CA1133615A

CA1133615A - Ring laser

Info

Publication number: CA1133615A
Application number: CA333,345A
Authority: CA
Inventors: David C. Grant, Jr.; Thomas J. Hutchings
Original assignee: Litton Systems Inc
Current assignee: Northrop Grumman Guidance and Electronics Co Inc
Priority date: 1978-10-02
Filing date: 1979-08-08
Publication date: 1982-10-12
Also published as: CH651157A5; IT1164049B; IT7950401A0; JPS5910078B2; JPS5548989A; JPS5821385A; SE449664B; FR2438357A1; IL57936A; SE7908117L; FR2438357B1; JPS584475B2; GB2032169B; DE2939804A1; GB2032169A

Abstract

ABSTRACT OF THE DISCLOSURE

A ring laser wherein, in the preferred embodiment, the laser path is substantially square, and the path length is adjustable by making at least one of the mirrors slightly tilted and one of the mirrors concave with at least the concave mirror translatable.

Description

1~33~

B~CKGRouND OF T~IE INVENTION
It is known to use a planar ring laser as a gyroscope.
Ring laser gyroscopes typically use a three or four sided laser path. The laser path usually occurs in a lasing chamber which is confined to bores formed in the general con-figuration of the laser path within a laser housing usually made of highly stable glass or ceramic.
~ he lasing mirrors are positioned where the laser chamber bores and laser path change direction. The bores ex-tend from mirror to mirror, and the bores are suffici~entlylarge to prevent vignett~ng of the laser light.
To excite the ring laser to cause two laser paths in opposite directions, ~t is customary to attach at least one cathode somewhere to the laser housing and to provide anodes on the laser housi,ng together with conduîts connecting the anodes and the cathodes into the laser bores i'n a geometric configuration whereby a motion of ions and electrons between the cathode and anodes excîtes the laser phenomenon.
T~pically, the lasing gas within the bores is a helium-neon mixture at very low pressure. Application of a voltage of sufficient magnitude to ionize the gas between "~

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the cathode and anodes is applied ~o the cathode and to the anodes to cause a migration of electrons from the cathode to the anode and a migration of positive ions from the anodes to the cathode within the gain bores of the lasing gas, thereby exciting the lasirlg gas. The resonant cavity formed by said mirrors, is tuned in frequency by adjusting ~he laser length for the particular lasing frequency desired. The regions of interaction between the gas and the electrons of ions are designated "gain regions".
It is usually desired that only the TEMoo, or on-axis mode of oscillation be present. To that end, one of the mirrors is apertured to suppress off-axis modes of oscillation in the laser path.
With two laser oscillations occurring at the same time, one with the light trave~lling in a first direction around the laser path and the other with the light travelling in the other direction around the laser path, it is well known that such a laser may be used as a gyroscope to detect the ang~lar rotation of the laser housing about an axis perpendicular to the plane ~ of the laser paths.
To tune the length of the laser path, it is customary to move one of the mirrors inwardly, perhaps by a screw me~hanism or transducer, until the lasing amplitude peaks. The output of the laser, through a partially transmitting one of it~ mirrors, can be used to servo the position of the tuning mirror.
The laser beam is also typically focused by a large radius, preferably spherical, mirror to produce a laser beam of substan-tially uniform cross section. This feature is shown in Figure

2-4 D of "The Laser" by William V. Smith and Peter P. Sorokin, McGraw-Hill, 1966.

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., 1 BRIEF DESCRIPTION OF T~E INVENTION

