GB2193371A - Laser pumped by electromagnetic radiation - Google Patents

Description

1 GB 2 193 371 A 1

SPECIFICATION erate the laser beam.

In addition to the thermal gradients caused Laser apparatus and method of pumping a by the nonuniform pumping described above, laser high-power optically pumped laser systems 70 exhibit further thermal gradients induced by This invention relates generally to lasers and the use of a cooling system required to cool more specifically to a laser apparatus including the lasing medium. Such a cooling system a diffuser disposed between a pumping source typically includes support structures which in of electromagnetic radiation and a lasing me- terfere with uniform pumping by introducing dium. 75 unpredictable lensing effects between the In electromagnetically pumped laser sys- pumping apparatus and the lasing medium, tems, energy is supplied to a lasing medium thereby introducing thermal gradients into the through the use of a high-intensity source of lasing medium. Further, the cooling itself, typi electromagnetic radiation. Such pumping oper- cally performed by flowing a cooling medium ates, in a manner well known to those skilled 80 over the surface of the lasing medium, induces in the art, to excite the atoms in the lasing additional thermal gradients in the lasing me medium to a metastable state wherein lasing dium. In the manner described above, these can be induced. Optically pumped lasers, for thermal gradients operate to further diminish example, utilize high-intensity flash lamps of the power and quality of the subsequently selected power and wavelength to optically 85 generated laser beam. Additionally, extreme pump a solid-state lasing medium of a se- thermal gradients can cause thermal stresses lected material, and to excite the atoms in the sufficient to fracture and thus ruin the lasing lasing medium to a metastable state. Lasing is medium.

subsequently induced in the lasing medium The subject matter of the present invention either by the incidence of an externally gener- 90 is particularly directed to diminishing those ated coherent light beam, or by internally thermal gradients caused by nonuniform stimulated oscillation; both methods being well pumping of the lasing medium due both to the known to those of ordinary skill in the art. non-complementary geometries of the lamps When it is desired to operate such an opti- and the lasing mediums, and to the lensing cally pumped laser system in a high-power 95 effects introduced by the support structures in pulsed or, continuous duty mode, high-intensity the cooling apparatus.

lamps capable of generating the required It is known that helically shaped pumping quantity of optical radiation are only available, lamps can be used to pump rod shaped lasing to the best of the Inventor's knowledge, in mediun)s with a high degree of uniformity, straight, tubular configurations. Solid state las- 100 thereby greatly diminishing the thermal gradi ing media are available in various configura- ents described above. These helically shaped tions, typical configurations including rectangu- lamps, being closely shaped to the cylindrical lar, rod, and disc-shaped slabs. High-power surface of the rod shaped lasing medium, pro pulsed or continuous duty laser systems em- duce a relatively highly uniform pumping in ploying. such lasing mediums and high-intensity 105 comparison to the straight lamps described lamps suffer the disadvantage that the straight above, However, these helically shaped lamps lamps, normally used in combination with are very inefficient, tending to absorb much of reflectors of various configurations, are incapa- the pumping radiation that misses or passes ble of uniformly pumping the lasing medium. through the lasing medium. Further, it will be That is, optical radiation is not uniformly im- 110 apparent that these helically shaped lamps will pinged over the entirety of the lasing medium. not operate to more uniformly pump lasing This nonuniform purriping is mainly caused by mediums which are other than rod-shaped.

