DE4415242A1 - Quasi-continuous UV light producing excimer laser for photochemical industry, medicine, photolithography - Google Patents

Abstract

The laser includes a UV lamp (12), esp. an Excimer lamp, and a feedback resonator (30). The lamp emits quasi-continuous light with an undeformed wave-front in the UV spectrum. This is passed through correction optics to the feedback resonator which stimulates light emission and generates an output. The UV lamp has a rectangular or cylindrical discharge chamber (14) filled with a gas (16) that emits light rays spontaneously through two UV light transmission windows (24). The resonator (30) has a reflective mirror (32) and a decoupling mirror (34) on the same optical axis as the discharge chamber (14) and the transmission windows (24).

Description

The invention relates to a quasi-continuous emitting UV laser, especially a quasi-continuous Nuclear-emitting excimer laser. The invention is shown using an excimer laser, because this type of UV laser is technically and economically the largest Spread and importance. The construction principle can also be used with other UV laser types realize.

The advantage of excimer lasers over other light swell in the ultraviolet spectral range is that they short-wave laser radiation with high photon energy and high light output in a narrow-band emission make area available. The narrowband emission in the wavelength range from 190 nm to 310 nm is for many technical and medical applications very inter essential.

For other lasers, the direct generation is ultra violet laser radiation in the range of 190 nm-310 nm associated with a very low efficiency because the laser radiation emitted by these lasers takes place in the visible and infrared spectral range. With an argon laser that emits on many lines, for example, less than 0.03 per thousand of the elec power as ultraviolet laser radiation animals (approx. 1 watt light output).

As an alternative to the direct generation of ultraviolet One can use laser radiation through complex non-linear optical processes (frequency multiplication of the longer wavy laser radiation) ultraviolet laser radiation produce. However, this creates additional losses with loss factors in the range of 2-10 (depending on the process). Due to the frequency multiplication these lasers  systems are more difficult to handle and are more susceptible to about changes in environmental conditions (vibration, Temperature).

In contrast, excimer lasers are used in the active medium stored energy exclusively as narrow-band ultraviolet laser radiation is emitted (up to some 100 watts light output). However, who the only known pulsed excimer laser operated, the pulse repetition frequency of a few Hertz is up to some 100 Hertz.

The active medium of an excimer laser is one excited gas mixture, for example from noble gas, halo gengas and buffer gas is composed. During the In this gas mixture, gas discharges are caused by impacts excited molecules and atoms are created that interact with each other react to so-called excimers. The excited Ent Charge gas mixture is briefly called excimer gas in the following designated.

It is essential for the laser process that the excited State of the noble gas-halogen compound under emission of an energetic photon decays. I'm not excited The rare gas (halogen) state exists not bond because this condition is antibonding. Therefore, after formation of the excimer (excited Mo reading state) a cast inversion, the one essential requirement for stimulated light emission is.

With the excimer lasers known to date, the discharge is volume to form the excimers relatively large. This has a limitation of the pulse repetition frequency due to the large discharge voltages and the associated  loading times of capacities.

For many industrial and medical technology applications it would be beneficial to use an excimer laser too who can continue his high-energy radiation Lich or quasi-continuously with pulse repetition frequencies in the kHz or MHz range.

Due to the high photon energy, a UV laser is suitable with high pulse repetition frequency especially for cold separation and Joining processes in which the separating and joining through photochemically induced reactions without thermal loading load of the material is accomplished.

The high repetition rate is for example for fast ones High throughput material processing and photolithography set of interest. In addition to the microstructuring of the Materials through mask exposure is also in use to think in rapid prototyping. With this procedure causes the ultraviolet light of the laser beam Photopolymerization of paints and can be three-dimensional Generate models of micro and macro structures. Analogously, focused ultraviolet lasers can be used radiation for local hardening of adhesive bonds can be used as in microsurgery and Dentistry.

The invention has for its object a UV-emitting laser, in particular an excimer laser to create the simple structure and comparative wise low manufacturing costs quasi-continuously stimulated light emission.

To implement a quasi-continuous light emis sion must be the discharge volume in which the excitation of the  Molecules takes place to be kept as small as possible. To a silent electrical discharge can be used.