3 In its preferred embodiment the invention pertains

4 to a modification of the laser by mounting a large radius concave mirror at the intersection of two branches of the laser A 6 path, and the tilting of ~he symmetrically positioned ~or$lsu3 7 mirror at a p~ramid angle. Typically in a four sided laser 8 path, it is the planar mirror opposite the concave mirror which 9 is apertured and tilted. The tilted planar mirror and the concave mirror are moved up and down together until the proper 11 lasing occurs. ~hey are then fastened in place. Ihe tilt is 12 typically between one and three arc minutes, depending upon the 13 wavelength of the laser light, the gain bore diameter and the 14 lasing mode volume. One must be able to change the cavity length by at least a half wavelength without causing the mode volume 16 to be affected by the gain bores in a way to cause a substantial 17 loss in lasing gain. Tilting one of the mirrors to vary the length 18 of the lasing path also causes the plane of the lasing path to be 19 tilted upward through the same angle of tilt as the mirror. In a gyroscope the sensing axis needs to be perpendicular to the plane 21 of the laser path. To create a laser usable as a gyroscope, the 22 base of the gyroscope then also needs to be beveled through 23 the same angle of tilt so that the mounting base is parallel -24 to the plane of the lasing gases.
- 25 With the alignment improvement of thiq invention, 26 the ring laser ~yroscope may be made very small with the length 27 of each side of the laser path substantially less than an inch 28 in length. With such a small laser, the cathode of the laser .
29 is preferably the same order of size aA the laser block itsel~.
The cathode must be made large enough to produce an adequate 32 ..,.

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amount; of current within the gain bores of the lasing path to 2 supply the required energy to the laser. A cathode block having 3 a hemispherical cathode coated on the surface of a hemispherical 4 bowl formed in the cathode block is typically attached to the bottom of the laser block. A passageway is made substantially 6 from the center of the sphere defining the cathode surface upward 7 into the laser block, thènce directly outward to the laser ring.
8 A pair of anodes are symmetrically positioned to cause the 9 electron and ion path to split and travel in two directions through the gain bore portions of the laser path. The anodes 11 are positioned out of the laser path, and a conduit is built 12 into the laser block connecting the surface of the anodes with 13 the laser path.
14 Application of a voltage between the cathode and the anodes causes ionization of gas to occur within the cathode bowl 16 and upward through the substantially vertical passage, thence 17 outward to the laser paths, thence alon~ the gain bores of the 1 laser paths in different directions, thence to the surfaces of 19 the anodes.
2 To align the laser with its sensing axis perpendicular 2 to the plane of the laser path, the plane of the bottom of the cathode housing may be constructed parallel to the plane of the 2 laser path f-or easy alignment of the gyro.
2 It is therefore an object of this invention to provide 2 an improved optical resonator with a new tuning structure.
26 It is a morç specific object of this invention to tune 27 a ring laser.
2 It is a still more specific object of this invention .
29 to provide a ring laser which i8 configured to be used as a 3 gyroscope.

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The above objects are met by the present invention which pro-vides in an optical resonator having means forming a resonant cavity, active gaseous media within the cavity, a pumping source, and an energy abstract-ing ~eans, the means forming a resonant cavity including at least three mirrors with one mirror being concave and the others planar, the imr provement comprlsing support mRans for supporting the concave mirror at a tilted pyramid angle with respect to a plane defined by the other mirrors.
The invention also contemplates a ring laser, including means forming a resonant cavity, an active gaseous medium within the cavity, a pumping source, and energy abstracting means, comprising: a block defining the resonant cavity in a closed path containing the active gaseous medium, including at least one laser gain region within tHe~ cavity, the means forming a resonant cavity including a plurality of mirrors positioned with-in the gaseous medium in the cavity, a cathode and at least two anodes connected by passageways formed in the block through the gain regions of the cavity, the passageways between the cathode and the anodes including the gain regions; at least one of the mirrors being concave, and the re-maining mirrors being substantially plan æ; at least one of the concave : 20 mirrors being slideably mounted uFon a surface tilted at a pyramid angle relative to the other mirrors; at least one of the planar mirrors being - tilted at a pyramid angle relative to the other mirrors;and at least one of the mirrors being partly transmissive.
Furthermore the present invention may be seen as providing a method for adjusting the length of an optical resonator having a reson-ant cavity, and energy abstracting means, including at least two mirrors with one mirror being concave, and tilted supFort means for supporting the concave g/~ - 6 -~, , .
' ' ' ' .r~r at a ~ilt througll a pyramid anyle with resp~ct to the other mirror, comprising: translating the tilted concave mirror on the surface in the direction o tilt relative to any produced laser beam while maintaining the pyrami~ angle constant to tu~le the resonant cavity.
BRIEF DESCRIPTION OF T~IE DRAWINGS
Figure 1 is an outside view of a typical laser block and cathode block, attached together, showing the evacuation stem tipped off.
Figure 2 is a sectional view, taken at 2-2 in Figure 1.
Figure 3 is a top view, taken at 3-3 in Figure 1.
Figure 4 is a schematic ray diagram showing a preferred embodiment of a concave rnirror and its opposite planar mirror in the apparatus of Figure 1.
Figure 5 is a schematic diagram showing the relation of the curvature of the concave mirror to the displacement of the lasing plane.
Figure 6 is a schematic ray diagram showing the dis-placement of the laser rays with displacement of the concave and the tilted planar mirror.
Figure 7 is an enlarged schematic view taken at 7 in Figure 6.
Figure 8 shows the angllng of the base of the cat~node block into a contour parallel with the laser plane for use as a - ring laser gyroscope.
DETAILED DESCRIPTION OF THE INVENTION
The preferred embodiment of the ring laser of this invention which is used as a gyroscope is shown in the Figures.
The ring laser has a laser block 10 and a cathode block 12, ' sd~ 6A-.:

