Yanmin Duan

We systematically compare two passive symmetry-breaking schemes, output coupler (OC) lateral translation and gain crystal tilting, for chiral switching in an annular-pumped solid-state vortex laser system. In both approaches, the combination of cavity geometric asymmetry and intrinsic crystal anisotropy introduces differential round trip loss between the conjugate LG0,±1 vortex modes, thus supporting dominant oscillation of a single-chirality vortex mode. However, OC translation introduces transverse beam deviation, which inevitably distorts the annular vortex profile and degrades beam quality. In contrast, moderate crystal tilting achieves effective symmetry breaking while fully preserving the hollow annular morphology, owing to the optical confinement effect of the concave resonator that restricts the intracavity mode within the annular gain region. Under an incident pump power of 8 W, the laser delivers a maximum output power of 2.2 W for the degenerate vortex state and 1.7 W for stable single-chirality vortices. This work elucidates the fundamental similarities and differences between the two anisotropy-coupled chirality modulation mechanisms and provides a high-fidelity, robust solution for high-performance chirality-switchable vortex lasers suitable for orbital angular momentum communication and particle manipulation.

We demonstrate a compact Nd:YVO₄ laser with a plano-concave resonator for dynamic generation and switching of high-order Hermite–Gaussian (HG) and Ince–Gaussian (IG) via off-axis pumping and intracavity astigmatic modulation. By adjusting the orthogonal off-axis displacement of the output coupler, stable one-dimensional HG modes up to the 103rd order are obtained. Further tuning the crystal pitch angle modulates the ellipticity and enables efficient conversion into even–odd superimposed IG modes with tunable p and m indices. We also perform dedicated numerical and experimental analysis on this type of superimposed IG mode. All measured results are in good agreement with simulations. This integrated cavity design offers a compact solution for reconfigurable structured light sources in various photonic applications.

An all-fiber pulse burst generator featuring a high sub-pulse repetition frequency (PRF) was demonstrated by combining the inherent pulse replication capability of a fiber ring cavity with the Vernier effect. The system employs pre-modulation to deliver an ideally flat burst envelope even after amplification and supports flexible adjustment of both sub-pulse count and burst repetition frequency. Furthermore, we developed a temporal fractal burst with a self-similarity characteristic for the first time, to the best of our knowledge, which offers an additional degree of freedom for temporal adjustment. This laser system, featuring high PRF and adjustable parameters, demonstrates significant potential for applications in material processing and biomedical fields.

We demonstrate the generation of high‐order, 1D Hermite–Gaussian (HG) laser beams with independently tunable orthogonal directions in an off‐axis pumped Nd:YVO ₄ solid‐state laser. These HG modes are successfully converted to Laguerre–Gaussian (LG) modes using a mode converter. We independently adjusted the pump beam displacement in the horizontal and vertical directions, achieving HG modes up to the 87th order. With an input power of 4 W, the HG ₁ , ₀ mode exhibited an output power of 1.96 W and an optical‐to‐optical conversion efficiency of 49%, while the HG ₈₇ , ₀ mode delivered an output power of 1.1 W with a corresponding efficiency of 27.6%. Continuous selection of the mode order in a specific dimension was realized by independently controlling the off‐axis displacements in two orthogonal directions. Finally, using a cylindrical lens mode converter, we successfully converted the HG modes into LG modes. This laser system can serve as a versatile source for applications including long‐range free‐space optical communication, optical trapping and manipulation of particles, optical sensing, and laser‐driven electron acceleration.

We developed a novel ultra-short pulse burst laser based on a fiber ring cavity. A hybrid pulsed-continuous wave pumping scheme is employed in this cavity to generate relaxation oscillation gain, which subsequently modulates the injected mode-locked pulses into a burst mode through gain-switching effect. The characteristics of the generated burst can be adjusted conveniently by varying the pump parameters. In order to investigate the frequency dynamical behaviors in this method, we experimentally record the real-time spectra output from the fiber ring cavity by means of the dispersive Fourier transform technique. During the initial ring-down period, incomplete gain competition deteriorates the output burst spectrum upon the arrival of subsequent gain. Optimal increase of the pump-signal delay establishes resonant-frequency dominance in gain competition, which yields spectrally stable burst operation. The removal of the requirement for active modulators in this scheme yields a compact burst laser with greater robustness and lower cost, thereby facilitating its practical application.

