Optics express最新文献

In this study, we identified the optimal laser fluence range for the synthesis of optically relevant silicon nanoparticles (SiNPs) via femtosecond pulsed laser ablation in liquid (fs-PLAL). We used optimization via minimization to extract total nanoparticle population and concentration from UV-Vis absorption spectrum, and compared them to both single- and multiple-pulse ablation crater volumes. The optimal fluence between 20-30 J/cm² is found to maximize SiNP yield and minimize beam loss caused by persistent bubbles. A systematic analysis of ablation volumes showed that while single-pulsed crater volume increased with fluence, both multi-pulsed ablation volumes and measurable SiNP volumes peak near 25 J/cm² before decreasing. This drop is due to the formation of persistent cavitation bubbles that scatter incoming pulses and reduce ablation efficiency. The peak nanoparticle synthesis yield was ∼ 0.311 μg/min, which is comparable to the literature values. Importantly, this yield value is expected to be further improved by using high-speed scanning systems (e.g., galvo mirrors) to reduce pulse overlap and avoid cavitation bubble interference. These findings offer practical guidance for tuning PLAL parameters in future high-throughput, optically tuned SiNP production.

We demonstrate a laser emission scheme based on a 2-μm-thick Er³⁺-doped lithium niobate on insulator (Er:LNOI), using a Fabry-Pérot (FP) cavity with Sagnac loop reflectors (SLRs). The experimental results show a multimode laser output at a central wavelength of 1531.5 nm, with a measured on-chip power of 0.36 mW, and slope efficiency of 0.57%. We enhance the laser power of Er:LNOI lasers via a 2-μm-thick lithium niobate on insulator (LNOI) with an enlarged mode area. Additionally, it offers high coupling efficiency with the taper-lensed fiber, making it suitable for light sources in lithium niobate based photonic integrated circuits (PICs) and optical communication systems.

In recent years, we have developed a method to measure the 3D shape of transparent, glossy, or black objects without any surface preparation. For this purpose, we optically generate structured heat patterns on the surface and use a stereo mid-wave infrared camera setup to record re-emitted thermal patterns. We have demonstrated measurements in the second range, which is still too long for many applications, e.g., 100 % quality assurance or measurements in production lines. In this contribution, we present our high-speed thermal 3D sensor, enabling the reduction of the measurement time by one order of magnitude to the range of 0.1 s. We compare the resulting accuracy with that of previous thermal 3D sensors, present measurement examples of static objects with high thermal conductivity, and demonstrate a first dynamic measurement of a transparent object.

We demonstrate a high-power wavelength-tunable nanosecond mid-infrared (MIR, 3-5 μm) vortex laser based on a singly resonant optical parametric oscillator (OPO). With a MgO:PPLN crystal pumped by a first-order vortex at 1064 nm, efficient orbital angular momentum (OAM) transfer was achieved from the pump to the idler, while the signal remained a Gaussian-like profile without OAM. By varying the crystal temperature, the idler wavelength was tuned from 3142 to 3442 nm. At 3442 nm, the idler delivered a record vortex output of 3.87 W with 0.84% root-mean-square (RMS) fluctuation over one hour. To our knowledge, this is the highest reported vortex power beyond 3 µm among oxide-based OPOs, providing a stable and practical source for MIR applications such as spectroscopy, imaging, and material processing.

The planar compound eye has the advantages of a simple structure and no need for a complex relay optical element, but the field of view (FOV) is narrow, which is a limitation of the development of the planar compound eye. For breaking the limitation, a catadioptric planar compound eye with a large FOV is proposed in this article. This design captures more light in the edge part by reflection and light in the center part by refraction. Two rotationally symmetric mirrors are designed and processed by 3D printing. The experiments show that the FOV of the proposed prototype can reach 107°, which is larger than 90.7° obtained in previous work. In addition, images of the central FOV, which are unobtainable in previous work, have also been captured effectively. The proposed planar compound eye has great potential in virtual reality and detection since the FOV has been widened significantly.

We demonstrate the comparative 2.8 μm laser performance of the single and dual end-pumping Er:SGGG composite crystals. The thermal stress distribution reveals the reasons for the performance limitations of the single end-pumping Er:SGGG laser. The output power of 520 mW with a slope efficiency of 10.4% is achieved on the single end-bonding SGGG/Er:SGGG crystal, while excellent beam quality with M_x²/ M_y² of 1.06 and 1.11 is exhibited on the dual end-bonding SGGG/Er:SGGG/SGGG crystal. Through comparison, it is found that the bonding end-cap can optimize the beam quality, while the dual end-pumping scheme can further alleviate the thermal impact of the pump light on the basis of the bonding end-cap, reducing the cracking probability of the crystal during laser operation. This work provides a valuable reference for further exploration of the effects of bonding and dual end-pumping on the Er:SGGG laser performance.

