DE102007032576A1 - Measurement of the shape and refraction of a laser disk uses a test laser, emitting parallel beams, for the focused reflection to strike a detector to register angular deviations - Google Patents

Abstract

To measure the shape and refraction of a laser disk, a test laser (1) emits displaced and parallel beams with a wavelength so that they strike a laser disk (2) at least at two different points with a wavelength equal to the emission wavelength. The reflection from the disk is focused by a lens (9) to a detector (10) with position sensitivity. The detector can register angular variations in the reflected test beams.

Description

The invention relates to a simplified method and a measuring arrangement for measuring the shape and aberrations and the refractive power of a laser disk. With the aid of this solution according to the invention it is possible to carry out measurements not only in the pumped state but also in the laser mode. For example, from the publication "Scalable concept for diode-pumped high-power solid-state lasers", Applied Physics B 58 (1994), p. 365 (Giesen, A. et al.) It is known that the principle of the disk laser is to design the laser-active medium in the form of a disk only a few hundred micrometers thick, and to mount it in large-area contact on a heat sink. With a corresponding mirroring for the pump and laser wavelength, the disc in the laser resonator acts like a mirror.

The special geometry and mounting of the laser disc causes an efficient cooling of the crystal. This results in the simple scalability of the laser output power, and in addition the laser radiation due to the only comparatively weak thermal lens can simultaneously have a high beam quality, expressed by a small diffraction factor M ² . With the laser medium Yb: YAG, which is particularly advantageous for this scaling, it is possible to realize basic mode lasers (TEM ₀₀ mode, corresponding to M ² = 1) up to the 100 W power range (see Karszewski, M. et al. In "100 W TEM00 Operation of Yb: YAG thin disc laser with high efficiency", in Rosenberg, WA; Frejer, MM (ed.) / OSA Trends in Optics and Photonics 19; Advanced Solid-State Lasers 1998. Washington DC: Optical Society of America, 1998, p. 125 ), and even with kW laser systems M ² = 15-20 to achieve where comparable rod lasers have a 4- to 5-fold greater diffraction coefficient (see also in Stewen, C. et al. "Yb: YAG Thin Disk Laser With 1 kW Output Power"; in: Injeyan, H .; Keller, U .; Marshall, C. (ed.): OSA Trends in Optics and Photonics 34: Advanced Solid-State Lasers 2000 Washington DC: Optical Society of America, 2000, p. 35 ).

Nevertheless, despite effective cooling, the refractive index profile within the laser disk caused by radial temperature gradients causes the formation of a lens due to the temperature-dependent refractive index n (T). In addition, due to different polarizability of electrons of the lower and upper laser level so-called electronic components of a refractive index change n (e) occur (see Antipov, OL et al. In "Electronic mechanism for refractive index changes in intensively pumped Yb: YAG laser crystals"; Opt. Lett., Vol. 31, pp. 763-765, 2006 ).

After all may be due to the axial temperature gradient, the disc bend and thereby a concave or convex surface shape accept.

Therefore, even in disk lasers, a pumping power-dependent focussing or defocusing effect of the laser disk acting as a mirror occurs, which is much lower in comparison to bar lasers. The deformation of the disk and the effect of the n (T, e) lens together can be called a thermal lens. In the narrower sense, the approximately parabolic course of refractive index and / or curvature is referred to as a thermal lens and describes its effect by specifying a refractive power D or focal length f = D ^-1 or also in the case of the mirror acting as a laser disc of a radius of curvature R = f = D ^-1 . However, the above-mentioned sources give no indication as to how the refractive power of this thermal lens is to be determined. In detail, it would be possible to calculate the resonator with the known ABCD matrix formalism and to optimize it by dynamically stable by choosing the radii of curvature of the other resonator mirrors and their distances to each other accordingly (see V. Magni: "Multielement stable resonators containing a variable lens"; J. Opt. Soc. At the. A; vol. 4, pp. 1962-1969, 1987 ).

In addition, the pumping of the disk also causes thermally induced deformations and Brechzahlverläufe, which differ from a sphere or a parabolic curve. As a result, the reflected wavefront suffers aberrations, which limits the scaling of the power of fundamental model lasers or the beam quality is degraded to diffraction magnitudes M ² > 1.

