Abstract: Amplified spontaneous emission (ASE) effects is presented for small as- pect ratio (length/width) laser amplifier and oscillator. And the three-Dimensional formulation is given. Approximations are introduced included nonsaturable absorption, ASE line-narrowing effects, and end mirrors that reflect ASE flux back into the active gain medium. The results are presented that show the optimum scaling of extraction effi- ciency and power gain for large fusion class lasers.