DE102007048463B4 - Multilayered laser medium with a pentagonal shape in cross-section - Google Patents

Abstract

A multilayered laser medium comprising a first layer (3) of laser material excitable for stimulated emission at a laser wavelength and a second layer (1) of an absorber material absorbing at the same wavelength, the first and second layers are optically coupled to each other directly or via an intermediate layer (2), characterized in that the entire layer structure in cross-section perpendicular to the layer planes has a pentagonal shape and extends perpendicular to the cross section over a desired length and thus forms a pentagonal prismatic body.

Description

The The invention relates to a multilayer laser medium, which is a first layer of a laser material that stimulates to Emission on a laser wavelength is stimulable and a second layer of an absorber material comprising absorbing at the same wavelength, wherein the first and second layers are optically direct or via an intermediate layer are coupled to each other.

A multilayer laser medium is z. B. from the US 5,335,237 A known.

laser media are well known in the art. It can, for example as a laser medium solid be used, such as. As crystals, amorphous glasses and also ceramics. In particular, solid state laser media are commonly used used to laser resonators for generating laser radiation or also laser amplifier for reinforcement build up of already generated laser radiation.

laser media characterized by the fact that it is a medium, in particular solid-state medium, partly with additional Doping is, in which a population inversion of the electrons by external stimulation, For example, optical excitation generated by so-called pump light can be, so that a stimulated emission of photons one or even multiple laser wavelengths is produced. Depending on the desired Laser wavelength can do it different laser media, especially different solid state media with or without an extra Doping be used.

Problematic is in the operation of laser resonators or laser amplifier systems, that the efficiency of these systems is enhanced by the spontaneous Emission (ASE-amplied spontaneous emission) as well as parasitic modes, can be reduced, d. H. by the oscillation of the laser or amplifier on not desired, in particular transversal modes, in particular those of a possibly. existing subresonator.

The The object of the invention is therefore to provide a laser medium ready through which the possibility given due to the special configuration spontaneous emissions, which is not emitted in the direction of the laser beam, to absorb causing the gain the spontaneous emission as well as parasitic modes can be suppressed.

According to the invention Task solved by a multi-layered laser medium, which is characterized that it comprises a first layer of a laser material, the to stimulated emission excitable on a laser wavelength and a second Layer of an absorber material absorbing at the same wavelength acts, with the first and second layers directly or via a Intermediate layer are optically coupled to each other and the entire Layer structure in cross section perpendicular to the layer planes a pentagonal Shape, in particular with five inner angles respectively greater or equal 90 degrees and extending perpendicular to the cross section over a desired length and so a pentagonal one prismatic body formed.

essential Core idea of the laser medium according to the invention is it that spontaneous emissions that are within the laser material occurs and not in the direction of the generated or reinforced the laser material passing laser beam passes, in the absorber material enters because this directly or at least indirectly via a Intermediate layer is optically coupled to the laser material, there sufficiently is absorbed, so no feedback and reinforcement the spontaneous emission on closed paths within the multilayer according to the invention Lasermediums can be done and thus parasitic laser modes effectively repressed can be.

So can just by the pentagonal in cross section embodiment of the be achieved multilayer laser medium that preferably all spontaneous emission within the laser material, its direction outside the direction of the generated or amplified laser beam is preferred completely over internal Total reflection at the interfaces of the pentagonal prismatic body is passed into the absorber material, which is part of this prismatic body, In particular, a layer of the prismatic body is formed and thus absorbed sufficiently will be to feedback into the laser material to prevent and thus the parasitic modes to suppress.

In a preferred embodiment it is thereby provided that the layer of the laser material is parallel to a base area arranged the pentagonal body is.

at the contemplation of the pentagonal Body in Cross-section becomes a horizontal lower surface than footprint understood in the meaning of the invention, whereas the two opposite this base surface surfaces of the pentagonal prismatic body, which are at an angle to each other, referred to as roof areas become. Each of the roof surfaces stands with the base area over one adjacent area in connection.

