Yu Ding

Lasers operating in the 2 µm spectral region have significant application value and development potential in fields such as lidar, medical surgery, and mid-infrared nonlinear optics because they are located in the atmospheric absorption window and coincide with a strong absorption peak of water molecules. This article first briefly introduces the energy level characteristics and commonly used crystal matrices of Tm³⁺, Ho³⁺ and Tm³⁺/Ho³⁺ codoped systems, and then reviews the research progress of 2 µm side-pumped solid-state lasers based on these ions and matrices. This review summarizes the research progress of 2 µm side-pumped solid-state lasers, categorized by operating mode and gain medium. Particular attention is given to the mature advantages of Tm-doped garnet lasers in high average power output and the potential of Tm/Ho-codoped fluoride lasers in high-energy, high-beam-quality pulse output. Finally, this paper further reviews the development of side-pumped laser structures and offers a prospective outlook on the future development of 2 µm region side-pumped lasers.

To generate cylindrical vector beams (CVBs) with high mode purity and high beam quality, a polarization-maintaining fiber oscillator was built, followed by high-efficiency mode conversion with an S-waveplate. This system leverages the S-waveplate as a mode converter to transform the fundamental LP₀₁ mode into radially and azimuthally polarized beams, which both feature a central polarization singularity. The experimental results demonstrate that the system successfully yielded a radially polarized beam with an output power of 3.93 W and a high mode purity of 96.99%, as well as an azimuthally polarized beam with an output power of 3.71 W and a mode purity of 96.5%. The corresponding beam quality factors (M²) were measured to be 2.17 and 2.01, respectively. After 60 min of continuous operation at maximum power, the radially and azimuthally polarized beams had average powers of 3.988 W and 3.785 W, with RMS stabilities of 0.788% and 0.590%, respectively. To the best of our knowledge, this represents the highest power reported to date for both radially and azimuthally polarized CVBs that simultaneously possess high mode purity and beam quality. This work provides an effective solution to obtain high-power CVB sources that simultaneously possess high mode purity and beam quality, establishing a solid foundation for subsequent power scaling and practical applications.

Narrow-linewidth lasers play a crucial role in nonlinear optics, atomic physics, optical metrology, and high-speed coherent optical communications. Precise linewidth measurement is essential for assessing laser noise characteristics; however, conventional methods are often bulky, costly, and unsuitable for integrated applications. This paper presents a compact and cost-effective delay self-homodyne system for laser linewidth measurement, leveraging a field-programmable gate array (FPGA)-based data acquisition circuit. By employing fast Fourier transform (FFT) analysis, the system achieves high-precision linewidth measurement in the kHz range. Additionally, by optimizing the fiber length, the system effectively suppresses low-frequency and 1/f noise, providing an integrated and efficient solution for advanced laser characterization with enhanced performance and reduced cost.

We report a 2.8 μm all-fiber high-power and high-energy gain-switched Er³⁺:ZBLAN laser based on dielectric fiber mirror and fiber-tip protection. The fiber pigtail mirror, specifically designed for dichroic operation (i.e., anti-reflection at 976 nm pump wavelength and high-reflection around 2.8 μm laser wavelength), shows high damage density of >10 MW/cm². An anti-reflection protective film is coated on the input tip of Er³⁺:ZBLAN fiber and an AlF₃ endcap is spliced to the output tip of Er³⁺:ZBLAN fiber for mitigating the fiber-tip photodegradation and high-power catastrophic failure at 2.8 μm. The compact all-fiber cavity is formed by efficiently connecting the Er³⁺:ZBLAN fiber with dielectric fiber mirror using the standard FC/PC fiber adaptor. When the 976 nm pump operates in pulsed regime, the all-fiber mid-infrared gain-switched laser can be attained with two states of single-pulse and pulse-burst output. The extracted maximum pulse energy is 4.8 μJ in the single-pulse state, and the shortest pulse width is 426 ns. The pulse-burst mode can generate a maximum average power of 5.291 W and burst energy of 264.55 μJ. This work may offer a promising way to realize the low-cost, all-fiber, high-power and high-energy gain-switched laser at MIR wavelengths.

In this paper, we demonstrated an efficient degenerate middle infrared (mid-IR) ZGP-OPO that is pumped by an electro-optically Q-switched diode-pumped Tm:YAP laser. The Tm:YAP laser, operating at a repetition rate of 1 kHz, produced a peak pulse energy of 9.66 mJ at 1.94 μm and a minimum pulse width of 25 ns. Utilizing the Tm:YAP laser as the pump source, a peak average output power of 3.14 W at 3.88 μm was achieved in the degenerate ZGP-OPO with an incident Tm power of 9.4 W, resulting in a slope efficiency of 62.7% and an optical conversion efficiency of 33.4%. The minimum pulse width was measured at 21 ns, leading to a peak power of 149.5 kW. Additionally, the beam quality factor of the degenerate mid-IR ZGP-OPO was evaluated to be approximately 2.7 at the maximum output power level.

A high-efficiency Nd:LuVO₄ laser, pumped by a fiber-coupled laser diode at 916 nm, was successfully demonstrated. Employing a recycling-pumping architecture, an output power of 12.1 W at 1,343.2 nm was achieved with an incident pump power of 20 W, resulting in a slope efficiency of 62.1% and an optical conversion efficiency of 60.5%. Furthermore, the beam quality factor was measured to be approximately 1.1 at the maximum output level.

We developed a high-power, double-intracavity-frequency, diode-side-pumped, Q-switched Nd:YAG laser. The thermal birefringence effect of Nd:YAG crystal was compensated by a quartz rotating mirror, and the stable cavity structure was designed according to the thermal focal length of a single module. A 532 nm laser with a maximum linearly polarized output power of 96 W was obtained at a pumping power of 1300 W and repetition rate of 10 kHz. The pulse width was 55.8 ns, and the beam quality was measured to be M²_x = 5.98, M²_y = 8.14 at the maximum output power; therefore, a brightness as high as 6.97 × 10⁸ W·cm⁻²·Sr was achieved. To the best of our knowledge, this is the highest brightness obtained for a high-power Nd:YAG laser at 532 nm.

Femtosecond laser-induced nanogratings generation inside transparent materials has been the focus of research in the field of femtosecond laser precision processing. Due to the advantages of optical birefringence phenomenon, periodicity, thermal stability, controllability of delay value and optical axis direction, and re-writability, nanogratings are widely used in research fields such as optical storage and optical devices. This mini-review explores the existing mechanism of femtosecond laser-induced formation of nanogratings and the progress of inducing nanogratings in different types of glass and sapphire crystals. It also describes the prospects of nanogratings for a wide range of applications in optical components and optical devices.