Note: Descriptions are shown in the official language in which they were submitted.
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FIELD OF THE INVENTION
The present invention relates to laser optics and in particular to
an optical system for combining laser beams.
BACKGROUND OF THE INVENTION
In isotope separation by isotopically selective photo-excitation of ~
one isotope in an environment of plural isotopes, as for example discussed in ~-
United States Patent 3,772,519 which issued to Levy and Janes in November
1972, lt is common to find a plurality of laser beams separately generated.
It is desired to combine these into a composite beam having components from
each of the separate laser beams. It is known that laser beams, or radiation
in general, of differing frequencies in separate beams may be combined onto a
single path having colinear superimposed beams composed of components of each
of the original beams by the use of dichroic elements. Additionally, it is
known as, for example, discussed in United States Patent 3,924,937 which is-
sued to George Sargent Janes on February 17, 1976, that a plurality of laser
beams of pulsed radiation having sequentially triggered pulses in each beam
may be combined using a system of rotating optics.
For high power applications, the losses inherent in dichroic ele-
ments, particularly when combining laser beams of closely spaced frequency,
2Q will reduce the efficiency, or power available in the combined beams. Simi-
larly, the use of rotating optics to provide beam combining in the case of
time sequenced, pulsed beams while feasible, presents an element of mechanical
complexity which it might be preferable to avoid.
BRIEF SUMMARY OF THE INVENTION
~n t~e present invention, an optical system o~ passive and station-
ary~elements is employed to combine the radiation from a plurality of spa-
ciall~ distinct beams so that a plurality of composite beams result. Each
composite beam contains colinear and superimposed beam components from each
of the original, distinct laser beams. The system can also provide power
3Q splitting of the energy in the distinct beams into the equal components in
each of the composite beams so that each component in a single composite beam -~ -
can represent the same percentage of the energy in the original input beam.
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.
Apparatus for combining the distinct input beams of laser radiation
according to the present invention comprises an array of beam splitter ele-
ments. Each beam splitter element receives an input laser beam which may be
an original, uncombined beam or a beam already possessing components from
several beams, and receives this radiation on opposite surfaces at the same
location of the beam splitter. Each beam of input radiation will be partially
transmitted and partially reflected such that the output beams will include
components of each input beam, each component typically representing half of
the energy in each input beam. The process may be repeated with other beam -
1~ splitter elements to combine a greater number of input beams into a corres-
ponding number of output beams each having components from all of the input
beams.
According to one broad aspect of the present invention, there is :
provided a system for combining laser beams of diverse frequencies into a
plurality of beams, each comprising laser radiation having components of each
of said diverse frequencies, said system comprising: a plurality, greater
than two, of sources of laser radiation including at least first and second
source sets; said plurality of sources of laser radiation providing respective
,
input beams of laser radiation of different frequencies; a first plurality of
2a beam splitting elements positioned to receive on one surface of each radiation
input beams from said first source set and to receive on the second surface
of each the radiation input beams from said second source set; said first
plurality of beam splitting elements providing a plurality of sets of composite
beams of ratiation comprising: _a first set of composite beams including a
fraction of the radiation from said first source set superimposed on a frac-
tion of the radiation from said second source set; and a second set of com-
po~ite ~eams oomprising a fraction of the radiation in said first source set
.i~ ~ ..
superimposed on a fraction of the radiation in said second source set; a
~ further plurality of beam splitting elements responsive to the plurality of -
.
3~ ~ets of composite beams for providing a set of output beams, each beam thereof ~
fiaving a raction of the radiation in each o~ the input beams from said first ~-
,
and ~econd set~ of sources.
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According to another broad aspect of the present invention, there
is provided a system for combining a multiplicity of beams of laser radiation
of diverse frequencies to provide a multiplicity of output beams of laser
radiation, each beam including a componen~ beam from each of said plurality
of beams of diverse frequencies, said system comprising a multiplicity of
beams of laser radiation of diverse frequencies; and a plurality of beam
splitter elements which include: a first plurality of beam splitters each
received on different surfaces thereof respective laser radiation from said :
multiplicity of beams and providing a set of output beams, the output beams
from each beam splitter including in combination all of the frequencies of
laser radiation applied to the surfaces thereof; and a further plurality of
further beam splitters each positioned to receive different laser radiation
of combined frequencies from a plurality of beam splitters other than said
further plurality of beam splitter elements on respective surfaces thereof
and to provide a further set of output beams of laser radiation each of the
further set of output beams of laser radiation including laser radiation of
each frequency in said multiplicity of beams.
According to a further broad aspect of the present invention, there
i`s provided a static system for combining laser beams from a plurality of
20 sources of laser radiation comprising: a plurality, greater than two, of
sources of laser radiation each providing a spacially distinct input beam of
laser radiation; a first plurality of beam splitting elements each receiving
on first and second surfaces thereof laser radiation in input beams from
; corresponding ones of the plurality of laser radiation sources to provide
plural respective composite beams therefrom with the composite beams being . ~::
physically distinct and each containing radiation from different combinations
each less than all of said plurality of sources of laser radiation whereby
said composite beams contain substantially all of the energy in said input
beams; a further plurality of beam splitting elements responsive to different ~
3Q com~inations of the composite beams from said first plurality of elements for :
di~ecting separate fractions of the radiation in each input beam along separate
patbs defining output beams thereby providing in each output beam a portion of
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the radiation in each of said plurality of input beams.
The invention will now be described in greater detail with reference
to the accompanying dra~ing, in which:
Figure 1 is a diagram of a prior art technique for combining laser
beams;
Figure 2 is a pictorial view of the technique of the present inven-
tion for combining two laser beams; and
Figure 3 is a diagram of an array according to the present invention
for combining a greater number of laser beams.