It is also of great interest, the surveying the thermally induced lens and aberrations not only in the pumped Condition, but also in the laser mode, because the temperature gradients and n (e) usually differ in both cases can.

Out The prior art discloses methods and arrangements for this purpose, in interferometric and non-interferometric methods can be distinguished.

With interferometric measuring methods using, for example, a Mach-Zehnder interferometer ( Mudge, D. et al .: "Power Scalable TEM00 CW Nd: YAG Laser with Thermal Lens Compensation"; IEEE J. of Selected Topics in Quant. Electronics, vol. 6, pp. 643-649, 2000 In principle, the wavefront can be detected with high resolution, which requires the determination of thermally induced aberrations or deformations of the wavefront and the refractive power of the thermal lens corresponds. However, it is particularly disadvantageous in these methods that due to the interference between an object and reference wave, particularly high demands are placed on the stability of the structure and on the coherence of the light source used. Interferometric measurement setups can therefore only be realized with comparatively great equipment complexity.

Non-interferometric methods overcome at least the above-mentioned major disadvantage of the interferometric measuring methods. Comparatively simple methods are based on measuring the focusing or deflection of a collimated test beam and determining therefrom the refractive power of the thermal lens (see Hodgson, N .; Weber, H .: Laser Resonators and Beam Propagation, 2nd edition, Springer Series in Optical Sciences; Springer Science + Business Media, Inc., 2005, p. 704-708 ). However, the spatial resolution of these methods is very low, and it is not possible to measure wavefront deformation.

It is known, however, that a Shack-Hartmann sensor (SHS) allows non-interferometric wavefront detection. The SHS consists of a microlens array and array detector (CCD camera), the microlens array scans the wavefront with a determined by the size of the microlenses, comparatively high spatial resolution and in the spaced at a few millimeters parallel plane of the Detector arrays generates a field of focus spots. The geometric position of the focus spots is determined by the inclination (gradient) of the respective wavefront segment. From the measured gradient field, the wavefront can be reconstructed by integration (see Pfund, J., Beyerlein, M .: "Shack-Hartmann Sensors for Quality Control in Classical and Laser Optics", Photonik 4/2002, pp. 6-8 ). Examples of the use of a SHS for detecting the wavefront deformed by a thermal lens can be found, for example, in FIG Nishimura, A. et al.: "Temporal Change of Thermal Lens Effects on Highly Pumped Ytterbium Glass by Wavefront Measurement"; J. of Nucl. Science and Techn., Vol. 38, pp. 1043-1047, 2001 or in Mansell, JD et al.: "Evaluating the effect of transmissive optical thermal lensing on laser beam quality with a Shack-Hartmann wave-front sensor"; Appl. Opt., Vol. 40, pp. 366374, 2001 ,

In 1 is a schematic structure shown how the thermal lens or the wavefront deformation of a laser disk can be determined by SHS. The laser disc to be examined ( 2 ) acts like a mirror and forms together with other mirrors a laser resonator, here schematically by a second mirror ( 4 ). This laser resonator emits laser radiation of wavelength λ _L. On the laser disc incident so-called pump light that provides for the formation of the thermal lens is not shown. The laser disc ( 2 ) with a flat as possible, aberration-free wavefront of a test laser ( 1 ) irradiated.

This laser must have a wavelength λ _T which is equal to or nearly equal to the emission wavelength of the disk laser λ _L , in order to be reflected by the back side of the laser disk which is mirrored in the region around λ _L. In order to illuminate the entire region of interest of the laser disk, the test laser beam is usually used with a telescope ( 5 ) widened accordingly (widening telescope). In order to determine the deformed wavefront at the location of the laser disk, after reflection of the test laser radiation on the laser disk, an image of this location on the SHS (FIG. 3 ), to which an imaging telescope ( 6 ) can be used. Finally, attenuation and long-pass filters ( 7 ) ensure that the maximum permissible intensity for the sensor is not exceeded and short-wave pump light is blocked.

This However, construction has serious disadvantages.

The test laser ( 1 ) must emit TEM ₀₀ in the fundamental mode. The helium-neon gas lasers typically used in interferometers, which operate in the red spectral range, have this property. However, due to the requirement λ _T ≈ λ _L and the laser wavelength λ _L, which is typically in the near infrared (IR), a solid-state laser is required as the test laser. A basic mode operation is disadvantageously to achieve in these types of lasers only with great effort.

