Abstract
X‐ray emission from the 2s → 1s transition in hydrogenic ions stimulated by an optical laser is proposed as a means of achieving lasing action in the x‐ray region. A net gain of 0.27 cm−1 is calculated for the 18.97‐Å 2s → 1s transition of O+7 at an inverted population density of 1015 ions/cm3 in the presence of a Nd laser field of 5 × 108 W/cm2.