The present invention contemplates a system of one or more passive,
stationary beam splitting elements for combining the radiation on a plurality
of separate, spacially distinct laser beams into combined beams each having
components of all of the input laser beams. The use of beam splitters in
accordance with the teaching of the present invention permits the realization
of a high efficiency beam combining system, particularly for combining beams
o~ dlfferent, but onl~ slightly different frequencies. The present invention
avoits the losses inherent in the use of dichroic elements for the combination
of beams as, for example, shown in another technique in Figure 1, or the addi-
tional elements required with rotating optics.
According to a technique which might be employed to combine beams
of laser radiation illustrated in Figure 1, a set of dichroic elements 12, 14
and 16 ma~ be employed to combine four beams 18, 20, 22 and 24 of laser radi-
ation, each having the same power level P ~or different power levels as de-
sired) at distinct frequencies, Fl, F2, F3 and F4. Mirrors 26, 28 and 30 are -
shown in use to direct radiation for proper application to each of the di-
chroic elements 12, 14 and 16. There results from the system of combining
optics, a composite beam 32 combining the components of all of the input beams
18, 20, 22 and 24.
For isotope separation, particularly uranium enrichment, according
3a to the technique shown in the above referenced Patent 3,772,519, it may then
be desired to divide the power in the beam 32 into separate beams having
identical spectral content but sharing the power in the beam 32 in order to
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excite various portions of the uranium vapor simultaneously. A set of beam
splitters 34, 36 and 38 are employed with reflecting mirrors 40 and 42 to
split the beam onto four separate beams 44, 46, 48 and 50, each having com-
ponents at the frequencies Fl, F2, F3 and F4 and one quarter of the power at
each frequency as in the input beams 18J 20, 22 and 24.
In addition to the use of a large number of optical elements for
the beam combining and splitting system of Figure 1J all of which require
precise and stable optical alignmentJ the use of dichroic elements 12J 14
and 16 introduces a significant loss inherent in the dielectric layers parti-
cularly where the frequencies F1J F2J F3 and F4 are closely spaced as may be
the case where the laser beams are employed in isotope separation.
The same results of combined and power split radiation may be
achieved more simply and with less potential energy loss in the incident laser
beams using a beam splitter concept as illustrated basically in Figure 2. As
shown there, a beam splitter 52 which is typically 50% reflecting and 50%
transmitting and typically consisting of a multilayer dielectric element ~or
thin metal film element) is provided to receive radiation in input laser beams
54 and 56 on opposite surfaces. The fabrication of such a beam splitter is
~ell known in the art. The radiations in the beams 54 and 56 are of different
frequencies, Fl and F2, which may be selected for producing excitation of an
isotope between different energy states in a process of is~topically selective
ionization as described in the above-referenced Patent 3J772J519. The powerJ
P, in each beam is typically the sameJ but need not be so. The radiation in ~ -
the beam 54 having a powerJ P, is divided between an output beam 58 contain-
ing one half of the power, P, and an output beam 60 containing the other half
of the power, P, in the beam 54. The beam 58 will also contain a component of
transmitted energy from the input beam 56 and the output beam 60 will contain
a component of reflected radiation from the input beam 56, each at a power
level of one half P.
3Q The two output beams 58 and 60 will each rontain equal components
cf' the rad~ation in the input beams 54 and 56, typically half the power in
each input beam. Each component in the output beams 58 and 60 will be com-
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pletely ~uperimposed upon and colinear with the other beam and only slightly
displaced therefrom due to the dispersive properties of the beam splitter 52.
A beam splitter array for combining and power splitting a multipli-
city of input beams as might be used in isotope separation is more completely
illustrated in Figure 3. As shown there, the array consists of four beam
splitter elements 62, 64, 66 and 68 positioned to combine the output radiation
of four lasers 70, 72, 74 and 76, each of different frequencies, Fl, F2, F3
and F4. While shown for use with four lasers, the array of Figure 3 may be
employed with a lesser number, such as three, as desired.
The radiation from the lasers 70 and 72 is applied to opposite sur-
faces of the beam splitter 62 as input beams 78 and 80. The resulting output
beams 82 and 84 each have component beams at the frequencies Fl and F2 at
half the power level, P, of the original input beams 78 and 80. Similarly,
the radiation from the lasers 74 and 76 are applied as input beams 86 and 88 ~1
to opposite surfaces of the beam splitter 66 to provide resultant output beams
90 and 92. The beams 82 and 92 are directed toward beam splitter 68 on op- -
posite ~urfaces for combining into beams 94 and 96. Beams 84 and 90 are di-
rected toward beam splitter 64 on opposite surfaces for combining into output
beams 98 and 100.
Each of the four output beams 94, 96, 98, 100 contains a quarter of
th~ power of each input beam 78, 80, 86, 88 and thus is a composite beam con-
taining each of the colors or frequencies generated by the lassers 70, 72, 74,
76. No elements except four beam splitters are required for this exemplary
system and these may be made to operate with very low losses~
~ The four output beams 94, 96, 98 and 100 are then advantageously
l applied through parallel enrichment channels 102, 104, 106, 108 respectively
~hich may be spaced regions of a uranium isotope separation chamber or separate
chambers as shown in the above mentioned United States patents.
It is intended that extensions and modifications of this preferred
3Q embodiment be within the scope of the invention, the foregoing description be-
i~ ing only exemplary. Accordingly, the area of invention is to be limited only
as defined in the following claims and their equivalents.
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