We demonstrated the capability of a Martinez-type multipass pulse stretcher to produce the pulse duration of about 1 ns stretched from 100 fs with well-preserved quality of the beam pattern and spatial spectral uniformity in the multipass configuration. The beam pattern after being stretched through the pulse stretcher depends significantly on the incident angle to the stretcher grating and the accuracy of adjustment of the optical elements. The observed spatial distribution of the wavelength in the beam cross section after being stretched is in good agreement with the simulation results.

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We have been investigating the possibility of ultimate down sizing of the CPA system by improving over all efficiency to convert the green pump energy to the Ti:sapphire wavelength by optimizing the regenerative amplifier. A regenerative amplifier with high gain to achieve small signal and saturated amplification was constructed. By selecting cavity parameters which allow for large gain cross section in the regenerative amplifier we obtained a pulse energy of l3mJ amplified from sub-nano joule of the seed pulse in 11 round trips. We achieved over all efficiency of 15% in single amplifier pumped by single green source.

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