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Патент USA US3064211

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Nov. 13, 1962
R. w. DAMON
3,064,201
PRESSURE TUNED THREE-LEVEL PARAMAGNETIC MASER
Filed March 19, 1958
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In van 1.‘: 02-.
F?/'char-ol W Damon,
His Attorney.
United grates
3,664,201
Patented Nov. 13, 1962
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In these maser systems, signals having only a narrow
range of frequencies can be ampli?ed because if the
external direct magnetic ?eld is changed in order to alter
3,064,201
PRESSURE TUNED TI-IREE-LEVEL PARA
MAGNETHC MASER
Richard W. Damon, Schenectady, N.Y., assignor to Gen
the energy levels and thus the frequency that can be am~
eral Electric Company, a corporation of New York
pli?ed, this ?eld varies from the magnitude of the internal
magnetic ?eld produced by the orbit distortions. The
Filed Mar. 19, 1958, Ser. No. 722,556
6 Claims. (Cl. 330-4)
result is an adverse effect upon the transitions of the elec
tron spins between energy'levels and consequently a de
crease in ampli?cation. Thus, before amplifying a signal
The present invention relates to a three-level para
magnetic maser for amplifying microwave signals.
An ampli?er has been recently developed in which the 10 of a certain frequency one must ?nd a paramagnetic ma
terial having an internal ?eld comparable to the applied
properties of paramagnetic materials are utilized. It is
magnetic ?eld for this frequency. Obviously, it would be
called a “maser,” which is an acronym derived from the
advantageous if the system were adjustable so that many
principle of operation: microwave ampli?cation by stimu
frequencies could be ampli?ed through the utilization of
lated emission of radiation. The operation is based upon
electron spins, which produce an effect comparable to 15 a single paramagnetic crystal.
Accordingly, an object of the present invention is to
that obtained with a dipole magnet mounted on a gyro
provide an improved three-level maser system.
scope.
Another object of the present invention is to provide a
In the atoms of most materials the electron spins are
three-level maser system that can be adjusted to amplify
“paired” such that for every electron spinning in one
signals over a range of frequencies.
direction, another electron spins in the opposite direction.
A further object of the present invention is to provide
The magnetic dipole moments of each “pair” of electron
a three-level maser system having a high gain over a
spins cancel leaving no net magnetic effect. In certain
greater range of frequencies than prior three-level maser
solids, however, this pairing of electrons is incomplete
systems.
and elements in the crystal, usually ions, which are ?xed
These and other objects are achieved in one embodi
in location, can be found with unpaired electrons local 25
ment of my invention in which a crystal of paramagnetic
ized in them. When one of these ions-called paramag
material is subjected to an external pressure causing the‘
netic ions-is placed in a magnetic ?eld, it has an
internal crystal electric ?eld to have di?ierent magnitudes
orientational energy of a magnitude depending upon the
at the paramagnetic ions along the three principal axes.
angle between the magnetic dipole of the unpaired spins
The novel features that I believe are characteristic of
and the applied ?eld. When the dipoles are aligned with
my invention are set forth in the appended claims. My
the ?eld, the electrons have their lowest energy. They
invention itself, together with further objects and ad
have highest energy when the dipoles oppose the applied
vantages thereof may best be understood by reference
?eld. The separation between these energy levels is a
to the following description, taken in connection with the
function of the applied magnetic ?eld.
accompanying drawing, in which the single FIGURE
According to the quantum theory, an electron moving
illustrates a preferred maser ampli?er embodiment of
from a level of energy WH to a lower energy level of
my invention.
WL emits radiation of frequency f=(WH~ WL)/h, where
- In the ?gure those circuit elements which may in them
maser ampli?es are approximately the same as the fre 49 selves be entirely conventional and whose details form
no part of the present invention have been indicated in
quency associated with two energy levels of the maser
in h is Planck’s constant. The signal frequencies that a
paramagnetic material.
a simpli?ed block form with appropriate legends. I have
illustrated a signal source 11 of the signals to be ampli
ed, which source may be, for example, a radar‘ antenna
_
In three-level masers, the ampli?cation process is re
lated to three energy levels, two of which produce am
receiving echo signals from an object in space. The sig
pli?cation while the third supplies energy to the system.
