DE102008040188A1 - Multimode laser i.e. laser diode, has optical element arranged at discharging surface for selectively filtering transverse modes of higher order, where thickness of optical element and wavelength of laser satisfies preset equation - Google Patents

Abstract

The laser (10) has a resonator for forming transverse modes of higher order adjacent to a fundamental transverse mode (20) and propagating the modes along an upper cladding layer (12-1), a lower cladding layer (12-2) and a waveguide core (14) at an angle of impact (alpha 0) relative to a reflecting inner wall (13) of the layers and the core. An optical element (16) is arranged at a discharging surface (15) of the layers and the core for selectively filtering the modes of the higher order, where the thickness of the optical element and wavelength of the laser satisfies a preset equation. An independent claim is included for a method for producing laser radiations.

Description

The The invention relates to a laser with the features mentioned in claim 1 and a method for generating coherent radiation with the features mentioned in claim 12.

In the generation of a laser beam, depending on the type of resonator of the laser used, there are significant differences in the beam quality. Thus, when operating a semiconductor laser, both longitudinal modes and transverse modes are produced. Transverse modes are the result of diffraction and interference phenomena in the resonator and reflect the spatial distribution of the vibrational energy in the resonator. The zero order transverse mode (also referred to as TEM ₀₀ ) will be referred to hereinafter as the fundamental mode. In order to achieve a high beam quality, it is particularly important to suppress the transverse modes of higher order compared to the fundamental mode in such a way that a single-mode operation can be realized.

at High-power semiconductor lasers, it is desirable that the cladding layer on the one hand a large band gap (high barrier against leakage currents) and the waveguide one low band gap (for a low forward voltage) having. However, this leads to strong differences in the Refractive index between the waveguide and the surrounding cladding layer, so that transversal modes of higher order occur, which disturb the fundamental mode due to interference phenomena or influence. The filtering out of this disturbing Higher order modes by conventional means (e.g. a mode aperture) can be technically complex and relatively expensive.

DE 697 37 855 T2 discloses a laser in which a lattice-like diffraction structure is arranged around the waveguide so that radiation is directed out of the waveguide at locations at certain distances along the waveguide. Filtering out transversal modes in this way is associated with fabricating a complex optical grating structure around the waveguide, thereby adding cost to the use of this method.

Of the The present invention is therefore based on the object at a multimode laser (also called multimode laser) with simple and cheap technical means unwanted transverse modes higher order within the resonator to suppress so that a single-mode operation can be realized. Especially the fundamental mode should be more effective than the transversal modes higher Order to be strengthened.

These The object is achieved by a laser with the in claim 1 and a method with that in claim 12 Characteristics solved. Preferred embodiments are in the Subclaims included.

The The idea of the invention is to drive through the resonator of a laser at least one front facet (also called exit facet) and form at least one back facet, the back facet preferably highly reflective for the wavelength the radiation generated by the active medium (preferably reflectivity R> 90%, more preferably R> 99%) and the front facet According to the invention sufficient reflection for the basic mode to achieve a stable laser operation, however an insufficient reflection for at least one transverse mode higher order (preferred for all transversal modes higher order), so that the loss for the at least one transversal mode of higher order within of the resonator is so large that it does not become a stable laser operation.

There all radiation propagating within the laser the same wavelength or almost the same wavelength has, the selective reflection of the fundamental mode and the transverse modes becomes higher Order according to the invention by an interference element, preferably realized a thin optical layer. The The idea of the invention is that the individual transverse modes at a different angle (relative to the longitudinal axis of the resonator) within the resonator, so that the Radiation energy of the individual transverse modes also under one (specific) different angles on the (preferably) transversely or perpendicular to the longitudinal axis of the resonator (or to Beam main propagation direction) arranged front facet meet. Due to the different angles of incidence on the front facet depends on the reflectivity of the (the front facet forming or in the front facet containing) interference element for the individual transversal modes in particular also of the thickness of the (preferably planar) interference element. Therefore the thickness can be chosen so that the reflectivity for the fundamental mode higher than the reflectivity for the at least one transverse mode higher Order (preferred for all transversal modes higher Order). Further, the excitation conditions (for example the current in a semiconductor laser) is set such that the increased reflectivity for the fundamental mode is sufficient for a stable laser operation, but for the at least one transversal mode of higher order (preferred for all transversal modes of higher order) none stable laser operation is realized. This can according to the invention realized a single-mode operation with simple technical means become.