Becomes Now the layer of the laser material according to the aforementioned embodiment in parallel to a base area of the pentagonal body arranged, this has the advantage that the adjacent to the base surface surfaces, to the base area below an angle greater than 90 degrees, cause that in the laser material produced spontaneous emission upon reflection on such area always be reflected out of the laser material and so directly or optionally via get an intermediate layer in the absorber material, where a sufficient Absorption of this spontaneous emission takes place, bringing a feedback and thus any closed path is avoided, so that the Training parasitic modes repressed becomes.

spontaneous Emission that does not exceed the side surfaces or even the faces of the prismatic body is reflected in the absorber medium, passes outside the laser beam path the prismatic body and thus does not make a disturbing contribution.

Around To achieve this reflection while doing a total reflection to the interfaces between the layers, it is provided according to the invention, that the individual layers are optically coupled to each other, d. H. cohesively merge, which, for example, technically by the method of thermal Diffusion bonding or the so-called optical wringing achieved can be, with the coupled layers at least similar or preferably have the same refractive indices.

there is understood to mean the same refractive indices that the refractive indices at most only from the first, preferably only in later decimal places, preference, that the difference in the percentage of or per thousand range or even less.

Around an internal light guide in the prismatic body to ensure, which causes spontaneous emission, as far as they are outside the direction of the laser beam in the laser material is always off the laser material is passed out into the absorber material, It may preferably be provided that the two to the base surface in the same Angle adjacent surfaces in cross-section same side lengths and in each case at its end facing away from the base surface below a right angle to the respective other of the base surface opposite roof adjoin.

there It may furthermore be provided that the length of the adjacent to the base surface surfaces selected in this way is that the two equal-length roof surfaces at least substantially the same length have like the base surface.

This has the advantage that optical pumping of the laser material thereby can be done by one of the two roof surfaces, in particular vertically to this, pumping light coupled into the multilayer laser medium and this pump light is parallel to a side surface of the prismatic body runs, the to the roof area the coupling and adjacent to the base surface, so that the pump light enters the layer of laser material through the absorber material, at the base area due to the total reflection or a highly reflective Mirror reflection is reflected, propagated again by the laser material, then propagated through the absorber material towards the second roof surface, is reflected at this and the same way back. This is how it is achieved Light of a pump wavelength, which is perpendicular to the one roof surface in the pentagonal prismatic body coupled, a four-fold passage through the laser material takes place.

there It is furthermore preferably provided that one of the roof surfaces for the coupling the light of a pump wavelength antireflex-coated and the other roof surface, especially the footprint for one Pump wavelength coated for optical excitation of the laser material high-reflective is.

Also It can be provided that each roof surface in one or more Part areas highly reflective coated and in each other Partial areas is antireflex-coated, so some of the pumping light sources up or over the antireflex-coated portions of a roof surface positioned can be and some on or over the antireflective coated portions of the other roof surface. For example can the sections are arranged like a checkerboard.

there is preferably further provided that the absorber material no, at least no significant absorption for the wavelength of the pump light has, so use as absorber material such a material which is at the desired Laser wavelength the laser material is absorbent, but no laser action itself this wavelength allows in which therefore no population inversion is achieved with the pump light.

Due to the quadruple passage of the pumping light through the laser material, it can preferably be provided to dissipate the heat generated in the laser material in that a heat sink is coupled to the base surface or to at least to the laser medium can be coupled.

So is sufficient heat dissipation achieved due to the one-sided coupling of a heat sink However, there is a temperature gradient within the laser material, so that it may be provided in a preferred embodiment, the multilayered laser medium in such a way that the and decoupling of the laser beam to be generated or amplified not along the extension direction of the prismatic body perpendicular to the cross section takes place, but rather in a particularly preferred embodiment of a Boundary layer of the laser material within the prismatic body an intermediate layer between the laser material and the absorber material in a preferred embodiment can be arranged.

So It may therefore be provided in a preferred embodiment, that between the layer of laser material and the layer of absorber material an intermediate layer of a for the laser wavelength transparent material is arranged, wherein the laser beam through an external beam path first through a frontal area of the prismatic body at an angle in particular not equal to 90 degrees to the face in the Interlayer and from this in particular at an angle of incidence greater than 55 ° and thus grazing in the laser material is coupled, inside of the base surface in the laser material totally reflective and back and forth in the interlayer this is propagated out of the laser medium out. Here can Accordingly, the propagation of the laser beam substantially along the extension of the prismatic body.

