Fiber-coupled Semiconductor Laser Research Articles

Cpa-free Yb:YAG thin-disk regenerative amplifier laser with hundreds of watts, hundreds of kHz, and hundreds of picoseconds

This paper introduces a CPA-free Yb:YAG thin-disk regenerative amplifier laser system. The seed pulse is generated by a passive mode-locked picosecond oscillator based on a semiconductor saturable absorber mirror, with a center wavelength of 1030.7 nm, a pulse width of 7.7 ps, and a repetition frequency of 26.3 MHz. After stretched and pre-amplified by an all-fiber front stage, the seed with a pulse width of 201.3 ps and a pulse energy of 15.2 nJ was obtained, then injected into the thin-disk regenerative amplifier. Yb:YAG crystal was chosen as the material for the thin-disk, with 100 μm thickness, 9 mm diameter and 7 at.% doping rate. In order to increase the one-way round-trip gain of the thin-disk regenerative amplifier, a symmetrical dual-pass resonant cavity was designed to double the number of passing through the crystal on a round trip in the regenerative resonant cavity to reduce the times of cycles, intra-cavity loss and improve optical efficiency. We used a 969 nm fiber-coupled semiconductor laser as the pump source to pump the Yb:YAG thin-disk crystal. With zero-phonon line pumping technology, the quantum loss and thermal effect were reduced. In the end, we obtained a regenerative amplification output with an average power of 104.5 W, a repetition frequency of 200 kHz, a pulse width of 143.9 ps, and a spectrum width of 0.39 nm. The amplified pulse had quite good beam quality with Mx2 = 1.09 and My2 = 1.14.

NGHIÊN CỨU CHẾ TẠO MÔ ĐUN CHUYỂN HƯỚNG BỨC XẠ LASER BÁN DẪN GHÉP SỢI QUANG 650 NM ỨNG DỤNG TRONG QUANG TRỊ LIỆU VÀ QUANG SINH DIỆT KHUẨN

Currently, diode lasers in the red wavelength region, especially at 650 nm, are extensively utilized in phototherapy and photodynamic inactivation of bacterials by numerous research groups in the field of lasers for biomedical application. These devices offer exceptional advantages, such as their compact size, ease of design and integration, user-friendliness, and high safety for both operators and patients. Among these, fiber-coupled diode lasers provide an efficient solution for delivering radiation from the laser chip to the desired location. However, further optimization is still required for the fabrication technological development of these devices to meet specific application needs. This includes aspects like reducing manufacturing costs, improving component usability during operation, and meeting specialized usage requirements. To develop the technology for device fabrication, addressing the aforementioned demands, we conducted research on the design, fabrication, and characterization of fiber-coupled semiconductor lasers operating at a wavelength of 650 nm. The characterization results demonstrate that the manufactured devices can operate at maximal pumping current of 100 mA and under varying temperatures from 25oC to 40oC. Additionally, a radiation output orientation module has been designed and integrated at the end of the optical fiber to meet various demands in phototherapy and photodynamic inactivation of bacterials.

Simulation and Experimental Research on a Beam Homogenization System of a Semiconductor Laser.

Aiming at the application of laser active imaging detection technology, this paper studied the beam homogenization system of a semiconductor laser based on a homogenizing pipe. Firstly, the principle of the homogenizing pipe was introduced. Secondly, the homogenization effect, which was influenced by several geometric parameters (aperture size, length, and taper) of the homogenizing pipe using the optical design software, was simulated for the fiber-coupled semiconductor laser. Finally, according to the simulated results, a laser illumination system composed of a fiber-coupled semiconductor laser, a homogenizing pipe, and an aspheric lens was designed, which can obtain a rectangular uniform light spot in a long distance. The effectiveness of the illumination system was verified by simulation and experiment, respectively. Simulation results suggested that the uniformity of the spot at a distance of 20 m was 85.6%, while divergence angle was 10 mrad. The uniformity of the spot at a distance of 120 m was 91.5%, while divergence angle was 10 mrad. Experimental results showed that the uniformity of the spot at a distance of 20 m was 87.7%, while divergence angle was 13 mrad. The uniformity of the spot at a distance of 120 m was 93.3%, while divergence angle was 15 mrad. The laser illumination system designed in this paper was simple and easy to assemble, and has strong practicability. The results in this paper have certain reference value and guiding significance for the homogenization design of semiconductor lasers.