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~1336i5 preferably made of a glass ceramic. Typical acceptable glass ceramics are known by the trademarks CE~NlT, ZERODUR and ULE. These materials ha~e a substantially zero expansion within a usable range of the laser.
The laser block 10 carries the lasing path 14. The cathode block 12 carries the cathode 16, and the laser block 10 c,arries two anodes 52 and 54.
Voltage between the cathode and anodes ionizes the lasing gas to deliver energy for lasing. No power supply for applying voltage between the anodes 52, 54 and cathode 16 ;s shown, but any typi~cal DC power,supply may be used, and the positive voltage is connected to the anodes 52 and 54 while the negative voltage is connected to the cathode 16. The laser block 10 and the cathode block 12 are held together both by atmospheric, pressure and a sealant such as indium.
The preferred laser path 14 is a rectangul æ laser path, and more particul æ ly a substantially square laser path as shown in the figures.
The laser hlock is typically a square laser block,~but unused portions of the block maiy optionally be cut off to minimize cost and fabr~cation difficulty so that the resulting block, as shown i`s shaped as an octagon.
Attached to four sides of the square laser block or to alternate nonadjacent sides of the octagonal laser block at the intersections of the laser branches æ e four mirror blocks 22, 24, 26 and 28 which have mirror surfaces on the interior thereof for reflecting the laser beam. At least one of the mirrors is ~,artially transmissive to allow the laser beam to be emitted, at least one of the mirrors is apertured to prevent the production of un-wanted m~des of oscillation, and at least one of the mirrors 22 is concave with a suitable radius of curvature to focus the laser beam.

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., The lasing in the laser path occurs in a helium-neon gas 2 ixture at a very low pressure of 3=~ Torr. The gas mixture, typical Y~
3 5 20 parts helium to 1 part neon 20 and 1 part neon 22. To contain 4 he lasing gas in the laser path, four substantially coplanar condui s 5 30a, b, c and d are bored in the laser block 10 connecting the mirro

