Search Results (406)

Fiber lasers have been widely used in surgery with the development of fiber photonics. Since the human body is prone to myocardial infarction caused by blood clots, laser thrombolysis was proposed as a safe and efficient treatment. Mode-locked fiber lasers have high peak power and narrow pulse width. In order to observe the effect of laser thrombolysis with mode-locked fiber lasers, a 1.5 µm mode-locked fiber laser based on carbon nanotubes was built, showing a pulse width of 1.46 ps, a 3 dB bandwidth of 1.65 nm, and a repetition rate of 29.5 MHz. The output pulses were amplified by an erbium-doped fiber amplifier to the hundred-milliwatt level and were applied to the surface of a self-made thrombus. The influences of lasing power and time on the damage diameter of the thrombus surface were evaluated. A low threshold damage power of 45 mW was observed, which resulted from the high peak power of the mode-locked pulses. These results demonstrate that high ablation efficiency can be achieved by using mode-locked pulses with a narrow pulse width and high peak power. Full article

In response to the demand for high-power, long-pulse-width 532 nm lasers in the medical and industrial processing fields, this paper explains how the laser cavity of a high-power Nd:YAG 532 nm laser can be extended while maintaining the laser’s q-parameter by using a 4f optical system. The results show that at a repetition rate of 10 kHz, the extended cavity achieved a maximum average power of 112 W. Compared with the short cavity, the power was not significantly reduced. The pulse width was extended from 56 ns to 85 ns, and its broadening ratio reached 46.5%. The laser maintained good beam quality during high-power operation. Full article

We report passively Q-switched pulse operation through an erbium-doped fiber laser (EDFL) utilizing graphene oxide/titania (GO/TiO₂) nanorods as a saturable absorber. The GO/TiO₂ nanorods were fabricated using a Sol–gel-assisted hydrothermal method. The optical and physical characterization of the GO/TiO₂ was then characterized using a field-emission-scanning electron microscope (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), and diffuses reflectance spectroscopy (DRS). To investigate the performance of the Q-switched EDFL based on the GO/TiO₂ SA, the prepared nanorods were mechanically deposited on the fiber ferrule employing adhesion effects of in-dex-matching gel. This integration of the nanorod SA resulted in a self-starting Q-switching opera-tion initiated at a pump power of 17.5 mW and sustained up to 306.9 mW. When the pump range was tuned from 17.5 to 306.9 mW, the emission wavelength varied from 1564.2 to 1562.9 nm, pulse repetition rates increased from 13.87 kHz to 83.33 kHz, and pulse width decreased from 30.27 µs to 3.75 µs. Moreover, at the maximum pump power of 306.9 mW, the laser exhibited an average output power of 0.74 mW, a peak power of 1.54 mW, and a pulse energy of 8.88 nJ. Furthermore, this study investigates the GO/TiO₂ damage threshold and prolonged stability of the proposed EDFL system. Full article

The pulse laser emission circuit plays a crucial role as the emission unit of time-of-flight (TOF) LiDAR. This paper proposes a nanosecond-level pulse laser diode array drive circuit for LiDAR, primarily aimed at addressing the issue of high-speed scanning drive for the laser diode array at the emission end of solid-state LiDAR. Based on the single pulse laser diode drive circuit, this paper innovatively designs a circuit that includes modules such as a boost circuit, linear power supply, high-speed gate driver, GaN field-effect transistor, and pulse narrowing circuit, realizing an 8-channel laser diode array drive circuit. This circuit can achieve a pulse laser array drive with a single channel operating frequency of greater than 100 kHz, an output pulse width of less than 5 ns, a peak power greater than 75 W, and a channel switching time that does not exceed 1 μs. A field programmable gate array (FPGA) is used to control the operation of this circuit and perform a series of performance tests. Experimental results show that this circuit has a high repetition rate, large output power, a narrow pulse width, and fast switching speeds, making it highly suitable for use in the optical emission module of solid-state LiDAR. Full article

We demonstrate a compact, partially end-pumping Innoslab laser based on a micro-cylindrical lens array homogenizer. A dimension of 12 × 0.4 mm² flat-top pumping line with a Gaussian intensity distribution across the line was simulated by the ray tracing technique. The rate equations considering the asymmetric transverse spatial distributions are theoretically developed. The simulation results are in good agreement with the experimental results. Preliminary data shows that for a pump power of 260 W, a maximum pulse energy of 15.7 mJ was obtained with a pulse width of 8.5 ns at a repetition frequency of 1 kHz. The beam quality M² factors in the unstable and stable directions were 1.732 and 1.485, respectively. The technology has been successfully applied to temperature and humidity profiling lidar and ozone lidar and has been productized, yielding direct economic value. Full article