We report a passively Q-switched self-Raman laser using a dual-end composite c-cut Nd:YVO₄ crystal, which generates switchable visible emissions at 533 nm, 560 nm, and 589 nm. A Cr⁴⁺:YAG/YAG composite crystal served the role of a saturable absorber to achieve passive Q-switching. An angle-tuned BBO crystal was used to achieve the frequency mixing between the first-tokes wave and the fundamental wave. At an incident pump power of 9.5 W, the maximum average output powers were 425 mW for the 589 nm yellow laser, 193 mW for the 560 nm lime laser, and 605 mW for the 533 nm green laser, with corresponding pulse widths of approximately 3.8, 3.6, and 35.1 ns, respectively. This result shows that a passive Q-switching operation with self-Raman crystals presents a promising approach for compact multi-wavelength pulse laser sources.

This study demonstrates the generation of a tunable all-fiber Fano resonance comb by incorporating a 10° tilted fiber Bragg grating (TFBG) into an all-fiber Mach–Zehnder interferometer (MZI). The TFBG generates the discrete state that couples with the continuum state of the MZI to produce all-fiber Fano resonance comb spanning an 80 nm spectral range. This system exhibits precise tunability, enabling continuous transitions among asymmetric Fano line shape, symmetric electromagnetically induced transparency, and electromagnetically induced absorption line shapes. The results also demonstrate that key spectral parameters, including the Fano parameter q, slope rate, and extinction ratio, exhibit periodic variation. The proposed approach offers a robust, low-loss, and scalable solution for multi-Fano resonance generation and holds promise for applications of high-sensitivity sensing and optical switching.

We report a parameter adjustable mid-infrared (MIR) ultra-short pulse-burst laser based on the difference frequency generation (DFG) within a periodically poled MgO:LiNbO₃ crystal. A uniform pulse laser at 1.03 μm with a sub-GHz repetition rate was first modulated into parameter adjustable burst modes, which subsequently served as the pump seed for the DFG process. A pulsed super-luminescent light emitting diode (SLED) was designed to synchronize with the pump burst duration and applied as the seed of signal wave. Synchronization was assured by utilizing separate channels of a single arbitrary waveform generator to control both the pulse picker and the SLED driver, thereby enabling the parameter-adjustment of the MIR burst. When the incident pump power was 18.8 W and the signal power was 2.51 W, a maximum MIR idler power of 1.33 W was obtained at 2941 nm with 1.5 MHz burst repetition rate and ∼ 60 ns width, corresponding to a total burst energy of 0.9 μJ. Such parameter adjustable MIR ultra-short pulse burst laser source is particularly promising for tissue ablation due to its high ablation efficiency, lower thermal damage and flexible operation mode.

In this work, a double-end diffusion bonded Nd:YVO₄ self-Raman laser was designed to drive an intracavity, noncritically-phase-matched KTiOAsO₄ (KTA) optical parametric oscillator (OPO). Both conversion efficiency and output power at 1.7 µm (the wavelength of the OPO signal field) were improved by effectively reducing the thermal lens effect and increasing the effective length of self-Raman medium. At an incident pump power of 15.4 W, the output power for 1742 nm output laser reached 2.16 W with a conversion efficiency of 14%, and the output having a pulse width of 10.5 ns and a pulse repetition frequency of 90 kHz. The competition between the OPO and cascaded Raman laser was observed when the incident pump power was above 12.4 W. The results highlight that in order to improve output power at 1742 nm, it is critical that both the cascaded, second-Stokes field at 1313 nm and the signal field generated at 1534 nm from the 1064 nm field driving the KTA-OPO be minimized, if not completely suppressed. This laser system combining the processes of stimulated Raman scattering and optical parametric oscillation for the generation of laser emission at 1742 nm may find significant application across a broad range of fields including biological engineering, laser therapy, optical coherence tomography and for the generation of mid-infrared laser wavelengths.

In this work, we demonstrate a watt-level laser producing high-order, petal-shaped output modes with tunable topological charge, by using an axicon-based divergent annular pump beam. The topological charge of the output beam could be varied in the range of 34–72 by adjusting the position of the Nd:YVO4 crystal relative to the focal plane of the pump beam. The highest order petal-mode beam generated from the system had a topological charge of 72 and a power of 1.3 W. The highest output power up to 2.1 W with a topological charge of 34 was achieved at an absorbed pump power of 5.8 W. The generated output modes were observed to be robust under power scaling and on propagation, with the same spatial profiles being maintained in the near- and far-fields. We anticipate that this system design may find use as a laser source in applications such as 3D optical trapping, fabrication of optical vortex arrays, optical communications, and high-sensitivity spatial measurement.