Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Specification:
The lnventlon of the instant appllcation relates to the excita-
tlon of a high-energy laser b~ an arc-free or non-arcing capacito~
discharge. Such laser constructions have become known heretofore J
for example, from the ~ournal "Opto Electronics" 4 ~1972)~ pages
43 to 49 as well as from "Applied Physlcs Lett~rs!' Vol. 25,
No. 12 of December 15, 1974, pages 703 to 705 In these and
other ~isclosures, reference is made to the use of a low-induc- !
tance capacitor constructed ln the form of a strip line, the
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energy of whlch is transmitted to the electrodes of the discharge
chamber of the laser tube through fast-acting switches e.g. spark
gaps, in order to e~fect excitation of the laser gas. In this
type of laser excitation, at least two problems must be solved,
namely, that of storing maximal electric energy in the capacltor
and that of effecting homogeneous excitation of the laser gas at
predetermined electric field intensities, while avoiding arcing
between the excitation electrodes in the la~er tube. For the
first problem or requirement, a limit to the maximal stored
electric energy is fixed by the capacitance of the strip line
which, for the de~ices described in the aforementioned disclosure
and for a discharge channel 1 m long, is between about 0.01 ~F
and 0.1 ~F, which is a limit that would have to be exceeded con-
siderably for a high-energy laser. To master the second problem
a special form of a strip-line capacitor as well as a special
construction of the discharge surface as a multiplicity of paral-
lel knife edgeq have been proposed heretofore. Xowever, electrod
surfaces of such construction are not suited to withstand con-
tinuous operation, so that the need has arlsen to solve the a~ore
stated problems in another more successful manner.
It is accordingly an ob~ect of the invention to provide a high-
energy laser of the foregoing type which solves the foregoing
two problems while avoiding the aforementioned disadvantages of
the heretofore known devices of this general type.
With the foregoing and other ob~ects in vlew, there is provided,
in accordance with the invention, an high-energy laser excitable
by an arc-free capacitor discharge comprislng a power capacitor
with minimal self-inductance formed o~ a stack of metal layers
mutually superimposed perpendicularly to a given axis~ with re-
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spective layers of insulation disposed between mutually adjacentmetal layers of the stack, the metal layers and the insulation
layers being formed with mutually aligned cut-outs in vicinity
of the given axis so as to form a free space within the stack,
respective surface portions of alternating layers of the metal
layers projecting into the free space above one another as
electrodes of given common polarity, the surface portions of the
metal layers of respective opposite common polarity being
disposed symmetrically with respect to the given axis in the
free space; and a laser tube formed with a discharge chamber
and having discharge electrodes, the laser tube being disposed
in the free space of the power capacitor, the electrodes of
given common polarity of the power capacitor being connected
to the discharge chamber of the laser tube.
Reference can be had to my copending application
Serial No. 284,168, filed August 5, 1977 and entitled POWER
CAPACITOR, for further details of a power capacitor that may be
employed in the high-energy laser of this application.
In accordance with another feature of the invention,
the discharge electrodes of the laser tube are spaced from at
least the electrodes of one common polarity of the power
capacitor, the space therebetween being formed as a switching
spark gap, a stripline capacitor with a fast-acting switch
being connected to the switching spark gap.
In accordance with a further feature of the invention,
the discharge electrodes of the laser tube at least partly
define respective chambers for the switching spark gap within
the laser tube.
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In accordance with a concomitant feature of the invention, the
high-energy laser include~ an ignitlon electrode extending over
the entire length of the laser tube and disposed parallel to
the dlscharge electrodes of the laser tube within the free space
formed in the power capacitor, a stripllne capacltor wlth a
fast-acting switch being connected to the ignition electrode for
applying a different potential thereto than at the discharge
electrode~.
Thus, the capacltor electrodes are connected elther dlrectly or
lndirectly to the discharge chamber of the laser tube, and the
connection between the capacitor electrodes and the discharge
electrodes of the laser tube 19 accordlngly effected with ex-
tremely low lnductance, which is true also for the swltchlng
spark gaps that are ~patlally or physlcally combined wlth this
system.
Other features whlch are consldered as characteristic for the ln-
vention are set forth ln the appended claims~
Although the inventlon ls illustrated and described hereln as em-
bodied in an high-energy laser, it is nevertheless not intended
to be limited to the details shown, since various modification3
and structural changes may be made therein without departing
from the spirit o~ the invention and within the scope and range
of equivalents of the claims. .
