GB1566716A

GB1566716A - Laser resonators and their manufacture

Info

Publication number: GB1566716A
Application number: GB1115776A
Authority: GB
Original assignee: General Electric Co PLC
Current assignee: General Electric Co PLC
Priority date: 1977-03-15
Filing date: 1977-03-15
Publication date: 1980-05-08

Description

(54) iMPROVEMENTh IN OR RELATING TO LASER RESONATORS AND ThEIR MANUFACrURE (71) We, THE GENERAL ELECTRIC COMPANY LIMITED, of 1 Stanhope Gate, London WIIA H, a British Company, do whereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be per formed, to be particularly described in and by the following statement:: This invention relates to laser resonators Ct the type (hereinafter referred to as the type specified) including, mounted within a housing having internally reflecting walls, components consisting of an optical pumping source, an elongated solid state active laser element disposed between a mirror which reflects substantially all of the radiation from said element incident upon it and an output mirror which is partially transmissive to said radiation, and a passage Qswitch comprising a saturable absorber re nsive to said radiation. The invention also relates to the manufacture of laser resonators of this type.

Saturable absorbers, usually comprising dyes which possess the property of bleaching in response to the absorption of sufficient radiation emanating from a laser element, so as to change from an opaque to a transparent state and thus permit the emission of a pulse d the laser output, and of relaxing back to the initial opaque state, the relaxation starting immediately after the passage of the pulse through the dye, are well known for use as Qvitches in laser resonators.

Hitherto the dyes have usually been employed in solution in suitable liquid solvents.

the solution being contained in a cell situated between, and in close proximity to, the laser element and one of the mirrors; however, dye solutions impose limitations on the permissible pulse repetition rate, due to cclmveotion currents set up in the liquid dye cell, and in addition are generally subject to limitations on operating temperature.

Evaporation of the solvent may also occur, restricting the operating life of the dye cell; this effect is distinct from that of degradation of the dye in the presence of radiation from the optical pumping source, which occurs with many dyes. It has also been proposed to incorporate a dye in a solid matrix, for example composed of glass or a polymeric plastic material, but difficulties have been encountered in the manufacture of solid dyecontaining components of these forms, the dye usually undergoing degradation at the temperatures employed for forming a glass matrix, or reacting with a polymerisation catalyst or plasticiser employed for forming a polymer matrix from a monomer.

It is an object of the present invention to provide an improved form of compact laser resonator including in its construction a saturable absorber Q-switch of the type consisting of a suitable dye incorporated in a polymer matrix, and it is a further object of the invention to provide improved methods of manufacturing a Q-switch of this type.

According to the invention, in a laser resonator of the type specified, the Q-switch is a rigid cell consisting of a solid solution of a dye, which is a saturable absorber responsive to radiation of the wavelength emitted by the active laser element, in a matrix consisting of a polymeric plastic material which is transparent to said radiation, the assembly of said dye and said matrix material being resistant to degradation by exposure to radiation from the pumping source, and the said Q-switch is located between, and in axial alignment with the laser element and one of the said mirrors and is spaced from such mirror by a substantial distance.

The said distance by which the Q-switch is spaced from one of the said mirrors is preferably at least equal to half the length of the laser resonator.

The conventional location of a Q-switch in a laser resonator is between the active laser element and the fully reflecting mirror, but the alternative location between the laser element and the output mirror can also be used; the latter arrangement has some advantages in the laser resonator of the present invention, in terms of ease of fabrication and alignment of components.

The dye and the polymeric matrix material employed for the Q-switch cell must, of course, be chemically inert to one another, and must be stable at all temperatures to which the resonator will be subjected in storage or in operation. The dye should be one which has fast relaxation, that is t say has the property of rapidly reverting to the opaque condition after the passage of each laser output pulse through the Q-switch in operation, but the relaxation should not be so fast as to produce mode-locking effects.

One preferred class of dyes consists of divalent transition metal-dithiene complexes having a square planar structure, the suitability of individual dyes depending on the wavelength of the laser output. Suitable polymers for use for the Q-switch matrix include, for example, acrylic resins such as polymethyl methacrylate, cyanoacrylic resins, cellulose acetate, and polyesters, the choice of a specific polymer being governed largely by the solubility of the particular dye used in the solid polymer, and freedom from absorption bands at the laser output wavelength.