Silent electrical discharges already become ozone generation and generation of spontaneous ultraviolet Light emission used. A device for generating spon Tan ultraviolet radiation (UV lamp) is an example described in EP 0254111 A1. The silent discharge for a short time in small current filaments, in which the formation of the excimers takes place. When decaying of the excimers generated in the micro-discharges spontaneous ultraviolet radiation is emitted. The structure such an excimer emitter is largely the same that of a commercial ozone generator, which also with respect the power supply of the radiator applies. In the sub is different to the commercial ozone generator at the in Excimer emitters described in EP 0254111 A1 at least one of the electrodes and / or walls that the with Limit discharge gas filled discharge space for the ultraviolet radiation generated is transparent.

For the simple and inexpensive generation of quasi-continuous ultraviolet stimulated light emission a quasi-continuously emitting UV laser, ins proposed an excimer laser with:

• - A UV lamp, in particular excimer lamp, the Light in the UV wavelength range is emitted spontaneously, and
• - the spontaneous light emission into the UV lamp feedback resonator for generation and decoupling stimulated light emission,
• - The UV lamp quasi-continuous spontaneous light emitted, whose wavefront without deformation or with a defined wavefront curvature that is defined by a downstream correction optics can be eliminated again,  strikes the resonator.

The structure according to the invention is based on the knowledge of a quasi-continuous spontaneous light-emitting UV lamp use for a UV laser, which is therefore quasi continuously stimulated light (laser light) is emitted. According to the invention, the spontaneous light of the UV lamp generated due to silent discharges. Furthermore, according to the Invention provided a resonator around the UV lamp to arrange, on the one hand the feedback of the spontaneous Light emission of the UV lamp through this serves and which, on the other hand, decouples light from the stimulated emission pelt is. It is further provided according to the invention that the wavefront of light from the lamp body of the UV lamp occurs without deformation or that the any resulting wavefront deformation a downstream optic is corrected. The the discharge So must enclose the wall of the UV lamp permeable to UV radiation at least in some areas be and in addition in these areas optical surface exhibit quality. Are the transparent sections or areas of the wall plane-parallel, it is required that the surface flatness is approximately λ / 10, where λ is the Is the wavelength of the laser light. With curved walls the curvature of the surface contour must be defined and be reproducible so that the wavefront deformation by a downstream correction optics can be compensated can, and the wavefront in any case without deformation strikes the resonator.

A high-power lamp is preferably used as the UV lamp used according to EP 0 254 111 A1.

In a further advantageous embodiment of the invention 3 the UV lamp has a discharge space that is connected with an under  Discharge conditions from spontaneous radiation from emitting Discharge gas is filled and the two face each other horizontal transmission window permeable to UV radiation having. The discharge space is with a wall connected gastight to the transmission windows Mistake. The two electrodes for producing silent electrical discharges within the electrode space are arranged outside of it and are of a AC power source. Crucial with this described construction of the UV lamp is that between the (discharge) electrodes and the discharge gas at which it is in particular an excimer gas Material that acts as a dielectric. With this The material is, for example, quartz glass.

The laser according to the invention can be a longitudinal one Have excitation geometry in which the propagation direction of the stimulated light essentially parallel to the electric field lines between the electrodes runs. The material of the transmission window then works as a dielectric. The electrodes are preferably two se from a material transparent to UV radiation. But it is also conceivable that the electrode geometry is chosen such that the UV radiation is the electrodes can happen. This is preferably achieved by that the electrodes as grid electrodes, hole electrodes or in the form of concentric rings, the electrodes are therefore provided with “cutouts” through which the UV radiation emerges.

In contrast to the longitudinal excitation geometry is at a transverse excitation geometry of the laser, in which the material of the wall acts as a dielectric that Translucency of the electrodes is not necessary. There in the case of the transverse excitation geometry, the propagation  direction of the stimulated light perpendicular to the elec tric field lines between the electrodes, only the transmission windows for the generated radiation be translucent.

Regardless of the selected excitation geometry, the following always applies that the electric field lines between the electrodes dielectric dimension delimiting the discharge space run through the material.

In particular, the discharge space has a cuboid shape or a cylindrical shape, with two end faces Wall sections is provided by two transmissions windows are formed.

At least one of the transmission windows is preferably at an angle to the direction of propagation of the stimu arranged light. This prevents the transmission window itself as an undesirable additional Liche resonator mirrors work. In some cases Achieving linear preferential polarization of the stimu the arrangement under the Brewster angle to strive for.

The discharge space advantageously consists of at least two subspaces that have a common electrode, which within the dividing the two subspaces Partition is arranged or integrated. On both sides this common electrode is then the two Counter electrodes, preferably with respect to the common Electrode are arranged symmetrically.