the non-complementary geometries of the Some increases in the uniformity of pump lamps and lasing medium (i.e. a rod shaped ing have been obtained by roughening the lamp and a disc shaped lasing medium), Such 115 reflectors in the pumping apparatus, and/or nonuniform pumping can be corrected in part by roughening the outer surface of the lasing by the selection of an appropriately shaped medium. This roughening tends to diffuse the reflector to more uniformly direct the optical optical radiation, resulting in more uniform radiation generated by the lamp. However, pumping. However, roughening the reflector even with selection of an appropriate reflector, 120 presents the disadvantage of substantially de the remaining nonuniformity of the pumping is creasing the pumping efficiency and hence sufficient to induce thermal variations or gradi- the efficiency of the laser system. Roughen ents within the lasing medium. These thermal ing the surface of the lasing medium presents gradients produce refractive effects in the las- the disadvantage of decreasing the efficiency ing medium, known as thermal lensing, which 125 of the lasing medium in laser systems that distort the subsequently generated laser beam. rely on multiple beam reflections within the These thermal lensing effects are usually most lasing medium. An exemplary system relying prominent proximate the surface of the lasing on multiple beam reflections within the lasing medium, and substantially limit the volume of medium is shown in 3,633, 126 (Martin et al.) the lasing medium which can be used to gen- 130 incorporated herein by reference. Further, 2 GB2193371A 2 roughening of the lasing medium surface pre- vice constructed in accordance with the inven sents the additional disadvantage of decreastion; ing the structural integrity of the medium by Figure 2 is a sectional view taken along line introducing local regions of high mechanical 2-2 of Figure 1; stress. These regions of high mechanical 70 Figure 3 shows an enlarged portion of tube stress substantially increase the possibility of 28 of laser device 10 of Figures 1 and 2, and fracturing of the lasing medium. schematically illustrates the radiation disper Thus, it would be desirable to provide a sion effects thereof; and laser apparatus wherein the pumping energy is Figure 4 shows a portion of the view of uniformly distributed to a lasing medium-with- 75 Figure 1 enlarged to better illustrate details out substantially decreasing the efficiency-of thereof.

the pumping apparatus or the structural integ- Referring now to Figures 1 and 2, a face rity of the lasing medium, and which is not pumped, optically-pumPed laser device 10 in limited to particular lamp or lasing medium cludes a generally rectangular lasing medium geometries. Such a laser apparatus would 80 12 comprising a homogeneous body of solid have particular application in high-power laser state lasing material such as yttrium aluminum systems, wherein the disadvantages of nonun- garnet (YAG) or neodymium doped silicate iform pumping are most apparent. glass. Lasing medium 12 includes a pair of According to one aspect of the present inopposing face surfaces, 14 and 16, disposed vention, a diffusing means is disposed be- 85 parallel to each other and to a longitudinally tween a solid-state lasing medium and a extending lasing axis 18. Face surfaces 14 pumping means disposed adjacent the lasing and 16 are polished to optical flatness, i.e. to medium for impinging electromagnetic radia- within about one-eighth of the wavelength of tion on the lasing medium. The diffusing the coherent light emitted by lasing medium means preferably comprises a material nor- 90 12. A pair of side surfaces 20, 22 are dis mally substantially transparent to the electro- posed generally perpendicular to face surfaces magnetic radiation having selected portions 14, 16 and parallel to axis 18. Side surfaces thereof adapted to diffuse electromagnetic ra- 20, 22 are polished to be sufficiently optically diation passing there through. clear so as not to interfere with the optical In a preferred embodiment of the invention, 95 pumping described hereinbelow. A pair of mu the laser apparatus is optically pumped, with tually parallel end surfaces 24 and 26 are dis the lasing medium selected-to be a solid-state posed at a 45 degree angle to lasing axis 18.

material having atoms excitable by optical radi- End surfaces 24, 26 are polished to optical ation. The pumping apparatus comprises a flatness and preferably coated with an anti- source of optical radiation such as a flash 100 reflective coating (not shown) to minimize dis lamp, and further includes a reflector at least tortion of light beams passing there through.

