Optics and Laser Technology最新文献

The laser-induced structural coloring technique holds significant potential for various applications due to its precision, controllability, and versatility across different materials. However, laser-induced structural colors face the problems of durability, homogeneity and indistinguishability, which are not conducive to their application as large-scale identifiable markers. In this paper, an innovative approach has been developed to achieve a circular-symmetric structural color display on durable SiC surfaces by fabricating periodic concentric ring structure arrays using the sidelobe light field of a femtosecond zero-order Bessel beam. The research involved a systematic study of the effects of laser power and pulse number on SiC, along with a detailed analysis of the micro-nanostructures evolving on the SiC surface after laser scanning. Additionally, an examination of the characteristics of circular-symmetric structural color displays and their wide viewing angles in periodic circular structures was conducted. Finally, a comparison was made between the structural color display effects of a concentric ring structure generated by a single pulse and the Laser-Induced Periodic Surface Structures (LIPSS) generated by three pulses. This comparison underscores the potential application of alternating between the high saturation color of the concentric ring structure and the low saturation dark light of the LIPSS for anti-counterfeit coding purposes. The findings of this research present promising opportunities for low-cost mass manufacturing in anti-counterfeit labeling and the advanced processing of photonic devices using SiC.

The stable ∼ 3 μm self-pulsing laser has been achieved for the first time, along with compact and efficient pulse compression and amplification, based on the growth of novel Ho,Pr:GdScO₃ crystals. Using the conventional Czochralski method, we have grown novel Ho,Pr:GdScO₃ crystals with three different polarization-directions and discovered the self-pulsing effect within the crystals. Leveraging this phenomenon, we have successfully obtained linearly-polarized self-pulsing lasers in the mid-infrared (MIR) band and demonstrated the strong stability of the pulse trains both theoretically and experimentally. In addition, a novel pulse compression and enhancement method has been developed to maximize the performance of the self-pulsed Ho,Pr:GdScO₃ lasers. Compared to self-pulsed lasers, the novel low-loss pulse compression can provide a more compact and efficient solution for enhancing the peak power of laser pulses. The results combine self-pulsed Ho,Pr:GdScO₃ crystals with pulse compression and enhancement techniques to facilitate miniaturization and integration of high-peak-power, narrow-pulse-width MIR pulsed lasers.

Perovskite solar cells (PSCs) represent an emerging technology in solar photovoltaics due to their outstanding optical and electrical characteristics. The urgency of lead-free solar materials has increased due to the environmental concerns. In light of these considerations, Cs₂SnI₆, a high-performance tin-based double perovskite, holds the potential to be a key absorber material in promoting the cell efficiency. In this paper, a device design of lead-free Cs₂SnI₆-based PSC is proposed based on an n-i-p planar structure. Through a comprehensive analysis by simulation using SCAPS-1D, the impacts of electron transport layer materials (SnO₂, TiO₂, CdS, GO, MZO) and hole transport layer materials (MoO₃, Cu₂O, CuI, Spiro-OMeTAD) with varying thicknesses as well as the donor density, acceptor density and the absorber thickness have been examined. Additionally, an examination is conducted on the performance metrics of PSCs, encompassing V_oc, J_sc, FF, and PCE, while taking into consideration the influences of temperature, R_series, and R_shunt. The results show that the optimized FTO/SnO₂/Cs₂SnI₆/MoO₃/Au device presents the highest PCE of 22.60 % at 300 K temperature, together with a visible quantum efficiency of 99.49 %. The appropriate thicknesses of the ETL, HTL, and absorber layer for achieving the optimal performances are 50 nm, 200 nm, and 450 nm, respectively. Also, the donor density and acceptor density for the best efficiency are both at 10¹⁸ cm⁻³. The values of R_series, and R_shunt are 2 Ω cm² and 6000 Ω cm², respectively. This investigation demonstrates that the proposed vacancy-ordered double perovskite Cs₂SnI₆ solar cell is promising for photovoltaic devices due to the highlighted characteristics and optical parameters.

The industrial production site for laser lap welding of thin stainless steel plates puts strict requests on the level and fluctuation stability of penetration depth. Hence, the penetration depth monitoring is increasingly garnering attention. This research proposes an optical coherence measurement-based approach to monitor penetration depth utilizing machine learning in laser lap welding for stainless steel sheets. After the acquisition of the keyhole depth signal by the coherent light beam, it is found that there is a significant association relationship between the reconstructed keyhole depth obtained by empirical modal decomposition and the penetration depth curve, but meanwhile a penetration depth monitoring error also exists. Accordingly, based on the cross-correlation analysis and numerical simulation, it is revealed that the formation mechanism and sources of this error are related to the “bottom melt layer thickness”, “hysteresis property” and “multiple reflections”. On this basis, a long short-term memory network is built to memorize the historical information of the reconstructed keyhole depth for predicting the penetration depth at each moment. The experimental results demonstrate that the prediction model has high accuracy and good generalization ability, and thus effective monitoring for penetration depth can be achieved.

We demonstrate the crystal structure, spectroscopy and laser performance of a novel Er:SGGG crystal grown successfully by Czochralski (Cz) method. The lattice constant is refined to be 12.42 Å and the FWHM of the crystal’s X-ray rocking curve is only 86.4″, indicating an excellent quality. The segregation coefficient of Er³⁺ ions in SGGG is determined to be 1.2. The Er:SGGG crystal displays a specialty in broadening spectrum. There is a wide absorption band near 962 nm, with an absorption bandwidth of 19 nm and a peak absorption coefficient of 5.57 cm⁻¹. Under the conditions of 969 nm laser diode (LD) pumping, with a 400 Hz repetition rate and 300 μs pulse duration, a maximum power 404 mW with slope efficiency of 15.6 % at 2.8 μm is achieved on the Er:SGGG crystal. The M² factors of horizontal and vertical are 1.4 and 1.5, respectively. The results indicate the mid-infrared laser output can be generated in the Er:SGGG crystal, and it is a potential and promising candidate for 2.8 μm laser material.

