Method For Producing A Continuous Diffractive Optical Element, Device For Carrying Out The Production Method And Continuous Diffractive Optical Element

Abstract

In one aspect, a method for producing a diffractive optical element for beam shaping of a laser beam having a first wavelength of at least 100 nm includes providing a laser mirror, the laser mirror having a layered structure made of a substrate, a dielectric layer and optionally an absorption layer, the dielectric layer resting against the substrate or the absorption layer being located between the substrate and the dielectric layer. The method also includes creating a plurality of bulges of the dielectric layer by treating the laser mirror with a series of focused heating laser beams having a second wavelength (λ.sub.2), the plurality of bulges having a height perpendicular to the dielectric layer, and at least one bulge having a height of at least half the first wavelength (λ.sub.1).

Claims

1. A method for producing a diffractive optical element for beam shaping of a laser beam having a first wavelength of at least 100 nm, comprising the steps: providing a laser mirror, the laser mirror having a layered structure made of a substrate and a dielectric layer, the dielectric layer resting against the substrate, or the laser mirror having a layered structure made of a substrate, a dielectric layer and an absorption layer, the absorption layer being located between the substrate and the dielectric layer, generating a plurality of bulges of the dielectric layer by treating the laser mirror with a series of focused heating laser beams having a second wavelength the plurality of bulges having a height perpendicular to the dielectric layer, and at least one bulge having a height of at least half the first wavelength.

2. The method according to claim 1, wherein the laser mirror provided and the diffractive optical element have a transmission of T≤10.sup.−2 for the first wavelength.

3. The method according to claim 1, wherein the absorption layer consists of silicon or gold, the substrate consists of glass, CaF.sub.2, MgF.sub.2 or sapphire and/or the dielectric layer consists of SiO.sub.2, Ta.sub.2O.sub.5, TiO.sub.2, HfO.sub.2, Al.sub.2O.sub.3, MgF.sub.2, LaF.sub.3, and/or ZrO.sub.2.

4. The method according to claim 1, wherein when treating the laser mirror with a series of focused heating laser beams, a heat input of the heating laser beam into a volume of the dielectric layer or into a volume of the absorption layer of the laser mirror is at least 30 kJ/cm.sup.3.

5. The method according to claim 1, wherein when treating the laser mirror with a series of focused heating laser beams, the second wavelength, a power of the heating laser beam, a focusing of the heating laser beam, a heating duration, the absorption layer of the laser mirror, the dielectric layer of the laser mirror and/or a layer thickness of the absorption layer are selected such that at least one bulge has a height of at least half the first wavelength.

6. The method according to claim 1, wherein the layer thickness of the absorption layer is greater than 30 nm.

7. The method according to claim 1, wherein when treating the laser mirror with a series of focused heating laser beams, the second wavelength is between 200 and 700 nm and the absorption layer of the laser mirror is made of silicon, or the second wavelength is between 200 and 2000 nm and the absorption layer of the laser mirror is made of gold and/or the second wavelength is between 100 and 2000 nm.

8. The method according to claim 1, wherein when treating the laser mirror with a series of focused heating laser beams, a power of the heating laser beam is at least 10 mW.

9. The method according to claim 1, wherein when treating the laser mirror with a series of focused heating laser beams, the heating laser beam is focused onto the absorption layer and/or the dielectric layer with a full width at half maximum of at most 5 μm.

10. The method according to claim 1, wherein when treating the laser mirror with a series of focused heating laser beams, the heating duration of the heating laser beam is between 1 μs and 1 ms.

11. The method according to claim 1, wherein when treating the laser mirror with a series of focused heating laser beams, the laser mirror is displaced during the treatment along a displacement direction perpendicular to the heating laser beam and the heating laser beam is deflected during the treatment perpendicularly to the displacement direction, or the laser mirror is displaced during the treatment along two mutually orthogonal displacement directions, both perpendicular to the heating laser beam.

12. A diffractive optical element for beam shaping of a laser beam having a first wavelength of at least 100 nm, the beam shaping of the laser beam having the first wavelength taking place by reflection of the laser beam on the diffractive optical element, the diffractive optical element having a layered structure made of a substrate and a dielectric layer, the dielectric layer adjoining the substrate, or the diffractive optical element having a layered structure made of a substrate, a dielectric layer and an absorption layer, the absorption layer being located between the substrate and the dielectric layer, in both variants, the dielectric layer having a plurality of bulges, the bulges having a height perpendicular to the dielectric layer, and at least one bulge having a height of at least half the first wavelength.

13. A device for performing the method according to claim 1, the device comprising a heating laser for producing a heating laser beam having the second wavelength, a laser mirror positioning device for providing a laser mirror, a focusing device for focusing the heating laser beam onto the laser mirror, a deflection device and a controller, the laser mirror positioning device being designed to displace the laser mirror in a displacement direction, the deflection device being designed to deflect the heating laser beam perpendicularly to the displacement direction, and the controller being designed to actuate the heating laser, the deflection device and the laser mirror positioning device.

Description

[0044] The drawings show FIG. 1 a schematic representation of the method for producing a diffractive optical element and a sectional representation of the diffractive optical element according to a preferred embodiment of the invention and

[0045] FIG. 2 a schematic device for carrying out the method for producing the diffractive optical element according to a preferred embodiment of the invention.