partially surrounding the source for directing Lasing medium 12 is situated in a tube 28, the optical radiation to impinge upon the las- the tube extending the length of the lasing ing medium. In this preferred embodiment of medium and being substantially coaxial about the invention, the diffusing means comprises 105 lasing axis 18. Tube 28 comprises a material optical glass, with the glass having selected which is normally transparent to optical radia portions thereof adapted to diffuse the optical tion, for example optically clear glass. In ac radiation. Such diffusion is preferably obtained cordance with the present invention, an outer by roughening the selected portions of the surface 29 of tube 28 is adapted to diffuse glass diffuser, for example using chemical 110 light radiation, preferably by roughening. Such etching, chemical frosting, or mechanical abra- roughening is obtained, for example, by a me sion. chanical roughening process such as grit blast In another aspect of the invention, a method ing, or a chemical roughening process such as of pumping a laser comprises the steps of etching with hydroflouric acid. A chemical providing a solid-state lasing medium and im- 115 coating, comprising magnesium oxide, barium pinging electromagnetic radiation thereon, with oxide, or fine glass powder would similarly at least a portion of the electromagnetic radia- suffice to roughen surface 29 of tube 28.

tion being diffused before it impinges upon A pair of optically clear glass supports 30, -the lasing medium, preferably through the use 32 extend between lasing medium side sur- of a diffuser of the- type described above. A 120 faces 20 and 22, respectively, and an inner preferred embodiment of this method is prac- surface 34 of tube 28 for supporting the las ticed using the laser apparatus described ing medium in a suspended position within the above. tube. A pair of optically clear glass fillers 36 The invention, together with further benefits and 38, each segmental in cross-section, are obtainable from it, may be better understood 125 fastened to tube inner surface 34 so as to from consideration of the following description provide flat glass surfaces 40, 42 spaced in conjunction with the accompanying draw- from lasing medium face surfaces 14 and 16, ings, in which: respectively. There is thus defined a fluid Figure 1 is a schematic, sectional, end view channel 44 between filler surface 40 and las showing a face-Cooled, face-pumped laser de- 130 ing medium face surface 14, and a fluid chan- 3 GB2193371A 3 nel 46 between filler surface 42 and lasing medium 12. It will be understood that various medium face surface 16. configurations of optical apparatus, well A lamp 50 in the form of a tube is dis- known in the art and not shown herein, can posed substantially parallel to and coextensive be used to oscillate and thus amplify beam with face surface 14 of lasing medium 12. 70 62. Such apparatus includes, but is not limited Similarly, a lamp 52 in the form of a tube is to, that shown in the Martin et al. patent ref disposed substantially parallel to and coexten- erenced above. During operation of laser de sive with face surface 16 of lasing medium vice 10, a liquid coolant (not shown) is flowed 12. Lamps 50, 52 are employed to generate over surfaces 14 and 16 of lasing medium 12 optical radiation and optically pump lasing me- 75 via channels 44 and 46.

dium 12, each comprising a flash-type lamp Figure 3 shows an enlarged portion of tube emitting optical radiation in a wavelength suit- 28 with its roughened outer surface 29. As able for exciting the atoms in lasing medium shown, roughened surface 29 diffuses a light 12 to a metastable state. For example, xenon beam 72 passing there through, resulting in a flash lamps, which provide optical radiation 80 plurality of diffused beams 74. As is shown having a wavelength of between 5,000 and schematically in Figure 4, diffused beams 74 9,000 angstroms, are suitable for pumping a are sufficiently numerous in quantity and ran lasing medium comprising neodymium doped dom in direction so as to uniformly radiate glass. To improve the uniformity of the pump- into lasing medium 12, and thereby uniformly ing of lasing medium face surfaces 14 and 16, 85 pump the lasing medium. This uniform pump the radiation emitting portions of lamps 50, ing of lasing medium 12 decreases the magni 52 each extend the entire length of the lasing tude of thermal gradients in lasing medium 12, medium face surface proximate the lamp. increasing the efficiency of laser device 10 A reflector 54 surrounds lamps 50, 52, and the quality of beam 62 generated thereby.

tube 28 and lasing medium 12. Reflector 54 90 For purposes of clearly illustrating the inven preferably comprises a high-intensity reflector, tion, it will be understood that all refractive for example a water-cooled copper shroud effects have been omitted from the illustration having a silvered interior reflecting surface 56. of rays 72, 74 in Figures 3 and 4.

