High‐energy, Yb:LuAG and Yb:YAG active mirror amplifiers

We report the first short-pulse amplification results to several hundred millijoule energies in ceramic Yb:LuAG. We have demonstrated ns-pulse output from a diode-pumped Yb:LuAG disk amplifier at a maximum energy of 580 mJ and a peak optical-to-optical efficiency of 28% at 550 mJ. We also compare our results with Yb:YAG within the same amplifier system based on active mirror design. Previous works reporting on diode-pumped Yb:YAG amplifiers with similar pulse energies or even more than 1 J either demonstrated a maximum optical-to-optical efficiency around 10% or relied on cryogenic cooling, and/or based on bulk material. While cryogenically cooled lasers allow for even higher efficiencies the gain spectrum is narrowed dramatically for both Yb:YAG and Yb:LuAG. Pulses as short as 2 ps, corresponding to a gain bandwidth of about 1 nm, can be amplified at room temperature, whereas at liquid nitrogen temperature the gain bandwidth reduces by about one order of magnitude. Hence, we also studied the spectral response of both materials at room temperature. Although the peak absorbtion cross section of Yb:LuAG around 940 nm is lower compared to Yb:YAG the broader absorption spectrum is more suitable for using pump diodes without wavelength stabilization. Furthermore, we report on CPA-free picosecond amplification to the 100mJ level in Yb:YAG demonstrating the potential of the active mirror approach for efficient energy extraction at low fluences without optical damage or nonlinear effects such as self phase modulation (SPM) or self-focusing.