These Type of coupling of the laser beam has the particular advantage that each part of the laser beam cross section perpendicular to it Propagationsrichtung the same temperature profile within the laser material goes through and thus optical path length differences can be avoided in the laser beam profile.

Around to ensure, that the interlayer does not affect the laser radiation takes, it is preferably provided that this intermediate layer transparent to the laser wavelength is, d. H. has no absorption and, moreover, no population inversion builds up because the pump light, which according to the aforementioned embodiment the prismatic body goes through in this arrangement, the intermediate layer passes through.

Around To achieve this, it can therefore be provided in a particular embodiment be that the laser material consists of a doped garnet host.

such Materials are known for their laser property, such as neodymium-doped yttrium-aluminum garnet. For the Realization of the intermediate layer can then be provided that this consists of an undoped garnet, in particular the Garnet of the intermediate layer the material of the garnet host of the laser material equivalent. Also suitable examples are other substituted ones Grenade and the class of vanadates.

In Referring to the aforementioned example, in which the laser material made Neodymium-doped Yttrium aluminum garnet is therefore the intermediate layer consist of undoped yttrium-aluminum garnet.

The typical laser wavelength of 1064 nm of the aforementioned laser material can therefore the intermediate layer pass through unaffected without being absorbed. any spontaneous emission from the laser medium, not along the laser beam propagated, but due to the geometric configuration, as mentioned in the beginning, due to internal total reflection always in the absorber material passed and absorbed there.

Out This reason is for the absorber material preferably selected a material which in the same wavelength the laser material is absorbent, but as mentioned above itself with an irradiation and fluoroscopy with the pump light no Occupational inversion and therefore does not build spontaneous emission strengthened but rather absorbed. So can the absorber material in one preferred embodiment also consist of a doped garnet host, but in particular such chosen is that the material of the doping and the material of the garnet host are matched to one another such that the absorber material is a maximum has its absorption at least substantially at the laser wavelength, especially without even the possibility to form, for this laser wavelength to build a cast inversion.

With Reference to the above-mentioned laser material, namely neodymium-doped yttrium-aluminum garnet can for the absorber material preferably comprises a samarium-doped gadolinium-scandium-aluminum garnet chosen in particular being in a realization of the aforementioned Interlayer these consist of undoped yttrium-aluminum garnet can.

For example, samarium-doped gadolinium-scandium-aluminum garnet in the sense of the invention has the same or at least almost the same refractive index as undoped or neodymium-doped yttrium-aluminum garnet and so on with suitable for the optical coupling, for example by means of diffusion bonding, however, beyond built-up population inversion when irradiated with the necessary pumping light and just for the laser wavelength of the neodymium-doped yttrium-aluminum garnet has a high absorption, as it has been in any other suitable Material was found so that even small path lengths in the absorber material are sufficient to absorb spontaneous emission sufficient.

Essential in the selection of materials for the formation of the aforementioned layers It is the case that these bind together materially let, thus the total reflection at the interfaces between These layers can be avoided and this the refractive indices of the Materials, at least in the sense of the invention, are the same.

For use as an absorber layer in the prismatic body of the type according to the invention, therefore, a gadolinium-scandium-aluminum-garnet crystal is used which is exclusively doped with samarium, in particular where it corresponds to the empirical formula Sm: Gd ₃ Sc ₂ Al ₃ O ₁₂ , It has been found that such a samarium doped GSAG crystal has a very high absorption at the laser wavelength of the neodymium-doped yttrium-aluminum garnet laser of 1064 nm and the laser wavelength is at least substantially at the center of this absorption.

in this connection can also to improve the crystal properties admixtures in the Garatwirt be made, such as yttrium, lutetium or gallium.

One Such samarium-doped gadolinium-scandium-aluminum-garnet crystal can therefore in combination with a neodymium-doped yttrium-aluminum-garnet crystal be used in an excellent way to parasitic modes to suppress by absorption of spontaneous amplified emission.

The Samarium doping of a gadolinium-scandium-aluminum-garnet crystal can be used in the order of magnitude from 0.1 to 5 percent, and more preferably from 1 to 2 percent based on the gadolinium content amount.