Reflector 54 includes a generally U-shaped A method of pumping a laser in accordance portion 58 surrounding lamp 50 for directing 95 with the present invention comprises providing the electromagnetic radiation emitted by lamp a solid-state lasing medium and impinging to impinge upon surface 14 of lasing me- electromagnetic radiation thereon. At least a dium 12. Similarly, a generally U-shaped por- portion of the electromagnetic maiation is dif tion 60 of reflector 54 surrounds lamp 52 for fused 6efore impinging upon the lasing me- directing electromagnetic radiation emitted 100 dium. It will be understood that a preferred therefrom to impinge upon face surface 16 of embodiment of the method is performed using lasing medium 12. Reflector portion 58 is pre- the laser apparatus described in Figures 1-3 ferably shaped so as to concentrate at least above.

some of the radiation at a focal point 57 on A laser device including a face-pumped, rec- surface 29 of tube 28. Reflector 60 is preferatangular YAG lasing medium and a tube bly shaped so as likewise to establish a focal roughened to diffuse optical pumping radiation point 59 on surface 29 of tube 28, focal yielded an increase in usable beam width on points 57 and 59 being on opposite sides of the order of 40%. This same laser device also the tube. showed an increase in beam quality of ap- In operation, in a manner described in the 110 proximately a factor of ten, beam quality being Martin et al. patent referenced hereinabove, determined as a function of beam ray devia lamps 50 and 52 are energized to pump opti- tion caused by thermal lensing effects within cal radiation into lasing medium 12, and the lasing medium. While it is theorized that thereby to excite the atoms in the lasing me- the diffuser may somewhat decrease the effi- dium to a metastable state. As described in 115 ciency of lamps and reflectors used for optical further detail hereinbelow, the concentration of pumping, it is further theorized that this de the optical radiation onto roughened surface crease in efficiency allowable increase in the 29 of tube 28 operates to diffuse optical radi- optical pumping power. This allowable in -ation generated by lamps 50, 52 before it crease in optical pumping power can be made impinges on lasing medium 12, thereby in- 120 as a result of the more uniform pumping pro creasing the uniformity with which the lasing vided by the invention. This more uniform medium is impinged by the optical radiation. pumping permits the lasing medium to accom After exciting the atoms in lasing medium 12 modate a more uniformly distributed pumping to a metastable state, a beam 62 of coherent power without the resulting thermal gradients light, generated for example by another laser 125 which can decrease beam quality, efficiency device, is oscillatingly passed through lasing and eventually cause fracture of the lasing me medium 12 by multiple internal reflections dium. The increased uniformity of pumping within the lasing medium in a direction gener- can be achieved in an economical manner us ally along lasing axis 18. Beam 62 is amplified ing known processes and materials compatible in magnitude during each pass through lasing 130 with the laser system. Moreover, it can be 4 GB2193371A- 4 achieved in a manner which increases, or at it will be clear that the invention is not so least does not decrease, the efficiency of the limited. Numerous modifications, changes, vari lasing medium, without compromising the me- ations, substitutions and equivalents will occur dium's physical integrity. It thus permits effici- to those skilled in the art within the scope of ent use of the lasing medium to produce a 70 the present invention.

high quality laser beam. The method and

Claims (1)

1. apparatus are not subject to the disadvantages CLAIMS of the prior art

   described above. Further, they 1. Laser apparatus comprising:

   are readily adaptable to various configurations a solid-state lasing medium; and geometries of laser system components. 75 pumping means disposed adjacent said las- While the invention has been shown and ing medium for impinging electromagnetic radi described with respect to a face-pumped, op- ation upon said lasing medium; and tically-pumped laser system employing a rec- diffusing means disposed between said 5 tangular lasing medium slab, it will be under- pumping means and at least a portion of said stood that the invention is not so limited. It 80 lasing medium for diffusing electromagnetic ra can be employed, for example, with infrared diation passing there through before said elec pumped lasers, or electromagnetically pumped tromagnetic radiation impinges upon said las lasers of other wavelengths with appropriate ing medium.