According to a feature of the invention, in the manufacture of the laser resonator the saturable absorber Q-switch cell is prepared by forming a solid solution of a stable dye, as aforesaid, is a polymer matrix, without the use of any plasticiser or polymerisation catalyst which might have a detrimental effect on the dye due to chemical reactions.

Thus a preferred method of manufacturing a laser resonator according to the invention includes the steps of forming a switch cell by preparing a solution consisting only of a dye and the monomer or polymer of the material which is to constitute the said matrix, in a suitable solvent, and consolidating the solution to form a body consisting of a solid solution of the dye in the polymer matrix, and then assembling the components of the laser resonator with the Q-switch cell so formed located between, and in axial alignment with, the laser element and one of the mirrors, and spaced from such mirror by a substantial distance.

In one method of forming the Q-switch cell, the polymer which is to constitute the matrix is dissolved in a suitable volume of solvent to give a solution of a relatively high concentration but of pourable consistency, the desired proportion of the dye is dissolved in the polymer solution, and the solvent is completely evaporated in a controlled manner, the solution first being cast in a suitable mould if desired. Where the polymer is an acrylic resin, the solvent employed is suitably a halogenated hydrocarbon such as chloroform, carbon tetrachloride, methyichloride, or dichloroethane; suitable solvents for cellulose acetate are acetone and other lower aliphatic ketones.

In some cases, for example when the matrix is an acrylic resin, after evaporation of the solvent the residual body consisting of the matrix and dye may be further consolidated by the application of pressure thereto in a heated mould, if desired the said body being sandwiched between plates of the matrix material or glass plates before being introduced into the mould. However, such hot pressing treatment is not required when cellulose acetate is used as the matrix. A mould used for casting or consolidation of the matrix-dye solution is preferably formed with two opposite optically flat internal surfaces, so as to impart optical flatness to those surfaces. of the dye cell through which the radiation emitted by the laser element will pass in operation of the laser resonator, thus avoiding the necessity for subsequent polishing of these surfaces.If the dye cell is required to have anti-reflection coatings, these can either be deposited directly on the optically flat plastic surfaces of the cell, or if the cell is supported between glass or plastic plates, anti-reflection coatings are formed on the outer surfaces of the plates before-the dye-matrix body is placed between the plates.

In an alternative method of forming the Q-switch, the solid dye cell is formed between two plates of glass or suitable plastic material transparent to the laser emission, with optically flat surfaces, by mixing a liquid monomer of an adhesive resin, such as a cyanoacrylic resin, which is to constitute the matrix, with a solution of the dye in a suitable solvent, on one plate, covering the resulting dye-monomer solution with the second plate, and allowing the solution to solidify in the cold. When glass plates are used, polymerisation of the monomer is cat-.

alysed by hydroxyl ions present on the glass surfaces. The outer surfaces of the plates may be previously provided with anti-reflection coatings if required.

The requisite concentration- of the dye in the cell matrix is determined by the total amount of dye required to give the desired degree of absorption, and hence by the active thickness of the cell in the direction of travel of the laser emission through the cell: the degree of absorption desired is directly related to the single pulse output energy required, and to the resonator configuration.

The laser element, which is usually in the form of a rod, may be composed of any known suitable host material, for example yttrium aluminium garnet, yttrium aluminate, silicate glass, phosphate glass, or calcium tungstate, containing a dopant, for example neodymium for producing emission of a desired wavelength. - The dye employed in the Q-switch must, of course, be one whose absorption band matches the wavelength of the laser emission.

The construction of a laser resonator in accordance with the invention, wherein either the fully reflecting mirror or the output mirror is spaced from the Q-switch by a distance preterably at least equal to lxalE the length of the laser resonator, is gdvantageous in imparting improved beam characteristics to the resonator, the beam divergence being reduced as compared with that resulting from the usual arrangement of Q-switch and fully reflecting mirror or output mirror in close proximity to one another, TheNfully reflecting mirror or the output mirror may be spaced from the Qswitch by a - gap, or by a solid component, such as a rod, composed of material which is transparent to the laser emission and which is suitably the same as the laser host material.

Thus one preferred form of laser resonator in accordance with the invention in clues, in addition to the pumping source, a series of separate components in axial alignment but spaced apart by gaps, which components consist of a laser rod carrying a first, fully reflecting, mirror un one end, a solid dye cell Q-switch spaced from the end of the laser rod remote from the said mirror, and an output mirror supported on a suitable substrate and appropriately spaced, as aforesaid from the side of the Q-switch remote from the laser rod. With this ar rangement, anti-reflection coatings are provided on the end of the laser rod remote from said fist mirror, and on the two op posite surfaces of the Q-switch respectively lacing the laser rod and the output mirror.