The constructlon and method of operation of the lnvention~
however, together with additional obJects and advantages thereof
will be best understood from the following description of
specific embodiments when read in connection with the accompanyir
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draw rgs, ln which: j
FIG. 1 ls a diagrammatlc ~ectional view of a capacitor utilizable
for exciting a high-ener~y la~er in accordance with the inven-
tlon; and
FIGS. 2, 3 and 4 are similar perspective views o~ three dlfferent
embodiments of a hlgh-energy laser in con~unction with a power
capacitor according to FIG. 1.
In FIGS. 2, 3 and 4, the connecting lines ror the laser meaium as
well as for the switching spark gaps have been omitted in the
interest of clarity, as have been the cooling devices which are
necessary for such high-power operation. In the figures~ like
features are identified by the same reference numerals.
The general external form of thepower capacitor 1 may be seen
from FIGS. 2 to 4, and the internal construction thereof fro~
FIG. 1, which corresponds to a cross sectional view of FIG~ 2
taken along the line I-I and rotated through 90~ It is con-
structed of metal layers or electrodes 2 and 4 which are stacked
one above the other, with interposed lnsulating discs 6, perpen~
dicularly to the laser axis, which is shown as a vertical, central
dash-dot line. These layers or electrodes 2, 4 are cut out in
the form shown in the other figures, 80 that a free space 7 ls
obtained. Into the latter space 7, there pro~ect, on the one
side, surface portions 3 of the capacitor layers or electrodes 2,
and on the other side, surface portions 5 of the capacitor layers
or electrodes 4. These pro~ecting surface portions 3 and 5 are
conne-cted by bridges 23 and 45, respectively. A charging voltage
s~urce or lead, namely, in the case at hand, a laser tube 8 wlth
discharge electrodes, ls connected to the brldges 23 and 45 per
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se can, in turn, constitute the discharge electrodes for the laser
tube 8, so that a feed line for the capacitor energy thereby be-
comes unnecessary and, moreover, the energy stored in the capacito 7
layers 2, 4 reaches the discharge electrode~ for the laser tube 8
with uniform distribution.
In order to provide some idea of the capacities which are possible
with such a capacitor construction, following is a description of
an embodiment thereof with appropriate numerical data. Wlth
generally clrcular layers or electrodes 2 and 4 hav1ng an outside
radius of 0.5 m and with a free space 7 having a radius of 0.15 m,
as well as with insulating layers 6 having a respective thickness
of 1 mm, a total area of about 530 m and, thus, a capacltance of
14 ~F per meter is obtained for a capacltor length of 1 meter.
Wlth a charging voltage of 50 kV, such a capacitor can store
18,000 Joule of energy. Increasing the outer radius to 1 m would
increase the capacitance per meter length to about 62 ~F and the
energy content at 50 kV to ~ust 80 x 103 Joule. It can be seen
from the numerical data of this embodiment that the use of this
type of capacitor construction permits very high output energies
with suitable laser media, which, however, are not the sub~ect of
this invention.
FIG. 2 shows the simplest embodiment of a high-power laser con-
structed in accordance with the invention~ The laser tube 8 is
builk into the free space 7 of the capacitor 1 in such a manner
that the surface portions 3 and 5 of the capacitor 1 pro~ect into
the interior of this space 7. A connecting bridge over these sur-
face portions 3 and 5 is unnecessar~; the connections between the
electrodes or layers 2, 4 of the same polarity required for the
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charglng proce~s can be applled to the outer surface o~ the capa-
citor 1 ln a non-illustrated manner. For exact control of the
electrodes 31 and 51 which are constructed in comb-like ~ashion
therebetween, it is advantageous to keep the charging voltage of
the capacitor l lower than the breakdown voltage of the discharge
space in the laser tube 8 and to provlde, as mean~ for trlggering
the discharge, an ignitlon electrode 84 which i5 ~astened to the
wall of the laser tube 8 ln the vicinity of the one electrode 51
As shown schematlcally, a supplemental high-voltage source 96 is
provided for triggering the discharge o~ the capacitor l; this
source 96 ls connected at the one pole thereof to the electrode
comb 31 and with the other pole thereo~, through the ~ast-acting
switch 95, to the ignition electrode 84~ If this switch 95 i~
actuated, a corona discharge develop~ at the ignltlon electrode
84, whlch distributes the charge carriers into the dlscharge
space and effects ionization thereo~ through ultraviolet radiatior
so that an extremely rapid and simultaneou~ arc-free discharge a~
the energy stored in the capacitor l thereby oocurs.
