LAUSR

We demonstrate temporal contrast improvement through cascaded second-order nonlinear processes in a 340-µm BBO crystal. The process was initiated by second harmonic (SH) generation, followed by difference frequency generation (DFG) between the SH and the short wavelength part of the fundamental wave (FW). The idler of DFG was selected by a spectral filter, and an output pulse energy of 573 µJ was obtained at 1 kHz with excellent spatial profile and a power fluctuation as low as 0.076% (rms) in 14 hours. The temporal contrast was improved by more than 2 orders of magnitude to approximately 1011, which could be further enhanced with different spectral filters. The excellent stability, energy scalability, and contrast enhancement ability make this simple and robust method very suitable to be integrated into the pulse cleaning system in many different ultra-intense laser facilities.