In an advantageous embodiment of the invention is furthermore provided that the discharge space as an annular space between two preferably concentric hollow profiles, in particular  formed between two tubes of dielectric material is, the axial ends of the transmission windows are closed. One of the two electrodes is there outside the annulus on the inside of the inside Hollow section arranged while the other electrode also outside the annulus on the outside of the outer hollow profile is located. This structure corresponds to one transverse excitation geometry.

Using a longitudinal excitation geometry of the structure of the discharge space described above are the the two electrodes are flush with the front of the Discharge space arranged and already have the above in the Connection with the longitudinal excitation geometry described material or the structure described there.

The resonator of the laser is connected in a manner known per se at least one highly reflective mirror and with one Decoupling mirror provided, both in the simplest case on one through the transmission window and the discharge arranged through the optical axis are.

In principle, all known types can be used as resonators of laser resonators, in particular those of Excimer lasers known to be used.

As an alternative to coupling the light out with a coupling mirror can also be used for coupling out the reflection or Diffraction of the light located inside the resonator optical, electro-optical or acousto-optical Elements are used. In particular, Reso nators with fixed or switchable resonator quality be used in quasi-continuous operation (Repetition rate 1 KHz) and repetitive pulse  operation (repetition rate 1 KHz) energy and power to be able to vary the individual light pulses.

With longitudinal excitation geometry, the Pro runs direction of pagination of the stimulated light through the two electrodes. In the simplest case are located on either side of the UV lamp Mirror, namely on the one hand the highly reflective mirror and on the other hand the decoupling mirror. This configuration allows that to return between the two mirrors coupled light on its route between the two Reflect the discharge space once each.

To realize a folded resonator structure within the resonator light beam deflection with opti elements (e.g. mirrors or prisms) be so. B. a compact at long resonator length te design of the laser can be realized. The change tion of the resonator length can be used to form a certain spatial laser mode or change of mode volume and Amplification dynamics turned on in the light-amplifying medium be set.

It is advantageous to use a resonator mirror geometry use the optical path of light between the decoupling mirror and the highly reflecting mirror crosses the discharge space several times. To this end highly reflective deflecting mirrors are used. By the deflecting mirror will leave the transmission window send light redirected in this way and back to the discharge space directed that it is the discharge space along an optical Path that is different from that path through which it can leave the discharge space before the redirection Has.  

This makes it possible in particular one in the direction perpendicular to the direction of propagation of the stimulated light spatially inhomogeneous amplification in the discharge space by means of spatial integration across different areas of the Discharge volume through the interrogating the gain Balancing light.

In the construction of the discharge space described above as an annular space between two hollow profiles, in particular two Tubing occurs stimulated light emission with one in the cross cut annular, especially an annular Profile from one of the two end faces of the discharge space out. The ring-shaped light beam leaves as far as the the necessary conditions are given, the decoupling mirror. Is light with such a cross-section not wanted and should the laser light with a circle shaped filled beam profile, so is it expedient to outside the resonator or inside the Resonators but an optical one outside the UV lamp To provide facility that the annular profile in one circular filled beam profile. For this are preferably cone optics, namely positive cones optical and negative cone-optical elements are used.

These cone optics can of course also be used any other laser or any other light source, whose beam profile in cross section is essentially ring is shaped, used for beam shaping.

In addition, the aspect ratio (that's it Ratio of inner to outer radius of the ring Beam profile) and the divergence of the discharge space Leaving light will be affected, a telescope with at least one cone-optical element and at least a spherical or aspherical optical element  intended.

Finally, an optical one can also be used with advantage Filtering is provided, the two collimating optics and one at the focus of these two collimating optics arranged perforated aperture. To reduce the intensity sity of higher spatial frequencies of the annular beam profile it is also advantageous if the previously described optical filter for spatial filtering of the ring-shaped A spherical or aspherical optical element and cone-optical elements having a telescope is switched.

Exemplary embodiments are described below with reference to the figures the invention explained in more detail. In detail show:

Fig. 1 shows schematically and in cross section the structure of a quasi continuous emission excimer laser with an excimer lamp, which radiates due to silent discharge, and an external resonator,

Fig. 2 and also in cross-section schematically a second embodiment of an excimer laser whose excitation geometry is like the execution example 1 shown in FIG. Transversal,

Fig. 3 shows a third embodiment of an excimer laser having a longitudinal excitation geometry and is constructed such resonator whose (folded) that the stimulated light repeatedly passes through the discharge space while passing through different regions of the discharge volume,

Fig. 4 is a schematic representation of a conversion optical system for conversion of a ring beam profile in a full-beam profile,

Fig. 5 is a schematic view of a tapered optical telescope for changing the aspect ratio and the divergence of a ring beam profile,

Fig. 6 is an optical filter assembly for spatial filtering annular beam profiles and

Fig. 7 shows a filter arrangement with kegeloptischem telescopic higher to reduce the spatial frequencies in an annular beam profile.