[0046] FIG. 1 shows a schematic representation of the method for producing a diffractive optical element 10, DOE 10 for short, and a sectional representation of the DOE 10 according to a preferred embodiment of the invention. The method provides for two steps, a laser mirror 12 being provided as a blank for the DOE 10 in a first step. The laser mirror 12 is suitable for reflecting a laser beam having a first wavelength λ.sub.1. In the present case, it is a laser mirror 12 for reflecting laser beams having a wavelength λ.sub.1 of 0.532 nm, that is, laser light in the green wavelength range. Furthermore, the laser mirror 12 is suitable for a high-power laser and has a high damage threshold. In this embodiment example, the laser mirror 12 has a layered structure made of a substrate 14, an absorption layer 16 and a dielectric layer 18. All three layers 14, 16, 18 are parallel to one another in the present case, the absorption layer 16 being arranged between the substrate 14 and the dielectric layer 18. The dielectric layer 18 in turn comprises a plurality of material layers 20, 22 made of two different materials which are layered alternately, the first material having a high refractive index in relation to the first wavelength λ.sub.1 and the second material having a low refractive index in relation to the first wavelength λ.sub.1.

[0047] Bulges 24 of the dielectric layer 18 are produced in a second step of the method for producing the DOE 10. In the embodiment example preferred here, said bulges are rotationally symmetrical bulges produced at an interface between the dielectric layer 18 and the absorption layer 16. An axis of rotation 26 of the rotationally symmetrical bulges 24 is perpendicular to the absorption layer 16. As can be seen in FIG. 1, in the present case, the dielectric layer 18 does not rest against the absorption layer 16 at the bulge 24 but is detached from the absorption layer 16 at the bulge 24. A cavity 28 is located at the bulge 24 between the dielectric layer 18 and the absorption layer 16. The bulge 24 has a Gaussian shape in relation to said plane in a section through the bulge 24 along a plane perpendicular to the absorption layer 16.

[0048] In the embodiment example preferred here, the substrate 14 of the laser mirror 12 and thus also of the DOE 10 is made of quartz glass and the absorption layer 16 is made of amorphous silicon. Furthermore, a layer thickness 30 of the absorption layer is 40 nm in the present case. The layer thickness 30 refers to the dimension of the absorption layer 28 perpendicular to its extension.

[0049] The bulges 24 of the dielectric layer 18 are produced by treating the laser mirror 12 with a series of focused heating laser beams 38 (shown only in FIG. 2) having a second wavelength λ.sub.2, a heat input 54 of the heating laser beam 38 in a volume of the absorption layer 16 of the laser mirror 12 being greater than 30 kJ/cm.sup.3. At least one bulge 24 of the bulges 24 produced thus has a height 32 of at least half the first wavelength λ.sub.1. The present case therefore has at least one bulge 24 having a height 32 of at least 266 nm.

[0050] FIG. 2 schematically shows a device 34 for carrying out the method for producing, the DOE 10. The device 34 comprises a heating laser 36 for generating the heating laser beam 38 having the second wavelength λ.sub.2, a focusing device 40 for focusing the heating laser beam 38, a laser mirror positioning device 42 and a controller 44. In the embodiment example preferred here, the heating laser 36 generates the second wavelength λ.sub.2 of 532 nm. Device 34 further comprises a deflection device 46 for deflecting the heating laser beam 38. In the present case, this is implemented using a 1-dimensional galvo scanner 46 which is designed to deflect the heating laser beam 38 in one direction. In FIG. 2, the direction of the heating laser beam 38 to the laser mirror 12 corresponds to the z-direction. The galvo scanner 46 allows the heating laser beam 38 to be deflected in the x-direction. Furthermore, the device 34 comprises an acousto-optical modulator 52 which can change the intensity and thus the power of the heating laser beam 38.

[0051] In order to produce a grid-like arrangement of bulges 24 of the dielectric layer 18 by means of the device, the laser mirror positioning device 42 is designed such that the laser mirror 12 can be displaced. The displacement direction of the laser mirror 12 here is the y-direction, that is, perpendicular to the direction of the heating laser beam 38 and perpendicular to the deflection direction of the galvo scanner 46.

[0052] Furthermore, the controller is designed to actuate the heating laser 36, the acousto-optical modulator 52, the deflection device 46 and the laser mirror positioning device 42.

[0053] Furthermore, in the embodiment example preferred here, the focusing device 40 for focusing the heating laser beam 38 is implemented by a confocal microscope. The confocal microscope (f.sub.objektiv=2 cm; f.sub.Tubus=f.sub.2=30 cm) focuses the heating laser beam 38 onto the absorption layer 16.

[0054] The heating laser 36, the focusing device 40, the laser mirror positioning device 42 and the deflection device 46 are arranged relative to one another with the aid of a mirror 50 and lenses 48 such that the heating laser beam 38 strikes the absorption layer 16 of the laser mirror perpendicularly. The heating laser beam 38 strikes a rear side of the laser mirror 12 and penetrates through the substrate 14 to the absorption layer 16. The absorption of the heating laser beam 38 results in a local heat input 54 of at least 30 kJ/cm.sup.3 in the absorption layer 16, which leads to the formation of the bulge 24.

LIST OF REFERENCE CHARACTERS

[0055] 10 diffractive optical element, DOE. [0056] 12 laser mirror [0057] 14 substrate [0058] 16 absorption layer [0059] 18 dielectric layer [0060] 20 material layer made of first material [0061] 22 material layer made of second material [0062] 24 bulge [0063] 26 axis of rotation [0064] 28 cavity [0065] 30 layer thickness of the absorption layer [0066] 32 height of the bulge [0067] 34 device [0068] 36 heating laser [0069] 38 heating laser beam [0070] 40 focusing device, confocal microscope [0071] 42 laser mirror positioning device, positioning stage [0072] 44 controller [0073] 46 deflection device, galvo scanner [0074] 48 lens [0075] 50 mirror [0076] 52 acousto-optic modulator [0077] 54 heat input