GB2270197A - Pulsed high-powered laser system - Google Patents

Abstract

A pulsed high-powered laser system comprises resonator mirrors 60, 62 with a resonator radiation field extending there-between and passing through an excitable laser medium over an active length. A Q-switch 46 determining the laser pulse is arranged in such a way that the active length of the resonator radiation field can be divided by the Q-switch into at least two segments. The Q-switch 46 comprises a conical mirror 80 which focuses branches 50, 52, 55, 58 of the active length to form a line focus 86 in a plane 84 and a chopper wheel 90 which can couple all branches together intermittently. The laser beam is uncoupled by a scraper mirror 114. Alternatively, the Q-switch comprises two cylindrical, parabolic mirrors and the branches of the active length are separated longitudinally. <IMAGE>

Description

2270197 PULSED HIGH-POWERED LMW SYSTEM The invention relates to a pulsed

high-powered laser system comprising a resonator with resonator mirrors and with a resonator radiation field extending between the resonator

mirrors, and an excitable laser medium with the resonator field passing through it over an active length.

In pulsed high-powered laser systems of this type there is the problem that the highest possible occupation inversion density has to be built up to produce the highest possible pulse outputs.

However the build-up of such a high occupation inversion density is prevented by the fact that laser activity starts up automatically from a given magnitude of occupation inversion, so a higher occupation inversion density cannot then be achieved.

The problem underlying the invention is therefore to provide a pulsed high-powered laser system wherein the highest possible occupation inversion density can be obtained.

This problem is solved, according to the invention, in that a switch determining the laser pulse is arranged in the resonator radiation field in such a way that the active length of the resonator radiation field can be divided by the Q-switch into at least two segments.

The advantage of the solution according to the invention is thus the fact that the Q-switch not only lowers the quality of the resonator but also makes it possible to divide the active length of the resonator radiation field into at least two segments and thus to raise the oscillation-starting threshold.

The active length of the resonator radiation field is the length thereof over which it fills a discharge chamber with laser-active medium.

2 A particularly advantageous example of the high-powered laser according to the invention provides for the Q-switch to have an image-forming optical system which forms an image of the resonator radiation field on a line focus, and a mechanical chopper effective in the region of the line focus. A mechanical chopper of this type exposes the line focus or covers it and, in conjunction with the line focus, provides an optimum possibility of Q-switching, since rapid switching is possible with this high performance.

The Q-switch may be equipped with many different types of imageforming optical systems. An advantageous example provides for the Q-switch to have a conical mirror as the image-forming optical system, the line focus being on the axis of the cone.

This conical mirror offers a simple, non-sensitive means of obtaining a layout of the resonator radiation field wherein its active length can be divided into a plurality of segments by the Qswitch.

Alternatively the Q-switch may have two confocally arranged cylindrical parabolic mirrors as the image-forming optical system, the line focus extending parallel with the direction of the cylinders thereof. Parabolic mirrors of this type also provide an optical system for the Q-switch which is simple and insensitive to adjustment.

It is especially advantageous for the parabolic mirrors to reflect radiation coming from the line focus in opposite directions, since distortions caused by curvatures of the parabolic mirrors are compensated with such a mirror arrangement.

In an advantageous embodiment of the invention the active length of the resonator radiation field can be divided into at least two segments of comparable active length. The segments preferably have approximately the same active length.

3 It is still more advantageous for the active length of the resonator radiation field to be divisible into three segments.

As a means of achieving the greatest possible division it is particularly advantageous for the resonator radiation field to run through the Q-switch twice.

With the Q-switch being passed through twice, the field could be divided by two mechanical choppers or by one mechanical chopper acting with a different chopping element, i.e. a different slot for example, each time the radiation field passes through it.

It is particularly advantageous for the resonator radiation field to run through the same line focus twice, since in this case only one mechanical chopper with one opening and closing chopper element is required, so there are no problems with synchronising e.g. two opening and closing chopper elements.

The idea of the invention can be realised in a particularly simple way if the resonator has a deviation mirror which reflects radiation coming from the Q-switch back into the Q-switch in a parallel offset position, the deviation mirror preferably being in the form of a conical mirror.

