Optics and Laser Technology最新文献

We propose and experimentally demonstrate a universal millimeter-wave noise source based on an optically injected multi-mode chaotic laser. The wideband multi-mode chaotic lights are sliced, amplified and then converted into continuous-wave noise through a photodetector. In our approach, the center frequency and the excess noise ratio of the generated noise signal can be easily adjusted by controlling the sliced spectral numbers and intensities, respectively. Moreover, pulsed noise can also be obtained by introducing an amplitude modulation as a chopper. In our proof-of-concept experiments, we successfully generate 140–220 GHz and 220–390 GHz broadband noise signals with a tunable excess noise ratio up to 52.42 dB. We also validate the tunability of the operation frequency though generating three narrow-band noise signals with center frequencies at 140 GHz, 252 GHz, and 364 GHz, respectively. Furthermore, the generation of pulse noise with durations of 500 ns and 0.5 ns per period are experimentally demonstrated. These results confirm that our proposed universal noise source is a promising candidate for multiple application scenarios.

Experiments on pulsed laser brazing of diamond grinding wheels were carried out in this paper. The crack characteristics and residual stress of brazed layer were detected and evaluated. The influence laws of pulse width, frequency, diamond mixing ratio, number of stacked layers, powder thickness and preheating temperature on crack characteristics were investigated. The pulsed laser characteristic coefficients (peak pulse power density/pulse interval time) and the correlation law between thermal stresses and cracks are discussed. The results show that the pulse width and frequency of the pulsed laser affect the cracking rate by varying the energy input and the time between pulses. The existence of a suitable value for the pulse characteristic coefficient corresponding to pulse width and frequency corresponds to a lower cracking rate. Thermal stress variations due to changes in process conditions at different diamond percentages, number of stacked layers, and preheating temperatures are the main causes of crack rate variations. Cracking is not only affected by thermal stresses, but also by the quality of the formed surface when pulsed laser brazing diamond to nickel–chromium alloy brazing material. For example, the main reason for the variation in cracking rate is the change in the morphology of the molded surface due to the variation in the thickness of the powder spread at different variations in the thickness of the powder spread.

Laser stripping has emerged as a pivotal technique for repairing anti-erosion coatings in the aviation and armored vehicle industries. This process entails complex thermodynamic interactions that remain incompletely explored. Unraveling the intricacies of the stripping mechanism, especially the evolution of surface morphology, is essential for advancing its industrial utility. This study characterizes the laser stripping effect on TiN anti-erosion coatings using confocal microscopy, scanning electron microscopy, and energy dispersive spectrometer. Notably, at an energy density threshold of approximately 10² J/cm², pulsed lasers are observed to induce a distinctive hydrodynamic surface morphology, marked by parallel asymmetric grooves. This phenomenon is accompanied by a redistribution of surface elements and a decrease in nitrogen content. To dissect the underlying mechanisms, we have developed simulation models that integrate principles of heat transfer and fluid dynamics. These models reveal that the high-temperature decomposition and vaporization of TiN, coupled with the ejection of molten material due to vapor recoil pressure, are central to the stripping process. Additionally, the formation of asymmetric groove profiles is predominantly attributed to the nonlinear superposition effect from overlapping laser spots.

With the rapid advancement of micro/nanoscale devices, there is a growing demand for hierarchical micro/nano porous-structure, particularly in fields of high-performance sensors, electrochemical energy storage, and photocatalysis. The fabrication methods for hierarchical micro/nano-porous structures have been limited by complex processes and high costs, making further development and application difficult. In this paper, a novel strategy of laser-induced in-situ electrohydrodynamic jet (E-Jet) printing of hierarchical micro/nano-porous structures was proposed. Based on the mechanism of high-energy laser beam induction on the jet, it successfully fabricated hierarchical porous ZnO structures from nanoscale to dozens of microns. The jet size focusing and solidification behavior were analyzed by combining experimental and simulative exploration. The resultant effects of the thermal field, flow field, and laser field on the spatial temperature distribution and the jetting morphology were examined. Furthermore, the laser-induced influence on the morphology of the printed micro/nano-porous ZnO structures was explored. Meanwhile, the performance of micro/nano-porous ZnO photoelectric sensors printed by E-Jet under different laser powers was investigated. The laser-induced in-situ E-Jet printing method provided an innovative pattern for the high-resolution additive manufacturing of hierarchical porous structures, demonstrating its potential for applications in advanced material and high-performance devices.

