Diode-pumped nanosecond laser with high pulsed energy of multijoules and high repetition rate of dozens to hundreds of hertz is attracting increasing attention due to its potential wide applications in industrial and scientific areas. Amplifier head in repetitive operation plays a key dominant role in determining the output energy and beam quality of the laser system, but suffers from serious heat effect such as wavefront aberration and birefringence-induced depolarization. In the present work, a new efficient architecture for a diode pumped liquid cooled active mirror amplifier was devised. First of all, a pump coupling way with low-cost, high efficiency and well-distributed pumping field was proposed. Pumping field with good uniformity benefited the heat distribution and thus the temperature field in the gain media, which plays important role in suppressing the wavefront aberration and depolarization. Water-gaped Cr4+-doped cladding was adopted to minimize amplified spontaneous emission (ASE) loss and prevent parasitic oscillations. Stress induced by expansion coefficient mismatch was completely avoided since no glue was adopted in this design. Last of all, an extremely low-stress flexible clamping architecture was devised, which helped to decrease stress-induced aberration and depolarization. Inlets and channels of the cooling liquid were seriously designed and optimized to insure an even cooling of the gain media. The gain, wavefront and depolarization of the amplifier with pump power of about 65kW and repetition rate up to 100 Hz were experimentally measured and the results agreed well with the numerical simulations.

liquid cooled; diode pumped; amplifier