Optics express最新文献

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.

We demonstrate a semiconductor microchip membrane external-cavity surface-emitting laser (MECSEL). This compact type of laser consists solely of a semiconductor gain region present as a micron-thin membrane, sandwiched between two transparent heat spreaders. The outer facets of the microchip MECSEL presented in this work have a highly reflective coating, which assembles the laser's plane-parallel solid-state cavity with a total length of just ∼ 1 mm. One of the coatings has a slightly reduced reflectivity to act as an outcoupling mirror. The membrane microchip laser is optically pumped with a standard fiber-coupled diode laser module emitting at 808 nm and stabilizes itself due to the occurrance of a thermal lens. More than one watt of continuous wave output power around 1123 nm and a record value in slope efficiency of ∼ 51.4 % with MECSELs, while maintaining excellent beam quality (TEM₀₀, M² < 1.05), is demonstrated. Important properties of semiconductor lasers such as the efficiency, beam quality, and polarization were investigated. Further, the laser setup itself was used to characterize the thermal lens and its dependence on the absorbed pump power. Such systems represent an attractive solution, when high-power output at customizable emission wavelength with excellent beam quality is needed in combination with a very compact built size.

This paper presents an efficient method for trapping and accelerating a 50 MeV relativistic electron beam in vacuum using radially polarized cylindrical vector Bessel-Gauss (BG) beams. Unlike conventional Laguerre-Gaussian (LG) beams, the non-diffracting property of BG beams extends the laser-electron interaction length, while their uniform field distribution enhances beam quality. The unique electric field structure of radially polarized light, featuring a strong longitudinal component, provides superior transverse confinement compared to circularly polarized beams, significantly reducing electron beam divergence. Three-dimensional particle-in-cell (PIC) simulations performed with the code EPOCH demonstrate that the electron energy increases from 50 MeV to 800 MeV, exhibiting less than 10.2% energy spread and a divergence angle below 1.5°. Further investigations reveal that higher laser intensity boosts electron energy without compromising beam collimation, while injection duration critically influences microbunch formation and maximum momentum. This approach offers a promising solution for compact high-energy electron accelerators, with potential applications in free-electron lasers and medical radiotherapy.

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.