The front facet of the resonator (the interference element) preferably has a reflectivity between 0.5-20%, more preferably between 1.0-10% relative to that through the active medium ( 11 ) predetermined specific laser wavelength.

Preferably the laser is a semiconductor laser whose active medium is from a Waveguide (core) and a surrounding this core cladding layer is surrounded. Then, a single-mode operation according to the invention despite high refractive index differences between waveguide (core) and cladding layer be achieved. Such a high refractive index difference is in particular necessary to make a great deal of high power semiconductor lasers Band gap of the cladding layer (high barrier against leakage currents) and low bandgap of the core (for a low Flow voltage). The refractive index of the core is preferably between 3.5 and 3.3 and the refractive index of the cladding layer is preferably between 3.4 and 3.0. The band gap of the core forming Materials is preferably between 1.4 eV and 1.9 eV and the Band gap of the cladding layer forming material is preferably between 1.7 eV and 2.2 eV. (everything for AlGaAs example)

One Another advantage is that on the use of a mode aperture for suppression of transversal modes higher Order can be waived. This can change the structure of the laser be simplified.

The The present invention is in principle in this sense of a multimode laser with optically active medium and a waveguide, in a resonator between a front facet (also exit facet called) and a Rückfacette are arranged, wherein a Variety of transversal modes, including a fundamental mode and at least a transversal mode of higher order, within the waveguide is generated and each transverse mode with respect to the inner wall of the Waveguide under a specific angle of impact for him along the waveguide (with a longitudinal and a transverse Directional share) propagated. As a longitudinal direction share is a directional component along the longitudinal axis (radiation main propagation direction) and as a transversal directional proportion, a directional proportion becomes transversal understood to the longitudinal axis.

The objects of the invention are achieved by that at the at least one exit facet of the waveguide at least one thin-layered optical (for the laser radiation semitransparent) element (also filter layer called) from a predetermined thickness to a selective filtering at least one transversal mode of higher order (preferably a plurality of transversal modes of higher order) is. The thickness of the filter layer in conjunction with each transverse mode own angles of incidence ensures that the beam path of the each transverse mode each have a specific distance within of the thin-layered optical element until its reflection experiences. This can be done on the inside the filter layer and on the outside of the filter layer (partially, that is according to the Fresnel equations) Waves interfere and depending on their specific angle of incidence (with respect to the filter layer) and depending on the thickness the filter layer selectively different in result the resonator are reflected back and thus different strongly contribute to the formation of the individual transverse modes. The Filter layer preferably forms the exit facet or is arranged on the outside of the outlet facet.

The idea of the invention is that the thickness of the filter layer (depending on the specific angle of incidence of the transverse modes and the materials used) is chosen such that the fundamental mode is reflected more strongly than transversal modes of higher order. Preferably, the thickness of the filter layer is selected such that the reflectivity of the exit facet (the filter layer) for the fundamental mode (also referred to as TEM ₀₀ ) is higher than at least one of the higher order transverse modes, in particular higher than at least one of the transverse modes TEM ₀₁ , TEM ₁₀ and TEM ₁₁ .

hereby can be achieved that a wave of an undesirable Transverse mode of higher order compared to the wave the fundamental mode at the interfaces of the optical element (Interference element) so out of phase reflected and superimposed is that this transversal mode suppressed or indeed only partially, but sufficient according to the invention is suppressed, so that no stable laser operation formed in this transverse mode.

A selection of the transversal modes to be canceled from the basic mode to be amplified is effected in that each mode has its own (specific) angle of incidence on the partially reflecting inner wall of the waveguide in the region of the exit facet (and thus also a specific angle of incidence with respect to the exit facet) the filter layer preferably adjoining the inner wall). Consequently, it must apply to the fundamental mode, for example, that the thickness of the thin-layered optical element (filter layer) according to the invention, the angle of incidence of the fundamental mode on the reflective inner wall of the waveguide and the wavelength of the fundamental mode are matched to one another A suitable phase shift of the fundamental mode does not take place or at least takes place to a significantly lesser extent than is provided for unwanted transverse modes of higher order by an appropriate configuration.

