An alexandrite pumped Nd:glass regenerative amplifier for chirped pulse amplification

For many high field physics studies a laser source capable of producing intensities of 1017 W/cm 2 or greater is necessary. Ideally, such a laser source should be compact and simple so that it is at once reliable and manageable. In order to make the laser as compact as possible it is extremely desirable to use solidstate amplifier materials because of their energy storage capability. If this energy can be safely extracted in an ultrashort pulse ( 1 ps or less) tremendous peak powers can be obtained with relatively modest optical energy requirements. For instance, a 3 TW system based on a 60 fs pulse only requires 200 mJ [ 1 ]. The combination of a short pulse, and the energy storage capability of the amplifier results in a very compact, high intensity laser source. The difficulty, of course, is safely extracting this energy from the amplifier in an ultrashort pulse. Because of the pulse duration, the peak pov'er becomes significant very early in the amplification process. Thus, nonlinear effects become important and can result in catastrophic damage to the amplifier (e.g., whole beam self-focusing). This problem is avoided by temporally stretching or chirping the pulse prior to amplification [ 2 ]. Normally this is accomplished through the use of a dispersive grating pair. A 100 fs pulse can be stretched more than 10000 times with standard size optical elements [ 3 ]. After stretching, the pulse is amplified to the desired energy level, then recompressed to its Fourier transform limit. The compression stage is also a grating pair arranged to provide the opposite sign of group velocity dispersion introduced by the stretcher. It is important throughout the stretching, amplification, and compression process that the spatial and temporal integrity of the pulse be maintained to the highest level possible. This results in the shortest, highestcontrast (peak intensity-to-background intensity) pulses and most focusable beams. The advantages of using Nd: glass as the amplifier include the fact that large rods of high optical quality can be fabricated, making it possible to produce near diffraction-limited beams which are critically important for achieving the greatest intensities on target. The technique of chirped pulse amplification used in conjunction with Nd: glass has produced peak powers in the 20-30 TW range [4,5 ] using large amplifier chains. More cOmpact systems have been shown to produce up toi l0 TW [ 6 ]. The two major limitations with Nd: glass amplifiers are narrow bandwidth, and poor thermal char-