   modifications of the diffuser taught herein. 2. The laser apparatus of claim 1 wherein Such modifications would include the selection 85 said pumping means includes:

   of a substantially transparent material for the at least one source for generating electro diffuser, and an appropriate adaptation to that magnetic radiation disposed adjacent said las material to obtain the desired diffusing effect. ing medium; and Further, the invention is not limited to face- a reflector at least partially surrounding said pumped slab lasers, but can be used in any 90 source for directing said electromagnetic radia other laser device configuration wherein it is tion to impinge upon said lasing medium.

   possible to interpose a diffuser between elec- 3. The laser apparatus of claim 2 wherein tromagnetic pumping radiation and a lasing said diffusing means comprises:

   medium. Such systems include, for example, a diffuser comprising material normally sub- rod or disc shaped lasing mediums, and lamps 95 stantially transparent to said electromagnetic or other radiation sources of various shapes radiation; and curvatures. A laser embodying the inven- said diffuser having at least selected por tion may be operated in a high power pulsed tions thereof adapted so as to diffuse electro mode or continuous duty mode. magnetic radiation passing there through.

   While the described embodiment includes a 100 4. The laser apparatus of claim 3 wherein diffuser incorporated on the surface of tube said source comprises a lamp for generating 28 and hence surrounding and substantially optical radiation.

   coextensive with lasing medium 12, it will be 5. The laser apparatus of claim 4 wherein understood that the invention is not so lim- said diffuser comprises glass.

   ited. The diffuser could, for example, be 105 6. The laser apparatus of claim 5 wherein placed only at locations surrounding lasing said selected portions on said diffuser are medium 12 where it would provide the most roughened to diffuse optical radiation.

   function. Such locations might include the por- 7. The laser apparatus of claim 6 wherein tions of tube 28 which would most affect said selected portions on said diffuser are "hot spots" within a lasing medium 12. Fur110 roughened by a process of chemical etching.

   ther, the reflector needn't be shaped to focus 8. The laser apparatus of claim 6 wherein the radiation onto the surface of the diffuser. said selected portions of said diffuser are While such an arrangement operates to most roughened by a chemical coating.

   effectively diffuse the radiation, the radiation 9. The laser apparatus of claim 6 wherein will be diffused as long as it passes through 115 said selected portions of said diffuser are the diffuser, regardless of the location of the roughened by a process of mechanical abra- focal point. sion.

   While the diffuser in laser device 10 is situ- 10. The laser apparatus of claim 3 wherein ated on a surface of tube 28, the invention is said reflector comprises a reflector shaped so not so limited. It will be appreciated by those 120 as to tend to establish a focal point at at skilled in the art that diffusion can be achieved least one of said selected portions of said by appropriately adapting, for example, surdiffuser, - faces of fillers 36, 38. Or a diffuser indepen- 11. Laser apparatus comprising:

   dent of that structure shown in laser system a generally rectangular slab of solid-state 10 could be introduced so as to otherwise 125 lasing medium having a longitudinally extend diffuse optical radiation generated by lamps ing lasing axis; 50, 52 before it impinges on lasing medium source means disposed generally parallel to 12. said lasing axis and substantially coextensive Thus, while preferred embodiments of the with said lasing medium for generating electro- invention have been illustrated and described, 130 magnetic radiation; GB2193371A 5 reflector means surrounding at least a por- at least one source disposed substantially tion of said source means for directing said parallel to said lasing medium and substantially electromagnetic radiation to impinge upon said coextensive therewith along said lasing axis lasing medium; and for generating electromagnetic radiation; diffusing means disposed between said 70 a reflector surrounding said source and said reflector means and at least a portion of said lasing medium, said reflector shaped so as to lasing medium for diffusing electromagnetic ra- direct said electromagnetic radiation to im diation passing there through before said elec- pinge upon said lasing medium; tromagnetic radiation impinges upon said las- a tube comprising material normally substan- ing medium. 75 tially transparent to said electromagnetic radia 12. The laser apparatus of claim 11 wherein tion disposed about said lasing medium be said diffusing means comprises: tween said source and said lasing medium, a diffuser comprising material normally sub- said tube substantially coaxial with said lasing stantially transparent to said electromagnetic axis and coextensive with said lasing medium radiation; and 80 and said source, said tube having selected said diffuser having at least selected porportions thereof adapted to diffuse electro tions thereof adapted so as to diffuse electro- magnetic radiation passing there through be magnetic radiation passing there through. fore said electromagnetic radiation impinges 13. The laser apparatus of claim 12 upon said lasing medium; and wherein: 85 cooling means including a fluid channel adja said lasing medium includes at least one op- cent said lasing medium defined within said tically plane surface disposed substantially par- tube for cooling said lasing medium.

   allel to said lasing axis, with said source 25. The laser apparatus of claim 24 means and said reflector means disposed rela- wherein:

   tive to said lasing medium so as to direct said 90 said source comprises a lamp for generating electromagnetic radiation to impinge upon said optical radiation; and optically plane surface. said tube comprises glass.

   14. The laser apparatus of claim 13 wherein 26. The laser apparatus of claim 25 wherein said source means comprises at least one said selected portions of said tube comprise lamp for generating optical radiation. 95 roughened portions on a surface of said tube.

   15. The laser apparatus of claim 14 wherein 27. The laser apparatus of claim 26 wherein said diffuser comprises glass. said roughened portions are roughened by a 16. The laser apparatus of claim 15 wherein process of chemical etching.

   said diffuser comprises a tube of optical glass 28. The laser apparatus of claim 26 wherein surrounding said lasing medium and coexten- 100 said roughened portions are roughened by a sive therewith along said lasing axis. chemical coating on the surface of said tube.

   17. The laser apparatus of claim 16 wherein 29. The laser apparatus of claim 26 wherein said selected portions are on a surface of said said roughened portions are roughened by a tube. process of mechanical abrasion.

   18. The laser apparatus of claim 17 wherein 105 30. The laser apparatus of claim 25 said selected portions are roughened to dif- wherein:

   fuse optical radiation. said lasing medium includes a pair of gener 19. The laser apparatus of claim 18 wherein ally parallel surfaces disposed parallel to said said selected portions are roughened by a lasing axis and a pair of generally parallel process of chemical etching. 110 sides disposed perpendicular to said surfaces.

   20. The laser apparatus of claim 18 wherein 3 1. The laser apparatus of claim 30 and said selected portions are roughened by a further including at least one of said lamps chemical coating on the surface of said tube. disposed adjacent each of said parallel sur 21. The laser apparatus of claim 18 wherein faces.

   said selected portions are roughened by a 115 32. The laser apparatus of 30 and further process of mechanical abrasion. including a support positioned between each 22. The laser apparatus of claim 18 and of said lasing medium sides and said tube for further including cooling means for directing a supporting said lasing medium within said -cooling fluid against at least one of said sur- tube; faces of said lasing medium. 120 said cooling means including a separate fluid 23. The laser apparatus of claim 17 wherein channel adjacent each of said lasing medium said reflector comprises a focusing reflector surfaces, each of said fluid channels defined shaped so as to tend to establish a focal po- by said tube, said supports and one of said int at at least one of said selected portions of lasing medium surfaces.

   said diffuser. 125 33. The laser apparatus of claim 26 wherein 24. A face-pumped laser apparatus compris- said reflector comprises a focusing reflector ing: shaped so as to tend to establish a focal po a generally rectangular slab of solid-state int at at least one of said selected portions of lasing medium having a longitudinally extend- said diffuser.