According to the invention the interference element (filter layer) is not on a single planar Layer limited. Rather, the interference element (the exit facet) formed from a stack of layers of a plurality of layer be, with respect to the selective reflectivity. For the individual fashions what has already been said applies in the same way. A calculation of the preferred layer thickness can be done with the aid of Fresnel's Formulas take place. The specific impact angles can either by numerical simulation of the energy distribution within of the resonator (depending on the materials and dimensions) or by measuring them.

The at the at least one exit surface of the waveguide attached optical element is according to a preferred Embodiment of the present invention in the form of a layer or a coating formed. Applying a layer an optical medium is a technologically well-controlled process, so that a variety of known methods and materials for this are suitable.

In a further preferred embodiment of the present invention this is attached to the at least one exit surface optical element in the form of a thin optical disk educated. This makes it possible to retrofit the invention to grow on a laser of the prior art, if a subsequent Coating without high effort is not possible.

wo λ die spezifische Laserwellenlänge innerhalb des optischen Elements ist.According to a preferred embodiment of the present invention, the thickness d of the optical element (also referred to as interference element or filter layer) satisfies the condition:

where λ is the specific laser wavelength within the optical element.

More preferably, it satisfies the condition:

und noch bevorzugter der Bedingung:

In a further preferred embodiment of the present invention, the predetermined thickness d of the optical element satisfies the condition:

and more preferably the condition:

In this preferred embodiment with layer thicknesses smaller than λ / 4 can also select transversal modes of higher order (ie reinforced), which is special for some Applications may be advantageous. However, to produce quality high-quality laser radiation by means of semiconductor laser generally layer thicknesses greater than λ / 4 is preferred.

Preferably, the optical element is formed in the form of a coating of Al ₂ O ₃ . However, other optically active materials can also be used.

The The present invention is in a further preferred embodiment implemented the present invention, when the thickness of the inventive optical element is specified such that under respective specific angle of incidence of each mode within the optical element associated distance in the quarter wavelength at least one of the higher-order modes to be filtered out lies, but to the greatest extent possible is different from the quarter wavelength of the fundamental mode. Here, the well-known effect of the anti-reflective coatings comes to light, by layer thicknesses in the quarter wavelength an extinction of reflected radiation by interference due to their mutual phase shift by half a period cause. However, the layer thickness of the filter layer is of the layer thickness a λ / 4-layer different, since the radiation of the filtered out Higher order modes under a different from 90 ° meet specific impact angle on the filter layer. typical Angles of transversal modes of higher order are included 5 ° -20 ° (with respect to the longitudinal axis the active layer or the waveguide) or at 85 ° -70 ° (in relative to the longitudinal axis of the filter layer or exit facet).

According to one preferred further embodiment of the present invention the optically active medium with such a limited energy supply operated that filtered or weakened Transverse modes of higher order their laser threshold do not reach while the fundamental mode their laser threshold reached stable. This causes the ones to be suppressed Fashions not even strengthened enough.

In a further preferred embodiment of the present invention is at the exit surface of the waveguide, a plurality of thin-layered optical elements of a respective predetermined thickness arranged behind one another, thereby to be able to act sequentially on the different transverse modes of higher order destructively.

In accordance with a further preferred embodiment of the present invention is used the waveguide as a resonator. In this case, an inventive Suppression of the transversal modes also in the reflected Beam path with each new reflection of the modes between the mirrors arranged on the front side (front facet and rear facet) the resonator instead.

To Another aspect of the present invention is a method for generating laser radiation with a laser having one in a resonator arranged optically active medium and a waveguide disclosed comprising at least one transverse to the main propagation direction of the electromagnetic radiation arranged exit surface. In this case, the resonator is designed such that (without the optical filter element) during operation in addition to Fundamental mode at least one transversal mode of higher order forms (or would train) and each transverse mode in relation on the reflective inner wall of the waveguide under a for them specific angle of incidence along the waveguide with a longitudinal and a transverse directional component propagated.