6 rhey are large enough in diameter to allow the plane of the laser

7 eam to be translated and tilted through a small angle, typically on

8 the order of 3 to 5 arc-minutes, without interference with the iaser

9 eam. The conduits could be tilted parallel to the laser beam. -Within the region whose perimeter is defined by the _ 11 laser path, and preferably in the center of the laser block 10 12 is a conduit which is perpendicular to the plane of the conduits 13 30a, b, c and d. That conduit has two portions 32, leading to 14 the top of the laser block 10, and 34 leading to the cavity 15 formed by the cathode surface 16. The conduits 32 and 34 are 16 connected with the conduitc 30a, b, c and d by a conduit 36 17 which is typically substantially in the plane of the conduits 18 30a, b, c, and d.
19 In the regions o~ the mirrors 22, 24, 26 and 28 are four chambers 38, 40, 42 and 44 which are terminal regions for 21 the branches 30a, b, c and d of the laser conduits and which 22 are large enough to prevent interference with the laser light.
23 Cavity 40 is connected by conduit 36 to the conduits 32 and 34.
24 The conduit 34 is preferably centered on the hemispherica cathode surface 16, but it is intended that this description shall 26 cover the situation wherein the conduit 34 is not so centered.
27 Further, although conduit 34 is shown perpendicular to the plane 28 of the laser path 14a, b, c and d, it iA intended that this 29 description shall i~clude slanting the conduit 34. The conduit 32 extends to the outer surface of the laser block 10 where it 31 ......... ~

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!! 1133615 GCD 78-3 1 i3 s~rrounded by a glass or metal stem which is sealed to the 2 laser block. It iq further to be understood that the conduit 3 32 is for the purpose of evacuating the conduits, and its position 4 in the center of the laser block is not critical. It i8, howe~sr, 5 convenient to form the conduits 32 and 34 colinearly by a single 6 pass of an appropriate glass drill. It is further to be noted 7 that conduit 32, although shown perpendicular to the path of laser 8 path 14a, b, c and d may ~lso be slanted, if de~ired.
9 The stem 50 is used to evacuate the system and to refill

10 it with the required gas at a low pressure. When the stem 50 i5

11 metal, it may also be used as an anode. Note that the conduit 32

12 is connected through the conduit 34 to the region within the 1~ cathode surface 16 and through the conduit 36 to the laser 14 conduits 30a, b, c and d. An exhaust pump (not shown) may be attached to the stem 50 to remove all air from the sy~tem.
16 ~urther, a getter (not shown) may either be positioned within the 17 stem 50 or within the region of conduits attached to stem 50 A 18 (not shown) adjacent the stem 50. After the system is evacuated 19 and gottorod~ the required lasing gas is filled into the system at a very low pressure, and the stem is tipped off to seal the 21 system. ~he cathode block 12 is held onto the laser block 10 22 both by the resulting low pressure vacuum within the chamber 23 fonmed by the cathode surface 16 and by a sealing material such 24 as indium s~ld~r.
In the region of the compartments 38 and 42 are a pair 26 of anodes 52 and 54 which are metallic conductors and extend 27 from the outside of the laser block 10 inward into the chamber~
28 38 and 42.
29 With a positive voltage connected to the anodes 52 and 54 and a negative voltage connected to the cathodes 16, Sl ....
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1 1 3 3 6 1 5 GCD 7~-3 l ~lectrons and ions commence to drift ~rom cathode to anode and 2 ~node to cathode in the path defined by the chamber formed by 3 Ithe cathode 16, the conduits 34 and 36 into the compartment 40.
4 ~t the compartment 40, the path splits, and a portion of the 5 ¦ion-electron drift is in one direction through a gain ~ore from 6 ¦the compartment 40 to the compartment 38 and thence to the anode 7 152. The other part of the drift is from the compartment 40 through ~ ¦the gain bore 30b to the compartment 42 and thence to the anode 9¦ 54 The motion of the electrons and ions in two directions within 10¦ the gain bores of the proposed laser path excites the gases 11¦ therein to a higher energy state from which they drop to a lower 12 ¦energy state to produce light at the frequency to which the laser

13 ~ath i9 tuned. Thus, energy is provided to the laser from the

14 ¦source which is connected to the cathode 16 and anodes 52 and 54.