The orientational energies of the spins must be capable
nals from source 11 are guided by a wave guide 13, a cir
culator 15, and another wave guide 17 to a cavity resona
of being changed directly from the lowest energy level
tor 18 formed by irises 19. In the bottom of cavity
of these three levels to the highest level Without assum
resonator 18 a crystal of maser material 20, which has at
ing the value of the intermediate level. Most maser ma
least two unpaired electrons per paramagnetic ion, is re
terials do not have this property but must be specially
operated to obtain it. In one three-level maser system, 50 tained within some insulating material 21 such as poly
styrene. Crystal 29 which preferably in an insulator so
transitions from the lowest energy level to the highest are
that microwaves will penetrate it deeply and which pref
obtained directly through use of an applied direct mag
erably has zero nuclear magnetic moment, can be formed
netic ?eld which interacts with the electric ?eld created
from: gadolinium ethyl sulfate diluted with lanthanum
ethyl sulfate, potassium chromicyanide diluted with po
tassium cobalticyanide, nickel silico?uoride diluted with
by the ions and atoms in the immediate vicinity of the.
paramagnetic ions.
If the ions and the atoms immediately surrounding each
paramagneticion produce a symmetrical electric ?eld,
zinc silico?uroide or some other suitable paramagnetic
material. At a side of cavity resonator 18 a threaded
the shapes of the orbits of the electrons around the para
screw 23‘ is positioned so that when turned it applies
magnetic nuclei are not aifected by the presence of these
pressure on the insulating material 21 which then distorts
ions and atoms. But asymmetrical ?elds cause the orbits 60 the
maser crystal 20.
of the electrons around the paramagnetic nuclei to be
Cavity
resonator 18 is Within a cryostat 25 containing
extended in the shapes of ellipses. The electrons mov
a low temperature coolant 27, such as liquid helium, for
ing in these elliptical orbits produce a magnetic ?eld
cooling crystal 2% to a few degrees above absolute zero.
affecting the dipole magnetic moment of the spinning elec
trons.
If a direct magnetic ?eld having a strength com
parable to the magnetic ?eld produced by this distortion
65
A Variable strength D.C. (direct current) magnet having
poles 29 and winding 31 submerges maser crystal 20 in a
direct magnetic ?eld, the magnitude of which can be con
trolled by a variable resistor 33 that controls the amount
of the current ?owing through winding 31 from a source
of the electron orbits is applied so that it has a compo
nent at right angles to the axis of the electric ?eld in the
material, transitions from the lowest energy level to the
highest energy level are possible to permit efficient am 70 of direct voltage 35. By adjusting this ?eld, a separation
in energy levels can be obtained within the paramagnetic
pli?cation.
>
crystal 20 such thatit ampli?es-the signal from source 11.
3,064,201
3
For ampli?cation, crystal 2r’! must be energized by
microwave energy at a frequency approximately equal to
W3—W1/l1, wherein W3 and W1 are the highest and
lowest energy levels respectively, of the three energy
signal that is to be ampli?ed, amaser crystal including
paramagnetic elements having at least two unpaired elec;
tron spins pcr element establishing at least ?rst, second
and third energy levels ‘in ascending order according to
Of course,
number, said crystal exhibiting interior electric and mag
the spacing of the energy levels, Viva-W1, depends on the
magnitude of the direct magnetic ?eld. In effect, crystal
20 “pumps” energy from the frequency of this microwave
energy to the frequency of the applied signal, thereby am~
netic ?elds, means for conducting said signal to said
levels utilized in the ampli?cation process.