Another preferred form of laser resonator in accordance with the invention includes a composite structure consisting of, in axial alignment, a laser rod, a solid dye cell Q switch, and an extension rod which is transparent to the laser emission, joined together with the dye cell sandwiched between the inner ends of the two rods, a fully reflecting mirror and an output mirror being carried by the outer ends of the laser rod and extension rod respectively. Preferably the laser rod and the extension rod are of substantially equal length, so that the Q-switch is located at or near the centre of the resonator housing, thus minimizing beam divergence in operation.

In either of the above-described preferred forms of laser resonator, both mirrors may be plantar; alternatively, with advantage in some cases, the fully reflecting mirror may be curved, the output mirror still preferably being planar, In one method of manufacturing a composite structure of the form described above, the plastic dye cell is bonded to the inner ends of both rods by means of a laser damage-resistant optical cement whip is capable of adhering to the plastic surfaces, which preferably has a refractive index as close as possible to that of the materials of the laser rod and extension rod, and which has low absorption at the laser emission wavelength.In an alternative method of manufacturing the composite structure, the inner ends of the laser rod and the extension rod, which have optically flat surfaces, are employed as the mould surfaces for consolidation of the dye cell: thus the polymer-dye solution is cast in a suitably shaped mould and complete evaporation of the solvent is effected slowly and under a carefully controlled temperature schedule in the mould, and the dye cell so formed is placed between the rod ends and pressure is applied to the rods, the polymer matrix being self-adherent to the rod surfaces under pressure. In either of these methods of manufacturing the composite structure, the two mirrors are first formed on the respective rod outer ends, and the rods and dye cell are accurately aligned in a jig before being joined together.The composite structure is advantageous, as compared with the arrangement of components separated by gaps, in that accurate alignment of the mirrors is facilitated in the composite structure.

The housing of a laser resonator in accordance with the invention may comprise an internally reflecting cavity of conventional form, in which the optical pumping source, laser rod, Q-switch and fully reflecting and output mirrors are mounted in appropriate relative positions. However, the housing preferably consists of a block, suitably of cylindrical shape, of a polymeric plastic material which is transparent to the pumping radiation. the block being formed with tubular cavities into which the optical pumping source and resonator components are inserted, and having on its external surface an internally reflecting layer the exterior of which is covered by a protective coating.The latter form of housing provides a robust construction for the resonator as a whole, and is especially advantageous where the resonator comprises a composite structure of laser rod, Q-switch and extension rod as described above, since the composite structure may suffer from mechanical weakness at the joints between the components, and the whole structure is adequately supported by the plastic block. The polymer constituting the housing material must be resistant to degradation under radiation from the optical pumping source.

The above-described form of solid plastic housing has the additional advantage that, according to a further feature of the invention, the plastic block can be impregnated with a fluorescent material which improves the pumping efficiency in operation of the resonator, by spectral conversion of ultra violet radiation emitted by the optical pumping source into radiation of wavelength, within the required pump band: for example, rhodamine 6G is a suitable fluorescent dye for us in this manner, at a concentration of 10-3 to 10-5 molar in the plastic material, in conjunction with a neodymium-doped laser rod.

Some specific saturable absorber Q-switch cells suitable for use in laser resonators in accordance with the invention, and the methods which we have employed for the manufacture of the Q-switch cells, will now be described in the following examples.

EXAMPLE .1 The dye employed in the Q-switch of this example is bis-(4,41-dimethylaminodithio- benzil)-nickel, and the Q-switch consists of a solid solution of this dye in polymethyl methacrylate. For the manufacture of the Q-switch, powdered optical quality polymethyl methacrylate is dissolved in chloroform to give a solution of concentration approximately 66 grams of polymer per litre of chloroform, and a small amount of the above dye is added to give an approximately 10-4 molar concentration of the dye in the polymer solution (the actual dye concentraction being adjusted according to the resonator configuration and the laser output energy required).The solution is poured on to a flat plate, and the chloroform is caused to evaporate by passing a stream of inert gas, for example nitrogen, over the solution at room temperature until substantially all the chloroform has been removed, and finally placing the plate in an oven maintained at 40"C. for 2 to 3 hours to remove the last traces of chloroform. This leaves a film of the polymer-dye combination, which is then sandwiched between two optically flat discs of polymethylmethacrylate under a pressure of 3000 pounds per square inch in a precision mould heated to 140 C: alternatively, glass discs may be used. If required, the discs, whether of polymethyl methacrylate or glass, may be coated externally with an anti-reflection film of a suitable composition depending on the wavelength of the laser output.The assembly of the two discs and the polymer-dye body forms a rigid disc 2 to 3 mm thick and, for example. 30 to 40 mm in diameter, from which individual cells of the desired Q-switch diameter are suS sequently cut.