15 ¦ Typically the length of the laser cavity is tuned by

16 ~aking the curved and apertured mirrors movable. One of the two

17 ~ovable mirrors is tilted at a pyramid angle so that upward and

18 ~ownward movement of that mirror also moves the mirror inward

19 nd outward relative to the laser path to peak the laser signal.
In the preferred embodiment of this invention, however, th~ , 21 pertured mirror is tilted inward at a small pyramid angle, typicall 22 rom 3 to 5 arc minutes, so that moving the concave mirror 22 23 n a direction normal to the conduits 30a, b, c and d and the 24 ~pertured mirror 26 to keep the aperture opening in the laser ath lengthens and shortens the laser path.
-26 A pyramid angle between two planes is defined as 90 27 ninus the dihedral angle between those planes. A dihedral angle 28 s defined by the "Mathematics Dictionary" third edition by ; 29 32 1....
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1~33~1S GCD 78-3 l ~ames a ~ames, published by VanNo~trand 6 Company. "The union ¦
2 of a line and two half-planeq which have this line as a common 3 edge. The line is the edge of the dihedral angle and the union of the line and one of the planes is a face. A plane angle of a dihedral angle is an angle formed by the two rays which are 6 the intersections of the faces of the dihedral angle and a 7 plane perpendicular to the edge. Any two p~ane angles are co~-ô gruent. A measure of a dihedral angle is a measure of one of 9 its plane angles." The dihedral angle between the tilted mirror and tbe plane defined by the conduits 30a, b, c and d and the 11 two parallel planar mirrors on the mirror blocks 24 and 28 is 12 slightly less than but almost 90 , differing from 90 by the 13 pyramid angle of the plane of the tilted mirror ~hich typically 14 is very small. The pyramid angle is governed by the lasing wavelength, the gain bore diameter and the lasing mode volume.
16 One must be able to change the cavity length by at least a half 17 wavelength of the laser light without causing the mode volume 18 to be affected by the gain bores in a way to cause a substantial 1 loss in lasing gain. As the concave mirror is moved up and down, the laser path is also moved up and down, thereby striking a 21 different portion of the tilted mirror, such portion forming a 22 shorter or longer path for the laser beam. By striking a 23 different portion of the tilted mirror, the on-axis beam would 24 be extinguished by the aperture stop unless the tilted mirror is also moved to re-align the aperture opening with the laser beam.
26 If all of the planar mirrors 24, 26, and 28 had the 27 planes of their mirrors perpendicular to the same plane defined 28 by thé plane of the conduits 30a, b, c and d, motion of the 29 concave mirror 22 up and down would merely mov~ the laser beam up and down without changing the length of the lasing path.
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l However, with the mirror 26 having its planar surface tilted 2 at a pyramid angle, the entire plane of the laser path is tilted 3 upward through that small pyr-amid angle so that the plane of 4 the incident and reflected laser rays on the tilted mirror is perpendicular to the surface of the mirror. This causes the 6 intersection of the laser beam and the concave portion of the 7 concave mirror 22 to move on that concave surface. If the 8 concave surface is a spherical surface, ~he amount of displace-9 ment is determined by the radius of that concave mirror and the a~ove-mentioned pyramid angle tilt of the planar mirror 26.
11 Alternatively, the block 22 carrying the concave mirror 12 surface could merely have been tilted inward through the small 13 pyramid angle where~y motion of the block 22 not up and down 14 but tilted inward at the small pyramid angle would lengthen and shorten the laser path length and move the intersection of 16 the laser path on the mirrors 24, 26 and 28. The mirror 26 17 would also need to be moved up and down to align the aperture 18 opening with the new laser path. The conduits carrying the lasing l9 path must be large enough to accommodate the variations in position described.
21 With the structure described, a very small laser gyro may 22 be constructed. The sum of the lengths of the four sides 14a, b, c 23 and d may have, for example, a nominal length of 6.8 centimeters.
24 The cathode surface 16 is typically made of aluminum, and indium scldcr may be connected to the aluminum and positioned 26 at 60 and 62 so that negative voltage may be applied to the 27 aluminum cathode 160 28 The exhaust and fill stem 50 is typically made from 29 a glass tube section which is flared at the bottom to ~ccommodate a radio frequency fired getter. Alternatively, the exhaust 3~ ....
