Kenneth B. Crozier

The high radiative efficiencies and strong absorption coefficients of van der Waals materials position them well for optoelectronic power generation via radiative exchange. These materials have been investigated for use in solar cells, however, their use in thermoradiative and thermophotovoltaic applications in the mid‐infrared remains unexplored. We fabricate a black phosphorus ()/molybdenum disulfide () van der Waals heterojunction diode and use it in both thermoradiative and thermophotovoltaic operation modes. Open circuit voltage and short circuit current measurements taken as a function of temperature difference between the device and its environment, show the device can effectively generate power in both regimes. A net power density of is achieved at (thermoradiative), and at (thermophotovoltaic). This represents the first demonstration of thermoradiative power generation using van der Waals materials. Optoelectronic modeling further indicates that the performance is primarily limited by optical out‐coupling and external quantum efficiency. By addressing these, the short circuit current density could be increased by up to three orders of magnitude, corresponding to an approximate six orders of magnitude increase in power density.

Accessing the rich information carried by infrared light typically relies on bulky, complex optoelectronic systems. Lanthanide-based upconverting nanoparticles (UCNPs) offer a compelling alternative by converting infrared light into visible photons through nonlinear anti-Stokes processes. However, achieving strong upconversion under the low excitation intensities relevant to infrared vision remains challenging, motivating strategies to enhance light–matter interaction. Here, we demonstrate enhanced infrared-to-visible upconversion imaging enabled by integrating alloyed Yb/Er UCNPs with a resonant dielectric metasurface. The metasurface supports an optical resonance aligned with the UCNP excitation band, leading to over three orders of magnitude enhancement in upconversion emission. Crucially, flat-band angular dispersion of this resonance enables uniform enhancement across incident angles relevant to imaging, thereby preserving spatial frequency content and yielding sharp, high-contrast images. In light of ongoing advances in lanthanide-based materials, this metasurface–UCNP hybrid screen provides a promising platform for compact, detector-free, and scalable infrared imaging technologies based on optical upconversion.

The van der Waals materials have emerged as promising candidates for infrared (IR) photodetectors. Among these, black phosphorus (BP)/ molybdenum disulphide (MoS ₂ ) photodiodes have shown high specific detectivity at room‐temperature. The signal‐to‐noise performance of such detectors can be further improved by employing a microlens to increase the total photon collection without changing the device size, and hence its noise current. In this study, we explore the direct integration of refractive microlenses on BP/MoS ₂ photodiodes, designed for operation at a wavelength of λ = 1.55 µm. The device's photoresponse is enhanced by up to 20× after microlens fabrication, enabling a detectivity of 1.83 × 10 ⁹ cmHz ^1/2 W ⁻¹ under zero‐bias at room‐temperature. Infrared imaging is achieved by integrating the device into a single‐pixel imaging set‐up. This enables a 255 × 192‐pixel image to be resolved from the transmission of a binary mask placed in front of a λ = 1.55 µm light source. These results demonstrate that direct integration of refractive microlenses with van der Waals photodiodes provides a simple and scalable route to enhance detectivity at room‐temperature, enabling practical near‐infrared computational imaging.

Chiral metasurfaces have emerged as a versatile platform for manipulating chiral light‐matter interactions in diverse applications. However, the design of arbitrary chiroptical responses remains challenging because conventional parameterized geometries severely constrain the accessible design space. To address this issue, we present a design framework for planar freeform chiral metasurfaces (FCMs) in the near‐infrared regime, enabling on‐demand inverse engineering of customized circular dichroism (CD) responses. The proposed framework allows flexible control over key CD spectral characteristics, including spectral feature position, amplitude, line shape, and bandwidth. Experimental and numerical results demonstrate representative capabilities. Specifically, high CD responses can be designed at selected target wavelengths, and tailored CD spectra with Fano, single‐Gaussian, dual‐Gaussian, and gate‐shaped profiles can be further realized. In addition, multiple fabrication‐compatible FCM candidates with distinct geometries can be obtained for the same target response. Good agreement between simulations and experiments confirms the reliability and flexibility of the proposed strategy. This work provides a practical route toward the on‐demand realization of customized CD responses in freeform metasurfaces.

