3.5147714
`A. w. ANGELBECK
`Ma)’ 26. 1970
`GAS LASER HAVING AXIAL AND TRANSVERSE MAGNETIC
`FIELDS CONNECTED IN PUSI-1—PULL RELATIONSHIP
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`TSMC-12
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`TSMC v. Zond, In
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`Page 1 of
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`TSMC-1206
`TSMC v. Zond, Inc.
`Page 1 of 3
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`

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`3,514,714
`United States Patent Office
`Patented May 26, 1970
`
`1.
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`2
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`3,514,714
`GAS LASER HAVING AXIAL AND TRANSVERSE
`MAGNETIC FIELDS CONNECTED IN PUSH-PULL
`RELATIONSHIP
`Albeit W. Angelbeck, East Hartford, Conn., assignor to
`United Aircraft Corporation, East Hartford, Conn., a
`corporation of Delaware
`Filed July 16, 1965, Ser. No. 472,551
`'
`Int. Cl. H01s 3/I0
`U.S. Cl. 331—94.5
`3 Claims
`
`ABSTRACT OF THE DISCLOSURE
`
`The light output and power from a DC discharge gas
`laser is increased by generating a magnetic field and ap-
`plying the field transversely across the laser. Varying the
`transverse magnetic field permits control of
`the laser
`output. Simultaneous application of transverse and axial
`magnetic fields through the laser provides push-pull type
`modulation with low power requirements.
`
`This invention relates to gas lasers, and particularly to
`a method and apparatus for increasing and controlling the
`light output of a gas laser by applying a transverse mag-
`netic field to the laser.
`Gas lasers possess many advantages compared with
`other types of lasers. The light output of a gas laser has
`a high degree of both spatial and time coherence, and
`with proper design the long term frequency stability can
`be made very high. The gas laser also will operate con-
`tinuously without excessive cooling requirements. How-
`ever, the light output power of a gas laser in continuous
`wave operation is limited to milliwatts. In order to fully
`capitalize on the inherent properties of the gas laser it
`is desirable to have a higher level of output power.
`It has been found that a transverse magnetic field ap-
`plied to a DC discharge gas laser increases the electron
`temperature and hence the efficiency of excitation of
`the upper laser level, thereby resulting in a higher light
`and power output for a given -geometry gas laser. Fur-
`ther, varying the transverse magnetic field permits con-
`trol of output light intensity independently of DC ex-
`citation, thereby providing a means for modulating the
`light output. The simultaneous use of axial and trans-
`verse magnetic fields results in a “push-pull” type of
`modulation which produces light
`intensity modulation
`requiring less power than the use of either an axial or
`transverse magnetic field independently since the same
`depth of modulation will be achieved by varying each
`field only half as much as would be required if each field
`was used .separately, and power dissipated in the sole-
`noids is proportional to the magnetic field squared.
`It is therefore an object of this invention to provide
`a novel method and apparatus for increasing the light
`output intensity of a gas laser.
`Another object of this invention is a novel method
`and apparatus for modulating the light output intensity
`of a gas laser.
`A further object of this invention is a novel push-pull
`modulation method and apparatus for a gas laser.
`A still further object of this invention is a transverse
`magnetic field for controlling a gas laser.
`These and other objects and a fuller understanding
`of this invention may be had by referring to the fol-
`lowing description and claims, read in conjunction with
`the accompanying drawings,
`in which:
`FIG.
`I shows a conventional DC gas laser with a
`transverse magnetic field applied thereto; and
`FIG. 2 is an end view of the gas laser of FIG. I; and
`FIG.
`3 shows a gas laser with the novel push-pull
`modulation apparatus.
`
`limitation of the gas laser is the low
`The principal
`power output. For maximum optical gain in the dis-
`charge it
`is desirable to have monoenergetic electrons
`with an energy that will preferentially excite the upper
`laser level. However,
`in the positive column of a DC
`excited gas laser there is a spread in energy of the elec-
`trons. The mean energy is much lower than the desired
`energy for the electrons. An increase in population in-
`version will occur with a corresponding increase in light
`output if the mean energy of the electrons is increased
`since this increases the percentage of electrons at
`the
`desirable energy level.
`In a positive column discharge the electron tempera-
`ture is controlled primarily by the product of PD, where
`P is the gas pressure and D is the diameter of
`the
`laser tube. Electron temperature, Te,
`is inversely pro-
`portional
`to PD and thus a small value of PD is re-
`quired to give a high value of Te. A high gas pressure
`P is advantageous, however, for creating a high density
`of excited atoms in the laser. In order to maintain a
`small PD and high pressure, the tube diameter D must
`be small. However there is a lower limit for tube diam-
`eter which is determined by diffraction losses in the
`laser. These confiicting requirements for gas pressure
`and tube diameter determine an optimum PD for a
`maximum of light output with a given gas laser ma-
`terial.
`This invention increases the electron temperature in a
`gas laser of given diameter operating at a given pressure,
`or conversely produces the same temperature at a higher
`pressure by applying a transverse magnetic field to a DC
`discharge gas laser. Referring to FIG. 1 there is shown a
`conventional DC discharge gas laser comprising a long,
`enclosed glass tube 10 filled with a gas such as a helium-
`neon mixture, argon or krypton. The ends of the tube
`10 are slanted at the Brewster angle. Reflective mirrors
`12 and 14 are positioned adjacent the ends of tube 10,
`one of the mirrors being less reflective than the other.
`Energy is supplied to the gas from a DC power supply 16
`to anode 18 and cathode 20 to produce a glow discharge
`in the gas. The result is a plane wave output which passes
`through the less reflective mirror. The operation of this
`type of laser is well known and need not be described in
`detail.