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1il33615 slnd ill st~m may be smaller than shown. It may al~o be made of metal, the ex~laust and Eill stem may be used as an anode.
The mounting faces of the octagonal laser block 10 are typically only one centimeter across, and the mirrors blocks 22, 24, 26 and 28 are typically 0.8 centimeters or` smaller in diameter.
The mirror surfaces themselves are typically 7.75 millimeters in diameter and have a typical thickness of 4 millimeters. The curved concave mirror surface of block 22 has a very long radius of curvature on the order of 60 centimeters. Mirror 26 is apertured to ensure that off-axis modes of operation are suppressed while allowing the on-axis TEMoo mode to lase. Lasing can best take place when the aperture of the tilted mirror 26 is aligned so that the ray which is normal to the outer of the aperture on the mirror 26 is also on a radius of the curved mirxor 22. The mirror blocks 22, 24, 26 and 28 are typically sealed with epoxy and the cathode block 12 is typically sealed with indium metal seals. The body of the laser block 10 is of glass ceramic material which has an extremely low, and preferably zero, coefficient of e~pansion over the range of temperatures desired.
The reflectivity of the mirror coating is typically on the order of 99.94%. Transmission is typically less than 0.1%
and the scattering losses are typically on the order of 100 parts per millions. A typical minimum lasing threshold anode-cathode current is on the order of ~ to 2~ milliamperes. Tuning is accomplished by moving the mirror blocks 22 and 26. Then, after the laser is tuned the positions of the mirror blocks are accurately attached by a suitable sealant such as epoxy.
The resonance frequency is an optical frequency which 1~
sd/~ -13-t ~33615 ~pically is on the order of lol4Hz. In normal use it is desired that tlle resollance frequency of the cavity be tuned to the center of tlle gain curve, or as near as possible to the center, to a fraction of the wavelength. In Figures 4, 5, 6, 7 and 8 the pyramid angle is designated by the symbol ~. In Figure 6, two laser paths are shown, one defined by the numerals 14a, b, c and d and the other defined by the numerals 14e, f, g, and h.
The laser path length is nominally a square, but movement of the laser path down varies the path length from that shown by 14a, b, c and d to that shown by the longer path 14e, f, g and h. The relation between the mirror motion and the path length is shown more graphically in Figure 7. Two restraints apply:
first, the lasing beam must not be vignetted by the laser bores 30a, b, c and d, and second, the beam must be within the aperture of the mirror on the mirror block 26. A vertical projection of Figure 6 is shown in Figure 4.
To a first approximation if we are to change the cavity length by a distance equal to a wavelength, then a displacement h (Fig. 4) effectively translates the aperture of the tilted mirror 26 inward a distance d = h tan ~. The desired motion in the directions shown in Figure 7 by the "s", is on the order-of ~
of a wavelength of the lasing light. From Figure 7 it is seen that s = 0.707d ~a square lasing path is assumed), and d = the - wavelength divided by 1.414 which is equal to 6.33 x 10 centimeters.
The lasing beam diameter, dB is less than or equal to 0.089 centimeters while the bores 30a, b, c, and d are sd/?~ -14-.. ~. ~ ' ~ .
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~133~i5 GCD 78-3 1 typically of a diameter dg at least equal to 0.1778 centimeters.
2 The t:otal allowable motion for d, ~d is 0.0880 centimeters where h = ~ 0.0440 centimeters. From this, the angle ~ may be cal-4 culat:ed as the ratio of d to h or 1.017 x 10 3 radians which is about 3.49 arc minutes. - ~
6 In Figure S the curvature of the surface has been 7 exaggerated, and the radius R is out of proportion. The radius 8 of the concave mirror on block 22 is shown very short, but in 9 actuality it is on the order of 60 centimeters. The beam position on the curved mirror face from dead center wherein 11 equals zero to a point Qr from the center, ~r = aR = (l.Oi7 12 x iO 3) ( 60) = 0.061 centimeters. The beam radius is Ou0898 13 centimeters divided by 2 or 0.0449 centimeters. With the beam 14 displaced a distance ~r = 0.061 centimeters, the edge of the beam lies at a distance of O.lOS9 centimeters from the center 16 of the curved mirror. The curved mirror typically has an aperture 17 on the order of 0.4 centimeters in diameter or 0.2 centimeters in 18 radius. Thus, a margin of 0.2 - 0.11 ~ 0.09 centimeters is provide .
19 This sets the limit on the amount of allowed increase in the angle