Due to the image of the plane of the laser disk on the plane of the sensor reaches fluorescent light, which also has the wavelength λ _L , on the sensor. For a sufficiently high "signal-to-background ratio", the test laser must therefore be sufficiently powerful (in the range of about 1 W), which additionally complicates compliance with the condition of a TEM ₀₀ operation and requires additional technical effort.

Of the made of precision microlenses and a CCD camera SHS is comparatively expensive. The control electronics of the CCD array is comparatively complicated. The equipment cost is so when using a SHS comparatively high and will meet the demands only insufficiently fair.

Starting from the prior art, it is an object of the invention, the measurement of the mold and To determine refractive power of a disk-shaped laser medium in a simple manner, and this can also be done in the laser mode. At the same time a high spatial resolution should be achieved and realized with relatively little effort.

It is thus the object of the invention, by the pump light thermally induced aberrations or deformations of the wavefront to determine. The object of the invention is furthermore a simple, compact and stable measuring arrangement to provide that no special environmental requirements and components of the Measuring arrangement provides. This applies z. B. in the event that it is frequent or routine Measuring tasks within the scope of a production of numerous laser devices or the integration of the measuring arrangement in a laser device for online diagnostics.

• a) einen Laser (1) zur Aussendung von parallel versetzbaren Strahlen mit einer emittierenden Wellenlänge λ_T, der so angeordnet ist, dass er die Laserscheibe (2) mit der Emissionswellenlänge λ_L in mindestens 2 verschiedenen Punkten treffen kann, wobei die Wellenlänge λ_T gleich oder nahezu gleich der Emissionswellenlänge λ_L ist,
• b) eine nach der Reflexion an der Laserscheibe (2) angeordnete Sammellinse (9) und
• c) einen positionsempfindlichen Detektor/PSD (10) zur Erfassung der Winkeländerungen der reflektierten Teststrahlen. Die parallele Versetzung des einfallenden Strahls um δx bzw. δy kann auf verschiedene Weise realisiert werden. Der Laser (1) kann dazu beweglich transversal zur Strahlrichtung angeordnet sein. In besonders bevorzugter Weise ist der Laser (1) ein fest stehender Laser mit einem geeigneten beweglichen optischen Element, welches in der Lage ist den Strahl parallel abzulenken. Ein solches optisches Element kann zum Beispiel eine zwischen Linse (12) und Laserscheibe (2) angeordnete Planplatte (10) sein, die um eine zur Strahlrichtung senkrecht stehende Achse verdreht wird.

To solve the task contains an optical measuring system

• a) a laser ( 1 ) for emitting parallel displaceable rays having an emitting wavelength λ _T , which is arranged so that it the laser disc ( 2 ) with the emission wavelength λ _L in at least 2 different points, the wavelength λ _{T being} equal to or nearly equal to the emission wavelength λ _L ,
• b) one after reflection on the laser disc ( 2 ) arranged converging lens ( 9 ) and
• c) a position sensitive detector / PSD ( 10 ) for detecting the angular changes of the reflected test beams. The parallel displacement of the incident beam by δx or δy can be realized in various ways. The laser ( 1 ) can be arranged to be movable transversely to the beam direction. Most preferably, the laser ( 1 ) a fixed laser with a suitable movable optical element, which is able to deflect the beam in parallel. Such an optical element may be, for example, an intermediate lens ( 12 ) and laser disc ( 2 ) arranged plane plate ( 10 ), which is rotated about an axis perpendicular to the beam direction axis.

Used For example, a glass plate with the refractive index n = 1.5 and a thickness of 5 mm, so causes a tilt of 30 ° one Offset of approx. 1 mm. With a plate twice as thick is for the same offset only about half the angle of rotation necessary.

Instead of But a tiltable plan plate are also other arrangements possible, for. B. those in which the test laser beam through a 90 ° roofside deflection prism runs and the beam offset by displacement of this prism perpendicular to the incident beam direction is produced.

Of the A person skilled in the art will also find further arrangements can provide the required parallel offset of the test laser beam cause.