Helix‐shaped polymorphic beams are structured optical fields formed by the coherent superposition of Bessel beams with carefully selected orders. Their intensity maxima trace a helical trajectory during propagation. By engineering the transverse phase and amplitude, these beams generate optical forces for particle propulsion and trapping. Upon interaction with particles, the resulting axial forces can be either attractive or repulsive, enabling operation in tractor‐beam or pushing‐beam regimes. Their generation has traditionally relied on bulky and expensive spatial light modulators, whereas metasurfaces provide a compact and cost‐effective alternative. While metasurfaces have been used to generate two‐component solenoid beams, a specific subset of helix‐shaped polymorphic beams using phase‐only modulation, metasurface‐based generation of more general helix‐shaped polymorphic beams remains unexplored. Here, we demonstrate the generation of general helical polymorphic beams using metasurfaces for the first time, to the best of our knowledge. Two approaches are used. First, a geometric‐phase‐based complex‐amplitude approach enables simultaneous amplitude and phase control, providing flexibility for complex field engineering. By incorporating intermediate‐plane holography via back‐propagation of the target field, we achieve a 30% relative improvement in experimental efficiency. Second, we demonstrate beam generation using a phase‐only encoding approach, simplifying metasurface fabrication using techniques commonly used with phase‐only spatial light modulators.

Optical nanotweezers, which integrate nanophotonic structures such as plasmonic antennas, dielectric resonators, and metasurfaces, have emerged as powerful tools for manipulating nanoparticles, biomolecules, and viruses with high precision. However, traditional designs rely heavily on heuristic approaches and simple geometries, limiting performance. Inverse design offers a paradigm shift by using computational optimization methods to discover non-intuitive, high-performance structures for optical trapping. This Review provides an overview of key inverse design methodologies, including adjoint-based optimization, topology optimization, and machine learning approaches, and highlights their broader impact across nanophotonics. We then focus on their application to optical nanotweezers, where recent advances demonstrate enhanced trapping stiffness, reduced optical heating, and tailored trapping landscapes. Representative examples include algorithmic design of plasmonic nanotweezers, topology-optimized plasmonic nanoapertures, inverse-designed dielectric nanocavities, and force-centric designs based on Maxwell stress tensor engineering. Collectively, these studies illustrate how inverse design enables stable, efficient, and versatile optical trapping at the nanoscale. Despite these advances, challenges remain in fabrication, computational cost, and the interpretability of optimized structures. We conclude with a perspective on future directions, emphasising opportunities in reconfigurable tweezers, lab-on-a-chip integration, and quantum nanophotonics. By bridging photonic optimization with nanoscale manipulation, inverse-designed optical nanotweezers offer promising opportunities for future applications in biophysics, materials science, and quantum technologies.

The use of individual fluorescent nanoparticles for imaging molecular-scale biophysics is often hindered by a size-brightness trade-off, where reduced particle volumes lead to diminished signal-to-noise ratios and increased requirements for excitation power. Plasmonic nanotweezers have shown promise in their ability to position and enhance the emission from single nanoparticles. However, traditional designs are typically optimized for a single resonance, failing to simultaneously address optical trapping and emission enhancement. Here, we utilize a multiobjective topology optimization framework to design a dual-resonant plasmonic nanocavity. Our inverse-designed architecture provides simultaneous electric field intensity enhancement for stable optical trapping and Purcell-accelerated emission. Surprisingly, the design strongly resembles a previously reported “antenna-in-a-box” configuration. Simulations demonstrate a 32-fold increase in electric field intensity enhancement at the emission wavelength and a 26-fold increase in the Purcell factor compared to conventional double nanohole designs, while maintaining the gradient forces necessary for stable single-particle localization. This platform offers a robust pathway for high-sensitivity, low-power sensing of diverse nanoscale emitters.

Solenoid beams are structured beams with the electric field rotating around the beam propagation axis. We generate solenoid beams using digital micromirror devices, overcoming key limitations of conventional liquid-crystal spatial light modulators.

Helix-shaped polymorphic beams and solenoid ones are non-diffracting beams generated by the superposition of Bessel beams of specific orders. Their fields rotate around the beam propagation axis and have promising applications in optical forces, where they can be designed to function as either tractor or repulsor beams. Traditionally, phase-only spatial light modulators (SLMs) based on liquid crystal technology have been used for their generation. However, such SLMs have several limitations. They operate within a limited wavelength range, have lower refresh rates (typically 60 Hz, with a maximum of a few hundred Hz), and require linearly polarized light. There is, therefore, a need for an affordable alternative for applications outside the wavelength range of liquid crystal-based SLMs, for those requiring fast refresh rates or those needing polarization independence. In this work, we show, for the first time to the best of our knowledge, the generation of solenoid and helix-shaped polymorphic beams with an amplitude-type SLM, namely, a digital micromirror device (DMD). These address the aforementioned problems faced by liquid crystal-based SLMs. Although there are advantages associated with the use of DMDs, they often suffer from lower efficiency, mainly because many pixels are required to be in the off state. To solve this issue, we apply an intermediate plane holography method. We show that it can be used to generate a complex field helix-shaped polymorphic laser beam with a ∼2.5 fold improvement in optical power efficiency.