, Arthur Ashkin at Bell Laboratories showed (1) that the force that light exerts on an object--the radiation pressure force--can be used to trap particles. This discovery has [...]