`As shown in FIGS. 1 and 2 a transverse magnetic field
`is applied by means of a “C” shaped magnetic core 22
`with its pole pieces 24 and 26 positioned on opposite sides
`of the laser tube 10. A DC power supply 28 is connected
`to field coil 30 which is wound about core 22 to supply
`energy thereto. The magnetic field passes transversely
`through the gas filled gas tube 10 as shown by lines “B.”
`The anode 18 is rotated 90° in FIG. 2 for purpose of
`clarity.
`The current-excited discharge passed through the gas
`Within tube 10 creates a plasma in which the atoms are
`ionized and electrons are freed. The transverse magnetic
`field increases the loss of electrons to the tube walls which
`results in an increase of the axial electric field in order
`to maintain the power balance in the discharge. This in-
`crease of the axial electric field and correspondingly the
`increased electric field to gas pressure ratio results in a
`higher electron temperature. The transverse magnetic
`field results in a higher electron temperature without
`necessitating a reduction in gas pressure, or results in the
`same electron temperature at a higher pressure, and pro-
`duces a higher level of light output power. Up to 100%
`increase in power has been measured using this technique.
`The transverse magnetic field allows an independent
`control of light output in a DC discharge gas laser. By
`modulating the magnetic field the light output may be
`varied. Any well known method of varying the magnetic
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`TSMC-1206 I Page 2
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`TSMC-1206 / Page 2 of 3
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`

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`3, 514,714
`
`3
`field may be used, the most obvious being by varying the
`DC power supply 28.
`A novel configuration for modulating the light output
`is shown in FIG. 3. In this embodiment a transverse mag-
`netic field is used in conjunction with an axial magnetic
`field to produce a “push-pull” type of modulation. As
`shown in the figure, a pair of solenoids 32 and 34 are
`positioned adjacent the gas filled tube 10, one solenoid
`being diametrically across from the other whereby a
`longitudinally extending magnetic field is produced through
`tube 10 when the solenoids 32 and 34 are actuated. A
`number of turns of conducting wire are positioned around
`the tube 10 in the form of an axial solenoid 36 whereby
`an axially extending magnetic field is produced through
`tube 10 when solenoid 36 is actuated. Solenoids 32 and
`34 are connected together to one output terminal of a
`push-pull type of amplifier driver 38, and solenoid 36 is
`connected to the other output terminal of the driver 38.
`A power supply 40 is connected through a modulator 42
`to actuate the driver 38 in push-pull fashion in response
`to the modulation applied to the input signal. The appli-
`cation of an axial magnetic field by solenoid 36 reduces
`electron temperature Te and decreases light output. Ap-
`plication of the transverse magnetic field by solenoids 32
`and 34 increases electron temperature Te and increases
`light output. To achieve the same depth of modulation,
`both the axial and transverse fields will require only half
`as much variation as either field alone. The advantage
`that accrues using this technique is that
`less power is
`needed to effect the same modulation since energy storage
`and ohmic (IZR) losses in the coils are proportional to
`the square of the magnetic field strength.
`In operation, modulator 42 varies the control signal
`received by driver 38 in response to some modulating sig-
`nal (not shown) or to some predetermined control ar-
`rangement. Driver 38 actuates coils 32 and 34 and coil 36
`alternately in response to the control parameter to thereby
`alternately increase and decrease the light output of the
`laser. Thus the laser intensity is modulated in response to
`the modulation signal by varying the magnetic fields ap-
`plied thereto.
`Although this invention has been described in its pre-
`ferred embodiment, it is apparent that numerous changes
`and modifications may be made to the structure and ar-
`rangement of parts by those skilled in the art without de-
`
`4
`parting from the inventive teachings embodied herein and
`encompassed by the following claims.
`I claim:
`1. A method for modulating the output intensity of a
`gas laser tube comprising the steps of:
`generating a first magnetic field and directing it trans-
`versely across said laser tube,
`generating a second magnetic field and directing it
`axially along said laser tube simultaneously with said
`first magnetic field, and
`selectively varying the intensity of said first and second
`magnetic fields in push-pull relationship.
`2. In a gas laser tube:
`a first means positioned adjacent said tube,
`means for actuating said first means to produce an
`axial magnetic field along said tube,
`a second means positioned adjacent said tube,
`means for actuating said second means to produce a
`transverse magnetic field -across said tube simultane-
`ously with said axial magnetic field, and
`modulator means for simultaneously varying the in-
`tensity of said axial and transverse magnetic fields
`in push-pull relationship to thereby modulate the
`light output intensity of said laser.
`3. A gas laser tube as in claim 2 in which said first
`means includes a coil positioned longitudinally about said
`tube, and in which said second means also includes a coil.
`
`References Cited
`UNITED STATES PATENTS
`
`3,149,290
`
`9/1964 Bennett et al. _____ __ 33l-——94.5
`OTHER REFERENCES
`
`Ahmed et al. (1): Gas Lasers in Magnetic Fields, Proc.
`IEEE, vol. 52, pp. 1356-57, November 1964.
`Ahmed et al.
`(II): Microwave Electron Cyclotron
`Resonance Pumping of a Gas L-aser, Proc. IEEE, vol. 52,
`pp. 1737-38, December 1964.
`Fork et al.: Broadband Magnetic Field Tuning of Op-
`tical Maser, Applied Physics Letters, vol. 2, pp. 180-81,
`May 1963.
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`JEWELL H. PEDERSEN, Primary Examiner
`E. BAUER, Assistant Examiner
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`TSMC-1206 I Page 3
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`TSMC-1206 / Page 3 of 3
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