We present a self-referenced, frequency-diverse beamlet architecture for characterizing underwater optical turbulence. Multiple mutually coherent, laterally separated beamlets co-propagate through turbulence and are detected on a single-pixel photodetector, generating a set of heterodyne beat tones that uniquely encode beamlet-pair separations. This intrinsic RF channelization enables simultaneous scale-resolved and directional turbulence sensing without scanning, imaging-based beam tracking, or an external local oscillator. Experiments conducted in a Rayleigh-Bénard convection tank demonstrate estimation of turbulence strength, anisotropy, and temporal dynamics across weak-to-strong fluctuation regimes, establishing the approach as a compact and scalable platform for optical turbulence measurements.

A frequency-diverse perfect vortex beamlet array enables compact, self-referencing underwater acoustic sensing. An eight-beamlet, 532 nm, 5 MHz-spaced array yields > 80dB beat-to-sidelobe ratios for kHz signals and near-pascal sensitivity in calm or turbulent water.

We introduce a free-space optical sensing architecture in which spatial refractive-index gradients are mapped directly into heterodyne modulation sidebands using a frequency-diverse beamlet array. Mutually coherent beamlets with distinct frequency offsets sample the medium at different transverse positions, producing a time-dependent interference signal on a single detector whose Fourier transform yields a comb of heterodyne beat frequencies. Spatially varying refractive index gradients induce differential phase shifts between beamlets, yielding symmetric sidebands around each beat frequency that encode the local gradient. This approach enables multiple parallel sensing channels on a single detector without a reference arm or embedded sensing elements, with spatial sampling and detection defined entirely by the optical field. An analytic framework describing beat formation and sideband scaling is developed and validated experimentally. Using an eight-beamlet array at 532 nm with 5 MHz spacing, the system achieves > 80 dB beat-to-sidelobe ratios and near-pascal acoustic sensitivity. Because the detection bandwidth is set by the optical beat frequencies, this approach supports extension to substantially higher acoustic bandwidths, establishing a compact, reconfigurable platform for remote, non-contact acoustic sensing. This approach establishes a general framework for non-contact sensing of refractive index gradients using structured light, with potential applications beyond acoustics including turbulence and thermal sensing.

We demonstrate a resonance-free Fabry–Pérot cavity enabled by an intra-cavity holographic phase mask that converts a Gaussian input into a sequence of Laguerre–Gaussian modes, suppressing coherent interference, and thereby eliminating conventional spectral resonances.

Orthogonal frequency-diverse arrays measure multi-scale, directional phase and amplitude fluctuations in underwater turbulence, revealing strong Rayleigh–Bénard anisotropy up to 70%. This represents the first single-probe method capable of fast, multi-scale, directional turbulence characterization.

Partially coherent fields with controlled properties offer distinctive optical sensing capabilities. We demonstrate that temporal fluctuations of integrated intensity provide robust means to measure the off-axis angular velocity of scattering objects embedded in disturbing media.

Skyrmions, topologically non-trivial localized spin structures, are fertile ground for exploring emergent phenomena in condensed matter physics and next-generation magnetic-memory technologies. Although magnetics and optics readily lend themselves to two-dimensional realizations of spin texture, only recently have breakthroughs brought forth three-dimensional (3D) magnetic skyrmions, whereas their optical counterparts have eluded observation to date because their realization requires precise control over the spatiotemporal spectrum. Here, we demonstrate the first 3D-localized optical skyrmionic structures with a non-trivial topological spin profile by imprinting meron spin texture on open and closed spectral surfaces in the momentum-energy space of an ultrafast optical wave packet. Precise control over the spatiotemporal spin texture of light - a key requisite for synthesizing 3D optical merons - is the product of synergy between novel methodologies in the modulation of light jointly in space and time, digital holography, and large-area birefringent metasurfaces. Our work advances the fields of spin optics and topological photonics and may inspire new developments in imaging, metrology, optical communications, and quantum technologies.

A modified HOBBIT system rapidly probes a dynamic turbulence environment, enabling investigation of the temporal evolution of the medium through the determination of turbulence-characteristic beams, along with their OAM spectrum and temporal coherence.

We present the first optical meron wave packet with a non-trivial spin structure mapped onto a 3D surface in momentum-energy space, demonstrating a propagation-invariant localized topological structure with dynamically tunable propagation characteristics and spatio-temporal evolution.

Introducing elements into an optical cavity that modify the transverse spatial field structure can also impact the cavity spectral response. In particular, an intra-cavity spatial mode-converter is expected to induce modal runaway: unrestricted ladder-up in the modal order, concomitantly thwarting coherent field interference, thereby altogether suppressing the resonant response - a phenomenon that has yet to be observed in an optical cavity. Here we show that a single intra-cavity holographic phase mask placed in a compact free-standing planar Fabry-Pérot cavity renders the cavity spectral response resonance-free. By acting as a mode-converter on a basis of Laguerre-Gaussian (LG) modes, an incident broadband fundamental Gaussian mode exits the cavity in the form of a superposition of a large number of collinearly propagating broadband LG modes of fixed parity whose spectra coincide with that of the input. Crucially, the resonance-free spectral response is maintained while changing the cavity length by ~ 350%, raising the prospect of stable resonant optical sensors whose performance is impervious to length perturbations.

