A pulse clean technique in time domain combining noncollinear optical-parametric amplification and second-harmonic generation is demonstrated. The measurement-limited >10(10) temporal contrast ratio of the 0.5 mJ/40 fs pulse near 800 nm is obtained over a large temporal range extending from <1 ps before the main pulse. The contrast ratio enhancement as fourth power of the initial contrast is demonstrated. The total efficiency is >6% for the 8.2 mJ/40 fs initial incident femtosecond pulse.