The assembly of glass and copper micro devices is widely applied in modern manufacturing industries. Laser welding is an efficient technique. However, weld defects and instability resulting from the low laser absorptivity of copper remain significant challenges. Surface roughness also poses a limitation for optical contact during welding preprocessing. In this work, femtosecond pulse and green light from the second harmonic generation were combined to increase the copper absorptivity. The silica glass and rough copper foil were effectively welded. Under the optimized parameters, a maximum shear strength of 17.19 MPa was obtained. The electron and lattice temperatures during the welding process were simulated using two-temperature model. The microscopical mechanism, element diffusion, and chemical reaction were investigated. A modified region in the glass was formed due to excessive laser energy and scattered subsequent laser pulses. Cu–O-Si bonds were detected on the welds. Welding stability at various temperatures was characterized, with shear strength maintained at approximately 12 MPa after thermal cycling from 0 to 100 °C and heating at 150 °C. This study demonstrated that effective and stable welding of silica glass and rough copper foil can be achieved using green femtosecond lasers.

A nonvolatile polarization switch is proposed numerically assisted by right-angle Sb₂S₃ inlaid in a strip 4H-SiC waveguide. The polarization of incident light can be engineered by the phase states of Sb₂S₃. When the Sb₂S₃ is crystalline, a TE0-TM0 polarization conversion is achieved with insertion loss (IL) of 0.22 dB and polarization conversion efficiency (PCE) of 98.36 % at the wavelength of 1550 nm. As long as the Sb₂S₃ is switched to the amorphous state, the polarization conversion effect becomes negligible with IL < 0.014 dB and PCE < 3.16 % across 1500–1600 nm waveband. Moreover, the robustness analysis demonstrates that the proposed structure maintains its functionality within ± 10 nm deviations of Δh, Δw, Δl, and Δd. The low-loss Sb₂S₃-assisted polarization switch offers a novel methodology for nonvolatile switching to programmable integrated optics, which can be deployed in polarization manipulation and neuromorphic optical computing.

We present, for the first time, a watt-level ultra-flat all-silica fiber supercontinuum (SC) source spanning from the near-infrared (NIR) to mid-infrared (MIR) region with negligible pump residuals. This SC source is pumped by amplified 1.57-μm rectangular noise-like pulses (NLPs), whose broad spectral and flat-top temporal characteristics enhance the spectral flatness and coverage of SC spectra. By cascading a piece of highly nonlinear silica fiber (HNLF), a SC ranging from 0.91 to 2.92 µm is obtained with a 3-dB bandwidth of ∼ 716.1 nm, a 10-dB bandwidth of ∼ 1533.6 nm, and an average power of 2.08 W. To our best knowledge, the spectral coverage, 3-dB, and 10-dB bandwidths represent the highest achieved levels for a watt-level all-silica fiber SC source covering the range from the NIR to MIR. Our system offers a simple and easily implemented solution for an ultra-flat NIR-to-MIR SC source, promising significant applications in optical coherence tomography and chemical detection.

The photoluminescence enhancement of a composite structure on porous silicon with surface-grown silver dendrites was discovered in this study. Silver dendrites are plasmonic antennas that exhibit a slight amplification effect. The small improvement of penetrating light intensity resulted in a significant increase in two-photon absorption, culminating in a remarkable increase in the photoluminescence intensity of the porous silicon material. The manifold enhancement of two-photon absorption was demonstrated by theoretical calculations of its probability.

Aiming at the uncertainties and limitations in the laser modification of material surfaces for the corrosion protection, we here exploit a method of double-pulsed femtosecond laser processing with variable picosecond time delays, to effectively reinforce the anticorrosion performance of aluminum alloys. Compared with the traditional single-beam femtosecond laser irradiation, the adoption of double-pulsed laser irradiation especially with the optimal time delay of 50 ps, can decrease about 16 times in the magnitude of the corrosion current density, associated with the increase by 77.8 mV and 23 times in the corrosion potential and the impedance, respectively. The comprehensive insight analyses reveal that such an enhanced anticorrosion phenomenon is originated from the strong modification of the chemical and phase compositions on the metal surface, thus resulting in the higher degree of in-situ material oxidation with a prominent feature of the amorphous state, which can be evidenced not only in the shallow outer-layer surface but also extending to the deep inner-layer region. The significant roles of these laser modifications can be well elucidated by the proposed scenario.

Phosphites are being recognized as the new emerging candidates for luminescence in the modern era. In the proposed research article, Sm³⁺ to Pr³⁺ to Eu³⁺ doped K₂Ba₂(PO₃)₅ (KBP) glasses synthesized utilizing melt quenching technique. Through the use of XRD confirmed the amorphous nature of glass sample. SEM is employed to analyze the morphology and elemental composition of the prepared sample. The sample shows orange-red emission in the phosphor on energy transfer with the Sm³⁺ to Pr³⁺ to Eu³⁺. This highly instance red emitting phosphor has color purity of more than 99 %. These all results confirm that the prepared glasses are potential candidate for WLEDs, display applications, smart window applications and red emitting glasses for plant cultivation applications.