maser crystal at a ?rst frequency corresponding to the
difference between the second and third levels, means
for applying a higher frequency pump signal to said
plifying the applied signal. For this reasonpthe micro 10 crystal corresponding to the energy difference between
?rst and third levels, mechanical means for phys
wave energy is called the “pump energy" and its source
ically compressing said crystal to a selectable degree, the
the “pump source.” In the ?gure the micro‘, 'ave energy,
compressing action distorting the crystal structure and
which is provided by a pump source 37, is guided by a
interior electric ?eld of said crystal which alters the mag
wave guide 39 to a directional coupler comprising a hole
netic ?eld interior to said crystal through altering the
41 in wave guide 17 and some absorbing material 43.
electron orbits of said paramagnetic elements, means for
The microwave energy passes through hole 41 to wave
submerging said crystal in a direct magnetic ?eld having
guide 17 and thence to cavity resonator 13.
a magnetic ?eld strength of the same order of magnitude
After ampli?cation, the signal re?ects out of cavity
as the magnetic ?eld interior to said crystal and having
resonator 18 up wave guide 17 to circulator 15, then to
a component perpendicular to the internal electric ?eld,
wave guide 45 which guides the signal to a utilization cir
and means for conducting the ampli?ed output signal
cuit 47 that, for example, in a radar application may be
from said crystal for utilization purposes.
an oscilloscope. A matched load 49 prevents energy
2. A three-level maser system comprising a- source of
from the utilization circuit 47 from reaching the signal
signal that is to be ampli?ed, a maser crystal including
source 11 from where some of it might be re?ected into
paramagnetic elements with at least four unpaired elec
wave guide 17.
trons per element, wherein each paramagnetic has at least
To understand the operation of my maser system the
three energy levels, W3, W2, and W1, wherein W2 is the
electrical ?elds in the maser material must again be con
intermediate energy level, mechanical means for phys
sidered. If the electrical ?elds at the paramagnetic ions
ically compressing said maser crystal acting to alter in
are different in magnitude along the three principal di
ternal crystal ?elds for permitting transitions between the
rections, or in other words if the ?elds are asymmetrical,
lowest energy level W1 to the highest energy level W3,
direct transitions from the lowest energy level to the
means for conducting the signal that is to be ampli?ed
highest energy level of the three energy levels are per
to said maser crystal, means for conducting a microwave
mitted. Preferably the asymmetry is such that the crystal
power signal to said crystal of a frequency approximately
?eld has a component of rhombic or lower symmetry.
Most crystals do not have a signi?cant crystal ?eld of
equal to W3—W1/h, wherein h is Planck’s constant, and
means for conducting the output of said maser crystal to
low symmetry in their natural form. However, I have
discovered that such a ?eld component can be induced
by applying to the crystal an external pressure that dis
torts the unit cell of the crystal such that the desired
transitions are permitted. This pressure not only permits
the desired transitions but for those cells containing para
magnetic ions with four or more unpaired spins per ion,
three energy levels are obtained between which transitions
are permitted even in the absence of a magnetic ?eld.
Consequently, the DC. magnet with poles 29 may be dis
pensed with. In such maser applications the energy level
spacing, which determines the frequency that the crystal
a utilization circuit.
3. A three-level maser system comprising maser ma
terial containing paramagnetic elements having at least
two unpaired electrons per element, said paramagnetic
elements therefore exhibiting at least three energy levels,
mechanical means for applying external physical pres
sure to said maser material for compressing the same
causing the maser material surrounding each paramag
netic element to produce asymmetrical internal electric
and magnetic ?elds at said element, means for applying
an external magnetic ?eld thereto of substantially equiv
alent strength to said internal magnetic ?eld at an angle
19 ampli?es, can be adjusted over a small range by pres
to the electric ?eld whereby transitions from the lowest
sure changes obtained by moving the screw 23.