EXAMPLE 2 The Q-switch of this example consists of a pair of glass discs about 1 mm thick and of substantially the same diameter as the laser rod with which the switch is to be operated, or of larger diameter, and having optically flat surfaces on both sides, cemented together by a solid solution of the dye referred to in Example 1 in an adhesive cyanoacrylic resin. The Q-switch is prepared by placing a small quantity of liquid cyanoacrylic monomer on one of the glass plates, adding a quantity of a nearly saturated solution of the dye in chloroform, causing the chloroform to evaporate, and then placing the second glass plate on top of the liquid and allowing solidification of the dye-cyanoacrylic resin solution to take place in the cold, forming a dye cell sandwiched between the glass plates.If desired, for con venience, glass plates of a relatively large diameter, for example 30 to 40 mm may be employed, small discs of the desired diameter of the Q-switches being cut from the completed dye cell sandwich.

The particular dye referred to in the above examples is suitable for use with a laser rod composed of neodymium-doped glass or neodymium-doped yttrium aluminium garnet, but it will be understood that dye cells containing different dyes, which may be required for us in conjunction with laser rods of different materials, may be manufactured by either of the techniques described in the examples, if desired also using different polymers for the matrices of the dye cells, and different solvents.

Some specific forms of laser resonators in accordance with the invention will now be described by way of example, with reference to the diagrammatic drawings accompanying the Provisional Specification, in which Figure 1 shows, in side elevation, an assembly of separate components for use in one form of resonator, Figures 2 and 3 show, also in side elevation, two forms of composite structure for use in other forms of resonator, and Figure 4 shows, in sectional side elevation, a complete resonator comprisin ga pumping source and a composite structure similar to that of Figure 3, in a common housing.

The arrangement shown in Figure 1 comprises, in alignment, a laser rod 1, a saturable absorber Q-switch 2, prepared by the method described in either Example 1 or Example 2 above, consisting of a disc 3 of solid dye-polymer solution sandwiched between a pair of glass plates 4, and an output mirror 5 carried on a sub plate 6 of optical glass or fused silica. A fully reflecting coating 7 is carried on the outer end of the laser rod, and the inner end of the laser rod and both flat surfaces of the Q-switch are provided with antireflecting coatings 8. Alternatively, the glass pates 4 may be omitted, the Q-switch consisting only d the disc 3 of dye-polymer solid solution, the opposite flat surfaces of which are provided with anti-reflecting coatinns.

In a specific example of an assembly of the form shown in Figure 1, the laser rod is composed of neodymium-doped yttrium aluminium garnet, and the composition of the dye cell 3 is as described in Example 1; the laser rod is 3 mm in diameter and may be from 15 to 30 mm long, the Q-switch is 4 mm in diameter and 4 mm in overall thickness, and the distance between the Qswitch and the output mirror 5 is 10 to 20 mm, depending on the length of the laser rod; the distance between the laser rod and the Q-switch is not critical, and may suitably be 8 to 10 mm.The reflecting coatings 5 and 7 and the anti-reflecting coatings 8 may be formed of known materials convention ally used for these purposes in laser reson ators operating at the neodymium wavelength; for example the anti-reflecting coat ings preferably consist either of cerium oxide and magnesium fluoride in combina tion, or of calcium fluoride. A resonator incorporating this assembly has been oper ated at a pulse rate of 10 pulses per second, at an output energy of 1OmJ, for 106 pulses, without any detectable deterioration of the Switch dye.