When laser gas is used as the laser medium the beam quality of 2.5 high-powered lasers according to the invention is limited on account of the variation, i.e. the reduction, of the density of the laser medium in the direction of flow. Hence with different partial radiation fields of the resonator radiation field adjacent one another in a direction crossing the resonator axis, the resultant gradient leads to tipping of the laser beam and aorsening of beam quality. It is particularly advantageous therefore for the resonator radiation field to be taken through the laser medium so that differences in the optical path lengths nf partial radiation fields of the resonator radiation field are

3 5 reduced.

4 A resonator radiation field as understood in the invention is made up of a plurality of partial radiation fields extending adjacent each other in the direction of propagation, and has a finite cross-sectional area transversely to the particular direction of propagation. A resonator radiation field may, for example, comprise a plurality of partial radiation fields extending adjacent each other in one common direction of propagation, or a plurality of partial radiation fields defined by reflection back and forth between two mirrors.

It is particularly advantageous for the different optical path lengths of the partial radiation fields substantially to be compensated for.

This can be done particularly advantageously if the high-powered laser system has two discharge chambers with the resonator radiation field passing through them, the discharge chambers preferably being identical. It is especially desirable for gas discharges to take place in the discharge chambers under identical discharge conditions, preferably with identical density varying in the direction of flow.

In this case the resonator radiation field is preferably constructed so that it passes through the discharge chambers in such a way that the effects of the different optical path length on the resonator radiation field are substantially compensated for.

Such compensation of the optical path length can be obtained in many different ways. Thus in a simple alternative embodiment each discharge channel has one branch of the resonator radiation field passing through it; with a concurrent flow the partial radiation fields of the two branches are turned through 180 from each other about the optical axis, or with a countercurrent flow 35 the partial radiation fields pass through the discharge channels unturned relative to the optical axis.

In a particularly efficient example each discharge channel has two branches of the resonator radiation field passing through it, the two branches in particular being substantially parallel with each other.

The examples so far described have not touched on the question of how the resonator radiation f ield is aligned relative to its position during the first passage through the line focus, when it passes through the line focus for the second time.

It is particularly advantageous for the partial radiation fields of the resonator radiation field to pass through the line focus on the second occasion in a different portion from that used during their first passage.

An appropriate method of compensating for geometrical errors provides for the partial radiation fields which are in an end portion of the line focus during the first passage to be in a central portion of the line focus during the second passage.

It is still more advantageous for the partial radiation fields which are in an end portion of the line focus during the first passage to be in the opposite end portion of the line focus during the second passage.

Other features and advantages of the invention are the subject of the following description and the accompanying drawings of some examples, in which:

Fig. 1 is a partial, perspective view of a first example, Fig. 2 is a larger-scale perspective view of the high-powered laser system in the region of the discharge channels, Fig. 3 is a perspective view of the resonator radiation field,

6 Fig. 4 is a side view of the courses followed in the radiation field in the direction of the arrow P4,

Fig. 5 is a larger-scale fragmentary view of the line focus and mechanical chopper, Fig. 6 is a representation of the radiation field similar to Fig 4, looking at external portions of the field,

Fig. 7 is a plan view of a second example without the circulating system, and Fig. 8 is a view in the direction of the arrow P8 in Fig. 7.

A first example of a high-powered laser according to the invention, shown in Figs 1 and 2, comprises a discharge housing shown generally at 10 which contains two discharge channels 12 and 14. The channels 12 and 14 have the same dimensions. They are preferably parallel and juxtaposed as illustrated in Fig. 1, so that they have laser gas from a common gas-circulating system flowing through them jointly in their transverse directions 18 and 20, the gas streams in the discharge channels 12 and 14 also being substantially identical.

The gas-circulating system 16 comprises a supply channel 22 from which a gas stream 24 is taken to an inflow port 26 and 28 of the discharge channels 12 and 14 respectively, the gas stream being divided in half between the two channels. After flowing through the two discharge channels 12 and 14 in their transverse direction 18, 20 the two partial streams combine in the region of outflow ports 30. 32 to form a joint exit gas stream 34; this flows through a cooler 38 in an outflow channel 36 and is taken from the cooler to a blower 40 which forces the gas stream back into the supply channel 22.

