DE102008035898A1 - Apparatus and method for reducing speckling in the field of laser applications - Google Patents

Abstract

The present invention relates to an apparatus for improving the laser beam quality for abrasive applications, comprising a laser (1) with asymmetric beam profile, comprising a first, short beam axis (20), a second, long beam axis (30), wherein the laser (1) at least an optical element (10) and / or a resonator mirror (11) with a cylindrical mirror surface (13) for reducing the spatial coherence and / or increasing the divergence in the short beam axis.

Description

The The invention relates to an apparatus and a method in Range of laser applications for reducing speckle.

at the use of a laser beam in lithography, micromachining and especially refractive surgery is an occurrence of speckles undesirable in the working plane. The bacon pattern of the laser beam is formed on the working plane and leads to inaccuracies. To avoid speckles and the associated Generation of a smooth beam profile are the following approaches known.

"The Laser Guidbook" (Author: Jeff Hecht, Copy Rights: McGraw-Hill Ins., ISBN: 0071359672) describes a use of spherical HR stable resonators to reduce the coherence, increase the divergences and thus avoid speckles. Many fashions and bad ray characteristics are the result. Another disadvantage is the lack of adjustment of the beam axes to each other and the associated different divergence and coherence in the axes. In addition, pulse shape and pulse duration may change with this solution.

In WO 2004021529 A1 For example, a resonator is described which uses spherical and aspherical hemispherical mirrors to approximate the divergence and coherence of the beam. Furthermore, it is described herein that diffusers mounted on or between the mirrors and acting only in the critical axis can solve the problem.

In WO 1996016455 A1 are described unstable resonators with convex cylindrical mirror surface which change the divergence and thus coherence axis-dependent. The coherence is increased and the divergence is reduced. Furthermore, the possibility is described of achieving this effect by cylindrical lenses lying in the resonator.

In US 5946337 is an unstable resonator with divergent (convex) reflective cylindrical mirror surface and dispersive wavelength selector described to obtain a beam with low bandwidth and yet high energy yield. Low bandwidth leads to an increase in temporal coherence.

In DE 4225781 is an unstable resonator with cylindrical mirrors described with which a Divergenzanpassung can be done. The coherence is increased and the divergence is reduced.

The known devices are not capable of occurring To reduce speckle in the working plane, without losing energy, pulse duration changes or having to accept heart rate changes.

task of the invention, it is the speckle effect in the working plane To reduce and provide a smooth beam profile.

The The present invention solves this problem by the invention Device and the method according to the independent Claims. Further advantageous embodiments of the invention are given in the dependent claims.

According to a first aspect of the present invention, there is provided an apparatus for improving laser beam quality for laser applications, comprising a laser ( 1 ) with an asymmetric beam profile and a first, short beam axis ( 20 ) and a second, long beam axis ( 30 ) and a beam propagation axis ( 35 ) and a resonator ( 60 ), whereby the laser ( 1 ) at least one optical element ( 10 ) and a resonator mirror ( 11 ) with a cylindrical mirror surface ( 13 ), for reducing the spatial coherence and / or increasing the divergence, in particular in the short, ie generally coherent beam axis.

When Lasers are preferably called sources, which are coherent, emit hardly divergent electromagnetic radiation.

According to the invention preferably gas lasers, particularly preferably discharge lasers of any kind used. The gas laser is most preferably the excimer laser used.

laser applications are preferably ablative or exposing laser application. Under it understands one prefers applications, which preferably by pulsed jet delivery Interact with material in a working plane, particularly preferred Remove material. This is preferably done in one point (spot). Preference is given to point-focused rays (Spots) also large-scale, homogenized rays understood in the working level. The resulting profile in the Working plane is called removal profile.

One Abtragsprofil can preferably by the known methods of Spotscannings most preferably by variable-iris methods, most preferably also be generated by mask exposure method.

Removal of material is preferably referred to as vaporizing or ablating material in this spot. By the local set side by side of preferably selective interventions, a machined surface is preferably created. Preferably, the cross-sectional profile of the spot is formed at the point of engagement. According to the invention, a Gaussian, smooth cross-sectional profile of the spot is preferred. It can also plateau-shaped cross-sectional profiles of the spot, depending on the application, are preferred. Laser lithography, most preferably laser micromachining, most preferably refractive surgery or other type of laser treatment are examples of ablative laser applications.