The composite structure shown in Figure Z oonsists of a laser rod 9 having a fully reflecting coating 10 on its outer end, a Q switch lil of the form described in Ex ample 1, above, and an extension rod 12, of the same length as the laser rod, composed Of the laser host material, and carrying a partially reflecting coating 13 constituting the output mirror on its outer end; the rods 9 and la and Q-switch 11 are joined to gether by layers of optical cement 14.In a specific example, the laser rod 9 consists of neodymium-doped yttrium aluminium 'garnet, the extension rod 12 is of yttrium aluminium garnet free from dopant, both rods being 3 mm in diameter and from 15 to 30 mm long, and the Q-switch 11 is of the nomposition described in Example 1 and is 4 mm in diameter and 3 mm thick. The mirror coatings 10 and 13 are of conven tonal materials, and the optical cement 14 'may suitably be one of the materials respectively sold under the names "Zockoll ACP Sealing Compound" and "Whilems C2 Optical Cement", or any other optical cement having negligible absorption at the laser output wavelengths and other suitable properties as aforesaid.

The composite structure shown in Figure 3 is similar to that shown in Figure 2, with the exception that instead of using optical cement to join the laser rod 15, Q-switch dye cell 16 and extension rod 17 together, the dye cell is adhered directly to the inner ends of the rods by employing the latter as the mould surfaces in the manufacture d the dye cell, which in other respects is produced as described in Example 1. The materials and dimensions of the components are the same as those of the composite structure of Figure 2, except that the dye cell 16 is of substantially the same diameter as the rods 15 and 17.

The laser resonator shown in Figure 4 comprises a composite structure similar to that of Figure 3, consisting of laser rod 15, Q-switch 16 and extension rod 17, with reflecting coatings 10 and 13 as in Figure 2 on the outer ends of the rods, and an optical pumping source consisting of a xenon flash tube 1'8, both supported in tubular channels in a solid cylindrical block 19 of polymethyl methacrylate, which also has formed in it two channels 20 for accommodating conducting leads 21 to the electrodes 22 of the flash tube. The surface of the block 19 is coated with a reflecting layer 23, which may be of silver or may be a diffusely reflecting layer of magnesium oxide or barium sulphate, and the reflecting layer is covered with a protective coating 24 of silicone rubber or epoxy resin or other suitable plastic material.

Preferably the polymethyl methacrylate block 19 in Figure 4 contains, in solid solution, the fluorescent dye rhodamine 6G, in a concentration af about 10-4 molar.

WHAT WE CLAIM IS: 1. A laser resonator of the type specified, wherein the said Q-switch is a rigid cell consisting of a solid solution of a dye, which is a saturable absorber responsive to radiation of the wavelength emitted by the active laser element, in a matrix consisting of a polymeric plastic material which is transparent to said radiation, the assembly of said dye and said matrix material being resistant to degradation by exposure to radiation from the pumping source, and wherein the said Q-switch is located between, and in axial alignment with, the laser element and one of the said mirrors and is spaced from such mirror by a substantial distance.

2. A laser resonator according to Claim 1, wherein the said distance by which the Q-switch is spaced from one of the said mirrors is at least equal to half the length of the laser resonator.

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Claims

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disc 3 of solid dye-polymer solution sandwiched between a pair of glass plates 4, and an output mirror 5 carried on a sub plate 6 of optical glass or fused silica. A fully reflecting coating 7 is carried on the outer end of the laser rod, and the inner end of the laser rod and both flat surfaces of the Q-switch are provided with antireflecting coatings 8. Alternatively, the glass pates 4 may be omitted, the Q-switch consisting only d the disc 3 of dye-polymer solid solution, the opposite flat surfaces of which are provided with anti-reflecting coatinns.

In a specific example of an assembly of the form shown in Figure 1, the laser rod is composed of neodymium-doped yttrium aluminium garnet, and the composition of the dye cell 3 is as described in Example 1; the laser rod is 3 mm in diameter and may be from 15 to 30 mm long, the Q-switch is 4 mm in diameter and 4 mm in overall thickness, and the distance between the Qswitch and the output mirror 5 is 10 to 20 mm, depending on the length of the laser rod; the distance between the laser rod and the Q-switch is not critical, and may suitably be 8 to 10 mm.The reflecting coatings 5 and 7 and the anti-reflecting coatings 8 may be formed of known materials convention ally used for these purposes in laser reson ators operating at the neodymium wavelength; for example the anti-reflecting coat ings preferably consist either of cerium oxide and magnesium fluoride in combina tion, or of calcium fluoride. A resonator incorporating this assembly has been oper ated at a pulse rate of 10 pulses per second, at an output energy of 1OmJ, for 106 pulses, without any detectable deterioration of the Switch dye.