A triplexer chip utilizing three cascaded butterfly multimode interference (MMI) couplers to output three optical signals from their respective ports is proposed. The chip consists of a borosilicate glass substrate, a JA photoresist core layer, and an RZJ photoresist cladding. The beam propagation method (BPM) is used to design and optimize the chip. The femtosecond laser processing is investigated, and the chip is processed with a laser power of 1.6 mW and an ablation speed of 4 mm/s. Tests show that the chip meets the design specifications with a low insertion loss of 4.34 dB, an extinction ratio of more than 15 dB, a crosstalk of less than −15 dB, and a 3 dB bandwidth up to 76.8 nm.

The combined application of coating and surface texture technology on the material surface can enhance its performance. However, the two procedure and their joint mechanism have not been fully revealed. Therefore, this paper takes the micro-textured coated cemented carbide as the research object, and focuses on the influence of preparation procedure and process parameters on surface characteristics and friction behavior. The results show that compared with the coating textured (XT) sample, the textured coating (XW) sample has more advantages in micro-hardness, microstructure and wear degree. The Rockwell hardness of the XT sample is better. Compared with the single coating sample, the coating micro-hardness of the XW sample is increased by 10 %, the Rockwell hardness is reduced by 2 %, the average grain size is reduced by 7.9 %, and the friction force is reduced by 6.2 %. Additionally, within a certain range, the increase of Al content will increase the sample hardness, reduce friction, and inhibit the Cr content and the growth of CrN phase grains. Complete process parameter optimization based on the ideal solution.

In this paper, we demonstrated stable continuous-wave passively mode-locked operation of an Er:Lu₂O₃ laser at 3 µm, utilizing a semiconductor saturable absorber mirror (SESAM). By operating the laser in a dry nitrogen environment and utilizing a thermoelectric cooler (TEC) temperature control device to mitigate the thermal effects of Er:Lu₂O₃ and enhance laser stability, we further compensated for group delay dispersion within the laser cavity through chirped mirrors, an shortest pulse duration of 12.0 ps at a average output power of 150 mW was achieved, which occurred at a center wavelength of 2844 nm, and a pulse repetition rate of 83.5 MHz. Additionally, we achieved a maximum continuous-wave mode-locked output power of 213 mW at an absorbed pump power of 8.3 W, equivalent to a pulse energy of 1.3 nJ. The RF spectrum analysis of the pulse train indicated a high SNR of nearly 70 dB, signifying excellent stability. To the best of our knowledge, This is the first report on the realization of an ultrashort pulse width mode-locked Er:Lu₂O₃ laser in the mid-infrared band.

Hard and brittle materials, such as ceramics, are extensively utilized in defense and military protection. Studies on laser damage to ceramic materials have garnered significant attention, with a focus on efficient disruption over long-range. The femtosecond laser filamentation allows energy transfer on the order of kilometers, providing a unique advantage for applications requiring long-distance destruction. However, the interaction mechanism between femtosecond laser filamentation with hard and brittle materials remains unclear. This study initially simulates the interaction of femtosecond lasers with alumina ceramics at various pulse energies using the two-temperature equation. The results reveal the variation in electron and lattice temperature under the irradiation of femtosecond laser. Subsequently, the damage performance caused by femtosecond laser filamentation on ceramic materials, considering various pulse energies, filament positions, and ablation times are systematically investigated. Additionally, at a pulse energy of 4 mJ, the filament length focused by a 500 mm lens can extend up to 25 mm, resulting in an ablation hole with a diameter of 340 µm and a depth of 440 µm along the middle part of the filament. The power-clamping effect ensures uniform damage hole morphology and size across the entire filament, attributable to the constant filament diameter and plasma intensity. This elucidates the damage mechanism of filaments and adequately validates the effectiveness of this method, establishing a theoretical foundation for investigating laser remote damage of hard and brittle materials.

Laser Ultrasound (LUS) is commonly used in many fields including thickness measurement and defect inspection. In a conventional LUS system, a piezo-based transducer (PZT) is generally used for detecting the ultrasound echo waves, which requires direct contact with a specimen and thus prolongs measurement time when any lateral scanning is necessary. We present a novel non-contact interferometric system based on a 3 × 3 optical fiber coupler. Even though the 3 × 3 interferometric system works stably at any operating point and allows quantitative measurements, it is generally known that careful calibration is necessary before main measurements. Experimentally, it was observed that the surface displacement, induced by the ultrasound wave of LUS, of a cornea phantom was so minute that averaging was necessary. In this study, we discovered that by using the multiple data sets acquired for averaging, we could obtain the system ad hoc characteristic ellipse without performing the conventional calibration process. Furthermore, by utilizing coherent average we could extract the displacement with a 0.14 nm sensitivity. We could also measure the thickness variation, induced by ocular pressure, of the cornea phantom with a resolution of 4.3 μm by measuring the time of a round trip of the ultrasound wave. This straightforward system, composed solely of a 3 × 3 coupler, is expected to promise a compact and efficient solution to diverse applications.