Method for Manufacturing an Optical Component

Abstract

A method for manufacturing an optical component in which an optical function of the component is created for electromagnetic radiation in an application wavelength range, using laser machining with laser radiation in a machining wavelength range, characterized in that the following steps are carried out: 1) A solid body is provided that is made from a material that in the raw state absorbs the laser radiation in the machining wavelength range,2) Laser machining is carried out on the solid body employing one or more machining steps and3) The material of the solid body is transformed into a final state in which the solid body is transparent to the electromagnetic radiation in the application wavelength range and thus fulfills the intended optical function.

Description

Due to the arrangement of a (multiple) layer system consisting alternately of absorbing (e.g. SiO_x) and transparent (e.g. SiO₂) layers of suitable thickness, a further possibility exists for producing a multi-level profiled optical component in which the application wavelength is independent of the machining wavelength. If, for ablation purposes, a fluence is set at which in each case one such double layer is ablated using front-side ablation, it is possible to produce a 2ⁿ-level element using n exposures, where one exposure may consist of one or more laser pulses per irradiation position.

Further details of the invention may be derived from the following detailed description and the attached drawing, in which a preferred exemplary embodiment of the invention is depicted. FIG. 1 shows a diagram for producing a four-level diffractive phase element by means of multiple layer deposition and laser ablation.

A method for manufacturing an optical component 6 is based substantially on carrying out several times a machining cycle consisting of a deposition step in which an absorption layer is deposited, and also consisting of a structure-forming laser ablation step, said method being also based on a material transformation step in which the component 6 is transformed into a final state that is transparent to the laser radiation.

The method is explained using the example of a four-level diffractive phase element (DPE) for UV wavelengths. The way in which it works is based on the diffraction of light at a finely structured surface relief in an optical material. Through diffraction and interference of an incident electromagnetic wave, for example of a laser beam, on the DPE it is possible to bring about a desired intensity distribution in a so-called signal plane. In the case of DPEs, only the phase of the light wave is modulated, i.e. they accept practically all transmittive elements (on the other hand, diffractive amplitude elements (DAE) modulate the amplitude of the incident light wave, i.e. they are always associated with losses). For example, in this way, the beam profile of an excimer laser can be shaped and homogenized for a subsequent application. The necessary surface relief is calculated beforehand using an in principle known calculation algorithm, for example a computer-generated hologram. The total depth of the structure is given by the equation D=(q−1)/q×λ/(n−1), where q is the number of levels, i.e. q−1 is the number of steps, λ is the wavelength at which the DPE is intended to fulfill its optical function, and n is the diffractive index of the material of the DPE in air. For a four-level element for an application wavelength of, for example, 193 nm, the total structural depth is thus 258 nm at a diffractive index of n=1.561 and a respective step height of 86 nm.

On a substrate 1, advantageously formed as a quartz body, a first absorption layer 2 is applied by means of vapour deposition using a suitable, in principle known apparatus. Via a first (calculated) mask (not shown) the absorption layer 2 is then ablated down to the height of the substrate at the irradiated positions using laser radiation 7 (FIG. 1a). Alternatively, machining may also be carried out by appropriately controlling the laser beam so that it scans pixel by pixel over the surface of the component 6. The laser energy required for ablation is adapted to the applied coating layer thickness and is selected in such a way that the absorption layer is completely removed without damaging the substrate 1. Machining is carried out on the substrate side, i.e. as a rear-side ablation. A UV excimer laser, for example, having a wavelength of 193 nm, i.e. the same wavelength that is intended for the later function of the DPE, is used for the laser ablation. The absorption layer 2 consists of an SiO_x material that is highly absorbent at 193 nm. This first machining cycle results in a surface having a structure 3 with two relief levels 4, 4′, i.e. with a step 5 (FIG. 1b). A four-level element thus has four relief levels and three steps. A second machining cycle starts with the deposition of a second absorption layer 2′, which is vapour-deposited onto the structure 3 formed in the first cycle (FIG. 1c). Then a second ablation is carried out with a structure-forming laser beam 7′ (via a second mask, or pixel by pixel), thus creating the structure 3′ having three levels 4, 4′, 4″ (FIG. 1d). In a third machining cycle consisting of coating (deposition) and ablation, the structure 3″ with four levels 4, 4′, 4″, 4′″ is formed in similar fashion via an absorption layer 2″ using laser ablation 7″ (FIG. 1e). In a final thermal material transformation step (FIG. 1f), in which the component 6 is heated in an oven for several hours in air to several 100° C., the structural material SiO_x is oxidized to SiO₂ and thus becomes transparent to the laser wavelength. As a result, the structure 3″ finally turns into a four-level transparent profile 8 that satisfies the desired optical function as a DPE for the operating wavelength.