The discharge channels are provided with electrodes 11, 13 and 15, the function of which is to generate a high frequency 7 discharge in discharge chambers 72 and 74 in the discharge channels 12 and 14. A high frequency source (not shown) is provided for this purpose, connected to the electrodes 11, 13 and 15.

The discharge channels 12 and 14 have a radiation field 42 of a resonator passing through them. The resonator, shown generally at 44 and separately in Fig. 3, is provided with a Q-switch shown generally at 46.

In the case illustrated the resonator radiation field 42 comprises a first branch 50 extending in the discharge channel 1.2. The first branch 50 of the field 42 is indicated by a single broken line. This first branch 50 is coupled with a second branch 52 which passes through the discharge channel 14 and is indicated by a double broken line. The second branch 14 is in turn (coupled), by a deviation mirror 54 of the resonator 44 in the form of a conical mirror, with a third branch 56 in the discharge channel 12, indicated by a triple broken line; and the third branch 56 is in turn coupled by the Q-switch 46 with a fourth branch 58 in the discharge channel 14, shown as a quadruple broken line.

The first branch 50 and fourth branch 58 are each directed onto one of two end mirrors 60 and 62 respectively of the resonator 44.

As illustrated in Fig. 2, the two end mirrors 60 and 62 and the deviation mirror 54 are arranged in a joint mirror housing 64 which adjoins the discharge housing 10 at a face 76, while a housing 66 for the Q-switch shown generally at 46 adjoins the opposing face 78 of the housing 10.

The respective innner chambers 68 and 70 of both the mirror housing 64 and the housing 66 are connected to the discharge chambers 72, 74 respectively, through which the gas stream passes. No gas-tight closure is therefore required between the 8 opposing faces 76 and 78 of the discharge housing 10 adjoined by the mirror housing 64 and housing 66, and consequently the same pressure conditions prevail in the inner chambers 68 and 70 as in the discharge chambers 72 and 74, although the inner chambers 68 and 70 do not have the gas stream 24 passing through them and thus constitute a dead space in respect of passage of the gas stream 24.

The mirror housing 64 and housing 66 are thus preferably joined 10 to the faces 76 and 78 of the discharge housing 10 in a gas-tight manner.

The Q-switch 46 preferably comprises a conical mirror 80 as an imageforming optical system; the axis 82 of the cone is located symmetrically between the branches 50, 52, 56 and 58 and preferably parallel therewith. A plane of symmetry 84 running through the axis 82 of the cone is located between the branches 52 and 58 at one side and 56 and 50 at the other side, and is preferably midway between them. A line focus 86, onto which the conical mirror 80 focuses all the branches 52, 50 and 56, 58, is further located on the axis 82 of the cone and thus also in the plane 84. For this purpose the individual branches have to be arranged so that the first and second branches 50, 52 and the third and fourth branches 56, 58 are opposite each other relative to the cone axis 82, and so that they impinge on the conical mirror 80 at the same distance from a geometrical cone apex 88 (Figs 2 and 3).

A chopper wheel 90, rotatable about an axis 92, is further 30 located in the plane 84; the axis 92 stands perpendicularly on the plane 84 and intersects the cone axis 82.

The chopper wheel 90 contains slots 94 located at the same distance from the axis of rotation 92. The slots are arranged so that the line focus 86 can be exposed by them or covered by portions 96 of the chopper wheel 90 between them, in such a way that when the line focus 86 is in one of the slots 94 all four 9 branches 50, 52 and 56, 58 of the resonator 44 are coupled together by the conical mirror 80, and when the line focus 86 is covered by a portion 96 the four branches 50, 52 and 56, 58 are not coupled together.

To allow the conical mirror 80 to be penetrated, slots 100 are provided in it, through which the chopper wheel 90 in the plane 84 extends into the mirror 80, to expose the line focus 86 with the slots 94 or to cover it with the portions 96 (Fig. 3).

The chopper wheel 90 is in turn driven in rotation by a drive 102 and is preferably seated directly on a drive shaft 103 thereof.

