Advanced Photonics Co-Editors-in-Chief Anatoly Zayats and Xiao-Cong (Larry) Yuan introduce the special issue celebrating 60 years of laser.

The Advanced Photonics special issue celebrating the 60-year laser anniversary is an ideal opportunity to review some highlights from its history, at the same time taking us on a tour of over a century of Nobel Prizes.

Semiconductor perovskite films are now being widely investigated as light harvesters in solar cells with ever-increasing power conversion efficiencies, which have motivated the fabrication of other optoelectronic devices, such as light-emitting diodes, lasers, and photodetectors. Their superior material and optical properties are shared by the counterpart colloidal nanocrystals (NCs), with the additional advantage of quantum confinement that can yield size-dependent optical emission ranging from the near-UV to near-infrared wavelengths. So far, intensive research efforts have been devoted to the optical characterization of perovskite NC ensembles, revealing not only fundamental exciton relaxation and recombination dynamics but also low-threshold amplified spontaneous emission and novel superfluorescence effects. Meanwhile, the application of single-particle spectroscopy techniques to perovskite NCs has helped to resolve a variety of optical properties for which there are few equivalents in traditional colloidal NCs, mainly including nonblinking photoluminescence, suppressed spectral diffusion, stable exciton fine structures, and coherent single-photon emission. While the main purpose of ensemble optical studies is to guide the smooth development of perovskite NCs in classical optoelectronic applications, the rich observations from single-particle optical studies mark the emergence of a potential platform that can be exploited for quantum information technologies.

A history and a glimpse into the future of spaser (acronym for “surface plasmon amplification by stimulated emission of radiation”) is provided. The spaser (also called a plasmonic nanolaser) is an active nanosystem including a gain medium and a nanoplasmonic metal core. It generates coherent intense nanolocalized fields. Theoretically predicted in 2003 by Bergman and Stockman, the spaser grew into a large fundamental research and application field with thousands of publications. We review a few of them to illustrate the most important and general fundamental properties of the spaser. We also review some selected applications of spasers, in particular, to ultrasensing and biomedical problems, concentrating on cancer-cell theranostics (therapeutics and diagnostics). In conclusion, we attempt to glimpse into the future by predicting that the next big development of the spasers will be topological nano-optics, and its “killer” application will be ultrafast, high-density on-chip communications for future information processing.

Microbubbles acting as lenses are interesting for optical and photonic applications such as volumetric displays, optical resonators, integration of photonic components onto chips, high-resolution spectroscopy, lithography, and imaging. However, stable, rationally designed, and uniform microbubbles on substrates such as silicon chips are challenging because of the random nature of microbubble formation. We describe the fabrication of elastic microbubbles with a precise control of volume and curvature based on femtosecond laser irradiated graphene oxide. We demonstrate that the graphene microbubbles possess a near-perfect curvature that allows them to function as reflective microlenses for focusing broadband white light into an ultrahigh aspect ratio diffraction-limited photonic jet without chromatic aberration. Our results provide a pathway for integration of graphene microbubbles as lenses for nanophotonic components for miniaturized lab-on-a-chip devices along with applications in high-resolution spectroscopy and imaging.

Recently, it was predicted that extraordinary light waves in hyperbolic metamaterials may exhibit two-time physics behavior. We report experimental observation of this effect via investigation of gravity-like nonlinear optics of iron/cobalt-based ferrofluid hyperbolic metamaterials. In addition to conventional temporal coordinates, the spatial coordinate oriented along the optical axis of the metamaterial also exhibits timelike character, which leads to very unusual two-time physics behavior in these systems on small scales.

We report a framing imaging based on noncollinear optical parametric amplification (NCOPA), named FINCOPA, which applies NCOPA for the first time to single-shot ultrafast optical imaging. In an experiment targeting a laser-induced air plasma grating, FINCOPA achieved 50 fs-resolved optical imaging with a spatial resolution of ∼83  lp  /  mm and an effective frame rate of 10 trillion frames per second (Tfps). It has also successfully visualized an ultrafast rotating optical field with an effective frame rate of 15 Tfps. FINCOPA has simultaneously a femtosecond-level temporal resolution and frame interval and a micrometer-level spatial resolution. Combining outstanding spatial and temporal resolutions with an ultrahigh frame rate, FINCOPA will contribute to high-spatiotemporal resolution observations of ultrafast transient events, such as atomic or molecular dynamics in photonic materials, plasma physics, and laser inertial-confinement fusion.

Interaction of electromagnetic, acoustic, and even gravitational waves with accelerating bodies forms a class of nonstationary time-variant processes. Scattered waves contain intrinsic signatures of motion, which manifest in a broad range of phenomena, including Sagnac interference, and both Doppler and micro-Doppler frequency shifts. Although general relativity is often required to account for motion, instantaneous rest frame approaches are frequently used to describe interactions with slowly accelerating objects. We investigate theoretically and experimentally an interaction regime that is neither relativistic nor adiabatic. The test model considers an accelerating scatterer with a long-lasting relaxation memory. The slow decay rates violate the instantaneous reaction assumption of quasistationarity, introducing non-Markovian contributions to the scattering process. Memory signatures in scattering from a rotating dipole are studied theoretically, showing symmetry breaking of micro-Doppler combs. A quasistationary numeric analysis of scattering in the short-memory limit is proposed and validated experimentally with an example of electromagnetic pulses interacting with a rotating wire.

Metasurface analogue of the phenomenon of electromagnetically induced transparency (EIT) that is originally observed in atomic gases offers diverse applications for new photonic components such as nonlinear optical units, slow-light devices, and biosensors. The development of functional integrated photonic devices requires an active control of EIT in metasurfaces. We demonstrate a reversible switching of the metasurface-induced transparency in the near-infrared region by incorporating a nonvolatile phase change material, Ge₂Sb₂Te₅, into the metasurface design. This leads to an ultrafast reconfigurable transparency window under an excitation of a nanosecond pulsed laser. The measurement agrees well with both theoretical calculation and finite-difference time-domain numerical simulation. Our work paves the way for dynamic metasurface devices such as reconfigurable slow light and biosensing.

The performance of fiber mode-locked lasers is limited due to the high nonlinearity induced by the spatial confinement of the single-mode fiber core. To massively increase the pulse energy of the femtosecond pulses, amplification is performed outside the oscillator. Recently, spatiotemporal mode-locking has been proposed as a new path to fiber lasers. However, the beam quality was highly multimode, and the calculated threshold pulse energy (>100  nJ) for nonlinear beam self-cleaning was challenging to realize. We present an approach to reach high energy per pulse directly in the mode-locked multimode fiber oscillator with a near single-mode output beam. Our approach relies on spatial beam self-cleaning via the nonlinear Kerr effect, and we demonstrate a multimode fiber oscillator with M²  <  1.13 beam profile, up to 24 nJ energy, and sub-100 fs compressed duration. Nonlinear beam self-cleaning is verified both numerically and experimentally for the first time in a mode-locked multimode laser cavity. The reported approach is further power scalable with larger core sized fibers up to a certain level of modal dispersion and could benefit applications that require high-power ultrashort lasers with commercially available optical fibers.

The article provides information about the image on the cover of Advanced Photonics, Volume 2, Issue 5.