If a direct magnetic ?eld is used, the magnetic ?eld 50 of said three energy levels to the highest energy levels
of three levels are permitted, means for subjecting said
produced by the distortion of the orbits of the electrons
around the paramagnetic ion nuclei can be adjusted by
maser material to an electromagnetic power signal at a
frequency corresponding to the difference in energy levels
changing the pressure on crystal 20 to a value suitable to
the applied magnetic ?eld. Consequently, the applied
of two of said three energy levels, and means for ab
magnetic ?eld can be adjusted to produce ampli?cation 55 stracting from said maser material electromagnetic energy
of signals with many different frequencies. The correct
having a frequency corresponding to a difference in energy
crystal distortion can be maintained for wide variations
levels of two or said three energy levels including the
in the magnitude of the applied magnetic ?eld and thus
highest energy level of said two energy levels and an
maximum ampli?cation obtained at many frequencies.
intermediate level.
4. The maser system as defined in claim 3 wherein
There are, of course, ways of applying pressure to the 60
maser crystal 19 other than by using a screw 23. For
said means for applying pressure is adjustable to produce
example, a more permanent technique is the encapsula
different amounts of external pressure on said maser ma
tion of the paramagnetic salt by immersion in a liquid in
terial whereby said maser system can be adjusted over
sulating material such as water, and also some glasses that
a wide range of frequencies of operation.
subsequently expand upon solidifying, thereby exerting
pressure on the crystal 20.
While the invention has been described with respect to
5. In a three-level maser system, a crystal of paramag
netic material containing paramagnetic elements having
at least two unpaired electrons per element and charac
certain speci?c embodiments, it will be appreciated that
terized by a plurality of energy levels, an array of atoms
many modi?cations and changes may be made by those
arranged about each paramagnetic element in a predeter
skilled in the art without departing from the spirit of the 70 mined crystalline order, said crystal being responsive to
invention. I intend, therefore by the appended claims to
physical pressure variation to alter the disposition of said
cover all such modi?cations and changes as fall within
atoms about each paramagnetic element from said prede
the true spirit and scope of my invention.
termined crystalline order to change the internal crystal
What I claim is:
electric and magnetic ?eld about a paramagnetic element,
adjustable mechanical means for adjustably compressing
1. A three-level maser system comprising a source of
5
3,064,201
said crystal for causing atoms surrounding each para
magnetic element to thus alter their positions from said
predetermined crystalline order, and electrical means for
raising the energies of said paramagnetic elements with
an applied radio frequency wave corresponding in fre
quency to the difference between a pair of said energy
levels.
6. In a three-‘level maser system, a crystal of material
containing paramagnetic elements having at least two un~
6
ing in frequency to the difference between a pair of said
energy levels.
References Cited in the ?le of this patent
UNITED STATES PATENTS
2,240,293
2,762,871
2,782,280
10 2,825,765
2,878,454
2,894,224
2,976,492
Goddard _____________ __ Apr. 29,
Dicke _______________ __ Sept. 11,
Bickford _____________ __ Feb. 19,
Marie _______________ __ Mar. 4,
Leming et al. ________ .. Mar. 17,
Iversen _______________ __ July 7,
Seidel ______________ _._ Mar. 21,
1941
1956
1957
1958
1959
1959
1961
paired electrons per element characterized by a plurality
of energy levels, ions arranged about each paramagnetic
element in a predetermined crystalline order, said crystal
being responsive to an adjustable physical pressure to
produce an assymmetrical disposition of said ions about
OTHER REFERENCES
each paramagnetic element di?ferent from said predeter 15
mined crystalline order to change the internal crystal
Bloemberger: Physical Review, vol. 104, No. 2, Oct.
electric and magnetic ?eld about a paramagnetic element,
15, 1956, pages 324-327.
adjustable mechanical means for adjustably compressing
said crystal to produce said asymmetrical disposition of
Feher: Physical Review, vol. 105, No. 2, January ‘1957,
elements to thereby cause the internal electric ?eld pro— 20 pages 760463.
Braunstein: Physical Review, vol. 107, No. 4, Aug. 15,
duced at the paramagnetic elements to have a component
1957, pages 1195-1196.
of symmetry at least as low as rhombic symmetry, and
“Introduction to Solid State Physics,” Kittel, 1956 (John
means for raising the energies of said paramagnetic ele
ments with an applied radio frequency wave correspond
Wiley & Sons of New York), pages 229 and 230 relied on.
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