Multi-objective numerical simulation of geometrical characteristics of laser cladding of cobalt-based alloy based on response surface methodology

The objectives of this study are to optimize the key process parameters of laser cladding remanufacturing parts, improve the sealing quality of the hemispherical valve and prolong and improve its service life and reliability. A high-power fiber-coupled semiconductor laser was used to fabricate a single Co-based alloy cladding layer on the pump valve material ZG45 plate. The key process parameters of laser power, scanning speed and powder feeding rate in the process of laser remanufacturing are taken as optimization variables, and the coating width, coating height, coating depth, aspect ratio and dilution rate are taken as response indexes. Based on the response surface analysis method, the central compound experiment is designed using Design-Expert software. The variance analysis of the experimental results is performed, and the regression prediction model of the process parameters relative to the corresponding index is established. Through analysis of the established perturbation diagram and three-dimensional response surface, it is concluded that the main influence factors of melting width and penetration depth are laser power and positive effect, and the main influence factors of melting height are scanning speed and negative effect. The average error of each regression prediction model is lower than 10%. The above research work has important guiding significance for optimizing the process parameters and improving the cladding quality of cobalt-based alloy on ZG45.

Bismuth nanosheets based saturable-absorption passively <i>Q</i>-switching mid-infrared single-crystal fiber laser

As a new two-dimensional material, bismuth nanosheet is an effective modulator for realizing a mid-infrared pulsed laser, which benefits from its suitable band gap, higher carrier mobility and better room temperature stability, as well as its excellent electrical and optical properties. The mid-infrared single-crystal fiber is a preferable gain medium for high-power laser because of its advantages of both crystal and fiber. In this paper, a bismuth nanosheet saturable absorber is successfully prepared by the ultrasonic method and used for the first time in a diode-pumped Er:CaF<sub>2</sub> single-crystal fiber mid-infrared passively <i>Q</i>-switching pulsed laser. A compact concave planar linear resonator is designed to study the <i>Q</i>-switching Er:CaF<sub>2</sub> single-crystal fiber laser with bismuth nanosheets serving as saturable absorbers. The pump source is a fiber-coupled semiconductor laser with a core diameter of 105 μm, a numerical aperture of 0.22, and a central emission wavelength of 976 nm. The pump light is focused onto the front end of the gain medium through a coupled collimating system with a coupling ratio of 1∶2. The gain medium is a 4 at.% Er<sup>3+</sup>:CaF<sub>2</sub> single-crystal fiber grown by the temperature gradient method, and this fiber has two polished but not coated ends, a diameter of 1.9 mm, and a length of 10 mm. To reduce the thermal effect, the single-crystal fiber is tightly wrapped with indium foil and mounted on a copper block with a constant temperature of 12 ℃. The input mirror has a high reflection coating at 2.7–2.95 μm and an antireflection coating at 974 nm, with a curvature radius of 100 mm. A group of partially transmitting plane mirrors are used as output couplers, respectively, with transmittances of 1%, 3%, and 5% at 2.7–2.95 μm. The total length of the resonant cavity is 26 mm. By inserting the bismuth nanosheet into the resonator and carefully adjusting its position and angle, a stable mid-infrared <i>Q</i>-switching laser is obtained. At the absorbed pump power of 1.52 W, a pulsed laser with an average output power of 190 mW is obtained for an output mirror with a transmittance of 3%. The shortest pulse width is 607 ns, the repetition frequency is 58.51 kHz, and the corresponding single pulse energy and peak power are 3.25 μJ and 5.35 W, respectively.

Generation of High-Power Ultrashort Optical Pulses Using a Semiconductor Laser with Controlled Current Pumping

Fiber-coupled semiconductor lasers are studied under pumping with high-power short current pulses. Appropriate parameters of the current pumping make it possible to substantially reduce the output pulse duration to 80 ps for a single-mode laser and 120 ps for a wide-stripe multimode laser at a pump pulse duration of 1 ns and to 40 ps for the single-mode laser at a pump pulse duration of 0.5 ns.

Integrated beam shaping and polarization beam combining design for fiber-coupled semiconductor laser stacks system.

The beam quality mismatch in the fast and slow axes of laser diode stacks limits their applications. An effective beam-shaping method was proposed based on a pair of step prisms. Using this technique, we can eliminate the lightless areas and achieve polarization multiplexing of laser diode stacks. Two laser diode stacks consisting of eight bars were coupled into a fiber with a core diameter of 200μm and a numerical aperture of 0.22. The simulation results demonstrated that the output power can reach 1083W and the optical-optical efficiency was 84.6%.

Generation of high-power ultrashort optical pulses by semiconductor lasers

Fiber-coupled semiconductor lasers have been studied when pumped by high-power short electrical pulses of 5 ns width and leading front duration below 1 ns. In this pumping regime, it is possible to ensure significant sharpening of output pulses, the duration of which decreases below 80 ps for a single-mode laser and below 120 ps for a broad aperture multimode laser at an output peak optical power as high as 1.5 and 27 W, respectively.

