We demonstrate few-cycle pulse generation based on double-stage all-fiber nonlinear pulse compression from a thulium-doped fiber laser at a repetition rate of ∼199.74 MHz. The homemade laser provides an average power of 130 mW, serving as the seed for subsequent amplification. After amplification, significant spectral broadening to an octave-spanning bandwidth (1.2 to 2.4 μm) is attained through self-phase modulation-dominated nonlinear effects in an ultrahigh numerical aperture fiber and a highly nonlinear fiber. Followed by a two-stage nonlinear compressor, the system directly delivers near transform-limited pulses with a pulse duration of 19.8 fs (2.9 cycles at a central wavelength of 2000 nm) and a pulse energy of 3.37 nJ. To the best of our knowledge, this result is the shortest pulse duration directly generated from a thulium-doped fiber laser. This robust and simplified all-fiber system provides a promising route toward practical mid-infrared frequency comb generation and mid-infrared spectroscopy.

In vivo imaging of human iris vasculature remains a persistent challenge, limiting our understanding of its relationship with ocular disease pathogenesis. Conventional raster scan optical coherence tomography angiography (OCTA) suffers from angular-dependent contrast (including blind spots), limited field of view, and prolonged imaging time—challenges that restrict its clinical utility. We introduce a circular interleaving scan OCTA method that overcomes these barriers by enabling 360 deg high-contrast iris angiography with consistent spatiotemporal sampling and optimized motion contrast. The circular scan design enables direction-optimized sampling: we configured circumferential sampling density to approximately twice the radial density, enhancing detection of radially oriented iris vasculature. A Cartesian–polar coordinate transformation was implemented for eye-motion compensation, vessel realignment, and vasculature reconstruction. Compared with raster scan OCTA, our circular scan protocol demonstrates 1.55× higher efficiency in iris vascular imaging, featuring a superior duty cycle (99.95% versus 82.00%) and eliminating redundant data acquisition from rectangular field corners (27.3% of the circular area). This method improves vessel density measurement by 39.0% and vessel count quantification by 25.2% relative to raster scans. By eliminating angular-dependent blind spots, our method significantly enhances vascular quantification reliability, paving the way to a better understanding of ocular diseases and holding promising potential for future clinical applications.

In this Letter, a quartz-enhanced photoacoustic spectroscopy (QEPAS) gas sensor based on a single off-beam acoustic micro-resonator (AmR) and dual quartz tuning forks (QTFs) was demonstrated for the first time, to our knowledge. The sensor offers advantages of a compact sensing structure and high acoustic energy utilization efficiency. The key parameters of the designed off-beam AmR were optimized based on standing wave enhancement characteristics. Water vapor (H2O) in the environment was chosen as the target gas to investigate the sensor performance. Under identical experimental conditions, the reported sensor achieved 15.02 times improvement in detection sensitivity compared to the bare QTF-based sensor system, as well as a 1.53 times enhancement over the traditional off-beam QEPAS technique.

We report the experimental observation of a three-dimensional abruptly autofocusing effect by synthesizing a radially distributed Airy beam with two counter-propagating Airy pulses in time. As the wave packet propagates in a dispersive medium, the radially distributed Airy beam converges inward to the center point. Two Airy pulses counter-propagate toward each other to merge to form a high-peak-power pulse. As a result, high intensity emerges abruptly as the wave packet achieves three-dimensional focusing. This autofocusing effect is believed to have potential applications such as material modification, plasma physics, and nanoparticle manipulations.

In this paper, a polarization full-feedback open-loop spectral beam combining (PFF-SBC) structure based on double-ridge stripe semiconductor parity-time-symmetric laser diodes (PTLDs) is proposed and demonstrated. The beam quality of the PTLD is optimized, and the combining efficiency is improved using the methods of polarization separation and full feedback. The maximum output power is up to 2.71 W, which leads to a spectral beam combining efficiency of 83.4% and a grating diffraction efficiency of 95.51% under continuous current operation at a current of 2.3 A. Additionally, the brightness of the SBC module is 116.2 MW·cm-2 sr-1 at a current of 1.6 A, which is 3.5 times that of a single PTLD. The PFF-SBC strategy provides, to our knowledge, a new approach for increasing the beam brightness of PTLDs.

Digital micromirror devices (DMDs) have emerged as essential spatial light modulators for holographic 3D near-eye displays due to their rapid refresh rates and precise wavefront modulation characteristics. However, since the modulation depth of DMDs is limited to binary levels, the quality of reproduced images from a binary computer-generated hologram (CGH) is often deficient. In this paper, we propose a stochastic gradient descent (SGD) based binary CGH optimization framework where a convolutional neural network (CNN) is employed to perform the differentiable hologram binarization operation. The CNN-based binary SGD optimization can significantly minimize the binary quantization noise in the generation of binary CGH, providing a superior and high-fidelity holographic display. Our proposed method is experimentally verified by displaying both high-quality 2D and true 3D images from optimized binary CGHs.

Multi-ring perfect vortex beams enable the multi-parameter detection of rotating objects, providing distinct advantages in various applications. Generating fine rings is essential in improving the signal-to-noise ratio (SNR) for microscopic detection. However, the current method of directly modulating with spatial light modulators is hindered by pixelization. Here, we propose an approach based on the Bessel beam kinoform and cross-polarization superposition to generate high-quality beams with fine ring radii. Through simulations and experiments, we demonstrate its advantages in enhancing the SNR and measuring the velocity gradient. This approach provides a universal strategy for beam design and velocity gradient detection in fluidic environments.

We propose a heterogeneous all-dielectric photonic molecule comprising a Mie nano-resonator (MNR) and a photonic crystal nanocavity (PCNC), forming a strongly coupled system. The coupling mechanism is rigorously analyzed using the coupled mode theory, unveiling key optical phenomena, including Fano resonance, mode splitting, and Rabi oscillation. By precisely tuning the spatial position of the MNR relative to the PCNC and the structural parameters of the MNR, we achieve modulation of near-field mode interactions and far-field radiation. Performance evaluation reveals highly directional radiation and tunable spectral properties, facilitating efficient light manipulation at the nanoscale. This study establishes a versatile platform for advancing quantum optics, integrated photonics, and optical antennas, with promising applications in high-purity quantum light sources, ultra-sensitive sensing, and low-threshold nano lasers.

Extended depth-of-field (DoF) imaging enhances longitudinal clarity but traditionally fails to record polarization information. Here, we propose a liquid-crystal Pancharatnam–Berry (PB) phase element that extends DoF while sensing polarization ellipticity. Leveraging cubic-phase-induced defocus-insensitive point spread functions, a 10 cm DoF is achieved in a 10-cm-focal-length 4f system. Linear PB phases enable spin-orbit interactions to detect polarization states, overcoming irreversible polarization loss in conventional methods. This dual-functionality system integrates DoF extension with polarization sensing, enhancing multidimensional imaging capabilities and holding promise for advancing machine vision, microscopic imaging, and optical detection by merging depth clarity with polarization-based object differentiation.

We present a fully three-dimensional kinetic framework for modeling intense short pulse lasers interacting with dielectric materials. Our work modifies the open-source particle-in-cell code EPOCH to include new models for photoionization and dielectric optical response. We use this framework to model the laser-induced damage of dielectric materials by few-cycle laser pulses. The framework is benchmarked against experimental results for bulk silica targets and then applied to model multi-layer dielectric mirrors with a sequence of simulations with varying laser fluence. This allows us to better understand the laser damage process by providing new insight into energy absorption, excited particle dynamics and nonthermal excited particle distributions. We compare common damage threshold metrics based on the energy density and excited electron density.