The synthesis of 2D MoWS₂ nanosheets involved the liquid-phase exfoliation technique was explored in this paper. The nonlinear optical response of MoWS₂ was characterized in the 1 µm wavelength range, and its suitability as a saturable absorber (SA) was confirmed. Experimental demonstrations were conducted by using MoWS₂ as an SA in an idler-resonant intracavity KTA optical parametric oscillator (OPO) driven by a dual-loss-modulated Q-switched and mode-locked (QML) YVO₄/Nd:YVO₄ laser with an acousto-optic modulator (AOM). By appropriately tuning the pump power and the AOM repetition rate, the Q-switched envelope pulse widths for the signal and idler waves could be significantly reduced to be shorter than the cavity round-trip transit time, i.e., the interval between two neighboring mode-locking pulses. Consequently, this enabled the generation of sub-nanosecond single mode-locking pulses with a low repetition rate, high pulse energy, and remarkable stability. With a repetition rate of 1 kHz and maximal pulse energies of 318 µJ and 169 µJ, respectively, sub-nanosecond single mode-locking pulses of the signal and idler waves were generated. The theoretical model was established using coupled rate equations with a Gaussian spatial distribution approximation. The numerical simulation results for generating sub-nanosecond single mode-locking pulses for the signal and idler waves within their respective Q-switched envelopes aligned fundamentally with the experimental results, proving that MoWS₂ can be a potential nanomaterial for further optoelectronic applications. Full article

In order to study the mechanism of microcrack generation in the process of pulsed laser polishing of zirconia ceramics and the influence of laser polishing process parameters on the surface temperature and surface stress, this paper establishes a finite element computational model of pulsed laser polishing of zirconia ceramics based on the COMSOL Multiphysics multi-physics field simulation software. Firstly, in the process of establishing the finite element model, the temperature field and stress field coupling is used to analyze the temperature field and stress field changes during the laser polishing process, which reveals the microcrack generation mechanism and size characteristics of zirconia ceramics in the process of pulsed laser polishing. Secondly, through parameterized scanning, the variation rules of surface temperature and surface stress were studied under different process parameters of laser power, scanning speed, pulse frequency and pulse width. Finally, the validity of the finite element calculation model is verified by the pulsed laser polishing zirconia ceramics experiment. The results show that, in a certain energy range, the high-energy laser beam can effectively reduce the surface roughness of the material, and with the increase in the time of laser action on the surface layer of the material, it will cause the temperature and thermal stress of the surface layer of the material to continue to accumulate, and when the stress value exceeds the yield limit of the material, cracks will form in the surface layer of the material; because the laser power, scanning speed, pulse frequency and pulse width are used to affect the laser energy density, and then, the pulse width will be affected by the process parameters of the laser energy density, and thus the surface temperature and thermal stress of the surface layer of the material. Because the laser power, scanning speed, pulse frequency and pulse width all affect the thermal stress on the material surface by influencing the laser energy density acting on the material surface, the laser energy density is the main influencing factor of the dimensional characteristics of the microcracks. In addition, the microcrack width and depth will increase when the laser energy density acting on the material surface layer increases. Full article

In order to improve the wear resistance of copper and enhance the surface properties of copper parts, this article uses BN nanoparticles as a reinforcing phase and the laser remelting method to prepare a Cu/BN remelted layer on the copper surface. The surface morphology, crystal structure, microhardness, and wear resistance of the samples were tested and characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), a microhardness tester, and a friction and wear tester. The effects of laser frequency, pulse width, and energy density on the surface morphology and wear resistance of the samples were analyzed and studied, and the effects of the laser parameters on the properties of the Cu/BN remelted layer were discussed. The research results indicate that laser frequency, pulse width, and energy density have a direct impact on the surface morphology and properties of the Cu/BN remelted layer, but the impact mechanism by the above parameters on the remelted layer is different. The effects of laser frequency on the remelted layer are caused by changes in the overlap mode of the remelting points, while laser pulse width and energy density are achieved through changes in remelting intensity. When the laser frequency is 10 Hz, the pulse width is 10 ms, and the energy density is 165.8 J/mm², the Cu/BN remelted layer has better surface properties. Full article

This study adopts a new surface pretreatment method, Laser Surface Remelting (LSR). This experiment aims to establish a set of laser welding process parameters suitable for aluminum alloy and glass under this specific pretreatment. This experiment explores the impact of laser welding parameters on the welding strength between high borosilicate glass and aluminum alloy. The study specifically investigates the effects of four process parameters: defocus amount, laser power, frequency, and pulse width on the welding outcome. The results indicate that the welding quality between the aluminum alloy and glass reaches its optimum when the defocus amount is zero (i.e., when the laser converges at the interface between the glass and the metal) and the laser welding parameters are set to a power of 250 W, a welding speed of 1 mm/s, a welding frequency of 10 Hz, and a pulse width of 2.5 ms. The experiment also analyzes the fracture morphology under different parameters, summarizing the locations and causes of fractures, and establishing the relationship between the fracture location and the welding strength. Full article