• – das aktive Medium durch Energiezufuhr zum Emittieren einer elektromagnetischen Strahlung bestimmter Frequenz angeregt wird;
• – die emittierte Strahlung im Resonator zwischen zwei reflektierenden Flächen mehrmals hin und her reflektiert und überlagert wird, sodass durch konstruktive Interferenz die emittierte elektromagnetische Strahlung (zu Laserstrahlung) verstärkt wird, wobei sich (ohne das optische Filterelement) innerhalb des Resonators neben einer Grundmode wenigstens eine Mode höherer Ordnung ausbildet (bzw. ausbilden würde);
• – die Laserstrahlung an der wenigstens einen Austrittsfläche des Resonators des Wellenleiters wenigstens in einem dünnschichtigen optischen Element von einer vorgegebenen Dicke zum selektiven Ausfiltern mindestens einer höheren Mode derart reflektiert wird, dass ein Teil der Strahlung an der zum Resonator zugewandten inneren Seite des dünnschichtigen optischen Elementes reflektiert wird und ein Teil der Strahlung an der zum Resonator abgewandten äußeren Seite des dünnschichtigen optischen Elementes reflektiert wird, wobei durch die vorgegebene Schichtdicke beide reflektierten Teilstrahlungen zueinander eine derartig bemessene Phasenverschiebung aufweisen, dass eine wenigstens teilweise gegenseitige destruktive Auslöschung der elektromagnetischen Wellen bewirkt wird, wobei die wenigstens eine höhere Mode im Vergleich zur Grundmode stärker unterdrückt wird,
• – die Grundmode in dem Resonator durch konstruktive Resonanz stärker verstärkt wird als sie durch die doppelte phasenverschiebende Reflexion an dem dünnschichtigen optischen Element gedämpft wird,
• – und ein Teil der elektromagnetischen Strahlung die wenigstens eine Austrittsfläche des Wellenleiters und das dünnschichtige optische Element hindurchpassiert.

The objects of the present invention are achieved by the method described above in that

• - The active medium is energized by the supply of energy to emit electromagnetic radiation of a certain frequency;
• - The emitted radiation in the resonator between two reflecting surfaces is reflected back and forth several times, so that the emitted electromagnetic radiation (laser radiation) is amplified by constructive interference, wherein (without the optical filter element) within the resonator next to a fundamental mode at least one Fashion of higher order forms (or would form);
• - The laser radiation is reflected at the at least one exit surface of the resonator of the waveguide at least in a thin-layered optical element of a predetermined thickness for selectively filtering at least one higher mode such that a portion of the radiation on the inner side facing the resonator of the thin-layered optical element and a portion of the radiation is reflected at the outer side of the thin-layered optical element facing away from the resonator, wherein the predetermined slice thickness causes both reflected partial radiations to have such a phase shift that one another causes at least partially mutual destructive extinction of the electromagnetic waves at least one higher mode is more suppressed compared to the fundamental mode,
• The fundamental mode in the resonator is amplified to a greater extent by constructive resonance than is attenuated by the double phase-shifting reflection at the thin-layered optical element,
• - And a portion of the electromagnetic radiation passes through the at least one exit surface of the waveguide and the thin-layer optical element.

• – Bestimmen der Auftreffwinkel wenigstens einer höheren Mode und der Grundmode auf die Innenwandungen des Wellenleiters (ohne das optische Filterelement bzw. Interferenzelement),
• – Berechnen der Reflexion des dünnschichtigen optischen Elementes gemäß der Fresnel'schen Formeln,
• – Bestimmen der Dicke des dünnschichtigen optischen Elementes derart, dass die Reflexion der Grundmode durch das dünnschichtige optische Element größer als die Reflexion der wenigstens einen Transversalmode höherer Ordnung ist.

Another aspect of the invention discloses a method for determining the thickness of a thin-layer optical element disposed on at least one exit surface of a laser equipped with a waveguide and a resonator. Determining the thickness of the optical interference element comprises the following steps:

• Determining the angles of incidence of at least one higher mode and the fundamental mode on the inner walls of the waveguide (without the optical filter element or interference element),
• Calculating the reflection of the thin-film optical element according to Fresnel's formulas,
• Determining the thickness of the thin-layered optical element such that the reflection of the fundamental mode by the thin-layered optical element is greater than the reflection of the at least one transversal mode of higher order.

Further give preferred embodiments and combinations of the invention from the rest, mentioned in the dependent claims Features.

