US3678409A

US3678409A - Deflectable light maser

Info

Publication number: US3678409A
Application number: US514723A
Authority: US
Inventors: Marion S Rose
Original assignee: Litton Systems Inc
Current assignee: Northrop Grumman Guidance and Electronics Co Inc
Priority date: 1965-12-17
Filing date: 1965-12-17
Publication date: 1972-07-18
Anticipated expiration: 1989-07-18
Also published as: DE1564294A1; DE1564294B2; FR1503386A; GB1163527A

Abstract

Laser apparatus having a coaxial cathode ray gun having its elements aligned along an axis, the elements including a heater element, a cathode element heated thereby, at least one accelerating electrode element axially removed from the cathode element to propel an electron stream from the cathode, a control grid element interposed between the cathode and the accelerating electrode elements in the electron stream, a focusing electrode element interposed between the control grid element and the accelerating electrode element, all of the elements being substantially symmetrical about the common axis and having apertures formed therein to clear an optical path in the region of said axis, the gun being surrounded and supported by a bulb having optical windows at both ends of the gun along the common axis, the bulb being filled with gas of a type to sustain laser action, and means for raising the energy of the gas in the region of the axis to a lasing threshold.

Description

United States Patent Rose [451 July 18, 1972 [72] Inventor:

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[56] I References Cited UNITED STATES PATENTS 3,406,3 66 9/ 1968 Williams et al. .33 1/945 OTHER PUBLICATIONS Lax: Scanatron-A Scanning Beam Semiconductor Laser," Solid State Design, Vol. 6, pp. 19- 23, March, 1965 Primary Examiner-William L. Sikes Attorney-Robert l-l. Lentz, Alan C. Rose and Alfred B. Levine [57] ABSTRACT Laser apparatus having a coaxial cathode ray gun having its elements aligned along an axis, the elements including a heater element, a cathode element heated thereby, at least one accelerating electrode element axially removed from the cathode element to propel an electron stream from the cathode, a control grid element interposed between the cathode and the accelerating electrode elements in the electron stream, a focusing electrode element interposed between the control grid element and the accelerating electrode element, all of the elements being substantially symmetrical about the common axis and having apertures fonned therein to clear an optical path in the region of said axis, the gun being surrounded and supported by a bulb having optical windows at both ends of the gun along the common axis, the bulb being filled with gas of a type to sustain laser action, and means for raising the energy of the gas in the region of the axis to a lasing threshold.

14 Claims, 8 Drawing figures PATENTEU JUL1 8 I972 SHEET 1 OF 2 MfiE/ON 5 Ross IHVENTOQ N IIE PATENTEDJUUBIS'IZ 3.678.409

sum 2 BF 2 MHz/0N :5 Ross INVENTOQ BVWOKW DEFLECTABLE LIGHT MASER This invention pertains to a deflectable maser, more particularly a deflectable light maser or laser.

Light amplification by stimulated emission of radiation has opened a new field in which the research or development engineer can provide a device for use by the systems engineer to extend the range of controlled electromagnetic radiation into the infrared, visible, and ultraviolet spectra. Ideally, the output of the light maser is a single monochromatic light having substantially parallel light rays.

Though substantial achievements have been realized in increasing the power, coherency, and isolation of discrete optical lines, there has been less progress in deflecting the optical laser beam.

The'use of lasers, particularly those of high power which are capable of modulation, are numerous. However, the ultimate potential of lasers will not be realized until a reliable, low cost means of deflecting the beam is produced. Preferably, the beam should be deflectable at rapid rates of the order at least of a television scan rate. Uses such as large screen display of information; search, acquisition, or track radar; and computer optical inputs by the physical shifting or pointing of the laser are possible though hardly practical in many environments.

One prior art method of deflecting a laser beam is to channel the laser beam through a series of crystals or substances whose indices of refraction may be changed with a voltage. Considerable power is used in the deflection and is absorbed in the process. Other prior art devices for deflecting laser beams use" a rotating mirror or other mechanical-optical means. 1

The device contemplated by this invention uses a gas laser in which the energy of the gas is increased to near the avalanche level. A deflectable beam of charged particles is injected into the gas to cause localized laser action. The position of the localized laser action is deflected with the particle deflection to cause the light, produced by the laser, to be deflected.

It is therefore an object of this invention to produce an electronically deflectable maser beam.

It is another object of this invention to produce an electronically deflectable coherent light beam.

It is still another object of this invention to deflect a laser beam.

It is another object of this invention to produce a laser beam by interaction between a gas and a stream of charged particles.

It is a more specific object of this invention to provide a deflectable maser, and more particularly a deflectable light maser or laser.