This paper primarily investigates the effect of the tilt of corner cube reflector (CCR) arrays on lunar laser ranging (LLR). A mathematical model was established to study the random errors caused by the tilt of the CCR arrays. The study found that, ideally, when the laser ranging pulse width is 10 picoseconds or less, it is possible to distinguish from which specific corner cubes within the CCR array each peak in the echo signal originates. Consequently, partial data from the echo can be extracted for signal processing, significantly reducing random errors and improving the single-shot precision of LLR. The distance obtained by extracting part of the echo can be reduced to the center position of the array, thereby providing multiple higher-precision ranging results from each measurement. This not only improves the precision of LLR but also increases the data volume. A simulation experiment based on the 1.2 m laser ranging system at Yunnan Observatories was conducted. By extracting one peak for signal processing, the single-shot precision improved from 32.24 mm to 2.52 mm, validating the theoretical analysis results. Finally, an experimental laser ranging system based on a 53 cm binocular telescope system was established for ground experiments. The experimental results indicated that the echo signal could identify the tilt state of the CCR array. By extracting the peak returned by the central CCR for signal processing, the ranging precision was greatly improved. Through theoretical analyses, simulation experiments, and ground experiments, a solution to reduce the random errors caused by the tilt of the CCR array was provided. This offers an approach to enhance the single-shot precision of future LLR and provides a reference for upgrading ground-based equipment at future laser ranging stations. Full article

A passively Q-switched Er:YAP laser of 2.7 µm, utilizing Au-doped CsPbI₃ quantum dots (QDs) as a saturable absorber (SA), was realized. It was operated stably with a minimum pulse width of 185 ns and a maximum repetition rate of 480 kHz. The maximum pulse energy and the maximum peak power were 0.6 μJ and 2.9 W, respectively, in the Q-switched operation. The results show that the CsPbI₃ QDs SA exhibits remarkable laser modulation properties at ~3 μm. Full article

Falling within the safe bands for human eyes, 1550 nm semiconductor lasers have a wide range of applications in the fields of LIDAR, fast-ranging long-distance optical communication, and gas sensing. The 1550 nm human eye-safe high-power tunnel junction quantum well laser developed in this paper uses three quantum well structures connected by two tunnel junctions as the active region; photolithography and etching were performed to form two trenches perpendicular to the direction of the epitaxial layer growth with a depth exceeding the tunnel junction, and the trenches were finally filled with oxides to reduce the extension current. Finally, a 1550 nm InGaAlAs quantum well laser with a pulsed peak power of 31 W at 30 A (10 KHz, 100 ns) was realized for a single-emitter laser device with an injection strip width of 190 μm, a ridge width of 300 μm, and a cavity length of 2 mm, with a final slope efficiency of 1.03 W/A, and with a horizontal divergence angle of about 13° and a vertical divergence angle of no more than 30°. The device has good slope efficiency, and this 100 ns pulse width can be effectively applied in the fields of fog-transparent imaging sensors and fast headroom ranging radar areas. Full article

In this paper, using laser direct writing technology, a femtosecond laser was used to process a periodic grating structure on a 99.99% tungsten target. The specific parameters of the laser are as follows: a center wavelength of 800 nm, pulse width of 35 fs, repetition rate of 1 kHz, and maximum single pulse energy of 3.5 mJ. The surface morphology of the samples was characterized and analyzed using a scanning electron microscope (SEM, Coxem, Republic of Korea) and atomic force microscope (AFM, Being Nano-Instruments, China). The thermal radiation infrared spectrum of the tungsten target with grating structures was measured using a Fourier transform infrared spectrometer (Vertex 70, Bruker, Germany). The results show that as the laser fluence increases, the depth of the groove, the width of the nanostructure region, and the width of the direct writing etching region all increase. The peak thermal radiation enhancement appears around the wavenumber of 900 cm⁻¹ when the laser fluence is sufficient. Additionally, its intensity initially increases and then decreases as the laser fluence increases. If the grating period is too large, the impact on thermal radiation is not clear. The heating temperature significantly affects the intensity of thermal radiation but does not have a noticeable effect on the position of thermal radiation peaks. Moreover, the relative weighting of different wavenumbers changes as the temperature increases. Full article

A single-frequency, Q-switched Er:YAG laser, pumped by a 1532 nm fiber laser, has been demonstrated. At the pulse repetition frequency (PRF) of 200 Hz, the maximum single-frequency laser of 5.5 mJ is attained, and, correspondingly, the pulse width is 212 ns. Using the heterodyne technique, the single-frequency laser spectrum’s full width at half maximum is determined to be 2.73 MHz. The experimental results show that the single-frequency laser has excellent beam quality factors (M²) of 1.18 and 1.21. Full article

A method for enhancing the resolution of 3D imaging reconstruction by employing the polarization modulation of electro-optical crystals is proposed. This technique utilizes two polarizers oriented perpendicular to each other along with an electro-optical modulation crystal to achieve high repetition frequency and narrow pulse width gating. By varying the modulation time series of the electro-optical crystal, three-dimensional gray images of the laser at different distances are acquired, and the three-dimensional information of the target is reconstructed using the range energy recovery algorithm. This 3D imaging system can be implemented with large area detectors, independent of the an Intensified Charge-Coupled Device (ICCD) manufacturing process, resulting in improved lateral resolution. Experimental results demonstrate that when imaging a target at the distance of 20 m, the lateral resolution within the region of interest is 2560 × 2160, with a root mean square error of 3.2 cm. Full article