The basic structure of a quasi-continuously emitting excimer laser 10 is shown in FIG. 1 in accordance with a first exemplary embodiment. Essential components of the excimer laser 10 are a UV lamp 12 , which emits spontaneous light quasi-continuously, and the laser resonator 30 for feedback of the spontaneously emitted light. The UV lamp 12 has a discharge space 14 which is sealed gas-tight on all sides. The discharge space 14 is filled with a discharge gas 16 , hereinafter also referred to as excimer gas. The wall 18 of the discharge space 14 consists of a dielectric 20 . The parts of the wall 18 consisting of this dielectric 20 run parallel to the optical axis of the resonator 30 , which coincides with the direction of propagation of the stimulated light 22 . The wall regions extending transversely to the optical axis are designed as transmission windows 24 with optical quality. The transmission windows 24 can also consist of a dielectric material. The wall 18 of the UV lamp 12 preferably consists of quartz glass.

The laser 10 of FIG. 1 has a transverse excitation geometry, which is why the UV lamp 12 is provided with a pair of electrodes, the two electrodes 26 , 27 are arranged such that the electrical field formed between them is perpendicular to the direction of propagation of the stimulated Light 22 extends. The electrodes 26 , 27 are fed by an AC power supply 28 , as is known from ozone generators.

The resonator 30 , which consists of a highly reflecting mirror 32 and a decoupling mirror 34, is arranged outside the UV lamp 12 . These two mirrors 32 , 34 are arranged like the transmission window 24 perpendicular to the direction of exposure of the stimulated light 22 .

The UV lamp 12 works on the principle of "silent discharges". The electrical discharges between the electrodes 26 , 27 are influenced by the dielectric of the wall 18 of the discharge space 14 . As already stated above, the discharge space 14 is hermetically sealed by the dielectric (quartz glass). The transmission windows 24 do not necessarily have to be made of dielectric material, but must be transparent to the radiation generated. The electrodes 26 , 27 lie outside the discharge space 14 . The silent discharges are operated by the AC voltage generated by the energy supply 28 . The current flows in the discharge space 14 in the form of thin current threads, each of which is only maintained for a few nanoseconds. The generation and disintegration of the current filaments is such that on average there is always a certain number of current filaments at the same time. So there are spatially averaged micro-discharges within the discharge space 14 instead. Excimer formation takes place within these micro-discharges. Due to the short current pulses, free electrons are available for as long as is necessary to excite the atoms or molecules of the filling gas. During the collision processes that occur, an atom or molecule of the filling gas takes over almost the entire energy of an electron within a very short time (fractions of a nanosecond), which is why it is put into an excited state. The electron continues to fly at a greatly reduced speed after the impact. Here, it is accelerated again in the electric field between the electrodes 26 in order to be able to excite another atom / molecule. The excited atom or molecules, on the other hand, can collide with the neutral atoms / molecules present in the filling gas in order to form new molecules which are only stable in the excited state (excimers). The excimer is formed within a fraction of a nanosecond. Excimer molecules are not very stable and decay when the excitation energy is released in the form of a UV photon.

The spontaneous UV radiation generated in this way emerges from the discharge space 14 via the transmission windows 24 and is reflected on the mirrors 32 , 34 . The mirrors 32 , 34 bring about a feedback of the spontaneously emitted light into the discharge space 14 . This creates spatially directed stimulated light emission. As soon as the amplification of the stimulated emission is greater than the losses, the laser threshold is exceeded and part of the laser radiation can leave the resonator 30 through the coupling mirror 34 .

In the case of the laser 10 , the UV lamp of which can also be regarded as a pump for the laser process, the spontaneous quasi-continuous UV radiation is coupled out via the transmission window 24 without wavefront deformation and is fed to the resonator 30 . Because of the quasi-continuous generation of spontaneous light emissions, excimers, i.e. excited molecules, are always present spatially averaged. According to the invention, these are used to amplify the stimulated light emission. Because excimers only exist in the excited molecular state and consequently the ground state cannot be occupied, the reversal process for stimulated emission, namely the absorption of light, cannot take place in the excimer gas.