The Laser beam quality is in this invention in the laser spot Are defined. The laser spot is the point where the bundled Laser beam hits the working plane and unfolds its effect, d. H. Material removes. The working level is the level understood in which the laser beam in the context of laser application interacts with matter. Is in profile section through the spot the profile of the laser beam, equal to the profile of the theoretical desired beam, is the laser beam quality Good. According to the invention, a Gaussian profile cut preferred in the spot. Also top hat or other distributions will be preferably used.

When long beam axis is preferably the direction from electrode to electrode designated. Along this axis preferably runs the Discharge in discharge-pumped gas lasers. The beam profile in This direction is preferably top-hat-shaped. The number Transverse modes in this direction are large, dependent from the electrode gap. The coherence length is corresponding low and mostly uncritical with regard to the interference effect on micro-optical elements (eg beamshapers). The divergence is correspondingly large.

The short beam axis is at right angles to the long beam axis. According to the propagation of the discharge, at discharge-pumped Lasers, the beam profile in this direction is preferably Gaussian. The suggestion concentrates according to the Gaus distribution of the Discharge excitation to the center of the discharge. Training Transverse modes in this direction are restricted accordingly and their number is smaller. This results in a larger one Coherence length in this direction, which is critical on the interference effect when using micro-optical elements effect. The divergence is correspondingly lower in this direction.

short and long beam axis are preferably formed in their properties in cooperation with micro-optical components in the working plane from. The interference effect and thus speckle formation occurs preferably in the critical short beam axis to day. The short beam axis is so when compared with the long beam axis usually the more coherent beam axis.

short and long beam axis are also preferred for orientation used at the working level. Particularly preferred tension they work as coordinate axes on the working plane. As a working level For example, the convex cornea is also referred to.

The Beam propagation axis is preferably the axis along which the laser beam propagates. The beam propagation axis is preferably perpendicular on the short and long beam axis.

Of the Resonator of the laser is an optical resonator, which serves reflected light as often as possible back and forth. Due to interference then forms a standing in the resonator Wave, when the optical path length of the resonator is a multiple the wavelength of the incident light is. According to the invention, stable resonators are preferred used.

Especially Preferably, lasers with asymmetric beam profile are used in this invention Application. The beam profile is preferably formed depending on the material properties of the machined material also in the removal profile from. According to the definition of long and short beam axis the beam profile is considered asymmetric when the beam shape (Energy-power distribution over the area) is different in both directions. This results in preference different properties of the beam, such as coherence and divergence along these beam directions. A beam profile is asymmetric when beamform, coherence and the resulting resulting divergence preferably in the beam axes of the processing planes differ.

One Optical element is preferably an element which at least preferably reflects an electromagnetic beam breaks, most preferably affects phase or amplitude of the beam.

Under Imaging optics is preferably understood optics, with which the beam, preferably in the course of beam shaping, on the working plane is shown to preferably a predetermined shape and size to get the intensity distribution.

Under Spatial coherence is the ability a light source, in two different places, but to each same time to cause stationary interference phenomena. It is the statement of the correlation of the phase of the signal to spatial separate points at the same time.

Under Temporal coherence is the ability a light source, in a fixed place with light that is two different Time points left the light source, still stationary To cause interference phenomena. It is the statement of the correlation the phase of the signal at different times in the same place.

When Divergence is the property of a beam, which of a center, perpendicular to the propagation direction, diverge. Divergence angle is the angle, which is formed by the line pair, the asymptotic envelope represents the increasing beam dimension.

When Resonator mirror is preferably one of the two outermost Mirror in a resonator called the active medium (Gain medium) with mutually facing mirror surfaces enclose. This resonator is preferably a HR mirror on the non-outcoupling side, more preferably one OC mirror on the outcoupling side of the resonator. The highly reflective Mirror preferably has the highest possible degree of reflection.

Prefers the resonator mirrors stand with the mirror surfaces parallel opposite. In this case, the invention in various Embodiments prefer the following configurations (Here, the shape of the resonator mirror on the output side called first and then the shape of the resonator mirror on the not Outcoupling side): concave-plan, plan-concave, concave-concave.

