New generation of high power laser systems based on multiple-pass amplifiers

Small, medium, and large solid-state rod amplifiers have typical diameters d and gains g of: l,d = 0.5-3cm, g = 15-50; II, d = 3-7cm, g = 5-15; lll, d = 7-12 cm, g = 2-5. Many applications require overall rod system gains of g = 103-106, terminating in class II or III sized beams. Conventional laser systems achieve this required gain using chains of increasingly larger amplifiers. A new generation laser would use only one or two multiple-pass amplifiers. We have successfully built multiple-pass (and multiple-beam) amplifiers with large fill factors, high coupling efficiency, nonresonant geometry, and using passive optics for polarization and angularly controlled beam steering. Gains of > 103 with output intensities in the saturated region were routinely achieved with triple-pass units. Diffraction-limited 100-GW, 1-4-ns temporally shaped laser pulses in one or two beams were obtained with only two multiple-pass amplifiers at half the cost of a conventional laser. Frequency conversion was successfully accomplished. Phase conjugation (Brillouin in organic liquid) and polarization compensation are being incorporated into an ultrahigh performance unit with good preliminary results. Ring laser configurations are being adapted to substantially improve intra amplifier and inter amplifier isolation. These additional improvements will yield multipass systems at a quarter of the cost of conventional lasers. (Poster paper)