It is also a more specific object of this invention to introduce a novel electron gun which is adapted to be used with the deflectable laser of this invention.

Other objects will become apparent from the following description, taken in connection with the accompanying drawings in which:

FIG. 1 is a schematic view of a typical deflection laser, fabricated in accordance with this invention;

FIG. 2 is a view, partly in section, showing a typical deflection laser and a novel electron gun adapted for use in this invention;

FIG. 3 is a view, partly in section, taken at 3-3 in FIG. 2; FIG. 4 is a view, partly in section, taken at 4-4 in FIGURE.

FIG. 5 is an alternate embodiment of the device in FIG. 2;

FIG. 6 is a second alternate embodiment of the device of FIG. 2 using deflection plates to deflect the electron beams;

FIG. 7 is a view, partly in section, taken at 77 in FIG. 6; and

FIG. 8 is a view, partly in section, showing an embodiment of the invention using anti-reflective windows.

Referring to the figures, particularly FIG. 1, a gas enclosing bulb 10 forms an optical maser, or laser, and encloses a gas which is capable of being raised to a maser or laser threshold. The bulb 10 has a pair of

optical windows

40 and 42, which may be at Brewster's angle, and an electron gun 12 at one end of the bulb 10 to inject electrons of controlled energy into the energized gas. The electron stream may be focused by focusing electrodes such as

electrodes

54, 56 and 58, by a focusing coil such as coil 14, or both. The electron stream is deflected by a set of deflection coils I6, by deflection plates shown in FIG. 6 and 7, or by both. Gas within bulb 10 is raised to a laser threshold by applying a voltage from source 22, through network 24, between an anode 20 and a cathode 18. The potential between electrodes 18 and 20 causes the gas energy between them to be increased to a laser threshold. The injection of an electron beam increases the energy in a particular region of the gas to cause localized laser action. A pair of

mirrors

36 and 38, which are front surfaced, and one of which is only partly light reflecting and partly light transmitting, form the resonant cavity of the laser.

The structure of a preferred electron gun 12 for use in the deflection maser of this invention is shown more particularly in FIG. 2. In FIG. 2 the electron gun 12 has coaxial elements with its elements aligned along the axis 48. A heater element 46 is adapted to heat the cathode 50. The control grid is shown at 52. At least one focusing electrode is used in the gun. Three focusing electrodes are shown at 54, 56 and 58. Two accelerating

electrodes

60 and 62 are also used. Only one accelerating electrode is required. The electrodes are axially spaced apart from the cathode element to propel an electron stream from the cathode, in the fashion shown more particularly in FIG. I, wherein the electron streams have two cross over

points

90 and 92, finally coming to a focus at 94. The focusing occurs by virtue of the potential on the focusing

electrodes

54, 56 and 58 and is assisted by the focusing coil 14. In any particular embodiment, focusing electrodes or a focusing coil may be used alone. As shown,

elements

46, 50, 52, 54, 56, 58, 60 and 62 are substantially annular shaped to form substantially circular aperatures in the region of the axis 48.

The electron gun may further have deflection plates such as

deflection plates

68, 70, 72 and 74, which are shown more particularly in FIGS. 6 and 7.

The focusing

electrode

54, 56 and 58 and the focusing coil 14 are adapted to bring the electron stream into focus in the region of the

deflecting plates

68, 70, 72 and 74.

Instead of the deflecting plates, a series of deflecting coils, shown generally at 16, and shown more particularly at 76, 78, and 82 of FIG. 4, may be used to deflect the electron stream and move the position of localized lasing of the gas.

Each of the electrodes is preferably brought through the glass bulb 10 by means of an attachment similar to that shown at 34 in FIG. 2. Additional feed-through electrodes, connected to the electrodes of the cathode ray gun 12, are not shown.

In the embodiment shown in FIGS. 1 and 2, the enlarged portion of the bulb surrounding the cathode ray gun 12 is shown reduced in size in the region of window 42. In FIGS. 5 and 6, that portion of the bulb I0 is shown with increased diameter for ease in construction of the bulb and insertion of the gun 12.

To collect the electrons, a coating 28 is placed on the inner wall of the bulb 10. The coating 28 is connected to a collection electrode 26 which is placed at a relatively high positive potential relative to the cathode 50 by means of a voltage source 30. The coating 28 may for example be a high resistance coating such as stannous chloride.

The focusing coil 14 is shown more particularly in FIG. 3. No means for supplying current to the coil is shown, but obviously current may be controlled in quantity and direction to cause the focusing of the electron stream to be at the appropriate and desired predetermined point 94.

The structure of typical deflecting coils is shown in FIG. 4. Two opposing coils are serially connected to cause the same current to flow there through. Deflection in one direction is caused by the current flow through two opposing

coils

76 and 80 while deflection at right angles to the first direction is caused by current flow through

coils

78 and 82.