The Mirror surface of the concave resonator is included preferably cylindrical. The concave mirror surface is preferred a segment of a cylinder. The radius of curvature of the cylindrical Inner surface is preferably 1 mm to 1000 m, particularly preferred 50 mm to 200 m, most preferably 1 m to 10 m. Is preferred the best possible adjusted radius of curvature depending on the resonator length, the coherence and the size of the individual elements of a micro-optical Component.

optical Elements are also preferred diffractive elements such as Grids or refractive elements such as lenses, which are the spatial coherence can influence. Particularly preferred Step structures shift the beams temporally to each other and so reduce the temporal coherence. This may be preferred the interference effect on micro-optical elements are reduced.

In a further preferred embodiment, the cylindrical mirror surface ( 13 ) of the concave resonator mirror ( 11 ) arranged so that the curved axis of the mirror perpendicular to the long beam axis ( 30 ) and / or perpendicular to the beam propagation axis ( 35 ) of the laser ( 1 ) lies.

When Curved axis of the mirror becomes the center axis of the imaginary cylinder.

By the preferred arrangement of this direction of curvature perpendicular to the long beam axis, d. H. along the short, usually more coherent Beam axis and perpendicular to the beam propagation axis is the coherence the coherent, short axis decreases and the divergence enlarged in this direction. The energy yield remains the same, because despite focusing by the Gaussian excitation distribution there is enough emission in the short axis. From the same reason, the pulse duration and shape is retained.

at a preferably stable resonator preferably increases with increasing Curvature of the concave mirror the divergence of the beam outside the resonator too. This is especially preferred cylindrical mirrors in the direction of curvature of Case. The increase in divergence is equal to a decrease spatial coherence.

In a preferred embodiment, the laser is 1 ) an excimer laser.

Of the Excimer laser is an ultraviolet gas laser whose resonator with Gas is filled. Preferably, the excimer laser is used according to the invention Use because it provides an asymmetric beam profile. The gases used in the resonator are preferably Fe2 or Xe or ArF or KrF or XeBr or XeCl or XeF. The excimer laser is preferred high UV pulse energies available.

In a preferred embodiment, the optical element ( 10 ) a homogenizer ( 42 ) and / or an integrator and / or a beamshaper.

One Homogenizer (beam homogenizer) is preferably an optical element, that an incident intensity distribution into an altered transferred uniform intensity distribution.

One Beam Shaper (Beam Shaper, Beam Integrator) is preferably a homogenizer, with an incident intensity distribution in an intensity distribution is transferred with laterally predetermined shape.

In a further preferred embodiment, the optical element ( 10 ) an imaging optics ( 44 ).

A Imaging optics is preferably at least one optical lens, especially preferably in parallel standing lenses, which the laser beam in to represent a point.

The Invention may preferably be with a micro-optical element, especially preferably also with an enlarging or reducing acting imaging optics are used. Most preferred becomes a refractively effective beamshaper and a telescope for downsizing Figure inserted.

In a further preferred embodiment, the optical element ( 10 ) a micro-optical element ( 40 ).

One Micro-optical element is an element which is preferably outside the laser apparatus is located, particularly preferably behind the outlet opening of the Lasers, particularly preferably in the axis of the laser beam. On the Properties of the micro-optical element is preferably the exiting Laser beam aligned. Preferably, the setting of the reduced Laser beam the speckle effect, which without adjustment of the laser beam would occur to the micro-optical element. By the Adaptation of the laser beam to the optical properties of the micro-optical Elements, preferred is the spatial coherence reduced and the divergence of a preferred excimer laser beam in the short beam direction with constant pulse properties (Pulse energy, pulse duration, pulse shape) increased. Thereby is preferred the disturbing speckle effect in the working plane reduced.

microoptic Elements are preferably optical elements whose geometric dimensions only a few orders of magnitude above the wavelength of the they are radiating light. Because of these proportions the wave characteristic of the light strongly comes to the fore.

In a further preferred embodiment, at least one micro-optical element 40 a beamshaper 41 or a beam homogenizer 42 or a beam integrator 43 or an imaging optics 44 ,

Prefers the micro-optical element is a beamshaper, in order to prefer the radiation distribution to shape. This makes it preferable to set erosive Laser beams possible.

The micro-optical element is preferably a beam homogenizer, with which Irregularities in the laser beam profile balanced be and prefers a uniform beam is formed.

