A high-energy picosecond 355 nm ultraviolet (UV) laser operating at 100 Hz was demonstrated. A 352 mJ, 69 ps, 1064 nm laser at 100 Hz was realized firstly by cascaded regenerative, laser diode end-pumped single-pass and side-pumped main amplifiers. The stimulated Raman scattering-based beam shaping technique, thermally induced birefringence compensation and 4f spatial filter-image relaying systems were used to maintain a relatively homogeneous beam intensity distribution during the amplification process. By using lithium triborate crystals for second- and third-harmonic generation (THG), a 172 mJ, approximately 56 ps, 355 nm UV laser was achieved with a THG conversion efficiency of 49%. To the best of our knowledge, it is the highest pulse energy of a picosecond 355 nm UV laser so far. The beam quality factor ${M}^2$ and pulse energy stability were ${M}_x^2$ =3.92, ${M}_y^2$ =3.71 and root mean square of 1.48%@3 hours. This laser system could play significant roles in applications including photoconductive switch excitation, laser drilling and laser micro-fabrication.

Two-dimensional (2D) violet phosphorus (VP) plays a significant role in the applications of photonic and optoelectronic devices due to its unique optical and electrical properties. The ultrafast carrier dynamics and nonlinear optical absorption properties were systematically investigated here. The intra- and inter-band ultrafast relaxation times of 2D VP nanosheets were measured to be ~6.83 ps and ~62.91 ps using the pump–probe method with a probe laser operating at 1.03 μm. The nonlinear absorption coefficient βeff, the saturation intensity Is, the modulation depth ΔR, and the nonsaturable loss were determined to be −2.18 × 10⁴ cm/MW, 329 kW/cm², 6.3%, and 9.8%, respectively, by using the Z-scan and I-scan methods, indicating the tremendous saturable absorption property of 2D VP nanosheets. Furthermore, the passively Q-switched Nd:YVO₄ laser was realized with the 2D VP nanosheet-based SA, in which the average output power of 700 mW and the pulse duration of 478 ns were obtained. These results effectively reveal the nonlinear optical absorption characteristics of VP nanosheets, demonstrating their outstanding light-manipulating capabilities and providing a basis for the applications of ultrafast optical devices. Our results verify the excellent saturable absorption properties of 2D VP, paving the way for its applications in pulsed laser generation.

A high power, narrow bandwidth, synchronously pumped PPLN optical parametric oscillator is demonstrated. By using a reflective volume bragg grating (RVBG), the signal laser wavelength is locked at 1908.1 nm while the bandwidth is compressed to 0.25 nm with an output power of 4.3 W at the repetition rate of 80 MHz. The beam quality factors in the x and y directions are measured to be 1.30 and 1.68, respectively. The output power stability and directional stability are RMS = 1.4% and 49.58 μrad, respectively. Our results indicate that synchronously pumped OPO is an effective method for generating narrow bandwidth picosecond MIR laser sources.

A megawatt (MW) peak power, tunable repetition rate nanosecond (ns) laser system based on a quasi-continuous wave (QCW) laser diode (LD) end-pumped master oscillator power amplifier (MOPA) structure was demonstrated. A 1064 nm electro-optically Q-switched Nd:YVO₄ laser was used as the seed source, generating a pulse duration of 4.6 ns, a single pulse energy of 530 μJ, a repetition rate of 1 kHz, and beam quality factors of M_x ² = 1.38 and M_y ² = 1.20. After the two-stage QCW end-pumped Nd:YVO₄ amplifier, the single pulse energy was boosted to 16.58 mJ, the pulse duration was shortened to 3.5 ns with a peak power of 4.73 MW, and the beam quality was improved to M ²≤1.12. The repetition rate was adjustable by using an electro-optic pulse picker while maintaining the repetition rate of the seed laser unchanged, and thus was beneficial for improving the reliability of the output pulsed laser. Furthermore, the gain of QCW end-pumped amplifiers was theoretically estimated using a modified Frantz-Nodvik equation model, the theoretical results were great well with the experimental results.

Silicon carbide (SiC) is widely used in power electronic devices and other fields, the defects of which can significantly impact its performance in device fabrication. Laser ultrasonic non-destructive testing (NDT) as a novel and effective approach can detect these defects in real time. This study introduces a numerical model for the SiC NDT that elucidates the dynamic interactions between laser-induced ultrasonic waves and surface defects, and internal defects in SiC, respectively. Results show NDT is an effective way to locate the SiC defect and the ultrasonic waves’ vibration amplitude of detection points at defect edges increases by at least 16% compared to adjacent points, with a maximum of 43%. A comparative assessment between surface and internal defect vibration responses for acoustic is also made. For internal defects, the oscillation time of the acoustic wave at the detection point on the surface away from the edge of the defect at the excitation point exceeds that of surface defects by 100 ns, and the amplitude near the excitation point is more pronounced, reaching 1.44 nm, which is 4.2 times that of corresponding surface defects. Additionally, a linear relationship is observed between the arrival time of transmitted Rayleigh Waves (RSR) and internal defect length, with a correlation coefficient of 0.9878. Similarly, a linear relationship is established between the amplitude of reflected Rayleigh Waves (rR) and defect width, with a correlation coefficient of 0.9976, providing an effective way to quantify the inner defect. Furthermore, transient temperature profiles at distinct positions and transient acoustic fields and the relationship of acoustic vibration amplitude increasing with laser spot size under a fixed laser power density are also analyzed. This model provides a theoretical foundation for laser ultrasonic NDT setup and choice of micro-vibration detection device.