No abstract

The thermal effect of a diode pumped solid-state laser mainly caused by nonuniform thermal distribution is the significant bottleneck limiting the output power achievable. In this work, a novel strategy to synthesize YAG crystal thin rods with a designable axial dopant gradient based on the laser-heated pedestal growth (LHPG) method was developed. To make the pump light uniformly absorbed through the whole rod, the optimal doping concentration profile along the axis of single-crystal rods (SCRs) was theoretically deduced. Finite element simulation results demonstrated that the Nd:YAG crystal thin rods with a designed dopant gradient can significantly reduce heat loads under laser operation. Using the grown gradient doped SCRs as a gain medium, the laser diode pumped continuous-wave laser at ∼1.06 μm was achieved with the highest slope efficiency of 44% and a maximum output power of 6.46 W. Under the same conditions, the slope efficiency of the uniformly doped SCRs was 38.7% and the maximum output power was 4.95 W. The results show that the SCRs with gradient dopants possess better thermal management and superior laser performance. Significantly, this method also provides a new idea for realizing the controllable distribution of doped ions in crystal growth.

Nitrogen ions pumped by intense femtosecond laser pulses give rise to optical amplification in the ultraviolet range. Here, we demonstrated that a seed light pulse carrying orbital angular momentum (OAM) can be significantly amplified in nitrogen plasma excited by a Gaussian femtosecond laser pulse. With the topological charge of ℓ = ±1, we observed an energy amplification of the seed light pulse by two orders of magnitude, while the amplified pulse carries the same OAM as the incident seed pulse. Moreover, we show that a spatial misalignment of the plasma amplifier with the OAM seed beam leads to an amplified emission of Gaussian mode without OAM, due to the special spatial profile of the OAM seed pulse that presents a donut-shaped intensity distribution. Utilizing this misalignment, we can implement an optical switch that toggles the output signal between Gaussian mode and OAM mode. This work not only certifies the phase transfer from the seed light to the amplified signal, but also highlights the important role of spatial overlap of the donut-shaped seed beam with the gain region of the nitrogen plasma for the achievement of OAM beam amplification.

Nitrogen ions pumped by intense femtosecond laser pulses give rise to optical amplification in the ultraviolet range. Here, we demonstrated that a seed light pulse carrying orbital angular momentum (OAM) can be significantly amplified in nitrogen plasma excited by a Gaussian femtosecond laser pulse. With the topological charge of ℓ = ±1, we observed an energy amplification of the seed light pulse by two orders of magnitude, while the amplified pulse carries the same OAM as the incident seed pulse. Moreover, we show that a spatial misalignment of the plasma amplifier with the OAM seed beam leads to an amplified emission of Gaussian mode without OAM, due to the special spatial profile of the OAM seed pulse that presents a donut-shaped intensity distribution. Utilizing this misalignment, we can implement an optical switch that toggles the output signal between Gaussian mode and OAM mode. This work not only certifies the phase transfer from the seed light to the amplified signal, but also highlights the important role of spatial overlap of the donut-shaped seed beam with the gain region of the nitrogen plasma for the achievement of OAM beam amplification.