Prefers For example, the micro-optical element is a beam integrator, preferably relatively generate flat intensity profiles of the laser beam.

microoptic Component (eg beam shaper or homogenizer or integrator) prefers the following specifications.

The Micro-optical component is preferably a refractive micro-optical Element. The microlenses have a preferred diameter of 0.1 microns to 2 mm, more preferably a diameter from 1 μm to 1 mm, and most preferably one diameter in the range of 10 μm to 600 μm.

The Micro-optical component is furthermore preferably a diffractive effective micro-optical element with a grid spacing of 0.1 μm to 1 mm, more preferably 1 .mu.m to 500 .mu.m and most preferably in a range of 2 μm to 200 μm.

Apparatus according to claim 1 to 5, wherein the resonator ( 60 ) is an anamorphic stable resonator.

Prefers the resonator is an anamorphic stable resonator. An "anamorphic stable resonator "is a stable resonator with different beam axes Effect on coherence and divergence. Ie. axis-dependent Optimizing the coherence and thus reducing the speckle in the critical, short beam axis.

The object of the invention is further achieved by a method for providing a smooth beam profile, ie by reducing the speckle in the working plane, wherein a laser beam with asymmetrical beam profile comprising a first, short beam axis ( 20 ) and a second, long beam axis ( 30 ) is provided and the spatial coherence is reduced and / or the divergence of the short beam axis of the laser beam is increased.

Prefers are laser beams, optimized by this method so that they form a smooth beam profile. This is preferred in the refractive surgery allows for precise material removal.

One smooth beam profile preferably has no "outliers" in the profile section of the laser spot, but preferably a small Deviation in shape and roughness based on the desired Beam profile on. Most preferably, the profile section is possible Gaussian. Also preferred are profile shapes, such as Top-Hat.

Smooth beam profiles are particularly preferred in refractive corneal surgery. Preferably, smooth steel profiles are used in lithography or micromachining.

Prefers In this invention, lasers are used, which are preferred be pumped by two opposing electrodes and / or form an asymmetric beam profile.

It preferably forms on the short beam axis of the laser greater coherence and smaller divergence out than on the long beam axis.

The long beam axis is the distance from electrode to electrode that short beam axis is at right angles to the long beam axis.

The Reduction of spatial coherence and / or Increasing the divergence of the short beam axis of the laser beam is preferably by a concave cylindrical Resonator mirrors generated. As a result, the laser beams are preferred collimated the short beam axis. By the preferred Gaussian Excitation distribution in this axis produces enough emission and only a slight reduction in energy yield.

The Reduction of spatial coherence and / or Enlargement of the divergence arises through the Increasing the number of transversal modes due the changed resonator arrangement.

In the machining plane to meet the focused laser beams preferred to a point. This point is called a spot. The spot is the site of intervention, for example during an operation. Here is preferably removed material.

In a further preferred embodiment, a method is provided, wherein the laser beams with an imaging optics ( 44 ) on a working plane ( 45 ), an examination of the existing speckle pattern takes place, an adaptation of the radii of curvature of the resonator mirrors ( 11 ), the spatial coherence and / or increase of the divergence of the short beam axis ( 20 ) of the laser beam is further reduced, a re-examination of the speckle pattern is performed.

Under Imaging optics is preferably understood optics, with which the beam, preferably in the course of beam shaping, on the working plane is shown to preferably a predetermined shape and size to get the intensity distribution.

On In the working plane, the beam is preferably imaged in the focus. The test surface is an area that makes it possible to investigate the beam profile. Preferably, from the generated spot on the test surface a profile section through the spot preferably visually represent, particularly preferably calculate. Prefers a beam observation system is positioned in the working plane.

The Examination of the incident laser beam in the working plane and hence the analysis of the speckle pattern may be preferred with known ones Methods and systems are done automatically.

Prefers The method of moving slit is used. This is a slit with the smallest possible slot width (in relation to the beam size) in the working plane by the laser beam step by step Step moved through, and the energy after the iris with a Energy detector measured. The aperture positioning can preferably via automatic Moving tables are provided with stepper motor. The energy is thus split into small, location-dependent parts, and you get the spatial fluence distribution of the laser beam, the beam profile, and the speckle pattern. The Beam profile with recognizable speckle pattern is preferred in digital Form saved.