In an alternative embodiment, shown in FIG. 8, instead of using Brewsters Angle windows,

anti-reflective windows

84 and 86 are used with their centers ofcurvature substantially at the point of deflection of the gas, i.e. at point 88 in the region where the electron stream may conveniently be deflected.

Thus the device of this invention is a maser comprising a bulb enclosing a gas of a type capable of Sustaining maser action. Examples of this gas are helium and helium-neon mixtures. Means 18, 20, 22 and 24 are provided for raising the energy of the gas to a maser threshold. An electron gun 12 is used for injecting high energy electrons into the gas to cause localized maser action in the region of 94. Energy

transparent windows

40 and 42 are both ends of the bulb 10. Energy reflecting means 36 and 38 are used as the resonant cavity of the maser with one of the reflecting means 36 and 38 reflecting only a part of the energy and transmitting part of the instant energy.

More particularly, the maser is a laser, the energy transparent windows are optical windows such as Brewster's

angle windows

40 and 42 or

anti-reflective windows

84 and 86. The energy reflecting means 36 and 38 are front reflective surfaces, one of which is adapted to transmit part of the light and to reflect part of the light. The surfaces may be silvered, or have other light reflective surfaces such as gold or multi surfaced and the like.

The device further comprises a means 16 or a

means

68, 70, 72, 74 for deflecting the electrons to move the region of laser action of the gas.

More particularly, the means for injecting electrons into the gas is an electron gun 12, substantially coaxial with and surrounding the bore of the bulb 10 which encloses the gas.

The gas within the bulb 10 may be characterized as an active laser medium and the electron gun 12, together with the deflection means 16 or the deflection means 68, 70, 72 and 74 together form a means, responsive to control signals, for locally pumping the medium or gas to a condition of population inversion capable of sustaining laser action along a selectively deflectable path. More particularly, such means includes means for directing an electron beam from gun 12 into the gas and means for deflecting the electron beam along selected paths in the gas medium.

Still more particularly, the pumping means may be characterized as a means 18, .20, 22 and 24 for exciting the bulk of the gas medium to a level below the threshold for laser action and a cathode ray gun 12 for exciting the medium to exceed the threshold along selected paths in the gas. The means for exciting the medium to exceed the threshold along selected paths includes means for directing an electron beam through the gas medium, eg a cathode ray tube gun, and means for deflecting the beam along the paths selected, e.g. deflection coils 16.

Instead of using an electron beam, it is within the concept of this invention that a means for producing an ion stream would be used to raise the energy of the gas into a lasing condition.

The coaxial cathode ray gun 12 has its elements aligned along an axis 48 and has a heater element 46, an active cathode element 50, positioned adjacent the heater element to be heated by the heater; at least one accelerating

electrode element

60 and 62, axially spaced apart from the cathode element 50 to propel an electron stream from the cathode 50; a control grid element 52, axially spaced apart from and in the electron stream between the cathode 50 and the accelerating

electrode elements

60 and 62; at least one focusing

electrode element

55, 56 and 58, axially spaced apart from and between the control grid element 52 and the accelerating

electrode elements

60 and 62, said focusing electrode elements being electrically connected together to have a common electric potential. The elements of the cathode ray gun 12 are substantially symmetrical about the common axis 48 and have apertures formed therein to clear an optical path in the region of the axis 48 to allow light generated by the lasing action to be reflected between the reflecting

surfaces

36 and 38.

In general, the

elements

46, 50, 52, 54, 56, 58, 60 and 62 are substantially annular shaped and the apertures of the elements are substantially circular to provide a clearance path for the light beam of the laser.

ln operation, a glow or are is struck between electrodes 18 and 20. The cathode ray tube 12 is energized to inject electrons into the gas to raise it to a laser threshold at the region 94. The electron stream is deflectable by deflection plates or a deflection coil 16. When the electron stream is deflected, the region oflasing 94 is also deflected whereby the light from the laser is deflected.

Iclaim:

l. A deflectable maser comprising:

a resonant cavity defining a longitudinal axis ofsaid maser;

a gas capable of masing contained within said cavity;

means for locally establishing a population inversion capable of establishing maser action within a region of said cavity; electron beam gun means for establishing an electron beam along an axis parallel to the longitudinal axis of said maser through said region for increasing the population inversion to a level above the maser threshold level of said gas along the electron beam path through said region, said electron beam having a relatively narrow radial cross-section with respect to the radial cross-section of said region;

focusing means for focusing said electron beam to a focal point on said axis between said beam gun and said region; and

deflection means for deflecting said electron beam in a direction at a predetermined angle to said axis, the deflected beam diverging from said axis at said focal point.