All gases or gas mixtures known from the excimer high-power radiators, the excimer lasers or the ozone generators can be used as the filling gas 16 for the discharge space 14 . When using the UV laser in research, it will often be desirable to be able to operate the same laser using different filler gases at different emission wavelengths. For this purpose, the discharge space 44 of the laser 40 can be equipped with a nozzle provided with a valve for the supply and discharge of new discharge gas 46 or used excimer gas mixture.

FIG. 2 shows a second exemplary embodiment of an excimer laser 40 with a transverse excitation geometry. The laser 40 according to FIG. 2 has a UV lamp 12 with an annular discharge space 44 . A discharge or excimer gas 46 is located in this annular discharge space 44 . The discharge space 44 is delimited on the outside by an outer wall 48 and on the inside by an inner wall 49 . Both walls act as a dielectric 50 and run in a direction parallel to the direction of propagation of the stimulated light 62 . The transmission windows 64 , one of which has a ring structure and is at an angle of 90 ° to the direction of propagation of the stimulated light 62 , and of which the other is at an angle of ≠ 90 °, preferably that, are arranged on the two end faces of the discharge space ring arrangement Brewster angle to the direction of propagation of the stimulated light 62 of the laser 40 is. The outer wall 48 is provided with a continuous electrode 66 , while the second electrode 67 is part of the inner wall 49 . Both electrodes 66 , 67 are connected to the AC power supply 68 .

The resonator 70 is arranged outside the UV lamp 42 and has a highly reflecting mirror 72 and a decoupling mirror 74 . The high reflection mirror 72 is applied directly to the transmission window 64 arranged at an angle of 90 ° to the propagation direction of the stimulated light 62 , while the coupling mirror 74 is arranged at a distance from the other transmission window 64 running at the Brewster angle.

The operation of the UV lamp 42 corresponds exactly to that of the lamp 12 according to FIG. 1.

An exemplary embodiment of an excimer laser 80 with a longitudinal excitation geometry is shown in FIG. 3. The UV lamp 82 encloses a cylindrical or cuboidal discharge space 84 which is filled with an excimer gas 86 . The axial wall sections of the wall 88 consist of an electrically insulating material which is connected to the transmission windows 94 which are perpendicular to the direction of propagation of the stimulated light 92 . In contrast to the exemplary embodiments according to FIGS. 1 and 2, the two electrodes 96 , 97 , which are connected to the energy supply 98 , are arranged facing the transmission windows 94 . The two electrodes 96 , 97 consist of a material which is transparent to the UV radiation or, as shown in FIG. 3, have cutouts 99 through which UV light can exit.

The mirrors of the resonator 100 are arranged on the outside of the electrodes 96 , 97 facing away from the transmission windows 94 . These mirrors include the highly reflective mirror 102 and the decoupling mirror 104 as well as two or more (highly reflective) deflecting mirrors 106 . At least one deflecting mirror 106 is arranged on each side of the UV lamp 82 . The highly reflective mirror 102 and the coupling mirror 104 are also arranged on different sides of the UV lamp 82 . All mirrors are aligned in the direction of propagation of the stimulated light with recesses 99 of the electrodes 96 , 97 , the light beam crossing the discharge space 84 three or more times in the area between the highly reflecting mirror 102 and the coupling mirror 104 .

Starting from the highly reflecting mirror 102 , the light beam crosses the discharge space 84 for the first time in order to hit one of the deflecting mirrors 106 after passing through the opposite transmission window 94 and a recess 99 . This deflecting mirror 106 is constructed in the manner of a 90 ° angle, the two legs of which extend at an angle of 45 ° to the optical path of the stimulated light. The light emerging from the recess 99 reaches one of the two legs of the deflection mirror 106 and is reflected by the latter on the second leg, from which it is reflected back to the discharge space 94 . The light beam in turn runs through a cutout 99 in the electrode 96 in order to strike one of two legs of the second deflecting mirror 106 after crossing the discharge space 84 and passing through the opposite transmission window 94 and penetrating a cutout 99 . From this leg, the light is reflected on the second leg of the deflecting mirror 106 , from which it in turn runs back through the discharge space 84 . Two recesses 99 are also arranged in the electrodes 96 , 97 along this optical path. Finally, the light hits the coupling mirror 104 .

