ABSTRACT
This chapter considers the fundamental scaling relations which underlie X-ray laser design, independently of the details of the scheme. In contrast at short wavelengths lasing has been achieved relatively routinely into the far ultra-violet, but only with difficulty and at limited wavelengths in the soft X-ray region—a range of only two decades. An alternative approach for generating coherent, monochromatic radiation in the soft X-ray region is through high harmonic generation. Lasers can be constructed to operate by amplification of spontaneous emission noise in a single transit. As the intensity of the radiation within the laser beam increases due to amplification, the rate of transitions due to the stimulated emission becomes comparable to the net pumping rate on the transition, and the population inversion is reduced. The methods are based on laser produced plasmas from solid targets. The achievement of gain involves the coupling of the physics of laser-plasma interaction with the population dynamics necessary to achieve gain.