If, instead of multiple ablation and deposition of an absorption layer, a solid body is machined, or the entire layer thickness is not removed, the pulse energy density and the pulse count of the laser are used to obtain defined step depths or a quasi continuous profile in the absorbing material. It is important here to set the above parameters and also the beam profile (laser beam characteristics) very accurately, possibly with the help of upstream optical elements, in order to achieve a high degree of accuracy, because there is no longer any (helpful) “preset breaking point” between the substrate and the absorption layer.

Claims

1. A method for manufacturing an optical component in which an optical function of the component is created for electromagnetic radiation in an application wavelength range, using laser machining with laser radiation in a machining wavelength range, comprising: 1) providing solid body made from a material that in a raw state absorbs the laser radiation in the machining wavelength range,2) carrying out laser machining on the solid body, employing one or more machining steps and3) transforming material of the solid body into a final state in which the solid body is transparent to the electromagnetic radiation in the application wavelength range and thus fulfills the intended optical function.

2. A method according to claim 1, wherein the material of the component is ablated down to a defined depth at the irradiated sites using a UV pulsed laser with a preset pulse energy density.

3. A method according to claim 2, wherein a stepped profile having an optional number of steps with defined step heights is produced on the component by respectively adjusting the pulse energy density and the number of pulses.

4. A method for manufacturing an optical component in which an optical function of the component is created for electromagnetic radiation in an application wavelength range, using laser machining with laser radiation in a machining wavelength range, wherein, in order to produce a stepped profile (8) of the component (6) a machining cycle is carried out several times, consisting in each case of a deposition step in which an absorption layer (2, 2′, 2″) that in a raw state absorbs the machining wavelength range is applied to a substrate body (1) that is transparent to the machining wavelength range, and also consisting of an ablation step in which the applied absorption layer (2, 2′, 2″) is ablated at the irradiated sites, at least over part of the layer thickness, and characterized also in that a material transformation step, in which the profile (8) produced is transformed into a final state that is transparent to the application wavelength, is carried out at least once.

5. A method according to claim 4, wherein after each machining cycle or after selected individual machining cycles the material transformation step is carried out for the respective absorption layer (2, 2′, 2″).

6. A method according to claim 4, wherein the machining cycles comprise front-side ablation steps in which the absorption layer is directly irradiated and/or rear-side ablation steps in which the absorption layer is irradiated through the substrate body (1).

7. A method for manufacturing an optical component in which an optical function of the component is created for electromagnetic radiation in an application wavelength range, using laser machining with laser radiation in a machining wavelength range, wherein first a system of coating layers consisting of double layers comprising, respectively, an individual layer that transmits the machining wavelength range and an individual layer that absorbs the machining wavelength range, is deposited onto a substrate body that is transparent to the machining wavelength range, and characterized also in that subsequently an ablation step, in which in each case a double layer is ablated at the irradiated sites in order to produce a stepped profile on the component, is carried out several times, and also characterized in that a material transformation step in which the profile produced is transformed into a transparent final state that is transparent to the application wavelength is carried out.

8. A method according to claim 1, wherein a non-stoichiometric SiOx compound at an average 1<x<2 is used as the raw material, and that the SiOx material is transformed by the material transformation step into a final state consisting of SiO2.

9. A method according to claim 1, wherein the raw material is selected from a group of materials consisting of aluminium oxide, scandium oxide, hafnium oxide, yttrium oxide, tantalum oxide and titanium oxide.

10. A method according to claim 1, wherein the material transformation consists of an oxidation step carried out through thermal treatment of the component in an oxidizing atmosphere.

11. A method according to claim 10, wherein during thermal oxidation the component is exposed for eight to nine hours to a temperature of approximately 900° C.

12. A method according to claim 1, wherein by irradiating the component with a laser beam in an oxidizing atmosphere the irradiated material is photochemically transformed, at least in partial areas.

13. A method according to claim 1, wherein the machining of the component takes place by irradiating the machined area pixel by pixel in sequential steps or by carrying out the machining over the entire area using at least one imaging element.