In accordance with the invention the drive 102 is further located in and supported on the housing 66, so that both the drive 102 and the chopper wheel 90 are in the inner chamber 70, in which the same pressure conditions prevail as in the discharge chambers 72 and 74, i.e. preferably the low pressure normally used for CO, lasers with the gas mixture provided for normal C02 lasers.

The branches 50, 52 and 56, 58 of the resonator radiation field 42 can thus be separated or coupled by the Q-switch 46, and it should be borne in mind that the deviation mirror 54 in the form of a conical mirror permanently couples the second branch 52 with the third branch 56.

There is a consequent division of an active length of the resonator radiation field 42 into a plurality of segments, the active length being obtained from the length over which the field 42 passes through the discharge chambers 72 and 74. A first segment is formed by the length 104 of the first branch 50 passing through the discharge chamber 72, a second segment by the partial lengths 105, 106 of the second and third branches 52, 56 passing through the second discharge chamber 74 and the f irst discharge chamber 72, and the third segment by the length 107 of the fourth branch passing through the second discharge chamber 74. The conical mirror 54 is preferably constructed so that it has a cone axis 110 extending midway between the second branch 52 and the third branch 56 and preferably parallel therewith. In the same way as at the conical mirror 80, the second branch 52 and third branch 56 impinge on the conical mirror 54 at the same distance from a geometrical cone apex 111 thereof, and are coupled together to form an albeit uninterrupted line focus 108 on the cone axis 110.

By covering the line focus with one of its portions 96, the switch 46 thus makes it possible to divide the resonator radiation field 42 into three no longer coupled segments of its active length, viz into the active length 104 of the first branch 50, the active length 107 of the fourth branch 58 and the active length 105 plus 106 of the second branch 52 coupled with the third branch 56.

If on the other hand one of the slots 94 exposes the line focus 86, then all branches 50, 52 and 56, 58 are coupled together so that the desired laser action is initiated.

Further according to the invention a shatter 109 is provided in the region of the line focus 108 (Fig. 4); it acts as a threedimensional mode shutter and is also used to improve the switching slope by shortening the effective switching time, since additional diffraction losses when the resonator radiation field is not yet fully exposed are suppressed by the Q-switch.

A laser beam 112 is uncoupled preferably by means of an annular scraper mirror 114, which uncouples a peripheral ring of the first branch 50 in front of the end mirror 60 and reflects it e.g. perpendicularly to the first branch 50 in the form of the emerging laser beam 112.

As a means of improving the beam quality of high-powered lasers, which is limited by having the density of the laser gas in the discharge chambers 72 and 74 varying and particularly decreasing in the direction of f low 118, and which goes along with a 11 gradient of the optical path length in the resonator crossing the axis of the resonator, this example of the invention provides for multiple reversal of partial radiation fields T of the individual branches 50, 52, 56, 58 relative to a direction of flow 118 of the laser gas.

Starting with the first branch 50 of the resonator 44, if we consider its coupling with the second branch 52 by the conical mirror 80, the position of partial radiation fields TV and TH is seen to be reversed relative to the direction of flow 118 of the laser gas through the two discharge chambers 72 and 74. If the partial radiation field TV in the first branch 50 is at the front of a resonator radiation field 42 and a partial radiation field TH at the rear of the f ield 42 in respect of the direction of flow 118, coupling with the second branch 52 is effected so that the partial radiation f ield TH is at the f ront and the partial radiation field TV at the rear relative to the direction of flow 118 (Fig. 4).

A further reversal is carried out by coupling the second branch 52 to the third branch 56 through the deviation mirror in the form of the conical mirror 54. The partial radiation fields TV and TH are reversed again by focusing on the line focus 108, so that the partial radiation field TV in the third branch 56 is now in front again and the partial radiation f ield TH at the rear relative to the direction of f low 118. A further reversal is brought about by focusing through the line focus 86 in the case of the coupling between the third branch 56 and the fourth branch 58, so that in the fourth branch 58 the partial radiation field TH is again in front and the partial radiation field TV at the rear relative to the direction of flow 118.

Thus the overall position is that in the discharge chamber 72 in the first and second branches the partial radiation fields TV are in front and the partial radiation fields TH at the rear, while conversely in the discharge chamber 74 in the second branch 52 and fourth branch 58 the partial radiation fields TH are in front

12 and the partial radiation fields TV at the rear relative to the direction of flow 118.