2. Apparatus according to claim 1 wherein said cavity is defined by a bulb and said gas is contained in said bulb, said bulb having first and second energy transparent windows disposed respectively at each end of said bulb and intersecting said axis.

3. Apparatus according to claim 2 wherein said windows are disposed at Brewster's angle to said axis.

4. Apparatus according to claim 2 wherein said windows are substantially concave in shape and are constructed of antireflective glass.

5. Apparatus according to claim 4 wherein said windows have centers of curvature disposed substantially coincident with said axis.

6. Apparatus according to claim 1 wherein said maser is a laser and said gas is capable oflasing.

7. Apparatus according to claim 6 wherein said first and second windows are optical windows, energy reflective means having a front metallized light reflective surface intersecting said axis at one end of said bulb, and means for partially reflecting and partially transmitting incident light energy, said last named means including a front-metallized partially light reflective surface intersecting said axis at the end of said bulb opposite said one end.

8. Apparatus according to claim 7 wherein said lasing gas is a mixture of helium and neon, and said apparatus further includes a conductive surface on at least a portion of said bulb radially adjacent said region.

9. Apparatus according to claim 1 further including field generating means substantially surrounding said focal point, and means for selectively energizing said field generating means, whereby said field generating means generates a field substantially normal to said axis to deflect the direction of said electron beam at a predetermined angle at said axis.

10. Apparatus according to claim 9 wherein said field generating means comprises an electric coil and said field is a magnetic field.

11. Apparatus according to claim 9 wherein said field generating means comprises electronic deflection plates and said field is an electrostatic field.

12. A deflectable maser comprising:

a resonant cavity defining a longitudinal axis of said maser;

a gas capable of masing contained within said cavity;

means for locally establishing a population inversion capable of establishing maser action within a region of said cavity;

electron beam gun means for establishing an electron beam along an axis parallel to the longitudinal axis of said member through said region for increasing the population inversion to a level above the maser threshold level of said gas along the electron beam path through said region, said electron beam having a relatively narrow radial cross-section with respect to the radial cross-section of said region; and

deflection means for deflecting said electron beam at a direction at a predetermined angle to said axis, said deflection means comprising field generating means subgenerating means comprises an electric coil and said field is a magnetic field.

14. Apparatus according to claim 12 wherein said field generating means comprises electronic deflection plates and said field is an electrostatic field.

7 UNE'EED STATES PA'iENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,678, l-09 I Dated Julv 18 1972 Inventofls) MARION S.. ROSE It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

1 Column 3, line 13, after are" read--on--;

Column 5, line 6, for "member" read -maser Signedand sealed this 31st dayof October.l972'.

(SEAL) 'Attest:

i I Y ROBERT GOTTSCHALK 91 Commissioner of Patents

Claims

1. A deflectable maser comprising: a resonant cavity defining a longitudinal axis of said maser; a gas capable of masing contained within said cavity; means for locally establishing a population inversion capable of establishing maser action within a region of said cavity; electron beam gun means for establishing an electron beam along an axis parallel to the longitudinal axis of said maser through said region for increasing the population inversion to a level above the maser threshold level of said gas along the electron beam path through said region, said electron beam having a relatively narrow radial cross-section with respect to the radial cross-section of said region; focusing means for focusing said electron beam to a focal point on said axis between said beam gun and said region; and deflection means for deflecting said electron beam in a direction at a predetermined angle to said axis, the deflected beam diverging from said axis at said focal point.

3. Apparatus according to claim 2 wherein said windows are disposed at Brewster''s angle to said axis.

4. Apparatus according to claim 2 wherein said windows are substantially concave in shape and are constructed of anti-Reflective glass.

6. Apparatus according to claim 1 wherein said maser is a laser and said gas is capable of lasing.

12. A deflectable maser comprising: a resonant cavity defining a longitudinal axis of said maser; a gas capable of masing contained within said cavity; means for locally establishing a population inversion capable of establishing maser action within a region of said cavity; electron beam gun means for establishing an electron beam along an axis parallel to the longitudinal axis of said member through said region for increasing the population inversion to a level above the maser threshold level of said gas along the electron beam path through said region, said electron beam having a relatively narrow radial cross-section with respect to the radial cross-section of said region; and deflection means for deflecting said electron beam at a direction at a predetermined angle to said axis, said deflection means comprising field generating means substantially surrounding at least a portion of said region, and means for selectively energizing said field generating means, whereby said field generating means generates a field in said portion of said region and substantially normal to said axis to deflect the direction of said electron beam to a predetermined angle from said axis.

13. Apparatus according to claim 12 wherein said field generating means comprises an electric coil and said field is a magnetic field.