Especially preference is given to the method of blasting and / or the Specklemusterprüfung used by beam camera. at This method is preferably the beam z. B. over a Beam splitter in a suitable direction coupled to the beam camera. Depending on the laser wavelength, it may be necessary to make a frequency conversion to the beam for to make the camera chip visible. Preferred for one 193 nm laser beam is used for a fluorescent disc. The image of the laser beam must be in the working plane lie. The fluorescent light is transmitted through a lens to the camera chip (usually CCD or CMOS) and can be stored digitally.

The digitized beam profiles and / or speckle patterns of both preferred Measuring methods are preferably mathematically analyzed. In the beam profile the roughness is preferred as the difference of a fit function determined the measured data.

The Roughness is then preferably a measure of the Strength of Specklewirkung and may preferably in the inventive Method be iteratively reduced.

Preferably, the beam is thus visually inspected for speckle. By the beam observation system, preferably also checking other laser parameters such as energy, pulse duration, pulse shape can be monitored. This is preferably sicherge provides that with only minimal influence on the other laser parameters, the speckle effect is minimized.

The Beam profile offers preferably the possibility of the eventual Speckle pattern of ray represent. Is the beam profile, or the spot profile is not smooth, a speckle pattern is formed.

By Adaptation of the resonator elements, preferably by modification the radius of curvature of one or both resonator mirrors, is it possible the spatial coherence and / or increasing the divergence of the short ones Beam axis of the laser beam to influence. This is preferred iteratively carried out until the speckle stopped working occur. As a result, the beam or the spot profile is preferred optimized.

about another test, identical to the one described above first test, the beam quality is again checked.

In Another preferred embodiment is a method provided, which the laser beam with 193 nm wavelength on the cornea, the laser beam with a pulse duration of 4 to 15 ns scanning over the cornea, refraction-enhanced profiles with reduced roughness and optimized form fidelity ablates and with an energy in the range of 0.5 mJ to 1.5 mJ.

at This method is preferably laser with a wavelength used by 193 nm, which depart the cornea of the eye.

Prefers a spot scanning method is used to scan the cornea, wherein the preferably used laser steel in the working plane (Cornea) shown reduced. The reduced beam imaging is preferably referred to as a spot. By means of lateral Strahlauslenkenden optics (preferably Galvoscanner) the laser beam with a preferred pulse duration of 4 to 15 ns over the cornea emotional.

at In this preferred method, the spot is preferably the location the laser beam interacts with the matter (the corneal tissue). At the preferably exceeding a minimum energy surface density (Schwellfluence) it comes to ablation of tissue. The energy sector is preferably 0.5 mJ-1.5 mJ.

When Ablation is preferred as nonthermal molecule decomposition referred to, in which the material is removed. By the distribution many such spots over the cornea, this can be done by removal a change of the curvature and thus a change experienced the refraction.

at a second method of mapping is preferred over Apertures and variable stops the beam size during The treatment varies to obtain a removal of the refractive Properties of the cornea changed.

These Methods are preferred for the treatment of refractive disorders like myopia, hyperopia, astigmatism and their mixed forms, as well for the patient-adapted treatment of higher aberrations used.

The inventive method preferably leads smoother when used in refractive corneal surgery, more faithful removal profiles. An improved smoothness can Haze (clouding) as a result of surgery reduce. Due to the improved beam shape, the removal can be better be predicted, which stabilizes the generation of a target refraction.

In Another preferred embodiment of the invention used in a process for micromachining. Under these methods are particularly preferred applications like patterning, cutting, drilling and structuring. In this Embodiment are preferred materials such as ceramic, Glass and polymers processed. The laser beam enters the Working plane (spot) interacting with these materials. exceeds the laser has a minimum energy surface density in the working plane it comes to non-thermal ablation (ablation) of the materials. Preference is given to these methods ink jet heads, Masks and fiber structures produced. By the invention Method can significantly reduce the roughness and the form fidelity of the structures produced can be improved.

In The description of the figures will be further preferred embodiments shown. The figures show;

1 a schematic representation of a laser;

2a . 2 B a laser spot with profile section without device according to the invention; and

3a . 3b a laser spot with profile section with inventive device.

4a . 4b . 4c Three-dimensional views of embodiments of the inventive resonator.

5a . 5b Two-dimensional views of embodiment 4a of the resonator according to the invention.