The resonator radiation field 42 according to the invention is made up of a plurality of partial radiation fields T extending adjacent each other in their direction of propagation and has a finite cross-sectional area transversely to the particular direction of propagation. The field 42 may, for example, comprise a plurality of partial radiation fields T extending in one common direction of propagation, or partial radiation fields

T defined by reflection back and forth between two mirrors.

The invention thus also has the effect that the varying density of the laser gas can be substantially fully compensated for by the coupling of all the branches 50, 52, 56 and 58, thereby providing optimum conditions for beam quality.

During Q-switching 46 in the line focus 86 by means of the chopper wheel 90 irregularities further occur when the line focus 86 is covered by the portions 96, owing to the fact that the line focus 86 has a finite width B in the peripheral direction of the wheel 90 so that, even when a leading edge 122 and a trailing edge 124 (as seen in the rotary direction 123) extend radially of the axis of rotation 92, either exposure by the leading edge 122 or covering by the trailing edge 124 over a length L of the line focus 86 radially of the axis of rotation 92 will be dependent on the radius of the disc.

This dependence on the radius in the exposure or covering of the line focus 86 can also be partly compensated for by the invention, as illustrated in Fig. 6. When the first branch 50 is coupled with the second branch 52, the conical mirror 80 focuses the first branch 50 on the line focus 86 in such a way that a partial radiation field TA, passing through the outer portion A of the line focus, is formed by the outermost partial radiation field of the branch 50 relative to the cone axis 82, while a partial radiation field TI passing through the inner portion of

13 the line focus 86 is formed by the innermost partial radiation field of the branch 50. These relationships are found in the same way in the second branch 52.

However coupling of the second branch 52 with the third branch 56 s brings a change: images of both the outer partial radiation field TA and the inner partial radiation field TI are formed in the third branch 56, by focusing on the cone axis 108, in such a way that they are reflected by the conical mirror 80 in a central portion M of the line focus 86 when the third branch 56 is coupled with the fourth branch 58.

That is to say, when there is uneven exposure by the leading edge 122 or uneven covering by the trailing edge 124 of the line focus 86 over the length L, this has the greatest effect in the coupling between the first branch 50 and the second branch 52, since the partial radiation fields TA and TI in the outer portion A and inner portion I are af f ected most dif f erently, whereas this non- simultaneous covering and exposure only has a slight effect on the partial radiation fields TA and TI in the coupling between the third branch 56 and the fourth branch 58, since these are located in a central portion M during the second passage through the line focus 86.

The first example of the high-powered laser according to the invention operates in such a way that both the duration of the laser pulses and the intervals between them can be predetermined by the rotating chopper wheel 90 and the width of the slots 94 and portions 96, and in such a way that the active length of the resonator radiation field 42 is divided into three segments 104,

105 and 106, 107 during the intervals between pulses. A second example of the invention, illustrated in Fig. 7, similarly provides two discharge channels 12' and 1V, but instead of being directly adjacent as in the first example they are arranged one after the other longitudinally, with a Q-switch 146 seated between them.

14 The resonator 144 with its radiation field 142 also comprises two end mirrors 160 and 162 which are arranged in a mirror housing 164 seated on the face 761 of the discharge channel 12', while the Q-switch 146 with its housing 166 adjoins it on an opposing face 78'. The discharge channel 121 again has a discharge chamber 72' with a first branch 150 and a fourth branch 158 of the resonator 144 passing through it, while the second discharge channel 141 has a second branch 152 and a third branch 156 passing through it.

The face 7C of the discharge channel 14' is joined to the housing 166 of the Q-switch 146 at a side opposite the discharge channel 121, while a further mirror housing 165 in which the deviation mirror 154 is seated is joined to its opposing face 7V. As in the first example, the mirror 154 is conical and couples the second branch 152 to the third branch 156, the axis 208 of its cone being located symmetrically between the second branch 152 and the third branch 156 and preferably being parallel with these branches.