The Invention will be described below in embodiments the accompanying drawings explained. Show it:

1a a variant of the laser according to the invention in a schematic, sectional view, wherein the beam path of the fundamental mode is shown schematically,

1b the embodiment of the laser according to the invention according to 1a , wherein the beam path of the transversal modes of first order is shown schematically,

1c the embodiment of the laser according to the invention according to 1a , wherein the beam path of the transverse modes second Ord is shown schematically,

2a . 2 B the reflection of different transverse modes at the exit facet of the in 1a - 1c represented laser in a schematic, sectional view.

1a - 1c shows a variant of the laser according to the invention in a schematic, sectional view. The embodiment is a diode laser, but the present invention is not limited thereto.

The laser diode 10 has an upper cladding layer 12 ₁ and a lower cladding layer 12 ₂ on, between which an optical waveguide core 14 is arranged. The two cladding layers can alternatively also be regarded as an enclosing jacket. Between the upper and lower layers of the waveguide core 14 is an active layer 11 arranged. The resonator is through the waveguide 12 ₁ . 12 ₂ . 14 and by a (not shown highly reflective) rear facet and a front facet (interference element 16 ) educated. The resonator is designed such that without the interference element 16 Form transverse modes of higher order, which significantly reduce the beam quality. The interference element 16 is set so that without the interference element 16 higher order transversal modes are reflected back so weakly into the resonator that these higher order transverse modes do not contribute to a stable laser operation, whereas the fundamental mode by means of the interference element 16 is sufficiently reflected back into the resonator that the fundamental mode comes to a stable laser operation.

In the waveguide 14 are those beam paths of the fundamental mode 20 and (by way of example only) two higher transverse modes 30 and 40 schematically illustrated, each having a repeated reflection on the reflective inner wall 13 of the waveguide 14 under a mode own landing angle α ₀ , α ₁ , α ₂ experienced. In a conventional laser (without interference element 16 ) all modes would (partially) through this exit surface 15 emerge, but also all modes (partial) at the exit surface 15 reflected. In particular, the unwanted transversal modes of higher order, which regularly propagate at a larger angle α ₁ , α ₂ , would reflect more strongly than the fundamental mode according to Fresnel's formulas.

According to the invention, however, the beam paths of the modes strike a directly on the exit surface 15 that is, the front side of the waveguide, arranged optical element 16 , for example, as a thin optical layer 16 is executed on. The individual modes result from the configuration of the resonator, ie the dimensions and refractive indices of waveguide and cladding layers and the wavelength excited by the active layer. Starting from the specific angles of incidence of these modes, the layer thickness d of the optical element becomes 16 certainly.

Due to the higher refractive index of the waveguide core 14 in comparison to the cladding layer 12 ₁ . 12 ₂ become the transversal modes 20 (Fundamental mode), 30 and 40 on the inner wall 13 reflected and thus guided between the facets.

The exit surface 15 is formed partially permeable or partially reflecting, wherein the degree of permeability can be in a wide range, for example, from less than one percent to more than 50%.

At each of the interfaces of the interference element 16 is the radiation of each mode 20 . 30 . 40 reflected. It finds a first reflection of the beam paths of the respective modes at the exit surface 15 of the waveguide 14 , which is an inner surface of the filter layer 16 represents, and another reflection on the outer surface 17 the filter layer 16 instead of. The transmitted part of the radiation is exemplary along a route 20 ₁ for the basic fashion 20 shown.

For the transversal mode 40 higher order ( 1c ) is the beam path at the filter layer 16 through the routes 401 . 402 and 406 shown schematically. It is possible, the thickness d of the frontally attached filter layer according to the invention 16 to adjust so that the beam path 406 (after direct reflection) and the parallel beam path 402 (after one with the intermediate route 401 deflected reflection) are phase shifted to each other such that the transverse mode 40 is suppressed due to destructive interference or at least weakened so that sets in this transversal mode no stable laser operation.

In the case of the basic fashion 20 ( 1a ) run the routes 20 ₂ . 20 ₃ , and 20 ₄ for the direct reflection and for the reflection offset by the layer thickness d in a similar manner, however, the relations of the wavelength are the fundamental mode 20 and the length of the path caused by the impact angle α ₀ 20 ₄ in the optical layer 16 predetermined by the thickness d, that the phases of the reflected beam paths along the parallel paths 20 ₂ and 20 ₃ have no difference in the range λ / 2.