The composite structure shown in Figure Z oonsists of a laser rod 9 having a fully reflecting coating 10 on its outer end, a Q switch lil of the form described in Ex ample 1, above, and an extension rod 12, of the same length as the laser rod, composed Of the laser host material, and carrying a partially reflecting coating 13 constituting the output mirror on its outer end; the rods

9 and la and Q-switch 11 are joined to gether by layers of optical cement 14.In a specific example, the laser rod 9 consists of neodymium-doped yttrium aluminium 'garnet, the extension rod 12 is of yttrium aluminium garnet free from dopant, both rods being 3 mm in diameter and from 15 to 30 mm long, and the Q-switch 11 is of the nomposition described in Example 1 and is 4 mm in diameter and 3 mm thick. The mirror coatings 10 and 13 are of conven tonal materials, and the optical cement 14 'may suitably be one of the materials respectively sold under the names "Zockoll ACP Sealing Compound" and "Whilems C2 Optical Cement", or any other optical cement having negligible absorption at the laser output wavelengths and other suitable properties as aforesaid.

The composite structure shown in Figure 3 is similar to that shown in Figure 2, with the exception that instead of using optical cement to join the laser rod 15, Q-switch dye cell 16 and extension rod 17 together, the dye cell is adhered directly to the inner ends of the rods by employing the latter as the mould surfaces in the manufacture d the dye cell, which in other respects is produced as described in Example 1. The materials and dimensions of the components are the same as those of the composite structure of Figure 2, except that the dye cell 16 is of substantially the same diameter as the rods 15 and 17.

The laser resonator shown in Figure 4 comprises a composite structure similar to that of Figure 3, consisting of laser rod 15, Q-switch 16 and extension rod 17, with reflecting coatings 10 and 13 as in Figure 2 on the outer ends of the rods, and an optical pumping source consisting of a xenon flash tube 1'8, both supported in tubular channels in a solid cylindrical block 19 of polymethyl methacrylate, which also has formed in it two channels 20 for accommodating conducting leads 21 to the electrodes 22 of the flash tube. The surface of the block 19 is coated with a reflecting layer 23, which may be of silver or may be a diffusely reflecting layer of magnesium oxide or barium sulphate, and the reflecting layer is covered with a protective coating 24 of silicone rubber or epoxy resin or other suitable plastic material.

Preferably the polymethyl methacrylate block 19 in Figure 4 contains, in solid solution, the fluorescent dye rhodamine 6G, in a concentration af about 10-4 molar.

WHAT WE CLAIM IS: 1. A laser resonator of the type specified, wherein the said Q-switch is a rigid cell consisting of a solid solution of a dye, which is a saturable absorber responsive to radiation of the wavelength emitted by the active laser element, in a matrix consisting of a polymeric plastic material which is transparent to said radiation, the assembly of said dye and said matrix material being resistant to degradation by exposure to radiation from the pumping source, and wherein the said Q-switch is located between, and in axial alignment with, the laser element and one of the said mirrors and is spaced from such mirror by a substantial distance.
2. A laser resonator according to Claim 1, wherein the said distance by which the Q-switch is spaced from one of the said mirrors is at least equal to half the length of the laser resonator.
3. A laser resonator according to Claim