Due to the mirror arrangement of the resonator 100 described here, the light covers a path on its way between the highly reflective mirror 102 and the coupling mirror 104 , which crosses the discharge space 84 three times. The method of operation of the UV lamp 82 corresponds to that of the UV lamp 12 of the exemplary embodiment according to FIG. 1.

The embodiment of Fig. 3 is suitable for homogenizing the spatial beam profile with spatially inhomogeneous light amplification in the discharge space. However, due to the low mode volume (with grid electrodes), the energy extraction from the excitation volume (efficiency of the laser) is smaller. However, one can use a multi-pass amplifier arrangement according to FIG. 3, in which the excitation volume is interrogated in spatially separated beam paths again somewhat improved (effective extension of the light-amplifying medium), the efficiency of the laser.

The embodiments according to FIG. 1 and FIG. 2 are distinguished from the embodiment shown in Fig. 3 by a large mode volume in the discharge space from and are particularly suitable for applications in which as much of the data stored in the discharge space excitation Sener energy is to be extracted by the stimulated emission process . In the case of high demands on the beam quality, the resonator configuration in FIG. 3 should be preferred to the resonator configuration in FIG. 2.

As can be easily understood from the exemplary embodiment according to FIG. 2, in the case of an annular discharge space, light with an annular beam profile emerges from the end faces thereof. In Figs. 4 to 7 optics are presented, which allow to convert this circular ring-shaped light beam.

Fig. 4 shows a conical lens system 110 for the conversion of a circular beam profile in a completed beam profile or in a ring-shaped beam profile with a different aspect ratio. The annular beam 112 strikes the base of a positive cone-optical first element 114 to converge upon exiting the cone surface. At the intersection of the converging annular beam profile, the tip (sole) of a negative cone-optical second element 116 is arranged, from which the beam profile emerges as a filled beam 118 .

Fig. 5 shows a cone-optical telescope 120 for changing the aspect ratio and the divergence of an annular beam profile. The aspect ratio is the ratio of the inner radius R1 to the outer radius R2 of the ring-shaped beam profile. The divergence of the annular beam profile means the angles α1 and α2 with which the annular beam tapers or widens. In the cone optics 120th according to Fig 5, the annular beam 122 first meets a negative spherical optics 124, it exits the under expansion. The emerging beam strikes the base of a positive cone-optical element 126 , from the cone surface of which it emerges by changing its angle to the optical axis. The circular beam profile has a crossing line 128 behind the cone-optical element 126 . The divergence of the light behind the positive cone optics 126 and the propagation path of the light behind this cone optics 126 influence the aspect ratio R1 '/ R2' and the divergence angles α₁ 'and α₂'. Further optical elements such as lenses or further cone optics can be arranged subsequently in order to collimate the divergent light beam again.

The optics shown in FIGS . 4 and 5 can in principle be used both inside and outside the resonator of the laser. When used inside the resonator, filtering to influence the spatial light field distribution (laser mode) is possible with lower losses and less radiation exposure to the filter than if this filtering takes place outside the resonator.

Generally speaking, all spherical lenses included in this Invention description are called, by equivalents spherical or aspherical mirrors can be replaced to Losses due to absorption of UV light in the lens avoid material.

An example of spatial filtering of the circular beam profile is shown in FIG. 6. The filter device 130 shown there converts the circular beam profile 132 into the filled beam profile 134 . The circularly circular beam strikes a convex lens 136 and is focused by it. In the focal point of the converging annular beam there is a pinhole 138, which, viewed in the direction of light propagation, is followed by a convex lens 140 , the focal point of which is also in the plane of the pinhole 138 . The light that strikes the pinhole 138 as a converging annular beam leaves the pinhole 138 with a suitable choice of the opening of the pinhole as a conical full beam, which is converted by the lens 140 into a beam 134 of constant diameter. So you get with the filter device 130 shown in Fig. 6 from the circular annular beam profile directly a filled laser beam profile.

An alternative to spatial filtering with the filter device 130 according to FIG. 6 is shown in FIG. 7. The optics according to FIG. 7 reduce high spatial frequencies in that a cone-optical telescope according to FIG. 5 is connected upstream of the optical filter device according to FIG . In the optics 150 according to FIG. 7, the annular beam 152 strikes a concave spherical lens 154 in order to then hit a positive cone-optical element 156 . The light leaving the positive cone optical element 156 strikes a convex lens 158 , in the focal plane of which a pinhole 160 is arranged. Following the pinhole 160 , a convex lens 162 is again arranged on the optical axis of the optics 150 , the position of which is selected relative to the pinhole 160 such that the focal point of this lens 162 lies in the plane of the pinhole 160 . The beam 164 leaving the lens 162 has a full profile. The reduction in the proportions of high spatial frequencies in the plane of the pinhole 160 results in an increase in the transmission through the pinhole 160 compared to the filter arrangement shown in FIG. 6.