In contrast with the first example the Q-switch 146, instead of having a conical mirror as the image-forming optical system, has two cylindrical parabolic mirrors 180 and 182 arranged confocally to a line focus 186, the directions of the cylinders of the parabolic mirrors 180 and 182 being parallel with each other and parallel with the longitudinal direction of the line focus 186.

The line focus 186 can be exposed and covered in the same way as in the first example by a chopper wheel 190 which is constructed as in the first example and provided with slots 194 and closed portions 196 between them; a radial direction of the wheel 190 in respect of its axis of rotation 92 being parallel with the line focus. In addition the chopper wheel 190 can be driven in the same way as the chopper wheel 90 by a drive 202 held in a housing 166 of the Q-switch 146.

The cylindrical parabolic mirrors 180 and 182 are arranged so that they reflect beams coming from the line focus 186 in different directions, so that any beam deformation caused by the parabolic mirrors can thereby be compensated.

The two parabolic mirrors 180 and 182 preferably have identical curvature.

The mirror 180 thus couples the first branch 150 with the second branch 152 via the line focus 186, and the third branch 156 with lo the fourth branch 158 via the line focus. The branches 150, 152 and 156, 158 coupled by the parabolic mirrors 180 and 182 are symmetrical with the line focus 186 and perpendicular to a longitudinal extension thereof.

The active length of the resonator radiation field 142 can thus be divided into three segments by the chopper wheel 190, viz the active length 204 of the first branch 150, the active length 205 and 206 of the second branch 152 combined with that of the third branch 156 and the active length 207 of the fourth branch 158.

The discharge chambers 72' and 74' have laser gas flowing through them in the direction 118, the direction of flow 118 being in a plane which extends parallel with the longitudinal directions 151 and 159 of the first branch 150 and fourth branch 158 and the transverse direction 18 and which is thus defined thereby.

In the same way the direction of flow 118 in the discharge chamber 741 lies in a plane which extends parallel with the longitudinal directions 153 and 157 of the second branch 152 and third branch 156 and the transverse direction 20 and is defined thereby. The two planes further merge and stand perpendicular to the longitudinal extension of the line focus 186 and perpendicular to the direction of the cylinders of the two cylindrical parabolic mirrors 180 and 182.

16 If we consider the compensation for the change in optical path length by the density gradients of the laser gas occurring in the direction of flow 118 in the two discharge chambers 721 and 741, we see that the image of a front partial radiation field TV of the first branch 150 is formed by the two cylindrical parabolic mirrors 180 and 182 as the rear partial radiation field TV (sic) of the second branch 152. The same applies to the partial radiation field TH at the rear in the first branch 150. The partial radiation fields T are further reversed by the conical mirror 154 in such a way that the front partial radiation field TH of the secondbranch 152 is at the rear in respect of the direction of flow 118 in the third branch 156, while the rear field TV of the second branch 152 is at the front in the third branch 156.

Coupling takes place between the third branch 156 and the fourth branch 158 by means of the cylindrical parabolic mirrors 180 and 182, with the partial radiation fields T again being reversed, so that the rear partial radiation field TV in the third branch 156 is at the front in respect of the direction of flow in the fourth branch 158 and the front partial radiation field TV in the third branch 156 is similarly at the rear in respect of the direction of flow 118 in the fourth branch 158.

To summarise, the partial radiation fields T are coupled in such a way that the compensation effected in each of the discharge chambers 72' and 74' comprises a reversal of the partial radiation fields from one branch to another.

As illustrated in Fig. 8, in the second example the position of the partial radiation fields T during the second passage through the line focus 186 is the reverse of that during the first passage, as explained below. The partial radiation field TL, which is reflected by the parabolic mirror 180 into a left-hand portion L of the line focus 186 during a first passage through the line focus, is inverted by the conical mirror 154 after passing through the second branch 152, in such a way that it is 17 at the right-hand side R of the line focus 186 during the second passage through it. The same applies to the partial radiation field TR at the right-hand side R in the line focus 186, which is similarly inverted by the conical mirror 154 in such a way that it is at the left-hand side L of the line focus 186 after passing through the third branch 156.