6a . 6b a schematic representation of the pulse curve with curved resonator mirror.

In 1 a schematic representation of a laser is shown. The excimer laser 1.1 includes a resonator 60 , filled with excimer gas. The resonator has two parallel resonator mirrors 11.1 and 11.2 opposite, wherein the resonator mirror 11.2 on the outcoupling side and resonator mirrors 11.1 on the non-outcoupling side. resonator 11.2 is a planar resonator mirror. resonator 11.1 is a concave highly reflective mirror 12 with a cylindrical mirror surface 13 , Side of the resonator 60 lie the electrodes 70.1 and 70.2 , 70.1 and 70.2 are arranged so that they are parallel to each other and perpendicular to the direction of curvature of the cylinder mirror. Outside the laser 1 lies the micro-optical element 41 in the beam direction in front of the imaging optics 44 , in front of the working level 45 , 41 . 44 and 45 are arranged so that the exiting laser beam on the working plane 45 is displayed in the desired manner.

For Micro-material processing and corneal surgery are different physical quantities related to the laser beam.

In of refractive corneal surgery become output energies at the laser source of not larger than 500 mJ, particularly preferably 100 mJ, and most preferably less than 20 mJ, and machining energies (in the working plane) of preferably 10 μJ to 15 mJ, more preferably from 0.1mJ to 5mJ, and most preferably from 0.5 mJ to 1.5 mJ. It will be a wavelength used in the UV range, preferably 150 nm to 250 nm, especially preferably 180 nm to 200 nm. It is particularly preferred ArF as Excimer gas used. A pulse duration in the range of is preferred less than 2 μs, particularly preferably 0.1 ns to 50 ns, completely more preferably used in the range of 3 ns to 8 ns. It will preferably uses a Gaussian beam shape To make the removal of composite spots smoother. It is preferred to use a beam size in FWHM (Full Width at Half Maximum) range of less than 5mm, especially preferably in the range of 10 microns to 2.5 mm, especially preferably from 0.5 to 1.5 mm. There will be a pulse repetition rate in the Range of preferably 1 Hz to 5 kHz, more preferably from 5 Hz to 1 kHz, most preferably used from 10 Hz to 500 Hz.

In Micro material processing will have a pulse repetition rate in the range from 1 Hz to 100 kHZ, more preferably in the range of 500 Hz to 5 kHz, most preferably in the range of 1 kHz to 4 kHz. A wavelength in the UV range is used, preferably 150 nm to 250 nm, more preferably 180 nm to 200 nm. And Whole particularly preferably in the range from 240 nm to 260 nm. The excimer Laser gas is preferably ArF and more preferably KrF. It will a pulse duration in the range of preferably less than 2 μs, especially preferably 0.1 ns to 50 ns, very particularly preferably in the range of 5 ns to 25 ns used. There are energies from 0.1 mJ / cm to 10 J / cm, particularly preferably 0.1 J / cm to 5 J / cm used.

The ignition voltage for the gas discharge is from the electrodes 70.1 and 70.2 generated. By the gas discharge, provoked by the two opposite electrodes 70.1 and 70.2 , it comes to a development of an asymmetric beam profile. The short beam axis 20 the laser 1 has a greater coherence and a smaller divergence than the long beam axis 30 on.

The laser beams are generated in the cylindrically concave resonator 60 , The direction of curvature of the resonator mirror 12 lies along the short beam axis 20 the laser 1 , This will be the coherence of the coherent short axis 20 decreases and increases the divergence in this direction. The energy yield and pulse duration / shape remain the same because, despite focusing by the Gaussian excitation distribution in the short axis, sufficient emission is produced.

The thus changed laser beam now passes through the OC mirror 11.2 and hits the micro-optical element first 41 , then on the imaging optics 44 and then to the editing level 45 , The task of the micro-optical element is to homogenize the beam in the working plane and / or to provide the desired beam shape. The imaging optics has the task of scaling the beam in the working plane to the desired size.

In 2a becomes a laser spot 2 a laser beam on a working plane 45 shown in the prior art. You can see a spot 2 with a non-homogeneous edge. Ie. in the focused laser beam interference occur, which leads to a speckle effect in the spot 2 to lead. This structure would be mapped on the machined material during removal.