We present an all-silicon anisotropic effective-medium half-wave plate (HWP) that provides broadband, low-loss polarization control in the terahertz (THz) band. A two-dimensional anisotropic effective medium was created by etching elliptical air holes on a rhombic lattice through high-resistivity silicon using standard techniques based on micro-electromechanical systems. Finite element simulations predict a phase difference between orthogonal polarizations of π ± 0.08π across 1.2-2.0 THz for a single 200 µm-thick layer. The results of terahertz time-domain spectroscopy are presented to demonstrate this HWP performance. Moreover, they show that stacking two, three, and four identical layers to effective thicknesses of 400, 600, and 800 µm shifted the operating band to 0.6-1.0, 0.4-0.67, and 0.3-0.5 THz, respectively, without degrading the phase response. Experimental spectra agree closely with the theory, showing that arbitrary effective thicknesses-and thus target frequency windows-can be achieved by simply stacking thin, easily processed wafers. Parametric sweeps indicated that performance was preserved under standard photolithography tolerances and lateral misalignments of up to 10% of the lattice period. By combining high transmission, wide bandwidth, and straightforward fabrication, the proposed device offers a scalable route for compact THz-band polarization optics for spectroscopy, imaging, and next-generation (6G) wireless communications.

In high dynamic range (HDR) imaging, exposure parameters determine the efficiency of image acquisition and have a great impact on image quality. Two exposure selection methods are proposed to improve the efficiency of HDR imaging while maintaining image quality. The target signal-to-noise ratio (SNR) is derived from the contrast sensitivity of the human visual system under a given adaptation condition. Combining the target SNR and imaging model, a histogram-independent iterative method and a histogram-based exhaustive method are developed to determine the exposure time set. The two methods are complementary: the former offers low computational cost, while the latter enhances control over exposure parameters and improves image acquisition efficiency. An HDR dataset with 1/3-stop exposure intervals and diverse illumination conditions is established, which is utilized alongside a publicly available HDR dataset to evaluate the proposed methods in comparison with existing methods. The proposed methods achieve high quality while reducing image capture time, demonstrating the superior efficiency of HDR image acquisition.

In satellite laser ranging (SLR) applications, the array superconducting nanowire single photon detectors (SNSPDs) introduce the range walk error due to the response characteristics, which affects the ranging accuracy. To reduce the impact of range walk errors, what we believe to be a novel experimental approach, termed the differential attenuation walk compensation (DAWC) method, is proposed based on a comprehensive theoretical analysis of the influencing factors. By establishing a detection probability model that incorporates factors such as echo pulse energy, time jitter, and pulse width, this study systematically examines the contributions of various factors to range walk errors. Theoretical analysis indicates that attenuating the echo signal to the single-photon level and leveraging the differential delay between the reference arm and the measurement arm can effectively compensate the range walk error. To validate this approach, experimental studies are conducted, incorporating a corner reflector positioned behind the secondary mirror and a fiber optic attenuator placed before the SNSPDs. The experimental results demonstrate that the strategy enhances the ranging accuracy by 0.14 ns in terms of RMS. This corresponds to an effective compensation of at least 40%. This method provides a promising solution for improving the precision of SLR.

This study introduces a ring compensated Airy beams (RCAB) array, incorporating a compensation factor b to precisely regulate the auto-focusing limitations of conventional ring Airy beam arrays. The compensation factor b acts as a powerful regulatory parameter, enabling simultaneous and predictable control over the array's focusing dynamics. An Airy term governs the spatial oscillation, while an exponential term controls the longitudinal energy gain and sets the focal position. Systematic analysis shows that a negative b significantly enhances auto-focusing capability. The focal length has a stable, negative linear relationship with b; it extends further as b becomes more negative. The number of sub-beams needed for saturated focusing also depends on b, increasing from 22 to 60 as b decreases from -0.2 to -0.8. Crucially, a critical threshold is identified at b = -0.8 under the chosen parameters. Beyond this value, energy detrimentally transfers from the main lobe to the surrounding secondary lobes. This degradation is severe. At b = -4.0, the number of secondary lobes surges to 442, and their intensity can exceed the main lobe by several hundred times, defeating the focusing effectiveness. This work establishes b as a core parameter for precisely regulating RCAB arrays. The findings provide a robust basis for advanced beam manipulation, with potential applications in laser processing, optical trapping, and bio-imaging.