Another possible construction of the high-power laser is dia-
grammatlcally shown in FIG. 3. The laser tube 8 is agaln disposed
between the electrodes 45 and 23 of the capacltor l; these elec-
trodes 45 and 23 represent connectlng bridges of the respective
sur~ace portions 5 and 3 of the capacitor layers 2> 4 and pro~ect
into the interlor of the laser tube 8~ The space of this tube 8
is subdlvided by auxlliary electrode~ 82 and 83 into three super-
imposed chambers 85, 86 and 87. To the auxiliary electrode 87 as
well as to the capacitor electrode 45, there is then connected a
stripline capacitor 9 whlch is formed o~ conduct~ve layers 91 and
92 and an lnsulating layer 94 disposed therebetween. Between thes
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two conductive layers 91 and 92, a ~ast-acting switch e.g. a
thyratron 93, is connected for trlggering the laser 8. This em-
bodiment of the lnvention functions as follows. A laser medium,
for example, the gas which is to be excited by the capacitor dis-
charge and which has a breakdown voltage that is below the charg-
ing voltage of the capacitor 1, is found ln the chamber 86. Be-
~ore the discharge is triggered, the potential difference o~ the
electrodes 82 and 83 is below the breakdown voltage of the en-
closed gas. The chambers 85 and 87 respectively above and below
the laser space 86 proper are llkewise filled with gas andS with
suitable choice of the gas, the pressure thereof and the spacing
of the electrodes, no voltage breakdown occur~ there either~
These chambers may also be constructed, however, as vacuum spark
gaps.
The elctrode 83 is connected to the stripline conductive layer 92
and the other conductive layer 91 to the electrode 45 of the
capacitor.
For triggering the discharge of the capacitor 1, the switeh 93
e.g. a thyratron, is short-circuited. A pQtential is thereby
developed at the electrode 83, which causes the voltage break-
down to the electrode 23 and places the electrode 83 at the
potential of the capacitor electrode 23. The breakdown field-
intensity between the auxiliary electrodes 83 and 82 is thereby
exceeded, however, as well as the breakdown field-intensity be-
tween the electrodes 82 and 45, so that the fast, homogeneous
discharge of the capacitor is thereby initiated.
A further possible construction of such a high-power laser is
shown in FIG. 4. If one were to refer to the embodiment con- ¦ -
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structed in accordance with FIG. 3 as a three-chamber system,
then the sy~tem according to FIG. 4 represents a two-chamber
system. The lower chamber 8g is the laser space proper, and the
upper chamber 88 i~ the switching spark gap, similar to the spaces~
87 and 85 in the embodiment of FIG. 3. Slmilarly to the embodi-
ment according to FIG. 2, an ignition electrode 84 is disposed
in the space 88 and connected to the conductive layer 91 of a
stripline capacltor 9. The other conductive layer 92 is elec-
trically connected to the capacitor electrode 23 which, in this
embodiment of FIG. 4, represents one la~er electrode. An aux-
iliary electrode 81 disposed between the chambers 88 and 89 is th
other laser electrode. The laser gas ls provided ln the dlscharg
chamber 89; the potential between this auxiliary electrode 81 and
the capacitor electrode 23 is below the breakdown voltage. Also~
the corresponding fleld inten~ity in the chamber 88 ls insufficle t
to lnitiate or introduce an lndependent gas dlscharge therein~
If the switch 93 of the stripline capacitor 9 is then closed, the
potential at the ignition electrode 84 is changed so that a coron
discharge to the electrode 45 is instituted immedlateiy, which
allows the voltage of this electrode 84 to break through to the
auxiliary electrode 81. m us, the full voltage o~ the capaci~or
is located between the auxiliary electrode 81 and the capacltor
electrode 23, so that there, too, the breakdown ~ield strength
or field intensity is exceeded, and the discharge and, according-
ly, the excitation of the laser medium, result therefrom.
Supplementing this discussion, it should be mentioned that it is
advantageous to charge the capacitor 1 to +25 k~ if a charging
voltage of 50 kV is desired, since this simplifies the insulatlon
problems with respect to the environment. The gas charge of the .
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switching spark gap~ may contain an additive conslsting of an
electronegative ~as such as SF6, for example. The physical or
spatial combination of a laser with such a capacitor results in
an almost absolutely uniform supply of the energy over the entire
length of the discharge electrode, so that the arcing between the
electrodes, which is otherwlse initiated by irregularitles of the
current supply and, consequently, also of the voltage develop-
ment, is thereby avolded.
Other embodiments of the invention are, of course, also con-
ceivable, but the ones shown and described herein should be
sufficient to illustrate adequately the operation of a high~
power laser that is made pos~ible by such a power capacitor 1.
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