ASE contrast improvement with a non-linear filtering Sagnac interferometer

A new method to improve the temporal contrast of an ultra-short laser pulse has been developed. This technique uses a Sagnac interferometer in combination with a non-linear medium. A phase shift induced in the ultra-short pulse by non-linear effect separates it from the amplified spontaneous emission background. Experiments with a 1 kHz, 55 fs, 1 mJ Ti:Sa laser were performed. The temporal contrast measurements have shown a contrast improvement of four orders of magnitude.