So shows in general that, in particular in direct or indirect optical coupling via an intermediate layer a crystal of this type can be used for suppression from reinforced spontaneous emission and / or parasitic laser mode at the emission wavelength of any neodymium-doped garnet hosts, especially the neodymium-doped ones Yttrium aluminum garnet and thus especially at the emission wavelength of 1064 nm.

Also Other neodymium-doped garnet hosts and the aforementioned neodymium-doped vanadates can thereby Laser emission wavelengths provide within the absorption band of the aforementioned Samarium-doped gadolinium-scandium-aluminum-garnet crystal so that there are pairings for the purpose of suppressing reinforced spontaneous emission and / or parasitic laser modes.

One embodiment The invention is illustrated in the following figures. Show it the

1 : a multilayer laser medium according to the invention in a laser structure in cross-sectional representation,

2 : the side view of the same arrangement,

3 : the absorption spectrum of samarium-doped gadolinium-scandium-aluminum garnet.

The 1 shows in a cross-sectional view in plan view of one of the end faces of the multilayer laser medium according to the invention, which is composed here of a total of three layers 1 . 2 and 3 ,

The lower layer 3 , which is parallel to the base surface B of the pentagonal prismatic body 1-2-3, is formed by a laser material which can build up a population inversion by irradiated pumping light so as to enable laser operation. In this case, the illustrated arrangement can be used both as a laser resonator or as a laser amplifier.

Above the shift 3 The laser material is an intermediate layer in this configuration 2 arranged, which is transparent to the laser radiation, that has no absorption of the laser radiation and also does not build a population inversion, so that an amplification of the radiation is excluded in this area. It can therefore be provided that the layers 2 and 3 consist of the same garnet-hosts, where the layer 2 is undated and the layer 3 has a corresponding doping to allow laser operation.

Above the layers 3 and 2 is a layer 1 arranged from an absorber material, which is also unsuitable for generating a population inversion when irradiated with pump light, but at the laser wavelength of the Material of the layer 3 has an absorption.

The Layers are superimposed here stacked, with the cross-sectional design of the entire realized body in such a way that the cross-section is pentagonal and the prismatic pentagonal body into the plane of the paper in a longitudinal direction over one desired, in itself any length extends.

The Geometric configuration is still such that the faces S to the base area B at an angle α> 90 ° adjacent to the upper Ends below β = 90 ° two each roofs D adjacent, the same width over have the cross section, so that the entire prismatic arrangement in terms of the contact line of the roof surfaces D is symmetrical in cross section.

The length of the side surfaces S and thus the height of the prismatic body in the representation of 1 is selected such that the width of the roof surface D substantially corresponds to the width of the base surface B. This has the particular advantage that with a pump light source 5 Pumplicht by a roof surface in this arrangement, the left-side roof surface D1 can be coupled into the prismatic body, for which this roof surface D1, for example, antireflex coated for the pumping light to be coupled.

The coupling takes place perpendicular to the roof surface D1, so that the pump light is parallel to the side surface S1 through the prismatic body and thereby first through the absorber layer 1 propagated, then through the intermediate layer 2 and via these into the laser material of the layer 3 , at the base surface B, the pumping light is reflected, wherein the angle of incidence is equal to the angle of reflection and thus propagates the pumping light parallel to the side surface S2 in the direction of the roof surface D2, where it is internally reflected back, for which the roof surface D2 is a highly reflective coating for the Pump light may have.

The beam path of the pump light is thus reversed by this reflection on the roof surface D2 in itself, so that the pump light four times the laser material 3 penetrates.

Too high heating of the laser material in the layer 3 To avoid, it is provided here, below the base surface, a heat sink 4 to couple to this surface B. This one-sided coupling creates a temperature gradient within the laser material 3 so that it is provided here in this embodiment, the laser beam 6 , in this version with triple folding, considering the 1 first in the plane of the paper, ie through an end face obliquely down into the layer 2 coupled, after which the laser beam from the layer 2 in the layer 3 propagated, reflected at the base surface B, again through the layer 3 propagated to the laser material and back into the layer 2 occurs while it can escape from the other end of the prismatic body.