In 2 B becomes a profile cut 3 the "rough" laser beam in the spot 2 , out 2a shown. The profile section clearly shows an inhomogeneous, non-Gaussian distribution. This effect occurs when using devices according to the prior art.

In 3a becomes a laser spot 2 a laser beam according to a device according to the invention on a working plane 45 shown. To see is a spot 2 with a homogeneous border. Ie. no speckle pattern can be seen in the laser beam. In this embodiment, the laser beam was generated and imaged with the device according to the invention.

In 3b becomes the smooth beam profile 3 of the laser beam in the spot 2 shown. The profile section clearly shows a largely homogeneous Gaussian distribution. This effect is achieved by the use of the device according to the invention.

In 4a an embodiment of the resonator according to the invention is shown. The resonator mirrors 11.1 as a highly reflective mirror and 11.2 as Auskoppelspiegel are facing each other with the reflective surfaces facing each other and close the active medium 80 one. It is 11.1 a concave arched mirror 12 with a cylindrical mirror surface 13 , 11.2 is a flat surface. The axis 30 So the axis between the electrodes is the direction of the discharge. The axis 30 is the long beam axis. The axis 20 is the short beam axis and stands upright 30 , The axes 30 and 20 span a plane on which the axis 35 is vertical. The axis 35 is the optical axis of the beam.

In the direction 30 Axis discharges the discharge voltage producing a top-hat shaped excitation and beam profile. Perpendicular to the discharge direction, ie in the direction of the axis 20 a Gaussian similar excitation and beam profile is created. In the direction of the axis 35 the laser beam spreads out.

In 4b an embodiment of the resonator according to the invention is shown. The resonator mirrors 11.1 as a highly reflective mirror and 11.2 as Auskoppelspiegel are facing each other with the reflective surfaces facing each other and close the active medium 80 one. It is 11.1 a mirror with a flat surface. 11.2 is a domed mirror with a cylindrical mirror surface. The axis 30 So the axis between the electrodes is the direction of the discharge. The axis 30 is the long beam axis. The axis y is the short beam axis and is perpendicular 30 , The axes 30 and 20 span a plane on which the axis 35 is vertical. The axis 35 is the optical axis of the beam.

In the direction of the axis 30 discharges the discharge voltage with a top hat-shaped excitation and beam profile is formed. Perpendicular to the discharge direction, ie in the direction of the axis 20 a Gaussian similar excitation and beam profile is created. In the direction of the axis 35 the laser beam spreads out.

In 4c an embodiment of the resonator according to the invention is shown. The resonator mirrors 11.1 as a highly reflective mirror and 11.2 as Auskoppelspiegel are facing each other with the reflective surfaces facing each other and close the active medium 80 one. It is 11.1 a concave arched mirror 12 with a cylindrical inner surface 13 , mirror 11.2 is also arched outward and has a mirror surface 13 , The axis 30 So the axis between the electrodes is the direction of the discharge. The axis 30 is the long beam axis. The axis 20 is the short beam axis and stands upright 30 , The axes 30 and 20 span a plane on which the axis 35 is vertical. The axis 35 is the optical axis of the beam.

In the direction of the axis 30 discharges the discharge voltage with a top hat-shaped excitation and beam profile is formed. Perpendicular to the discharge direction, ie in the direction of the axis 20 a Gaussian similar excitation and beam profile is created. In the direction of the axis 35 the laser beam spreads out.

In 5a becomes a resonator 60 , viewed from the direction of the axis 20 , shown. Furthermore, the figure shows an HR mirror 11.1 and an outcoupling mirror 11.2 , The long beam axis 30 lies along the direction of discharge between the electrodes. The concave cylindrical mirror is not curved according to the device according to the invention in this direction.

The intensity distribution of the laser beam in the direction of the axis 30 is top-hat-shaped according to the discharge distribution. axis 35 is the propagation direction of the laser beam, ie the optical axis.

In 5b becomes a resonator 60 , viewed from the direction of the axis 30 , shown. Furthermore, the figure shows an HR mirror 11.1 and an outcoupling mirror 11.2 , The short beam axis 20 is perpendicular to the direction of discharge between the electrodes 70.1 and 70.2 , The concave cylindrical mirror 11.1 is curved according to the device according to the invention in this direction.

The intensity distribution of the laser beam is similar according to the discharge distribution Gauss. axis 35 is the propagation direction of the laser beam, ie the optical axis.