Feasibility and influencing factors of laser cutting of tomato peduncles for robotic harvesting

Due to the dissatisfactory effect of fruit detaching methods in robotic fruit harvesting, the laser may now be a new method to cut off the peduncle. In this paper, the feasibility of cutting tomato peduncles with 30 W, 980 nm fiber-coupled semiconductor laser was firstly verified by tests and calculations. The maximum power density of focusing spot and the depth of focus (DOF) were 4.95 W/mm2and 8.4 mm, respectively, so this laser was able to cut through a peduncle even under large position and angle errors between the focus lens and the peduncle in view of its lower burning temperature, smaller diameter, rougher surface and lower thermal conductivity. It was also found that the drilling through time was linearly correlated with the diameter of peduncle, negative correlated with the laser power and incident angle, binomial correlated with defocusing distance, respectively. The high-success-rate, high efficiency and energy-saving laser cutting can be achieved by adopting better quality or higher power laser and optimization of defocusing distance and incident angle in practical operation of robotic harvesting. Key words: Feasibility, influencing factor, laser cutting, peduncle, harvesting robot.

Feasibility and influencing factors of laser cutting of tomato peduncles for robotic harvesting

Due to the dissatisfactory effect of fruit detaching methods in robotic fruit harvesting, the laser may now be a new method to cut off the peduncle. In this paper, the feasibility of cutting tomato peduncles with 30 W, 980 nm fiber-coupled semiconductor laser was firstly verified by tests and calculations. The maximum power density of focusing spot and the depth of focus (DOF) were 4.95 W/mm2and 8.4 mm, respectively, so this laser was able to cut through a peduncle even under large position and angle errors between the focus lens and the peduncle in view of its lower burning temperature, smaller diameter, rougher surface and lower thermal conductivity. It was also found that the drilling through time was linearly correlated with the diameter of peduncle, negative correlated with the laser power and incident angle, binomial correlated with defocusing distance, respectively. The high-success-rate, high efficiency and energy-saving laser cutting can be achieved by adopting better quality or higher power laser and optimization of defocusing distance and incident angle in practical operation of robotic harvesting. Key words: Feasibility, influencing factor, laser cutting, peduncle, harvesting robot.

An evanescent-coupling approach to making stable fiber-coupled semiconductor lasers

We present a fiber-coupled GaAs laser, which works on the principle of evanescent coupling between a semiconductor antiresonant reflecting optical waveguide and a side-polished single-mode fiber. Compared to conventional fiber-coupled semiconductor lasers, these devices enjoy more relaxed alignment tolerances and simpler packaging, as well as high immunity to catastrophic mirror damage that limits the maximum power output of most edge-emitting lasers. Moreover, the small coupling window here provides an inherent filter that guarantees wavelength stability without any gratings. The initial data show stable single-frequency operation with more than 27dB side-mode suppression ratio and a small thermal coefficient of 0.06nm∕°C.

Qualification and reliability testing of a commercial high-power fiber-coupled semiconductor laser for space applications

A compact microchip laser pumped by a single fiber-coupled semiconductor diode laser is developed for a space-borne scanning laser radar instrument. A commercial off-the-shelf component is used for the pump laser and undergoes a rigorous qualification approach to meet the requirements for the space-borne application. The qualification and testing process for the commercial pump laser is derived based on a nonstandard piece part screening plan and is presented along with the test results. These tests include mechanical, vibration, thermal cycling, and radiation tests as well as a full destructive parts analysis. Accelerated lifetests are also performed on the packaged device to demonstrate the ability to meet an operational lifetime of 5000 h. The environmental testing approach would be applicable to space qualification of a variety of commercial photonic systems, particularly in cost-constrained missions.

Design and characterization of a diode-pumped, single longitudinal and transverse mode, intracavity-doubled cw Nd:YAG laser

We report on the experimental results of a diode-pumped, intracavity-doubled cw Nd:YAG laser, pumped by a 10-W fiber-coupled semiconductor laser at 808 nm and emitting as much as 600 mW in a stable single longitudinal mode and TEM(00) spatial mode. We discuss the main issues of the resonator design and the optimization of the intracavity second harmonic conversion by interpreting our results using simple models. Improvements for the current project are also discussed.

Laser Doppler velocimeter based on the self-mixing effect in a fiber-coupled semiconductor laser: theory

A laser Doppler velocimeter that consists of a semiconductor laser coupled to a fiber and that uses the self-mixing effect is presented. The velocimeter can be used for solids and fluids. A theoretical model is developed to describe the self-mixing signals as a function of the amount of feedback into the laser and the distance from the laser to the moving object. Good agreement is found between this theory and measurements.