As a result, there is no (or at most slight) destructive interference of the fundamental mode 20 in their return beam path, so that amplification of the fundamental mode of the laser beam (above the laser threshold) can continue to occur, whereas the higher order modes are so destructive at the layer 16 interfere with not reaching the laser threshold.

Further, according to a preferred embodiment of the present invention, the pump power of the laser is adjusted so that the residual intensities of the suppressed transversal modes 30 . 40 remain below their respective laser threshold and at the same time the threshold for the fundamental mode 20 is reached or exceeded.

2a and 2 B show the reflection of different transverse modes at the exit facet of the 1 represented laser in a schematic, sectional view. The angles for transverse modes in typical laser structures are between 5 ° and 20 °. In the present example, the fundamental mode of wafer C1311-3 has an angle of 8.2 °, mode 1 (transversal mode of first order) 11.6 °, mode 2 (transverse mode of second order) 14.5 ° and mode 3 (transversal mode of first order) 15.9 °. This embodiment uses Al (x) Ga (1-x) As for waveguide and cladding layers. Waveguide uses x = 10% AlGaAs, cladding layer uses x = 85%. Quantum wells are formed of InGaAs and emit at 980 nm. The waveguide thickness is 1.5 μm. An upper mode (transversal mode of higher order) was measured in uncoated laser diodes (ie, no thin-layer optical element) at 1-mm resonator length and 100-μm stripe width. Also, a higher-order transverse mode was measured for a thin-film optical element having a thickness smaller than λ / 4. However, no higher-order transverse mode was measured for a thin-film optical element having a thickness of ~ 1.3 × λ / 4.

If one considers the modes idealized as plane waves, one can calculate the reflectance with known methods. 2a shows the results for a single layer of Al ₂ O ₃ (with a refractive index of 1696). For an approximately 170 nm thick layer d, it follows that the mode 1 and the mode 2 have a lower reflectance than the fundamental mode 0. It is thus possible to suppress these two modes. A more exact calculation for mode 3 shows that also mode 3 can be suppressed ( 2 B ), wherein the solid line shows the reflectivity of the fundamental mode and the dashed line the mode 3 reflectivity.

The previous embodiments of the present invention are by way of example only, and not to be construed as limiting the present invention. The present invention can easily be applied to other applications become. The description of the embodiment is by way of illustration provided and not to the scope of the claims limit. Many alternatives, modifications and Variants are obvious to one of ordinary skill in the art without that he is the scope of the present invention would have to leave the, in the following claims is defined.

10

multimodal Laser, laser diode

11

optical active medium

12 ₁

Waveguide cladding (upper layer)

12 ₂

Waveguide cladding (Lower class)

13

reflective inner wall

14

Waveguide core

15

exit facet

16

thin-layer optical element, filter layer

17

outer Surface of the filter layer

20

fundamental mode

20 ₁ , ... 20 ₄

distances the basic mode, ray path

30 40

transversal Higher order modes

A

Longitudinally Main propagation direction

B

Transversely transverse propagation direction

α ₀ , α ₁ , α ₂

angle of impact the fashions

d

thickness the layer

λ

wavelength the electromagnetic wave in the thin-film optical element

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

• - DE 69737855 T2 [0004]

Claims (15)

Multi-modal laser ( 10 ) with an optically active medium arranged in a resonator ( 11 ) and a waveguide ( 12 ₁ . 12 ₂ . 14 ), comprising at least one transverse to the main propagation direction (A) of the electromagnetic radiation arranged exit surface ( 15 ), wherein the resonator is designed such that during operation in addition to the transverse fundamental mode ( 20 ) at least one transverse mode ( 30 . 40 ) of higher order and each of these transversal modes ( 20 . 30 . 40 ) with respect to a reflective inner wall ( 13 ) of the waveguide ( 12 ₁ . 12 ₂ . 14 ) at a specific angle of incidence (α ₀ , α ₁ , α ₂ ) along the waveguide ( 12 ₁ . 12 ₂ . 14 ) propagated, characterized in that at the at least one exit surface ( 15 ) of the waveguide ( 12 ₁ . 12 ₂ . 14 ) at least one thin-layer optical element ( 16 ) for selectively filtering out at least one higher transverse mode ( 30 . 40 ), wherein the following condition:

where d is the thickness of the optical element ( 16 ) and λ the specific laser wavelength within the optical element ( 16 ). Laser according to claim 1, characterized in that the optical element ( 16 ) in the form of a flat layer ( 16 ) or in the form of a thin plate is formed. Laser according to at least one of the preceding claims, characterized in that the optical element ( 16 ) a reflectivity of between 0.5-20.0% relative to that through the active medium ( 11 ) has given specific laser wavelength. Laser according to at least one of the preceding claims, characterized in that the thickness (d) of the optical element ( 16 ) of the condition suffices:

Laser according to at least one of the preceding claims, characterized in that the thickness (d) of the optical element ( 16 ) of the condition suffices:

Laser according to at least one of claims 1 to 3, characterized in that the thickness (d) of the optical element ( 16 ) of the condition suffices:

Laser according to at least one of claims 1 to 3, characterized in that the thickness (d) of the optical element ( 16 ) of the condition suffices:

Laser according to at least one of the preceding claims, characterized in that the optical element ( 16 ) of Al ₂ O ₃ in the form of an at least one-part coating ( 16 ) is trained. Laser according to at least one of the preceding claims, characterized in that at the exit surface ( 15 ) A plurality of thin-layer optical elements is arranged one behind the other. Laser according to claim 9, characterized, that the number of thin-layered optical elements between 2 and 3 is. Laser according to at least one of the preceding claims, thereby marked that the laser is a semiconductor laser. A method for generating laser radiation with a laser comprising an optically active medium arranged in a resonator ( 11 ) and a waveguide ( 12 ₁ . 12 ₂ . 14 ), wherein at least one transverse to the main propagation direction (A) of the electromagnetic radiation arranged exit surface ( 15 ) is provided, wherein the resonator is designed such that during operation in addition to the transverse fundamental mode ( 20 ) at least one transverse mode ( 30 . 40 ) of higher order and each of these transversal modes ( 20 . 30 . 40 ) with respect to a reflective inner wall ( 13 ) of the waveguide ( 12 ₁ . 12 ₂ . 14 ) at a specific angle of incidence (α ₀ , α ₁ , α ₂ ) along the waveguide ( 12 ₁ . 12 ₂ . 14 ), with the following process steps: - Stimulating the active medium ( 11 ) such that electromagnetic radiation with an active medium ( 11 ) specific frequency is emitted; - amplifying the active medium ( 11 ) radiation by constructive resonance within the resonator, wherein the energy distribution within the resonator is such that in addition to a transverse fundamental mode ( 20 ) at least one transverse mode ( 30 . 40 ) of higher order is generated; Determining the specific incidence angle (α ₀ , α ₁ , α ₂ ) of the transverse fundamental mode ( 20 ) and the at least one transverse mode ( 30 . 40 ) of higher order with respect to the reflective inner wall ( 13 ) of the waveguide ( 12 ₁ . 12 ₂ . 14 ), - arranging at least one thin-layered optical interference element ( 16 ) for selectively filtering at least one transverse mode ( 30 . 40 ) of higher order at the exit surface ( 15 ), wherein the thickness (d) of the optical element ( 16 ) is set such that the reflection of the radiation of the fundamental mode ( 20 ) within the resonator at the optical element ( 16 ) greater than the reflection of the radiation of the at least one transverse mode ( 30 . 40 ) of higher order. Method according to claim 12, characterized in that the selective filtering out of the at least one transverse mode ( 30 . 40 ) of higher order at the exit surface ( 15 ) by destructive interference at the optical element ( 16 ) he follows. Method according to one of claims 12 and 13, characterized in that the optically active medium ( 11 ) is excited such that the transverse fundamental mode ( 20 ) due to the constructive interference on the optical element ( 16 ) reaches a stable laser operation, whereby all transverse modes ( 30 . 40 ) of higher order due to destructive interference at the optical element ( 16 ) do not reach a stable laser operation. Method according to one of claims 12-14, characterized in that the optical element ( 16 ) is adjusted such that it has a reflectivity of between 0.5-20.0% relative to that through the active medium ( 11 ) has given specific laser wavelength.