In 6a becomes a representation of the pulse progression 100 when using a curved resonator mirror 11.1 in the long beam axis 30 shown.

You can see the possible effects of a curved mirror on the top hat shaped excitation distribution in the long beam axis 30 , For mirror curvature in this beam direction to the range of feedback covers only part of the excited volume. Therefore, it can lead to pulse duration and pulse shape changes in the pulse progression 100 come.

In 6b becomes a representation of the pulse progression 100 when using a curved resonator mirror 11.1 in the short beam axis 20 shown.

It can be seen that the limitation of the range of feedback by the curved mirror 11.1 has less influence on the Gaussian discharge distribution. Since the majority of the population inversion is used, in this case, no change in pulse duration and shape of the pulse progression 100 induced. This effect is used in the device according to the invention.

6a and b show the effect of curved resonator mirrors on the beam axes. Using spherical mirrors would cause a pulse change accordingly 6a occur. By the cylindrical, concave mirror of the device according to the invention (curved only in the short axis and effective) a pulse duration change can be avoided.

1

laser

2

laser spot

3

Profile cross section of the spot

10

optical element

11

resonator

11.1

High reflective mirror

11.2

output mirror

12

concave HR mirror

13

cylindrical mirror surface

20

First, short jet axis

30

Second, long beam axis

35

axis the direction of propagation

40

The micro-optical element

41

beamshaper

42

Beamhomogenisator

43

Beam integrator

44

imaging optics

45

machining plane

60

resonator

70

electrode

80

Writer medium

100

pulse profile

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - WO 2004021529 A1 [0004]
• - WO 1996016455 A1 [0005]
• US 5946337 [0006]
• - DE 4225781 [0007]

Cited non-patent literature

• - "The Laser Guidbook" (Author: Jeff Hecht, Copy Rights: McGraw-Hill Ins., ISBN: 0071359672) [0003]

Claims (9)

Laser beam quality improvement apparatus for laser applications, comprising a laser ( 1 ) with an asymmetric beam profile and a first, short beam axis ( 20 ) and a second, long beam axis ( 30 ) and a beam propagation axis ( 35 ) and a resonator ( 60 ), characterized in that the laser ( 1 ) at least one optical element ( 10 ) and a resonator mirror ( 11 ) with a cylindrical mirror surface ( 13 ), to reduce the spatial coherence and / or increase the divergence in the short beam axis ( 20 ). Device according to claim 1, wherein the cylindrical mirror surface ( 13 ) of the concave resonator mirror ( 11 ) is arranged so that the curved axis of the mirror perpendicular to the long beam axis ( 30 ) and / or perpendicular to the beam propagation axis ( 35 ) of the laser ( 1 ) lies. Device according to claim 1 or 2, wherein the laser ( 1 ) is an excimer laser. Device according to claim 1 to 3, wherein the optical element ( 10 ) a homogenizer ( 42 ) and / or an integrator ( 43 ) and / or a beamshaper ( 41 ). Device according to claim 1 to 3, wherein the optical element ( 10 ) a micro-optical element ( 40 ). Apparatus according to claim 1 to 5, wherein the resonator ( 60 ) is an anamorphic stable resonator. A method for providing a smooth beam profile, ie reduction of speckle in the working plane, comprising the following steps: providing a laser beam with asymmetric beam profile, comprising a first, short beam axis ( 20 ) and a second, long beam axis ( 30 ), Reducing the spatial coherence and / or increasing the divergence of the short beam axis ( 20 ) of the laser beam. Method according to claim 7 comprising the additional following steps: imaging the laser beam with the imaging optics ( 44 ) to a working level ( 45 ), Examination of the existing speckle pattern, adaptation of the radii of curvature of the resonator mirrors ( 11 ) Further reduction of the spatial coherence and / or increase of the divergence of the short beam axis ( 20 ) of the laser beam, retesting the speckle pattern. A method according to claim 7 or 8, comprising the additional ones following steps: Imaging the laser beam at 193 nm wavelength the cornea, Scanning the laser beam with a pulse duration of 4 ns to 15 ns over the cornea, Ablation of refractive surgery Profiles with reduced roughness and optimized form fidelity, wear with an energy in the range 0.5 mJ to 1.5 mJ.