1 or 2, wherein the Q-switch is located be tween the laser element and the output mirror.
4. A laser resonator according to any preceding Claim, wherein the dye employed in the Q-switch is a divalent transition metaldithiene complex having a square planar structure.
5. A laser resonator according to any preceding Claim. wherein the polymeric matrix material employed for the Q-switch cell consists of an acrylic resin, or a cyanoacrylic resin, or cellulose acetate, or a polyester.
6. A laser resonator according to any preceding Claim, which includes a series of separate components in axial alignment but spaced apart by gaps, which components consist of a laser rod carrying a fully reflecting mirror on one end, a solid dye cell Q-switch spaced from the end of the laser rod remote from said mirror, and an output mirror supported on a substrate and spaced from the side of the Q-switch remote from the laser rod, anti-reflection coatings being provided on the end of the laser rod remote from the fully reflecting mirror and on the two opposite sides of the Q-switch respectively facing the laser rod and the output mirror.
7. A laser resonator according to any of the preceding Claims 1 to 5, which includes a composite structure consisting of, in axial alignment, a laser rod, a solid dye cell Qswitch, and an extension rod composed of material which is transparent to the laser emission, the dye cell being sandwiched between the inner ends of the laser rod and the extension rod, together with a fully reflecting mirror and an output mirror carried by the outer ends of the laser rod and the extension rod respectively.
8. A laser resonator according to Claim 7, wherein the said extension rod is of the same composition as the laser host material.
9. A laser resonator according to Claim 7 or 8, wherein the laser rod and the extension rod are of substantially equal length.
10. A laser resonator according to any preceding Claim, which has a housing consisting of a block formed of a polymeric plastic material which is transparent to the pumping radiation, the block containing tubular cavities into which the optical pumping source and the resonator components are inserted, and having on its external surface an internally reflecting layer the exterior of which is covered by a protective coating.
11. A laser resonator according to Claim 10, wherein the plastic block constituting the said housing is impregnated with a fluorescent material whereby spectral conversion d ultra violet radiation emitted by the optical pumping source into radiation of wavelengths within the required laser pump band is effected.
12. A method of manufacturing a laser resonator according to any preceding Claim, which includes the steps of forming a said Q-switch cell by preparing a solution consisting only of a dye and the monomer or polymer of the material which is to constitute the said matrix, in a solvent, and consolidating the solution to form a body consisting of a solid solution of the dye in the polymer matrix, and then assembling the components of the laser resonator with the Q-switch cell so formed located between, and in axial alignment with, the laser element and one of the said mirrors, and spaced from such mirror by a substantial distance.
13. A method according to Claim 12 wherein, for forming the said Q-switch cell, the polymer which is to constitute the said matrix is dissolved in a solvent, a desired proportion of a dye is dissolved in the polymer solution, and the solvent is then caused to evaporate completely in a controlled manner to form said solid solution body.
14. A method according to Claim 13, wherein after evaporation of the solvent the matrix-dye solid solution body is further consolidated by the application of pressure thereto in a heated mould.
15. A method according to Claim 14, wherein the said body is sandwiched between plates of the matrix material or of glass before being introduced into the mould.
16. A method according to Claim 13 or 14, wherein a mould having two opposite optically flat internal surfaces is employed either for casting of the dye-polymer solution before evaporation of the solvent, or for said further consolidation of the said matrix-dye body, for imparting optical flatness to those surfaces of the Q-switch cell through which radiation emitted by the laser element will pass in operation of the laser resonator.
17. A method according to Claim 12 wherein, for forming the said Q-switch cell, a liquid monomer of an adhesive resin which is to constitute the said matrix is mixed with a solution of a dye, on a first plate of glass or plastic material transparent to the laser emission and having optically flat surfaces, then the resulting dye-monomer solution is covered with a second said plate, and said solution is allowed to solidify in the cold.
18 4 method according to Claim 15 or Claim 17, wherein the outer surfaces of the said plates are provided with an anti-reflection coating before the said matrix-dye body or the said dye-monomer solution is placed between the inner surfaces of said plates.
19. A method according to Claim 13 or 14, for the manufacture of a laser resonator according to Claim 7, 8 or 9, wherein a fully reflecting mirror and an output mirror are first formed respectively on the outer ends of a laser rod and a said extension rod, and then the said Q-switch cell is bonded to the inner ends of the laser rod and the extension rod by means of a laser damage-resistant optical cement which is capable of adhering to the polymer surfaces of the Q-switch cell, which has a refractive index close to that of the materials of the laser rod and the extension rod, and which has low absorption at the laser emission wavelength,
20.A method according to Claim 13, for the manufacture of a laser resonator according to Claim 7, 8 or 9, wherein the said Q-switch cell is shaped by casting said poly merdye solution in a mould before evaporation of the solvent, a fully reflecting mirror and an output mirror are formed respectively on the outer ends Of a laser rod and a said extension rod, and then the Q-switch cell is placed between the inner ends of the laser rod and the extension rod, and pressure is applied to the rods for further consolidation of the cell, the polymer matrix of the cell being self-adherent to the rod end surfaces under pressure.
21. A method of manufacturing a laser resonator according to any of the preceding Claims I to 11, wherein the said Qswitch cell is formed substantially as hereinbefore in Example 1 or Example 2.
22. A laser resonator manufactured by a method according to any of the preceding Claims 12 to 21.
23. A laser resonator according to Claim 1, substantially as hereinbefore described with reference to Figure 1, Figure 2, Figure 3 or Figure 4 of the drawings accompanying the Provisional Specification.