Yu Yu

Yb:CaGdAlO₄ (Yb:CALGO) crystals, with an ultrabroad emission spectrum of approximately 80 nm and excellent thermo-optic properties, have become an ideal gain medium for overcoming the gain-bandwidth limitation of traditional Yb:YAG and for realizing high-energy sub-100-fs pulse amplification. This paper reports a 1035 nm chirped-pulse regenerative amplifier based on a Yb:CALGO crystal. The seed source is a fiber mode-locked laser with a pulse duration of 867 ps and a spectral width of 11.5 nm, operating at a repetition rate of 100 kHz. The regenerative cavity adopts a linear configuration with a cavity length of 1.2 m. A convex lens with a focal length of 300 mm is inserted into the cavity to compensate for the thermal lensing effect of the crystal, and a composite thermal-management scheme combining indium foil wrapping and a water-cooled copper heat sink ensures cavity stability under high-power pumping. At a 981 nm laser-diode pump power of 77.8 W, a stable amplified output with an average power of 16.54 W is achieved, together with an output pulse duration of 1.2 ns and an amplified spectral bandwidth of 6.9 nm. Over 2 hours of continuous operation, the root-mean-square (RMS) stability of the output power is 0.40%, and the beam quality factors M² are 1.48 and 1.33 in the X and Y directions, respectively. This amplifier provides a feasible technical solution for subsequent grating-pair compression to achieve ultrafast laser output with high peak power on the order of ~300 fs.

Thermally induced beam distortion is a fundamental limitation to power scaling in high-power solid-state lasers. Although stimulated Brillouin scattering phase-conjugate mirrors (SBS-PCMs) are widely employed for wavefront correction, the relationship between phase-conjugation fidelity and thermal compensation has remained unclear. As the pump power continues to increase, thermal effects become more pronounced, resulting in increasingly severe beam distortion and imposing more stringent requirements on the aberration-compensation capability of SBS-PCMs. We establish a theoretical model describing the compensation of spatial phase and intensity distributions by an SBS-PCM and reveal that the thermal depolarization compensation ratio increases monotonically with phase-conjugation fidelity. The theoretical predictions are validated experimentally through comparison with a conventional flat mirror, demonstrating the superior aberration-compensation capability of the SBS-PCM. At a pump repetition rate of 500 Hz, the SBS-PCM delivers 85% energy reflectivity, nearly 50% thermal depolarization compensation, and excellent beam quality.

High-repetition-rate and high-stability short-pulse lasers have broad application prospects in large-scale integrated equipment serving industrial manufacturing and scientific research. Pulse compression techniques based on transient stimulated Brillouin scattering (SBS) are an effective means of obtaining short-pulse lasers. The transient effects and thermal breakdown enhancement effects in the high-repetition-rate transient SBS process will cause significant gain attenuation, resulting in a decrease in output energy reflectivity and stability. In this study, we proposed a pulse compression technique based on transient self-pumped Brillouin scattering (SPBS). By combining pump intensity attenuation with gain compensation based on a self-feedback seed model, the transmission loss and sound field intensity fluctuations during scattering were significantly reduced. The experiment verified the compression capability of the transient SPBS, which improved the output energy reflectivity and stability. The results showed that at a repetition rate of 300 Hz, the transient SPBS had a maximum energy reflectivity of 96.5% and an output energy of 24.1 mJ. Without the interference of the breakdown effect, a stable pulsed laser output with an energy relative standard deviation of only 1.42%, a time-domain duration of 225 ps and a peak power of over 100 MW was finally obtained. Our research provides a valuable reference for the generation of high-repetition-rate, high-peak-power lasers.