It follows that the partial radiation fields T in the line focus 186 during the passage of the radiation from the third branch 156 into the fourth branch 158 are inverted relative to the partial radiation fields T in the line focus 186 during the passage of the radiation from the first branch 150 into the second branch 152, so that irregular exposure or irregular covering of the line focus by the leading edge 122 or trailing edge 124, as already described in connection with the first example, is completely eliminated in the second example.

The same applies to conditions concerning pulse operation by means of the chopper wheel 190.

The discharge channels 12' and 14' and discharge chambers 72' and 74' are of the same construction as in the first example, so readers can be referred to the discussion of the first example for a description of them.

In both examples the laser gas is excited in the normal, known manner, preferably by means of a high-frequency discharge in the case of known laser gas mixtures for transverse-flow lasers, for example C02 with the usual additives, in discharge channels 12, 12' and 14, 141, excitation being produced with appropriate high frequency in a manner known from prior art.

18

Claims (1)

1. C L A I M S

   1 A pulsed highpowered laser system comprising a resonator with resonator mirrors and with a resonator radiation field extending between the resonator mirrors, and an excitable laser medium with the resonator field passing through it over an active length, characterised in that a Q-switch (46; 146) determining the laser pulse is arranged in the resonator radiation field (42;l42), in such a way that the active length of the resonator radiation field (42;l42) can be divided by the Q-switch (46;l46) into at least two segments (104, 105 and 106, 107; 204, 205 and 206, 207).

   2. A system according to claim 1, characterised in that the Q- switch (46;l46) has an image-forming optical system (80; 180,182), which forms an image of the resonator radiation field (42;l42) on a line focus (86;l86), and a mechanical chopper wheel (90;190) effective in the region of the line focus (86;l86).

   203. A high-powered laser according to claim 2, characterised in that the Q-switch (46) has a conical mirror (80) as the imageforming optical system, with the line focus (86) located on the axis (82) of its cone.

   254. A laser according to claim 2, characterised in that the Qswitch (146) has two confocally arranged parabolic mirrors (180, 182) as the image-forming optical system, with the line focus (186) extending parallel with the direction of their cylinders.

   305. A laser according to claim 4, characterised in that the parabolic mirrors (180, 182) reflect radiation coming from the line focus (186) in opposite directions.

   19 6. The laser according to any of the preceding claims, characterised in that the active length (104, 105 and 106, 107; 204, 205 and 206, 207) of the resonator radiation field (142) can be divided into at least two segments having a comparable active length (104, 107; 204, 205).

   7. A laser according to any of the preceding claims, characterised in that the resonator radiation field (42; 142) passes through the Q-switch (46; 146) twice.

   8. A laser according to claim 7, characterised in that the resonator radiation field (42; 142) passes through the same line focus (86, 186) twice.

   9. A laser according to any of the preceding claims, characterised in that the resonator (44, 144) has a deviation mirror (54, 154) which reflects radiation coming from the Qswitch (46, 146) back into the Q-switch in a parallel offset position.

   10. A laser according to any of the preceding claims, characterised in that the resonator radiation field (42, 142) is guided through the laser medium so that differences between the optical path lengths of partial radiation fields of the resonator radiation field (42; 142) are reduced.

   11. A laser according to claim 10, characterised in that the different optical path length of the partial radiation fields (TV, TH) is substantially compensated for.

   12. A laser according to claim 10 or 11, characterised in that it has two discharge chambers (72, 74) through which the resonator radiation field (42, 142) passes.

   13. A laser according to claim 12. characterised in that gas discharges take place under identical discharge conditions in the discharge chambers (72, 74).

   14. A laser according to any of the preceding claims, characterised in that the partial radiation fields (TA, TI; TR, TL) of the resonator radiation field (42) pass through the line focus (86, 186) in a different portion during the second passage s from that used during the first passage.

   15. A laser according to claim 14, characterised in that the partial radiation fields (TA, TI) of the resonator radiation field (42) are located in an end portion (A, I) of the line focus (86) during the first passage through the line focus, and in a central portion (M) of the line focus (86) during the second passage.

   16. A laser according to claim 14, characterised in that the partial radiation fields (TR, TL) which are located in an end portion (R, L) of the line focus (186) during the first passage are located in the opposite end portion (L, R) of the line focus (186) during the second passage.