Significance High-energy rep-rated nanosecond diode-pumped solid-state lasers (DPSSLs), mainly referring to nanosecond lasers with pulse energies greater than 10 J and repetition rates greater than 10 Hz, are crucial in major fundamental and applied research domains and are emerging as one of the hot topics at the frontier of scientific research. This study first analyzes the preferred technical paths of high-energy rep-rated nanosecond DPSSLs in terms of the gain medium and amplifier geometry and then reviews the representative achievements and research progress of high-energy rep-rated nanosecond DPSSLs in detail. Furthermore, the prospects of future development of DPSSLs are discussed herein.
Progress Favored for its moderate saturation fluence and high thermal conductivity, Yb∶YAG at the cryogenic temperature and Nd∶LuAG at room temperature have been proven to be the most promising gain media in achieving rep-rated nanosecond DPSSLs with even higher energy. Conversely, gain medium with high saturation fluence at room temperature, such as Yb∶YAG, and that with low saturation fluence, such as Nd∶YAG, is not suitable for high energy lasers primarily owing to the defect of high pump threshold from the quasi-three-level structure and high passive loss from too many stages. In addition, the three preferred amplifier geometries are the multislab, active mirror, and zigzag slab (
For the multislab geometry, the Mercury system developed by Lawrence Livermore National Laboratory (LLNL) produced a nanosecond output with the pulse energy of 61 J at the repetition rate of 10 Hz based on Yb∶S-FAP multislabs, with ultralow wavefront aberration using a new high-speed gas cooling technology at room temperature (
For the active mirror mode, the LUCIA system reached 13.9 J at 2 Hz in 2013, using the Yb∶YAG laser head at room temperature at the pump intensity of 11 kW/cm2 by focusing on the mirror (
For the zigzag slab design, Hamamatsu developed the HALNA system, which demonstrated an output of 21.3 J, 10 Hz, 8.9 ns in 2008, with an optical-optical efficiency of 11.7%. The beam quality was controlled as 1.8 times diffraction limit, combining a thermally edge-controlled zigzag slab (TECS) design (
Conclusions and Prospects Over the past two decades, extensive efforts have been made into achieving the first milestone, that is, the output target of 100 J, 10 Hz, and 10 ns, which has been achieved in the development of high energy rep-rated nanosecond DPSSLs with breakthroughs in both cryogenic and room temperature. In the next two decades, as new geometry, new gain medium, and new technical approach will inevitably emerge, the main trend expected will be the continuous upgrade in beamlet pulse energy (beyond kJ level), repetition rate (hundreds to kilohertz), and plug efficiency (over 20%), whereas potential directions of development may include system miniaturization, open and flexible access to other operating mechanisms, such as chirped pulse amplification, and programmable control over temporal, spatial, and frequency tuning.