The further beam path can be achieved by external mirrors outside the prismatic body z. B. be designed such that the laser beam 6 in this embodiment is three times folded side by side through the prismatic body.

The beam guide used in the 2 shown in a side view, shows how the laser beam 6 first by the end face SF of the prismatic body, which may be arranged perpendicular to its longitudinal extent, in the intermediate layer 2 occurs at an angle other than 90 degrees and then across the interfaces between the layers 2 and 3 into the laser material.

This beam guidance has the advantage that each subregion of the cross section of the laser beam 6 is influenced equally by the thermal profile within the laser material so that there are no optical path length digits within the beam.

Especially when considering the 1 It becomes clear here that spontaneous emission is present within the laser material 3 arises and the outside of the direction of the laser beam 6 is, by the inclined side surfaces S1 and S2, which are attached at an angle> 90 ° to the base surface, always in the direction of the absorber material of the layer 1 is reflected by partial reflection or by total internal reflection at the side surfaces S1 or S2, or passes through reflection at the end face in this area or emerges through the end face of the crystal, but in a direction deviating from the laser beam.

Here, the spontaneous emission passes through the layer 2 However, this is not reinforced in this layer 2 has no population inversion for this light. In the shift 1 the light is then absorbed. Thus, in the entire prismatic body, there are no closed, self-feedback beam paths outside the desired laser beam, so that parasitic modes can be effectively suppressed.

For the execution of the multilayer laser medium, it is important, as mentioned above, that the individual materials of the layers 1 . 2 and 3 have the same refractive indices according to the invention, ie that they differ only in the first, and possibly also in later decimal places. This ensures that at the Boundary layers between the individual layers no significant reflection occurs, so that just the spontaneous emission from the laser material of the layer 3 in the absorber material of the layer 1 entry.

A concrete embodiment can be configured here such that the layer 3 is given by neodymium-doped yttrium aluminum garnet, however, the intermediate layer 2 by undoped yttrium aluminum garnet.

Thus, the refractive indices are substantially the same, whereas the layer 2 does not provide lasing like the layer 3 , so that the laser light of the beam 6 the layer 2 unhindered penetrates and a reinforcement only in the layer 3 experiences.

The routing of the laser beam 6 is basically outside the absorber layer 1 whereas the spontaneous emission inside the laser material 3 can arise and outside the laser beam direction of the laser beam 6 is always due to the total internal reflection at the inclined surfaces in the absorber medium of the layer 1 arrives.

Since neodymium-doped yttrium-aluminum garnet has an emission wavelength of 1064 nanometers, here is the layer 1 adapted in a concrete embodiment so as to absorb this exact wavelength significantly.

It was found that samarium-doped gadolinium scandium-aluminum garnet (Sm: GSAG) in the 3 shown absorption curve, which proves that especially at a wavelength of 1064 nanometers, the absorption is significant and thus just this material can be used excellently to in a pairing with neodymium-doped yttrium-aluminum garnet (Nd: YAG) to an absorption parasitic modes to be used at this wavelength. As a result, the efficiency of a corresponding laser is significantly increased.

The absorption band of the samarium-doped gadolinium-scandium-aluminum-garnet crystal, as described in the 3 is shown, further shows such a width, so that here also an insert for the same purposes is considered for other than the laser wavelength of 1064 nanometers, the z. B. can be achieved in other pomegranates that are doped with neodymium, such as. As neodymium-doped yttrium-lithium fluoride (Nd: YLF), so that the application of the absorber material is not limited exclusively to neodymium-doped yttrium-aluminum garnet hosts, but can generally find use in neodymium-doped garnet hosts use.

For other than the one in the 1 and the 2 In this case, it may also be provided that in the case of a deviating guidance of the laser beam 6 can be dispensed with the intermediate layer and the absorber material of the layer 1 directly to the laser material of the layer 3 , in particular at least substantially parallel to the laser beam guide, is optically coupled.