The laser disc ( 2 ) forms, together with other mirrors, schematically by a second mirror ( 4 ), a laser resonator ( 2 ). That on the laser disc ( 2 ) incident so-called pump light that provides for the formation of a thermal lens is not shown. The laser resonator emits laser radiation of wavelength λ _L. According to the invention, the laser disk ( 2 ) now with a beam of a test laser ( 1 ) irradiated.

In a preferred embodiment, the test laser ( 1 ) has a focus diameter w of 100 μm to 200 μm. In a particularly advantageous manner, this focus diameter w has a size of 150 μm. In addition, no high demands are placed on the test laser with regard to beam quality, M ² > 1 is possible. In a preferred optical measuring system, between the laser ( 1 ) and the laser disc ( 2 ) a focusing lens or a focusing element ( 12 ), thereby allowing the laser disc ( 2 ) with an optimized as possible thin beam of the test laser ( 1 ) can be irradiated. In a further preferred embodiment, in addition between the converging lens ( 9 ) and the PSD ( 10 ) an attenuation filter ( 11 ), which is responsible for ensuring that the PSD ( 10 ) maximum permissible intensity is not exceeded.

Since no fluorescent light on the PSD ( 10 ), a high signal-to-background ratio can already be achieved with a comparatively small power of the test laser in the milliwatt range. The PSD is also inexpensive and robust. It consists only of a large-area pin diode and a comparatively very simple evaluation. The PSD is small, and the test laser can be very small due to the low output power required, so that the structure can be easily integrated into a (slices) laser resonator.

The The present invention also relates to a measuring method according to the Arrangement.

The arrangement and the associated inventive method will be described with reference to 1 to 10 explained in more detail.

1 shows the schematic representation of a measuring arrangement with SHS, as it is known from the art.

2 shows the preferred measuring arrangement according to the invention.

3 includes the schematic dargestell te principle of the measurement according to the invention. For better illustration, the reflection is shown on a deformed surface of the laser disk (S).

4 shows the principle of the transformation of an angle change (Δγ) into a change of position (Δx) by means of a lens.

5.1 shows an example of a wavefront reconstructed from the measurement results of a laser disc in 2-D representation;

5.2 shows an example of a reconstructed from the measurement results wavefront of a laser disk in 3-D representation.

Out 6 the determination of the radius of curvature R can be taken by measuring the reflection angle 2φ.

In 7 the determination of the radius of curvature is shown by determining the linear increase of the dependence h (x).

In a surprisingly simple manner, the wavefront segments with the arrangement according to the invention can be connected in series by changing the point of impact of the test laser beam on the laser disk (FIG. 2 ) are scanned. The change of the impactor on the laser disc ( 2 ) is in 2 dotted in schematic form ( 8th ).

After all From the measured gradient field, the wave front can be integrated be reconstructed.

details The measuring method according to the invention will be described below explained.

The laser ( 1 ) Must emit a wavelength λ _T, which is the emission wavelength of the disc laser λ _L equal or nearly equal, to be reflected from the mirrored in the field to λ _L back of the laser wafer.

Ideally, the wavelength λ _T corresponds to the emission wavelength of the disk laser λ _L.

However, the wavelength λ _T may also be in a size range which satisfies an emission wavelength of the disk laser λ _L resulting from the antireflection layer of the laser disk on the front side thereof and the highly reflective coating on the rear side thereof. This can be in the range of +/- 5% of the wavelength λ _L. A typical Yb-doped YAG crystal (Yb: YAG) disk laser emits at λ _L = 1030 nm. It has a highly reflective coating on the back side for the laser radiation and an antireflective coating on the front side of typically about 100 nm spectral width. so that a test laser with a wavelength λ _T = 1064 nm could be used. The commonly used laser crystals Nd: YVO ₄ or Nd: YAG emit light at 1064 nm.

After reflection on the laser disc ( 2 ) the test laser beam advantageously passes through a long focal length condenser lens ( 9 ) and hits at a distance of a focal length f of this lens ( 9 ) on a position sensitive detector, PSD, (10). An advantageous focal length f is in the range of 0.5 m to 1 m.

This is based on the geometric position of the beam centroid on the PSD ( 10 ) determines the inclination (gradient) of a wavefront segment.

According to the arrangement according to 2 and the exemplary method illustration in FIG 3 is the optical path difference, only caused by a location-dependent refractive index within a planar laser disk, the reflection equivalent to a deformed surface of the laser disk equivalent and can be interpreted as reflection on a path difference corresponding curved surface. Another simplification in 3 is the representation in only one level. This turns a curved laser disk into a curved curve (S), and tangent planes of the surface become tangents of the curve.

