Laser Interaction and Related Plasma Phenomena: Volume 2 Proceedings of the Second Workshop, held at Rensselaer Polytechnic Institute, Hartford Graduate Center, Hartford, Connecticut, August 30–September 3, 1971

573 Pages·1972·18.984 MB·English

by  A. Jacques Beaulieu (auth.), Helmut J. Schwarz, Heinrich Hora (eds.)

Laser Interaction
and Related Plasma Phenomena
Volume 2
Laser Interaction
and Related Plasma Phenomena
Volume2
Proceedings of the Second Workshop, held at Rensselaer Polytechnic
Institute, Hartford Graduate Center, Hartford, Connecticut, August 3D
September 3, 1971
Edited by
Helmut J. Schwarz
Professor of Physics
Rensselaer Polytechnic Institute
and
Heinrich Hora
Adjunct Associate Professor of Physics
Rensselaer Polytechnic Institute
and
Max-Pianck-lnstitut fiir Plasmaphysik
Garching, Germany
~
Springer Science+Business Media, LLC • 1972
ADVISORY BOARD
N. G. BASOV J. M. DAWSON
P. N. Lebedev Physical Princeton University
Institute of the Academy
A. H. GUENTHER
of Sciences of the USSR
Kirtland Air Force Base
N. BLOEMBERGEN P. HARTECK
Harvard University Rensselaer Polytechnic Institute
ISBN 978-1-4684-7740-5 ISBN 978-1-4684-7738-2 (eBook)
DOI 10.1007/978-1-4684-7738-2
Library of Congress Catalog Card Number 79-135851
© 1972 Springer Science+Business Media New York
Originally published by Plenum Press, New York in 1972
Softcover reprint of the hardcover 1st edition 1972
All rights reserved
No part of this publication may be reproduced in any form without
written permission from the publisher
FOREWORD
Paul Harteck
Rensselaer Polytechnic Institute
Troy, New York
When the Maser and the Laser Were discovered, people were
speculating if this was the beginning of a new page, or even a new
chapter, in the Book of Physics. The Second Workshop on "Laser
Interaction and Related Plasma Phenomena" held in Hartford made it
clear that the perspective had changed, that people now question
if the consequences of these discoveries constitute a new chapter,
or possibly a new era in Physics.
While the papers presented were all stimulating and of out
standing quality, of special interest were the experiments which
demonstrated that triggering of thermonuclear fusion by Laser
techniques is indeed in the realm of the possible. Along these
lines, I enjoy recalling an anecdote concerning the late F. G.
Houtermans. I think that all who knew him will agree that he was
an unusual genius and at the same time a very amusing colleague.
He had, in fact, decades ago considered the possibility of Laser
type effects. Unfortunately, his experimental efforts ended with
the destruction of the transformers of his Institute. It hap
pened - so goes the anecdote - that a few years ago, there was a
meeting where the possibilities of thermonuclear fusion were dis
cussed. After the meeting a newspaper correspondent asked
Houtermans if he thought it would some day be possible to use
thermonuclear fusion for energy production. Houtermans answered
that he did not really understand this question because old
Jehovah had shown that thermonuclear fusion works. The curious
newspape rman asked: "Where is the laboratory of Professor Jehovah
and how long has he been performing this experiment?" Houtermans
answered that he thought the title Professor was not quite ade
quate, that the laboratory is the entire universe, and that these
experiments had been in progress for billions of years!
v
vi FOREWORD
You are all familiar with the brilliant names in Physics which
are connected with the discovery of the Maser and the Laser. In
recent years we have learned that old Jehovah's name must certainly
stand at the head of the list. Laser or, more precisely, Maser sig
nals have been found emanating from certain distant cosmic areas,
carrying messages concerning molecular makeup, temperature, and den
sity across many light-years of space.
Our knowledge of Laser phenomena is indeed increasing and
speculation on the future may be boundless. It appears that the
"Laser Conference" in Hartford will be a continuing series for some
time to come.
PREFACE
The First Workshop on "Laser Interaction and Related Plasma
Phenomena" held at Rensselaer Polytechnic Institute, Hartford Grad
uate Center, in 1969, brought out the complexity of the results ob
tained by different and differing theoretical and experimental
groups. The Second Workshop in 1971 corroborated this complexity
as more and more unexpected observations were reported indicating
the possible existence of non-equilibrium and non-linear plasma
properties. Tremendous advances were made in the interval between
the First and Second Workshops in the research of plasmas produced
by laser irradiation as well as in the development of very high
power lasers.