The samarium-doped gadolinium-scandium-aluminum garnet crystal can be obtained, for example, by methods known to those skilled in the art, e.g. B. after Czrochralski. In this case, in particular a Samariumdotierung of 0.1 to 5%, preferably 1-2%, based on the Gadoliniumanteil used to those in the 3 to achieve shown absorption bands.

to further shift of the absorption bands may continue be provided either by the composition of the pomegranate by addition or exchange materials or else by adding more To shift doping materials. It can be so the central wavelength of maximum absorption in an ideal manner adapted to the specific required laser wavelength become.

in this connection has in the application said absorption material the particular Advantage that it is in addition to the absorption at the desired Laser wavelength does not build up a population inversion when irradiated with pump light.

Claims (19)

Multilayer laser medium comprising a first layer ( 3 ) of a laser material excitable for stimulated emission on a laser wavelength, and a second layer ( 1 ) comprising an absorber material which acts to absorb at the same wavelength, the first and second layers being directly or via an intermediate layer ( 2 are optically coupled to each other, characterized in that the entire layer structure in cross-section perpendicular to the layer planes has a pentagonal shape and extends perpendicular to the cross section over a desired length and thus forms a pentagonal prismatic body. Laser medium according to claim 1, characterized in that the layer of the laser material ( 3 ) is arranged parallel to a base surface (B) of the pentagonal body. Laser medium according to claim 2, characterized ge indicates that the two surfaces (S1, S2) adjoining the base surface (B) at the same angle (α) have the same side length in cross section and at each end remote from the base surface (B) at a right angle (β) to the respective ones adjacent to the base surface (B) opposite roof surface (D1, D2). Laser medium according to claim 3, characterized that in cross section the length the to the base area (B) adjacent areas (S1, S2) are selected in this way is that the two equal length roof surfaces (D1, D2) at least in Essentially the same length have like the base surface (B). Laser medium according to one of the preceding claims, characterized in that one of the roof surfaces (D1) for one pump wavelength is antireflection-coated and the other roof surface (D2) for a pump wavelength for the optical excitation of the laser material ( 3 ) is coated high-gloss. Laser medium according to claim 5, characterized in that also the base surface (B) for a pump wavelength for the optical excitation of the laser material ( 3 ) is coated high-gloss. Laser medium according to one of the preceding claims, characterized in that light of a pump wavelength, which is coupled perpendicular to the one roof surface (D1) in the pentagonal body, a four-fold passage through the laser material ( 3 ) completes. Laser medium according to one of the preceding claims, characterized in that between the layer of the laser material ( 3 ) and the layer of the absorber material ( 1 ) an intermediate layer ( 2 ) is arranged from a transparent material for the laser wavelength, wherein the laser beam ( 6 ) by an external beam path in the intermediate layer ( 2 ) and from this into the laser material ( 3 ) can be coupled, inside at the base surface (B) in the laser material ( 3 ) totally reflective, into the intermediate layer ( 2 ) back and out of this is herauspropagierbar from the laser medium. Laser medium according to claim 8, characterized in that the propagation of the laser beam ( 6 ) takes place along the extension of the body. Laser medium according to one of the preceding claims, characterized in that the laser material ( 3 ) consists of a doped garnet host. Laser medium according to claim 10, characterized in that an intermediate layer ( 2 ) consists of an undoped garnet host. Laser medium according to claim 11, characterized in that the material of the garnet of the intermediate layer ( 2 ) the material of the garnet host of the laser material ( 3 ) corresponds. Laser medium according to one of the preceding claims, characterized in that the absorber material ( 1 ) consists of a doped garnet host. Laser medium according to claim 13, characterized in that the material of the doping and the material of the garnet host are coordinated with one another such that the absorber material ( 1 ) has the maximum of its absorption at least substantially at the laser wavelength. Laser medium according to one of the preceding claims, characterized in that the laser material ( 3 ) consists of neodymium-doped yttrium-aluminum garnet and the absorber material ( 1 ) of samarium-doped gadolinium-scandium-aluminum garnet. Laser medium according to claim 15, characterized in that an intermediate layer ( 2 ) is provided from undoped yttrium-aluminum garnet. Laser medium according to one of the preceding claims, characterized in that to the base surface (B) a heat sink ( 4 ) is coupled / coupled. Laser medium according to one of the preceding claims, characterized in that the layers ( 1 . 2 . 3 ) are interconnected materially. Laser medium according to claim 18, characterized in that the layers ( 1 . 2 . 3 ) are connected by diffusion bonding.