A 4-GW electron beam has been used to excite amplified spontaneous emission in hydrogen isotopes (ortho and para H2, HD, and D2). The laser energy has been measured with photodiodes, an ionization chamber, and film, and these different measurements are compared in detail. Analysis of the laser energy indicates the spectral linewidth is due to Doppler broadening, and, consequently, cooling the gas produces higher gain and power. This additional gain allows lasing to be observed at even shorter wavelengths (1098 A as compared to 1161 A) than reported previously. Also many (stimulated emission) spectral lines of the Werner and Lyman bands are reliably identified for the first time. © 1974 The American Physical Society.