This significant progress was indicated by the increased num
ber of highly qualified scientists participating in the Second Work
shop. Their lectures and discussions provided up-to-date knowledge
and stimulated further fundamental research, development of new
techniques, and possible industrial applications.
As in the First Workshop, many of the presentations gave valu
able fundamental insights for those starting in the field, while at
the same time bringing into focus very advanced material. In addi
tion to the invited lectures, attendees were given the opportunity
to present short papers on their own research, and several of their
contributions are included in these Proceedings.
As suggested by C. G. Young in his Review of the Proceedings of
the First Workshop ("Laser Focus", June 1971, p. 45), the editors
have attempted to include some of the discussions of the presenta
tions (for example, nuclear fusion plasmas), although these comments
may not reflect the exact view of the participants involved.
The first chapter contains results of the development of high
intensity lasers. Although at this time, one cannot tell in what
direction the research will go, the major results of experts in the
field were presented which indicated what one might expect from
future developments for plasma applications. Beaulieu, the pioneer
in C02-TEA-lasers reports on his present work and future plans, while
vii
viii PREFACE
DeMaria reviews the electric discharge lasers in more general terms.
Vlases presents many details of gasdynamic lasers. Miley reports
on how electrons and other particles of about MeV-energies originat
ing from nuclear radiation influenced the discharge of CO2 lasers.
Chemical lasers are reviewed by Bronfin; Hohla and Kompa supplement
this review with special results on a chemical low-cost 5-Joule
lO-nsec laser system. The most advanced neodymium glass laser sys
tem is described in a presentation by Basov, Krokhin and Sklizkov,
which is included in their paper in Chapter VI. From this system,
the next major results in laser produced fusion plasmas can be ex
pected. Gerstmayr, Harteck and Reeves describe the techniques of
multiphoton absorption in gases, which are important for many gas
lasers.
The second chapter is devoted to laser produced gas breakdown.
Our First Workshop did not deal in depth with the complex problems
of this field. However, due to the advances made, more detailed
information could be presented at the Second Workshop. Papoular
gives some unexpected experimental results. Although the question
of the "first electron" is still not answered, possible directions
for the solution of this problem are indicated. Guenther's and
Pendleton's contribution reveals many detailed measurements of laser
produced gas breakdown. Hull, Lencioni and Marquet report measure
ments for the decrease of the breakdown threshold by a C02-TEA-
laser focused in air, when NaCl dust particles of known size are
present. Bradley discusses switching of megavolt with subnanosecond
jitter applying laser produced gas breakdown. Hereby he develops a
new technique of studying the streamer processes. Alcock's ad
vanced diagnostic techniques for measuring the self-focusing in laser
produced gas breakdown shows numerous details of the self-focusing
filament, its inner hole in electron density, time behavior, and
dependence on the molecular state of the gas. Further observations
on self-focusing and gas breakdown are given by Tomlinson.
In the third chapter, plasma diagnostics and special interac
tion processes are considered. The scattering of laser radiation,
first successfully measured by FUnfer, Kronast and Kunze in 1963,
is a very important method for the diagnosis of plasmas of medium
density. Now, Kronast gives a report on recent developments in
this area, especially dealing with the micro-state of the plasma.
Experimental and new theoretical results of scattering of laser pho
tons by free electrons in vacuum (Kapitza-Dirac Effect) and in solids
(Quantum Mechanical Modulation) are reported by Schwarz. Probe
measurements in the diagnosis of plasmas produced by laser irradia
tion of solid targets in vacuum are sometimes difficult to interpret.
This leads to a presentation by Segall on the treatment of cylindri
cal Langmuir probes. Yablonovich gives results on his research of
C02 laser produced breakdown in alkali-halides. BUchl's contribu
tion deals with an advanced study of the plasma created by COLTEA
laser pulses from solid hydrogen. Siller, BUchl and Hora discuss
PREFACE ix
latest theoretical aspects of the anomalously high electron emis
sion from laser produced plasmas.
The fourth chapter deals with the interaction of laser produced
plasmas with gases and magnetic fields. Stamper, Dean and McLean
discuss unexpected interactions of laser produced plasmas with back
ground gas and the creation of magnetic fields within plasmas that
expand into the field free space. Vlases' paper in Chapter I also
touches the question of heating magnetically confined thermonuclear
plasmas of medium density by intense CO2 lasers. He also indicates
that the Lawson criterion of thermonuclear fusion by magnetic con
finement of a laser produced plasma might be reached by injecting a
neutral beam. Haught elaborates on this concept. Bhadra theorizes
on the behavior of a laser heated plasma in a magnetic field.