In the case of the resonator configuration shown in FIG. 3, high-frequency loss or gain modulation (modulation frequency in the MHz range), which can be implemented, for example, with acousto-optical modulators, should make it possible to couple resonator modes and thus the generation of short light pulses. Due to the spectral bandwidth of the amplifier media (excimer gases) xenon chloride and krypton fluoride, the generation of subpico or femto-second laser pulses (pulse duration 0.1 ps) is possible.

Since in the UV laser according to the invention the laser pulse duration and the tactile ratio (that's the ratio of La pulse duration to the sum of the laser pulse duration and subsequent pause time until the next laser pulse) essentially by the properties of the AC power source and the Power supply lines to the UV laser are still determined basically a simple change of these two gave way characteristics by changing the parameters AC power supply possible.

Reference list

10 , 40 , 80 lasers
12 , 42 , 82 UV lamp
14 , 44 , 84 discharge space
16 , 46 , 86 discharge gas
18 , 48 , 49 , 88 wall
20 , 50 , 90 dielectric
22 , 62 , 92 Direction of propagation of the stimulated light
24 , 64 , 94 transmission window
26 , 27 , 66 , 67 , 96 , 97 electrodes
28 , 68 , 98 AC power supply
99 recess
30 , 70 , 100 resonator
32 , 72 , 102 highly reflective mirror
34 , 74 , 104 decoupling mirror
106 deflecting mirror
110 optics
112 ring beam
114 positive cone optics
116 negative cone optics
118 full jet
120 telescope
122 ring beam
124 negative optics
126 positive cone optics
128 crossing line
130 filter device
132 ring beam
134 full jet
136 collimating optics
138 pinhole
140 collimating optics
150 optics
152 ring beam
154 optical element
156 positive cone optics
158 collimating optics
160 pinhole
162 collimating optics
164 full jet

Claims (18)

1. Quasi-continuously emitting UV laser, in particular special excimer laser, with

• - A UV lamp ( 12 ; 42 ; 82 ), in particular excimer lamp, which spontaneously emits light in the UV wavelength range, and
• - a resonator ( 30 ; 70 ; 100 ) which feeds back the spontaneous light emission into the UV lamp ( 12 ; 42 ; 82 ) for generating and coupling out stimulated light emission,
• - Wherein the UV lamp ( 12 ; 42 ; 82 ) quasi-continuous Lich emits spontaneous light, the front of the waves without deformation or with defined waves front curvature, which can be eliminated by a subsequent correction optics, hits the resonator.