One first incident beam S1 hits the laser disk, shown through the curve S, at location P1. The tangent on this point is the Straight T1, perpendicular to the normal N1. The first incident Beam S1 forms with the normal N1 the angle αl and becomes in P1 the law of reflection obeying the same angle of departure α1 reflected, represented as beam S'1. A second incident beam S2, which is offset parallel to the first beam S1 by δx, hits the laser disk or the illustrated curve S at the point P2 at the angle α2 to the normal N2 and becomes corresponding reflected.

The two reflected rays S'1 and S'2 enclose an angle which is in 3 is denoted by 2Δφ. For better illustration was in 3 the beam S2 is shifted in parallel (S''2).

Of the half angle, ie Δφ, is equal to the difference the increases to the curve S in the points P1 and P2, that of the the angles Δφ formed by the tangents T1 and T2. you thus measures the gradient of the curve or in generalized terms the gradient of a deformed wavefront.

The angle change 2Δφ must now be suitably measured. It is known that in the Bren next to a lens angle changes are transformed into place changes, see 4 , The resulting from the angle changes changes in location are measured according to the invention with a PSD. Its accuracy is, depending on the type of construction, in the range of 1 μm and better (lower, eg 0.9 μm). The focal length of the lens depends on the required angular resolution and the spatial resolution of the PSD and is typically in the range f = 0.5 m.

The spatial resolution of the measurement of the laser disc is determined by the focus diameter w of the test laser. A meaningful size is approximately between 100 and 200 microns. The surface is scanned with the test laser beam, by the incident beam suitably by δx is moved in parallel. For the accurate capture of Surface shape, the grid should advantageously about correspond to the size of the beam diameter, δx ≈ w.

The increases of the curve S along the x-axis are thus described by dS dx = Δφ = Ax 2f

The measurement of the ascents now takes place at several points, from which the curve shape is determined by integration: S = 1 2f ∫Δxdx or because of the discrete measurement:

The measurement and integration in the y-direction take place analogously. 5 shows exemparically a wavefront of a pumped laser disk obtained in this way.

With well-known methods such as the representation of the wavefront as a linear combination of Zernike polynomials one can obtain appropriate quantitative statements (see Pfund, J., Beyerlein, M .: "Shack-Hartmann Sensors for Quality Control in Classical and Laser Optics", Photonik 4/2002, pp. 6-8 ).

Subsequent embodiment for a simplified measuring procedure:

In practice, the laser discs are often substantially spherically curved or have a nearly parabolic refractive index course. One is therefore particularly interested in determining the refractive power of this pumped laser disk, if possible in laser operation. As stated above, regardless of the specific type of the thermal lens, the measurement method can be attributed to a reflection on a surface corresponding to the path difference and the refractive power can be given as the reciprocal of the radius of curvature, D = R ^-1 . For the optimization of the laser or the optimal design of the laser resonator, the knowledge of the two radii Rx and Ry (meridional and Sagittalstrahlradius) is necessary.

In 6 the reflection is shown on a curve S ', which is nearly circular (S) and has the radius R. Again, the simplified viewing of a curve in a plane takes place.

The reflected beam is detected on the PSD with the location coordinate h (x) (not shown), which is proportional to the angle 2φ, h (x) = f · 2φ + h 0 (h ₀ is a constant that expresses that at φ = 0 the place h = h _{0 is} hit). Furthermore, in a very good approximation, φ = x / R, so that the following applies to the increase m _{x of} the measurement curve h (x):

Analog wird R_y ermittelt.The radius of curvature R _x can therefore be determined simply by determining the linear increase m _{x of} the measured dependence h (= x coordinate of the point of impact on PSD) of x (= x coordinate of the place of impact on the laser disc),

Analogously, R _{y is} determined.

7 shows an example of such a measurement of the refractive power of a laser disc, expressed by an equivalent curvature.