20 to 0.09/60 = 1.5 x 10 3 radians, the allowable shift of the lasing

21 beam on the face of the curved mirror 22. Further, the bores 30 abc

22 limit the amount by which the mirrors can be shifted. When mirror 3

23 is tilted, the plane of the lasing path also tilts through an

24 angle ~, and the base of the cathode block 12, as shown in

-25 Figure 8 needs to be tilted through that same angle so that the

26 base is parallel to the lasing plane. The base of the cathode

27 block 12 may then be attached into, for example, a guidance

28 system with the knowledge that the angular measure determined

29 from information contributed by the ring laser is an angle and angular rate measured both perpendicular to the laser path and , 31 to the mounting face.
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~133615 GCD 7~-3 ~, 1 ¦ Although a square laser path has been shown, it is 2 ¦ obvious that the principles set forth herein may be used with 3 ¦ othes rectangular and quadrilateral paths. It is intended that 4 ¦ the concepts of this invention should be applied to such paths 5 ¦ by tilting at least one of the mirrorS at a pyramid angle. , ¦ It is also apparent that a three sided laser path may 7 ¦ be used or, alternatively, a multi-sided lasçr path having 8 ¦ more than four branches may be used with at least one of the 9 ¦ mirrors having a small pyramid angle so that slidlng of the 10 ¦ concave mirror shortens or lengthens the laser path, and with 11 ¦ the aperture on the concave mirror.
12 ¦ It is also apparent that the apparatus and methods of 13 ¦ this invention can be used to tune other optical resonators by 14 ¦ tilting one of the resonator mirrors so that movement of the 15 ¦ tilted mirror in the direction of tilt shortens or lengthens the 16 ¦ resonator path length.
17 It is intended that the coverage shall include tuning 18 of straight as well as nonstraight optical resonator paths.
19 It shall also cover the tuning not only of active resonators but of passive resonators as well.
21 Further, it shall not matter if the optical resonator 22 is stable or nonstable.
23 The invention has been described in detail above, 24 and a specific embodiment has been given. It is not intended, however, that the invention shall be limited by that description, 26 but only by that description taken together with the descriptive ~ ~ pP~
A 27 matter in the a~7r'--~ claimq.
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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A ring laser, including means forming a resonant cavity, an active gaseous medium within said cavity, a pump-ing source, and energy abstracting means, comprising;
a block defining said resonant cavity in a closed path containing said active gaseous medium, including at least one laser gain region within said cavity, said means forming a resonant cavity including a plurality of mirrors positioned within said gaseous medium in said cavity, a cathode and at least two anodes connected by passageways formed in said block through said gain regions of said cavity, the passage-ways between said cathode and said anodes including said gain regions;
at least one of said mirrors being concave, and the remaining mirrors being substantially planar;
at least one of said concave mirrors being slideably mounted upon a surface tilted at a pyramid angle relative to the other said mirrors;
at least one of said planar mirrors being tilted at a pyramid angle relative to the other said mirrors; and at least one of said mirrors being partly trans-missive.

2. Apparatus as recited in claim 1 in which at least one of said tilted mirrors has an aperture for suppressing unwant-ed modes of oscillation.

3. Apparatus as recited in claim 2 in which said mirrors are four in number, said concave mirror being mounted upon said surface which is tilted at a pyramid angle relative to planes normal to said planar mirrors whereby the position of said tilted mirror defines the lasing path.

4. Apparatus as recited in claim 3 in which said concave mirror is apertured to suppress unwanted modes of oscillation.

5. Apparatus as recited in claim 3 in which two of said planar mirrors are substantially parallel to each other, and one of said planar mirrors is apertured to suppress unwanted modes of oscillation.

6. Apparatus as recited in claim 1 in which said mirrors are positioned and configured such that laser beams reflected by said mirrors are substantially coplanar, at least said tilted planar mirror being apertured to suppress unwanted modes of oscillation.

