X-RAYS FROM OPTICAL-FIELD IONIZED PLASMAS AT LOW-DENSITY

We present results of an experiment in which x rays from an optical-fi eld ionized plasma are generated under well-controlled conditions in a low-pressure gas cell. In this way high-density effects such as elect ron heating, collisional ionization, and ionization defocusing are avo ided. Using N-2 as the medium, we show that many features of the soft- x-ray emission follow theoretical predictions. In particular, higher x -ray intensity is observed on most lines for circularly than for linea rly polarized light. However, several Li-like lines show anomalously s trong emission for linear polarization. Mechanisms that may be respons ible for this effect are discussed. (C) 1997 Optical Society of Americ a.