The Sixth International Symposium on Gas Flow and Chemical Lasers (GCL) was held in Jerusalem, Israel, on September 8-12, 1986. The charm and beauty of Jerusalem and the unique blending of ancient and modern made this Symposium an enjoyable experience for the 165 participants and the accompanying persons. Yet, it seems that the invited and contributed papers presented at the Symposium were equally attractive so that most of the participants attended most sessions, resisting the temptations outside the session hall. Indeed, many speakers presented up-to-date results that were obtained, or cleared, just a few days before the Symposium. This volume is a compi lation of 19 invited and 61 contributed papers and of a panel discussion on the prospects for short wavelength chemical lasers held at the closing session of the Symposium. This discussion is presented as recorded in order to re tain the flavour of spontaneous presentation at the risk - or advantage - of presenting some venturous ideas, and the danger of misquoting. In editing the book, a deductive approach has been attempted. The book starts with some fundamental issues, namely fluid dynamics and optics, and then deals with the design, diagnostics, propagation and applications of various gas laser systems, covering the wavelength spectrum from XUV to infrared. Then follow recent developments of general interest to the laser community and the book concludes with an eye to the future, i.e., with a section on short wavelength chemical lasers.

This volume contains eight invited papers and seventy-three contributed papers presented at the Fourth International Symposium on Gas Flow and Chemical Lasers. which was held in Stresa. Italy. from September 13 to 17. 1984. The purpose of the Symposium was to record and discuss current research developments and applications related to high power lasers. Papers were solicited from the entire spectrum of activities, includ ing basic physics, aerothermodynamics, new laser media, laser design, diagnostic techniques, laser propagation. interaction phenom ena, applications. The Symposium was an opportunity for scientists and engineers representing all these disciplines to come together to report their recent work, to exchange ideas and to provide an up-to-date account of international progress in these fields. The contributed papers were reviewed by the members of the Scientific Advisory CoEmittee. who also took responsibility for formulating the program of invited lectures. As editor I wish to express my appreciation and my gratitude to people and organizations that made this Symposium a success: the Members of the Scientific Advisory Committee, the Members of the Local Organizing Committee, the Sponsors and the Symposium Secretary. A grateful acknowledgement is expressed to Dr. M. Sandra Oggiano for assistance in the organization of the Symposium and publication of these proceedings.

Optical science, engineering, and technology have grown rapidly in the last decade so that today optical engineering has emerged as an important discipline in its own right. This series is devoted to discussing topics in optical engineering at a level that will be useful to those working in the field or attempting to design systems that are based on optical techniques or that have significant optical subsystems.