7. Apparatus as recited in claim 6 in which said mirrors include two nonadjacent substantially planar parallel mirrors, a concave mirror, and a third planar mirror which is tilted at a pyramid angle relative to the other said mirrors.

8. Apparatus as recited in claim 7 in which said mirrors are positioned and configured to support a substantially rec-tangular laser path;
in which said cathode is attached to said block;
said anodes being a pair of anodes each positioned adjacent a different one of said two nonadjacent planar par-allel mirrors;
said passageways formed in said block between said cathode and said anodes extending from said cathode, thence to the region of said tilted planar mirror, thence in two opposite directions through said gain regions of said lasing path into the regions of said parallel mirrors and said anodes.

9. In an optical resonator having means forming a resonant cavity, active gaseous media within said cavity, a pumping source, and an energy abstracting means, said means forming a resonant cavity including at least three mirrors with one said mirror being concave and the others planar, the improvement comprising support means for support-ing said concave mirror at a tilted pyramid angle with res-pect to a plane defined by the other said mirrors.

10. Apparatus as recited in claim 9 in which the im-provement further comprises a guiding surface on said support means at said pyramid angle relative to said defined plane for each said tilted mirror for guiding the positioning of its said tilted mirror.

11. A method for adjusting the laser path length of a ring laser, said ring laser having at least a resonant cavity defined by a plurality of mirrors, active gaseous media within said cavity, a pumping source, and energy abstracting means, including a first block with said resonant cavity therein for containing said gaseous media and having sufficient volume to allow formation of a multisided ring laser beam within said gaseous medium, a cathode and two anodes connected by gas-contain-ing passageways to said resonant cavity, the path between said cathode and anodes including two gain regions of said cavity and configured to cause electrical discharge in opposing directions in said gain regions, at least one of said mirrors being concave and apertured to suppress unwanted modes of oscillation, and the remaining said mirrors being substantially planar with at least one of said concave mirrors being mounted to slide upon a surface which is tilted at a pyramid angle relative to the other said mirrors comprising:
translating at least one said concave mirror on said surface in a direction substantially perpendicular to the optical axis of said resonant cavity while maintaining said pyramid angle constant to tune said resonant cavity.

12. A method for adjusting the laser path lengths of a ring laser, said ring laser having at least a resonant cavity, active gaseous media, a pumping source, and energy abstracting means, including a first block with four conduits therein for containing a ring laser beam, a gaseous laser gain medium within said conduits, said resonant cavity being defined by at least four mirrors positioned and configured to produce said ring laser beam in said conduits, a cathode and two anodes connected by passageways to said conduits, the path between said cathode and anodes including gain regions of said conduits in opposing direction of supportable laser beams, one of said mirrors being concave, and the remaining mirrors being substan-tially planar with the planar mirror nonadjacent said concave mirror being mounted upon a surface which is tilted at a pyramid angle relative to the other said mirrors and having an aperture to suppress unwanted modes of oscillation comprising:
translating said concave mirror to tune any produced laser beam;
translating said tilted mirror along said surface in a direction substantially perpendicular to the optical axis of said resonant cavity while maintaining said pyramid angle constant to tune said resonant cavity and to align said aperture to suppress unwanted modes of oscillation.

13. A method for adjusting the length of an optical resonator having a resonant cavity, and energy abstracting means, including at least two mirrors with one said mirror being concave, and tilted support means for supporting said concave mirror at a tilt through a pyramid angle with respect to the other said mirror, comprising:
translating said tilted concave mirror on said surface in the direction of tilt relative to any produced laser beam while maintaining said pyramid angle constant to tune said resonant cavity.

14. A method for adjusting the length of an optical resonator having a resonant cavity, and energy abstracting means including at least two mirrors with at least one said mirror being concave and the remaining mirrors planar, and support means including a supporting surface tilted through a pyramid angle with respect to the other said mirrors for supporting one of said planar mirrors at at tilt, said tilted mirror being apertured to suppress unwanted modes of oscillation comprising:
translating said apertured mirror on said surface in the direction of said tilt and translating said concave mirror to track said aperture to suppress unwanted modes of oscillation and to tune the length of said resonant cavity.