Recently, OPA was shown to be an efficient method for improving the contrast ratio to 1010-11(instrument limit) and to be useful as the front end of the high-power laser with 1 μm working wavelength.
Researchers at State Key Laboratory of High Field Laser Physics——Shanghai Institute of Optics and Fines Mechanics (SIOM/China) demonstrated at 800nm working wavelength a pulse clean technique based on a tunable noncollinear optical-parametric amplification and second-harmonic generation.[Optics Letters 36 (6), 781, 2011].The cleaned pulse with a measurement-limited temporal contrast ratio >1010 over a large temporal range extending from < 1 ps before the main pulse is obtained. The total energy efficiency is >6%. By introducing a reference pulse, we demonstrated that the contrast ratio of the pulse can be enhanced as fourth power of the initial contrast. This technique is a good candidate for high-contrast front ends for large scale high-power femtosecond laser systems.