2. UV laser according to claim 1, characterized in that the UV lamp ( 12 ; 42 ; 82 ) has a discharge space ( 14 ; 44 ; 84 ) which with a discharge gas spontaneously emitting radiation under discharge conditions ( 16 ; 46 ; 86 ) that the discharge space ( 14 ; 44 ; 84 ) is formed by two opposite transmission windows ( 24 ; 64 ; 94 ) which are transparent to UV radiation and a gas-tight wall ( 18 ; 48 , 49 ; 88 ) connected to them , which has a dielectric ( 20 ; 50 ; 90 ) and that for generating silent electrical discharges inside the discharge space ( 14 ; 44 ; 84 ) outside the discharge space ( 14 ; 44 ; 84 ) from an AC power source ( 28 ; 68 ; 98 ) fed electrodes ( 26 , 27 ; 66 , 67 ; 96 , 97 ) are arranged. 3. UV laser according to claim 2, characterized in that the electrodes ( 26 , 27 ; 66 , 67 ; 96 , 97 ) are arranged such that between each electrode ( 26 , 27 ; 66 , 67 ; 96 , 97 ) and the discharge gas ( 16 ; 46 ; 86 ) is a material acting as a dielectric. 4. UV laser according to claim 2, characterized in that the electrodes ( 96 , 97 ) are transparent to the UV radiation and are arranged such that there is a transmission window between each electrode ( 96 , 97 ) and the discharge gas ( 86 ) ( 94 ). 5. UV laser according to claim 4, characterized in that the electrodes ( 96 , 97 ) are designed as grid electrodes, perforated electrodes or in the form of concentric rings. 6. UV laser according to one of claims 2 to 4, characterized in that the discharge space ( 16 ; 86 ) is cuboid or cylindrical and is provided with two end wall sections and that the transmission window ( 24 ; 94 ) form the end wall sections and in the other the wall ( 18 ; 88 ) delimiting the discharge space ( 16 ; 86 ) consists of a dielectric material ( 20 ; 90 ). 7. UV laser according to one of claims 2 to 6, characterized in that at least one of the transmission window ( 64 ) is arranged at an angle to the direction of propagation of the stimulated light ( 62 ), in particular at the Brewster angle. 8. UV laser according to one of claims 2 to 6, characterized in that the discharge space ( 44 ) is formed as an annular space between two preferably concentric hollow profiles, in particular tubes, made of dielectric material, the axial ends of which are closed by the transmission windows ( 64 ) . 9. UV laser according to claim 8, characterized in that the electrodes ( 66 , 67 ) to the discharge space ( 44 ) respectively facing sides of the two hollow profiles are arranged. 10. UV laser according to one of claims 2 to 7, characterized characterized in that the discharge space at least two from each other by a partition arrangement a subdivision of a dielectric material has that the partition assembly one with the AC electrode connected electrode and that the subspaces are transparent to UV radiation Have transmission windows, the walls of the subspaces between the transmission windows have dielectric material. 11. UV laser according to one of claims 1 to 10, characterized in that the resonator ( 30 ; 70 ; 100 ) has a highly reflecting mirror ( 32 ; 72 ; 102 ) and a decoupling mirror ( 34 ; 74 ; 104 ), their respective optical axis coincides with the direction of propagation of the stimulated light ( 22 ; 62 ; 92 ) running through the transmission window ( 24 ; 64 ; 94 ) and the discharge space ( 14 ; 44 ; 84 ). 12. UV laser according to one of claims 1 to 11, characterized in that the highly reflective mirror ( 32 ; 72 ) and the coupling mirror ( 34 ; 74 ) are each aligned with or in projection of the transmission window ( 24 ; 64 ). 13. UV laser according to one of claims 1 to 12, characterized in that at least one in the propagation direction of the stimulated light ( 92 ) arranged deflecting mirror ( 106 ) is provided and that the decoupling mirror ( 104 ), the highly reflective mirror ( 102 ) and the at least one deflecting mirror ( 106 ) are arranged such that the stimulated light crosses the discharge space ( 84 ) several times along the direction of propagation ( 92 ). 14. UV laser according to one of claims 8 to 10 and 11, characterized in that in an annular, in particular annular profile ( 112 ; 132 ; 152 ) of the beam leaving the discharge space, an optical device ( 110 ; 130 ; 150 ) for conversion the annular beam profile ( 112 ; 132 ; 152 ) is provided in a circular filled beam profile ( 118 ; 134 ; 164 ). 15. UV laser according to claim 14, characterized in that the optical device ( 110 ) has cone-optical elements ( 114 , 116 ), the annular beam ( 112 ) first on a positive cone-optical first element ( 114 ) and after transmission strikes a negative conical-optical second element ( 116 ) through this first element ( 114 ). 16. UV laser according to one of claims 8 to 10 and 11, characterized in that in an annular, in particular annular profile ( 122 ) of the beam leaving the discharge space to change its aspect ratio (R1 / R2) and divergence (angle α₁, α₂) a telescope ( 120 ) with at least one cone-optical element ( 126 ) and at least one spherical or aspherical optical element ( 124 ) is provided. 17. UV laser according to one of claims 8 to 10 and 11, characterized in that with an annular, in particular annular profile ( 132 ; 152 ) of the beam leaving the discharge space, an optical filter device ( 130 ; 150 ) for spatial filtering of the annular beam profile ( 132 ; 152 ) is provided, which has two collimating optics ( 136 ; 140 ; 158 ; 162 ) and a pinhole ( 138 ; 160 ) arranged at the focal point of both collimating optics ( 136 ; 140 ; 158 ; 162 ). 18. UV laser according to claim 17, characterized in that a telescope is connected upstream to reduce the intensity of higher spatial frequencies of the annular beam profile ( 152 ) of the arrangement of the two collimating optics ( 158 , 162 ) and the pinhole ( 160 ) arranged between them , which has spherical or aspherical optical elements ( 154 ) and cone-optical elements ( 156 ).