This work presents a method of structured light ranging that utilizes a relative phase modulation between two orthogonal beams. Application of a linear frequency modulated (LFM) signal in the relative phase between two Orbital Angular Momentum (OAM) states within a coherently coupled OAM (CCOAM) beam provides a ranging technique that achieves 21.7 mm resolution and removes the need for optical mixing. Results are provided for different distances, distributed targets, and estimation of target velocity.

This work provides for rotational velocity measurements of a dense bubble cloud through coherently coupled OAM beamlets. A heterodyne HOBBIT system is used to create unique beat frequencies related to the distribution of local velocities.

Off-axis Bessel-Gauss (BG) beams are used as a generation basis within an optical system that rapidly probes an underwater turbulent environment. Due to the rapidity of the scan, implemented using a modified Higher Order Bessel Beams Integrated with Time (HOBBIT) system, instantaneous realizations of the turbulence can be probed allowing optimal transmission paths in which the beams propagate, with minimal perturbations, through the complex turbulent environment. The results show a marked reduction in the effects of the turbulence, including over a 91% decrease in scintillation index, experienced by the beams propagated through these paths when compared to a centered on-axis BG beam. Results also confirm the ability to transmit higher-order BG beams. Lastly, the spatial and temporal characteristics of these robust channels are presented, demonstrating the propensity to transmit multiple beams through unperturbed transmission paths simultaneously.

This paper introduces a method that leverages frequency diversity in a scanning optical source to extract distinctive features of an unmanned aerial vehicle (UAV) using a single photodetector in a bistatic sensing configuration.

A modified HOBBIT system generates non-diffracting beams using a Bessel beam basis. Phase and amplitude control is realized to create customizable distributions, allowing complex intensity patterns to be tailored for desired function. These beams are propagated through underwater turbulence and show resilience to its effects.

Customizable, non-diffracting light modes are dynamically generated using a modified HOBBIT system. Amplitude control is realized to create the intensity distributions, allowing for highly complex structured modes that are tailorable to desired functions.

AimsThe purpose of this research was to understand the experience of older adults who completed an 8-week cervical spine home exercise program (HEP) designed to reduce visual reliance for postural stability, potentially impacting fall risk.MethodsNineteen older adults completed a semi-structured, one-on-one interview. Qualitative verbatim data from one open-ended prompt, "Tell me about your experience with the home exercise program," were analyzed using an inductive, emergent approach.ResultsEleven subthemes emerged within two overarching themes: motivational factors and perceived barriers. Two subthemes within the motivational factors category aligned with the Self-Determination Theory (SDT): autonomy and competence, impacting motivation. Participants reported a positive HEP experience despite the perceived barriers of time and commitment required for HEP completion.ConclusionThis study provides insight into the experiences of older adults participating in an HEP and highlights the importance of considering their fundamental psychological needs when designing HEPs, impacting motivation and adherence.

VO2 thin films synthesized via direct oxidation on piezoelectric GaN/AlGaN/GaN/Si and SiO2/Si substrates have been used to demonstrate free space modulation of near and mid-IR light using a pulsed electric field. Interdigitated metal finger patterns deposited on high-quality 140 nm VO2 thin films on suspended III-nitride or SiO2/Si membranes were used to apply the pulsed electric field and modulate laser beams of wavelengths varying from 1064 to 2600 nm passing through it as it switched between metal and semiconducting phases. Strong wavelength dependence of the intensity modulation is observed with the modulation magnitude varying from 23.4% at 1550 nm to 52.1% at 2600 nm for VO2 film grown on the III-nitride membrane. The VO2 film on SiO2/Si resulted in an intensity modulation of almost half of that on III-nitrides due to higher IR absorption in the SiO2 and Si layers. Infrared microscopic images of the membrane recorded across the phase transition of the VO2 film indicate significant temperature change over only a small fraction of the interdigitated finger pattern, clearly indicating the localized nature of the phase transition enabled by both the electric field and thermal heating. The intensity modulation depth did not change significantly over a frequency range of 10 kHz, which is likely limited by the thermal mass of the structure, so improved design concentrating electric field and reducing thermal mass and conductivity is expected to further improve the frequency response.

Optical ranging systems have growing interest but often encounter difficulties in measuring small distances. Combining traditional techniques of linear frequency modulated radar with phase modulation of coherently combined OAM beams, 15 mm range resolution and 150 m maximum range is achievable.

Phase only modulation of CCOAM beams provides a system with 15 mm resolution is achieved. This system’s resolution is independent of beam size and propagation allowing precise measurement of a target over 8 m away.