The simplified method for determining the refractive power D _x , D _y (or the radii R _x , R _x ) can be further simplified by using only 2 measuring points for the determination of m _x , m _y , ie, the scanning the laser disk is limited to the irradiation on each 2 measuring points in the x and y direction. The measurement process including evaluation is thereby particularly simple and preferably suitable for implementation in a laser device for the continuous measurement and monitoring of the refractive power of the thermal lens. From the knowledge of this measured value, in turn, a targeted influencing of the resonator, z. As an adjustment of the distance of resonator, done to thereby con parameters of the laser radiation despite changing thermal lens to keep constant.

The simplified measurement procedure presented here corresponds to the measurement method proposed by Evans ( Evans, JD: "Method for Approximating the Radius of Curvature of Small Concave Spherical Mirrors Using a He-Ne Laser"; Appl. Opt., Vol. 10, pp. 995-996, 1971 ). However, it only deals with the measurement of the radius of a spherical mirror, ie a passive component. However, the present invention employs the measurement of reflection angles on the particular "laser active medium" device, especially "laser disk". In this element, various effects described above in the pumped state or in laser operation bring about refractive index and shape changes that can be evaluated with the method described here complex (wavefront reconstruction) and simplified (determination of the refractive power or the equivalent radius of curvature). 8th unf 9 show further measuring examples of the simplified measuring method according to 7 in which only Rx (or Ry) is measured. It can be seen that the unpumped laser disc already has a certain curvature. This is technologically conditioned and results above all from the mechanical stresses caused by the coating and assembly of the laser disk. In laser operation, this refractive power now changes due to the described effect of the so-called thermal lens.

The refractive power of the thermal lens is mainly dependent on the pump power in laser operation. In the example shown ( 9 ) the pumping power in "laser mode 1" is 60% of the pumping power of "laser mode 2"; the measured radius of curvature changes from 3150 mm to 4210 mm in this example.

1

test laser

2

laser disc

3

Shack-Hartmann sensor (SHS)

4

mirror or mirror arrangement

5

expanding telescope

6

imaging telescope

7

filter (Longpass)

8th

ray tracing 2 (poarallel) of the test laser

9

converging lens

10

detector (PSD)

11

Abschwächfilter

12

focusing lens or element

13

Planplatte

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 non-patent literature

• Scalable concept for diode-pumped high-power solid-state lasers, Applied Physics B 58 (1994), p. 365 (Giesen, A. et al.) [0001]
• - Karszewski, M. et al. In "100 W TEM00 Operation of Yb: YAG thin disc laser with high efficiency", in Rosenberg, WA; Frejer, MM (ed.) / OSA Trends in Optics and Photonics 19; Advanced Solid-State Lasers 1998. Washington DC: Optical Society of America, 1998, p. 125 [0002]
• - Stewen, C. et al. "Yb: YAG Thin Disk Laser With 1 kW Output Power"; in: Injeyan, H .; Keller, U .; Marshall, C. (ed.): OSA Trends in Optics and Photonics 34: Advanced Solid-State Lasers 2000 Washington DC: Optical Society of America, 2000, p. 35 [0002]
• - Antipov, OL et al. In "Electronic mechanism for refractive index changes in intensively pumped Yb: YAG laser crystals"; Opt. Lett., Vol. 31, pp. 763-765, 2006 [0003]
• - V. Magni: "Multielement stable resonators containing a variable lens"; J. Opt. Soc. At the. A; vol. 4, pp. 1962-1969, 1987 [0005]
• - Mudge, D. et al.: "Power Scalable TEM00 CW Nd: YAG Laser with Thermal Lens Compensation"; IEEE J. of Selected Topics in Quant. Electronics, vol. 6, pp. 643-649, 2000 [0009]
• - Hodgson, N .; Weber, H .: Laser Resonators and Beam Propagation, 2nd edition, Springer Series in Optical Sciences; Springer Science + Business Media, Inc., 2005, p. 704-708 [0010]
• - Pfund, J., Beyerlein, M .: "Shack-Hartmann Sensors for Quality Control in Classical and Laser Optics", Photonik 4/2002, pp. 6-8 [0011]
• Nishimura, A. et al.: "Temporal Change of Thermal Lens Effects on Highly Pumped Ytterbium Glass by Wavefront Measurement"; J. of Nucl. Science and Techn., Vol. 38, pp. 1043-1047, 2001 [0011]
• - Mansell, JD et al.: "Evaluating the effect of transmissive optical thermal lensing on laser beam quality with a Shack-Hartmann wave-front sensor"; Appl. Opt., Vol. 40, pp. 366374, 2001 [0011]
• - Pfund, J., Beyerlein, M .: "Shack-Hartmann Sensors for Quality Control in Classical and Laser Optics"; Photonik 4/2002, S. 6-8 [0054]
• Evans, JD: "Method for Approximating the Radius of Curvature of Small Concave Spherical Mirrors Using a He-Ne Laser"; Appl. Opt., Vol. 10, pp. 995-996, 1971 [0061]