   ing lasing axis; 130 34. A method of pumping a laser compris- 6 GB2193371A 6 ing the steps of: step of diffusing comprises the steps of:

   providing a solid-state lasing medium; positioning a diffuser, comprising material impinging electromagnetic radiation upon normally substantially transparent to said elec said lasing medium; and tromagnetic radiation, between said reflector diffusing at least a portion of said electroand said lasing medium; and magnetic radiation before said electromagnetic adapting at least selected portions of said radiation impinges upon said lasing medium. diffuser so as to diffuse electromagnetic radia 35. The method Of Claim 34 wherein said tion passing there through.

   impinging step comprises the steps of: 46. The method of claim 45 wherein:

   disposing at least one source of electromag- 75 said lasing medium includes at least one op netic radiation adjacent said lasing medium; tically plane surface disposed substantially par and allel to said lasing axis; and positioning a reflector to at least partially said source means and said reflector means surround said source and direct said electrodisposed relative to said lasing medium so as magnetic radiation to impinge upon said lasing 80 to direct said electromagnetic radiation to im medium. pinge upon said optically plane surface.

   36. The method of claim 35 wherein said 47. The method of claim 46 wherein said diffusing step comprises the steps of: source means comprises at least one lamp for positioning a diffuser, comprising material generating optical radiation.

   normally substantially transparent to said elec- 85 48. The method of claim 47 wherein said tromagnetic radiation, between said reflector diffuser comprises glass.

   and at least a portion of said lasing medium; 49. The method of claim 48 wherein said and diffuser comprises a tube of optical glass sur adapting selected portions of said diffuser rounding said lasing medium and coextensive so as to diffuse electromagnetic radiation 90 therewith along said lasing axis.

   passing there through. - 50. The method of claim 49 wherein said 37. The method of claim 36 wherein said selected portions of said diffuser are on a sur source comprises a lamp for generating optical face of said tube.

   radiation. 5 1. The method of claim 50 wherein said 38. The method of claim 37 wherein said 95 selected portions are roughened to diffuse op diffuser comprises glass. tical radiation.

   39. The method of claim 38 wherein said 52. The method of claim 51 wherein said adapting step is performed by roughening por- selected portions are roughened by a process tions of said diffuser to diffuse optical radia- of chemical etching.

   tion. 100 53. The method of claim 51 wherein said 40. The method of claim 39 wherein said selected portions are roughened by a chemical roughening step is performed by a process of coating on the surface of said tube.

   chemical etching. 54. The method of claim 51 wherein said 41. The method of claim 39 wherein said selected portions are roughened by a process roughening step is performed by the applica- 105 of mechanical abrasion.

   tion of a chemical coating. 55. The method of claim 45 and further 42. The method of claim 39 wherein said including the step of cooling said lasing me roughening step is performed by a process of dium by directing a cooling fluid against at mechanical abrasion. least one of said surfaces of said lasing me- 43. The method of claim 36 wherein said 110 dium.

   reflector comprises a focusing reflector shaped 56. The method of claim 45 wherein said so as to establish a -focal point at at least one reflector comprises a focusing reflector shaped of said selected portions of said diffuser. so as to establish a focal point at at least one 44. A method of pumping a laser compris- of said selected portions of said diffuser.

   ing the steps of: 115 57. Laser apparatus or laser pumping providing a generally rectangular slab of method substantially as hereinbefore described solid-state lasing medium having a longitudi- with reference to the accompanying drawings nally extending lasing axis; or the indicated alternatives thereto.

   disposing a source generally parallel to said Published 1988 at The Patent Office, State House, 66/71 High Holborn, lasing axis and substantially coextensive with London WC 1 R 4TP. Further copies may be obtained from said lasing medium for generating electromag- The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD.

   netic radiation; Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87.

   positioning a reflector to surround at least a portion of said source for directing said elec- tromagnetic radiation to impinge upon said lasing medium; and diffusing at least a portion of said electromagnetic radiation before said electromagnetic radiation impinges upon said lasing medium.

   45. The method of claim 44 wherein said