Schwarz reports measurements of the increase of ion energies in
laser produced plasmas due to magnetic fields, and Hora interprets
these results with his nonlinear theory of ponderomotive forces.
The fifth chapter covers the theory of high intensity laser
interaction with plasmas. The gasdynamic or thermokinetic theory
as discussed in the First Workshop and supplemented in the meantime
by a paper of R. G. Rehm (Phys. Fluids 13, 921 (1970) seems to have
been substantiated. Therefore, the main interest in this Workshop
was directed towards instabilities and nonlinear effects. Dawson
and coworkers were among the first in this specific field of laser
produced plasmas. A review of the present status is given in the
paper by Kruer and Dawson. Godwin comments by presenting a classi
cal mechanism of anomalous absorption. Hora reviews his concepts of
nonlinear forces by bringing his previous contribution in the First
Workshop up-to-date. Palmer reports on stimulated scattering and
self-focusing processes in dense plasmas. New results of numerical
dynamic treatments with the nonlinear ponderomotive force are given
by Green and Mulser.
The sixth chapter focuses on the possibility of achieving nu
clear fusion with laser irradiated high density plasmas. Included
in the Second Workshop were all groups that had reported fusion
neutrons up to August 1971. The first fusion neutrons were detected
from LiD targets irradiated by 10 psec laser pulses (Basov et a1
1968). Basov, Krokhin and Sk1izkov now report longer laser pulses
(in the order of 1 nsec) which led to up to 105 neutrons per pulse.
Immediately after our First Workshop (see Appendix of Floux' presen
tation, Proceedings of First Workshop), Floux et al applied this
technique successfully for the first time and measured an increase
of the neutron production higher by orders of magnitude in relation
to the first psec pulses. Floux, Bernard, Cognard and Saleres give
an extensive description of their measurements performed under vary
ing conditions. Lubin's work on laser produced neutrons concentrates
on laser pulses of a little less than one nsec duration applying
tailored prepulses; he justifies his techniques in a theoretical
x PREFACE
analysis. Jones, Gobeli and Olsen contribute w~th measur~ents re~
lated to carefully generated laser ~ulses selected from ~repulses,
which indicate the problems involved in such techniques. Yamanaka
points out new aspects of neutron production using high power neo
dymium glass lasers. In an Appendix to his paper, there is a valu
able investigation of the damages occurring in glass lasers used for
such high power applications. BUchl, Eidmann, Mulser, Salzmann, and
Sigel report on refined diagnostic techniques of glass laser pro
duced plasmas for the detection of neutrons, x-rays, and reflectivity
properties. Hora and Pfirsch contribute with numerical treatments
on the fusion gain of laser produced plasmas. Finally, Shatas gives
calculations on laser assisted dense plasma focus whereby fusion
neutrons and soft x-rays are generated.
The success of the Second Laser Workshop was mainly due to the
high caliber of the lecturers and participants, who also enthusi
astically contributed to the discussions. At the writing of this
Preface, there are indications that one of the main objectives,
namely to initiate and stimulate further work, has been accomplished.
The organizers (the editors) gratefully acknowledge not only the ex
cellent presentations of the invited speakers but also those who
contributed with short presentations.
We should like to thank the following Advisors of the Second
Workshop for their counsel: Professor N. G. Basov (P. N. Lebedev
Physical Institute, Moscow, USSR), Professor N. Bloembergen (Harvard
University), Professor John Dawson (Princeton University), Dr. A. H.
Guenther (Kirtland Air Force Base) and Professor P. Harteck
(Rensselaer Polytechnic Institute).
We are indebted to Rensselaer Polytechnic Institute of Connecticut
for partial financial support, and to Vice President Warren C.
Stoker, Dean Harry Kraus, and Director of Special Programs Preston T.
Reed.
We wish to acknowledge permission of the American Institute of
Physics, the IEEE, and the American Chemical Society to print figures
and texts as indicated by the references.
Again, as in the First Workshop, Mrs. Lucy Myshrall of Rensselaer
Polytechnic Institute, Hartford Graduate Center, was an invaluable
assistant in the organization of the Workshop and for the prepara
tion of these Proceedings. Her care and interest were an important
contribution to its success.
January 1972 Helmut Schwarz
Heinrich Hora