Claims (16)

Arrangement for optically measuring the shape and refractive power of a disk-shaped laser medium, comprising a) a test laser ( 1 ) for emitting parallel displaceable rays having an emitting wavelength λ _T , which is arranged so that it the laser disc ( 2 ) with the emission wavelength λ _L in at least 2 different points, wherein the wavelength λ _{T is} equal to or nearly equal to the emission wavelength λ _L , b) one after the reflection at the laser disc ( 2 ) arranged converging lens ( 9 ) and c) a position-sensitive detector / PSD ( 10 ) arranged to detect the angular changes of the reflected test beams. Arrangement for optical measurement according to Claim 1, in which the test laser ( 1 ) is a laser arranged transversely to the beam direction. Arrangement for optical measurement according to Claim 1, in which the test laser ( 1 ) is provided as a fixed laser with a suitable movable optical element capable of deflecting beams of the test laser in a defined manner. Arrangement for optical measurement according to claim 3, characterized in that the movable optical element has a tiltable plane plate ( 13 ). Arrangement for optical measurement according to claim 3, characterized in that the movable optical element a 90 ° roofside deflection prism is. Arrangement for optical measurement according to at least one of the preceding claims, in which the test laser ( 1 ) has a focus diameter w of 100 μm to 200 μm. Arrangement for optical measurement according to claim 6, characterized in that in a particularly advantageous manner this Focus diameter w a size of 150 microns Has. Arrangement for optical measurement according to at least one of the preceding claims, wherein between the laser ( 1 ) and the laser disc ( 2 ) a focusing lens or a focusing element ( 12 ) is arranged. Arrangement for optical measurement according to at least one of the preceding claims, wherein between the convergent lens ( 9 ) and the position sensitive detector / PSD ( 10 ) an attenuation filter ( 11 ) is arranged. Method for optical measurement of the shape and refractive power of a disk-shaped laser medium, characterized in that the wavefront segments are serially displaced by changing the point of impact of a test laser beam on the laser disk ( 2 ) is scanned in the way that at least two test laser beams of wavelength λ _T successively the laser disc ( 2 ), reflected by the mirrored in the region of the wavelength λ _L back, and a convergent lens ( 9 ) at a distance of a focal length f to a position-sensitive detector / PSD ( 10 ) are steered. Method for optical measurement of the shape and refractive power a disc-shaped laser medium according to claim 10, characterized characterized in that from the measured gradient field, the wavefront is determined by integration, where S = 1 / 2f∫Δx dx and S = 1 / 2f∫Δy dy for the respective ones Directions x and y apply. A method of optically measuring the shape and refractive power of a disk-shaped laser medium according to claims 10 and 11, characterized in that the emitted wavelength λ _{T is} equal to or nearly equal to the emission wavelength of the disk laser λ _L. Method for optical measurement of the shape and refractive power a disk-shaped laser medium according to the claims 10 to 12, characterized in that the test laser beams in suitably by a distance of the grid dimension δx are offset in parallel. Method for optical measurement of the shape and refractive power a disc-shaped laser medium according to claim 13, characterized characterized in that the grid size is about the size of the beam diameter, δx ≈ w. Method for optically measuring the shape and refractive power of a disk-shaped laser medium according to claims 13 to 14, characterized in that the parallel deflection is effected by a suitable optical element, preferably by a tiltable plane plate ( 13 ) or a 90 ° roof deflection prism. Method for optical measurement of the shape and refractive power of a disk-shaped laser medium according to claims 10 to 15, characterized in that the radii of curvature R _x and R _y are determined by the fact that the linear increase m _x or m _{y of} the measured dependences h (= x or y-coordinate of the point of impact on PSD) of x or y (= x-coordinate of the point of impact on the laser disc)

respectively.

be determined.