1. A method for filtering noises in an optical parametric chirped-pulse amplifier comprising steps of: 1) generating a seed beam dressed with spatial chirp, which is realized by using a single-pair grating stretcher configuration, which has functions of producing a (stretched) chirped pulse that has simultaneous temporal and spatial chirp; instead of eliminating the spatial chirp, the spatial chirp is deliberately left to form a spatial-chirp-dressed seed beam, thus the seed beam does not need to be reflected back after a first leg of passing through the single-pair gratings; 2) conducting optical parametric amplification, which is realized by using a nonlinear optical crystal or multiple nonlinear optical crystals in series; the spatial-chirp dressed seed beam generated in the step 1) is injected into the nonlinear optical crystal for parametric amplification; 3) removing temporal and spatial chirp in amplified signal, which is realized by a compressor comprising a pair of parallelly-placed gratings; the compressor operates on the same principle with the stretcher in the step 1), for providing spatial and temporal dispersions that closely matches dispersions produced by the stretcher, but opposite in sign; after the amplified signal pulse output from the step 2) passes through the pair of gratings, the temporal and spatial chirp are removed completely, and the amplified signal is compressed close to its original pulse duration, in such a manner that an ultra-short laser pulse with very high peak-power is output; and 4) filtering noises in spatial domain, which is realized by using a one-dimensional slit or aperture at an output of the step 3); the slit or aperture has its center aligning with the output beam of the step 3) and its width equal to the beam width in the transverse dimension where the spatial chirp exists.