An optical waveguide is the basic structure of quantum optics, which has a strong confinement effect on light. It can complete the low-loss transmission of light and the enhancement of the nonlinear effect. Direct writing of optical waveguide structures in transparent crystals can enhance the electro-optic, acousto-optic, and nonlinear optical properties of crystals, making them widely used in the optical field. Femtosecond laser direct writing technology is a non-contact processing technology without thermal damage. The direct writing accuracy is high, and it is easy to fabricate the three-dimensional optical waveguide structure in the crystal. It is the best choice of a direct writing optical waveguide structure in a transparent crystal. This paper reviews the recent progress of femtosecond laser direct writing of transparent crystal materials to form optical waveguide structures. The basic mechanism of optical waveguide fabrication by femtosecond laser direct writing in transparent crystal, the methods of waveguide fabrication combined with different techniques, and the obtained optical waveguide structures are introduced, including single-line waveguides, double-line waveguides, depressed-cladding waveguides, ridge waveguides, and photonic crystal waveguides. The applications of optical waveguide structures in lasers, quantum memories, and quantum telecommunication devices are also presented.

Lasers are increasingly used in the biomedical field because of their concentrated energy, good stability, ease of use, and other advantages, promoting the development of precision medicine to a higher level. Medical laser equipment has transformed from a single therapeutic tool in an intelligent and precise diagnostic system. Existing clinical laser equipment has significant technical bottlenecks regarding soft-tissue ablation precision and multimodal diagnostic compatibility, which seriously restricts its clinical application. High-power thulium-doped fiber lasers with operating wavelengths of 1.9–2.1 μm provide a revolutionary solution for minimally invasive surgery due to their high compatibility with the absorption peaks of water molecules in biological tissues. This study reviews recent advances in high-power thulium-doped fiber lasers for minimally invasive therapies in the biomedical field. Breakthrough results in four major clinical application scenarios, namely, urological lithotripsy, tumor precision ablation, disfiguring dermatological treatment, and minimally invasive endovenous laser ablation, are also summarized. By systematically evaluating its potential for multimodal diagnostic and therapeutic applications and thoroughly exploring the technical challenges and strategies for clinical transformation, we aim to provide a theoretical basis and practical guidance for the clinical transformation and industrialization of new-generation medical laser technology.

Based on a 4f system, a 0° reflector and a single laser diode side-pump amplifier, a new amplifier is designed to compensate the spherical aberration of the amplified laser generated by a single laser diode side-pump amplifier and enhance the power of the amplified laser. Furthermore, the role of the 4f system in the passive spherical aberration compensation and its effect on the amplified laser are discussed in detail. The results indicate that the amplification efficiency is enhanced by incorporating a 4f system in a double-pass amplifier and placing a 0° reflector only at the focal point of the single-pass amplified laser. This method also effectively uses the heat from the gain medium (neodymium-doped yttrium aluminium garnet) of the amplifier to compensate the spherical aberration of the amplified laser.

The aerospace sector requires materials, particularly aluminum all, to possess advanced mechanical properties for aircraft skins. Consequently, the industry implements protective coatings to counteract erosion and abrasion. Yet, as time progresses, these coatings can degrade, prompting careful paint removal to extend the longevity of aircraft. This research investigates methods to improve laser cleaning efficiency while safeguarding paint quality. It utilizes a nanosecond pulsed laser to assess factors such as laser energy, cleaning angle, and out-of-focus volume on cleaning efficacy. The findings demonstrate that the optimal energy for cleaning is 20 mJ; exceeding this threshold results in damage to the substrate. Additionally, the cleaning angle significantly impacts efficiency, with an 11° angle yielding the highest effectiveness. Manipulating the laser’s focal point also alters cleaning quality, with 30 mm providing the best outcomes. Single-point laser cleaning tests examined energy levels and cleaning cycles, highlighting that increased energy and cycles lead to surface damage and greater roughness. Furthermore, paint color affected cleaning performance, with blue paint exhibiting superior cleaning effectiveness. This study advances the development of laser cleaning methods for aircraft skins, catering to industry needs for efficient, environmentally friendly maintenance practices.