The 1.3 μm diode-pumped solid-state laser has garnered significant attention in various technical applications, including medical and spectroscopy. The transition from ⁴F_3/2 to ⁴I_13/2 of Nd ions represents an outstanding method for generating high-performance 1.3 μm laser radiation. The conventional Nd:YAG crystal has been extensively employed in diode-pumped lasers operating at 1.3 μm [1–3]. Nd-doped vanadate crystals are distinguished by their substantial absorption and emission cross-sections. Consequently, Nd:YVO₄ and Nd:GdVO₄ crystals represent popular options for producing 1.3-μm laser [4–8]. However, the quantum defect of 39.7% between pump and laser photons constrains the enhancement of output performance of Nd lasers at 1.3 μm. One potential solution involves utilizing a pump wavelength close to 880 nm, enabling the pump photon to directly excite the Nd ions to transition to the laser upper level (4F3/2). This technique, known as in-band pumping technology, leads to a reduced quantum defect and increased efficiency [9–11]. In 2005, researchers demonstrated a Nd:YAG laser operating at a wavelength of 1,341 nm. The laser was pumped by a LD at 885 nm and achieved a slope efficiency of 45% [12]. Similarly, in the same year, a continuous-wave (CW) Nd:GdVO₄ laser operating at 1,341 nm was reported, achieving a slope efficiency of 60% under the pumping of an 879 nm Ti:Sapphire laser [13]. In 2008, a Nd:YVO₄ laser operating at 1,342 nm was demonstrated using a Q-switched Ti:Sapphire laser at 879 nm [14]. Moving forward to 2010, researchers demonstrated a CW Nd:YLF laser operating at 1,321 nm. The laser had an output power of 3.6 W and a slope efficiency of 52%. It was achieved using a fiber-coupled LD at 880 nm [15]. In 2018, the 1.3-μm lasing performances of Nd:Gd_0.69Y_0.3TaO₄ and Nd:Gd_0.68Y_0.3NbO₄ mixed crystals were investigated under 879-nm LD pumping [16].

The Nd:LuVO₄ crystal exhibits larger absorption and emission cross sections compared to Nd:YVO4 and Nd:GdVO₄, making it a suitable choice for use as the laser medium in the near-infrared spectral region. Nd:LuVO₄ lasers operating at 0.9 μm, 1.06 μm, and 1.3 μm wavelengths have been reported, utilizing laser diode (LD) pumping near 808 nm [17–19]. In 2010, Nd:LuVO₄ lasers achieved output powers of 7.0 W and 6.2 W at 1,343 nm when pumped at 880 nm and 809 nm, corresponding to the slope efficiencies of 44.5% and 34.9% with respect to absorbed pump power, respectively [20]. In addition to the absorption peaks at 809 nm and 880 nm, the Nd:LuVO₄ crystal also exhibits a significant absorption peak at 916 nm. By utilizing this absorption peak for pumping, the quantum defect in Nd:LuVO₄ lasers operating at 1,343 nm can be reduced to 31.8%. This reduction results in higher efficiency and lower thermal loading for the laser system. In 2013, a Nd:LuVO₄ laser pumped by a diode-pumped 916-nm Nd:LuVO₄ laser achieved an output power of 1.12 W at 1,343 nm. This corresponds to a slope efficiency of 61.9% relative to the absorbed pump power [21].

In this paper, to the best of our knowledge, a high-efficiency Nd:LuVO₄ laser at 1,343 nm that is recycling-pumped by a fiber-coupled LD at 916 nm was demonstrated. By utilizing this approach, we achieved the maximum output power of 12.1 W at 1,343.2 nm, with an incident pump power of 20 W. This corresponds to a slope efficiency of 62.1% and an optical conversion efficiency of 60.5%. Furthermore, the beam quality factor (M²) was estimated to be approximately 1.1 at maximum output power.

The experimental setup of a diode-pumped Nd:LuVO₄ laser with a recycle pumping scheme was shown in Figure 1. The pump source utilized in the experiment was a wavelength-locked fiber-coupled LD with a maximum output power of 20 W at 916 nm. The pigtail fiber had a core diameter of 105 μm and a numerical aperture of 0.22. To focus the pump beam into the Nd:LuVO₄ crystal, a telescope comprising lenses F1 and F2 was employed, with focal lengths of 15 mm and 60 mm, respectively, resulting in a pump spot radius of 210 μm. A c-cut Nd:LuVO₄ crystal with a doping concentration of 1.0 at.% and dimensions of 3 × 3 (in cross-section) ×10 (in length) mm³ was used in the experiment. Both surfaces of the crystal were antireflection coated from 900 nm to 1,400 nm. The crystal, wrapped in indium foil, was mounted in a copper heatsink, with the operating temperature maintained at 18 °C using a thermoelectric cooler. The single-pass pump absorption of the Nd:LuVO₄ crystal was measured to be approximately 80% under nonlasing conditions.

The laser cavity consists of three mirrors. To achieve a lasing wavelength of 1,343 nm, the flat M1 mirror was coated with high transmission at wavelengths of 916 nm and 1,066 nm, as well as high reflectivity at the lasing wavelength of 1,343 nm. The M2 mirror was a flat 45° dichromatic mirror with high transmission at 916 nm and high reflectivity at 1,343 nm. In the experiment, an output coupler M4 with a plano-concave shape and a radius of curvature of 200 mm was used, with an output transmittance of 25%. The physical length of the cavity was approximately 50 mm. The flat M3 mirror, which had high reflectivity at 916 nm, and another lens F2 were utilized to achieve pump recycling.

Figure 2 displays the output powers of the Nd:LuVO₄ laser, which were measured using a Coherent PM 30 power meter. With an LD pump at 916 nm, a maximum output power of 12.1 W was achieved under an incident LD power of 20 W, resulting in a slope efficiency of 62.1% and an optical conversion efficiency of 60.5%. The pump threshold for the laser was approximately 1.0 W. In addition, the power fluctuation was about 2.1% within a period of 1 hour. Higher temperature-control accuracy and narrower output linewidth can improve the power stability. Limiting the pump power, more high output power was not presented in this work. No power saturation phenomenon was observed in Figure 2. We believe that output power could be increased under higher pump level. Furthermore, optimizing the overlap between pump and oscillating beams and output transmittance could further improve output performance.

The output spectra of Nd:LuVO₄ laser were recorded by a laser spectrum analyzer (Bristol, 771B). As depicted in Figure 3, a single oscillating line at 1,343.2 nm was observed, with an FWHM linewidth of approximately 0.1 nm. Throughout the increase in pump power from threshold to maximum level, no other wavelengths were detected.

The beam quality factor of Nd:LuVO₄ laser was measured by the 90/10 knife-edge method, as shown in Figure 4. The estimated value at maximum output power was approximately 1.1. Furthermore, images of the far-field beam in both 2D and 3D were captured using a camera (Ophir-spricon, Pyrocam IV), as illustrated in Figure 5. These images clearly indicate that the beam exhibits a TEM₀₀ Gaussian profile.

In conclusion, this work presents the successful demonstration of an efficient recycling-pumped Nd:LuVO₄ laser, achieved using a wavelength-locked fiber-coupled LD at 916 nm. The laser attained a maximum output power of 12.1 W at 1,343.2 nm 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 M²-factor at maximum output level was measured to be approximately 1.1. These results highlight promising prospects for enhancing the output power at 1,343 nm for the Nd:LuVO₄ laser.