Patent Application
20210260842
The invention concerns a method for the manufacture of a transmissive optical system from a blank. Here the transmissive optical system is usually a lens. The invention concerns in particular the manufacture of an intraocular lens, a contact lens, a refractive implant, or a spectacle lens. The invention also concerns the processing of optical surfaces, which are partially mirrored and partially translucent to radiation.
WO 96/31315 describes the treatment of arbitrary 3D-form surfaces by means of a laser. In particular, this involves the manufacture of precise sealing surfaces on moulding tools.
WO 2012/119761 A1 concerns a method for the production of optical elements by means of processing with energetic radiation, preferably with laser radiation. In this method, blanks of quartz glass are first treated by coarse ablation and subsequently by polishing and fine ablation. This iterative method with a plurality of steps is particularly suitable for hard materials such as glass or steel.
DE 10 2007 058 105 A1 describes a method for the manufacture of a transmissive optical system with an ablative laser. In this method, however, material ablation is not achieved with the laser on a blank, but with an ablative medium that is supplied separately by an evaporator onto the surface to be processed. In this method, the material ablation is achieved with the ablative medium, and the laser acts not on the surface of the blank, but rather on the ablative medium, which, as a vaporous phase or in a condensed liquid phase, absorbs the laser radiation between the laser and the blank. The pulse durations of less than 500 fs specified in this application relate to the laser radiation impinging on the vaporous or liquid ablative medium, and not to a laser beam that leads to material ablation on the blank. Such methods are suitable for particularly hard materials.
U.S. Pat. No. 5,143,660 A describes an injection moulding process for the manufacture of plastic lenses. Here special holes are formed in the lens, which serve to accommodate liquids, in particular such as medicaments.
The invention therefore has as its object the presentation of a generic method that can also be used for blanks made of softer materials. In particular, the method should enable rapid, cost-effective manufacture.
This object is achieved by a method with the features of patent claim 1. Advantageous developments are the subject matter of the dependent claims.
The extremely short pulse duration of the ablative laser has the consequence that the material of the blank that evaporates during the pulse does not hinder the energy input after the vaporisation, and that after each pulse, within the short interruption between two pulses, the vapour can also largely escape from the processing zone, or the laser can be directed onto another processing zone. This enables a precise surface finish, in which small craters located very close to one another can be created on the surface of the blank.
The short pulse duration has the consequence that virtually no interaction occurs between the melt or material of the blank vaporising under the laser radiation. The material ablation is achieved by direct vaporisation and thus the treated material is hardly damaged. The ultra-short laser pulses with durations ranging from a few femtoseconds to a few picoseconds or nanoseconds enable new processing methods that are not possible with conventional tools. These laser flashes lead to extremely high peak intensities, which can be achieved with relatively low pulse energies by virtue of the strong temporal compression. This enables highly precise material ablation and the processing of materials sensitive to temperature.
It is advantageous if the blank is manufactured from plastic. Monomers and polymers, and also combinations of these, and in particular transparent plastics, are suitable for this purpose.
The blank particularly preferably comprises an acrylate. At the same time the blank can also be manufactured from diverse plastics. The acrylate is preferably transparent or partially transparent. Acrylates with or without plasticisers can be used. Suitable materials are, for example, HI56 SPECS®, PMMA, CI26® or Contaflex CI18®, hydrogel, silicone, or combinations of a collagen and a polymer, such as Collamer®.
The blank can be cut from, or out of, a base body, such as, in particular, a cylindrical rod or a plate. It is particularly advantageous if the blank is manufactured by means of injection moulding or extrusion.
A particularly advantageous variant of embodiment envisages that the blank is manufactured from a powder-form, liquid or gaseous material by means of additive production (3D-printing). Here the blank can already have a three-dimensional shape matched to the final shape, which can also be of an asymmetric design. Both the build-up method, and also a combination with the described ablation method, can be applied here.
An advantageous variant of embodiment envisages that a blank is used that has a density gradient. Such a density gradient leads to a locally diverse optical refractive behaviour within the blank. The result is that by adjusting the optical density within the blank, a blank can be manufactured and used, which, with a lower surface curvature, effects the same light refraction as a homogeneous blank.
Alternatively or cumulatively, it is proposed that the blank be made of different materials or types of material. This results in a multi-material blank, which leads to a particular refractive behaviour by virtue of the material selection and the local arrangement of material. A density gradient can also be achieved as a result of a particular selection of materials with diverse densities, which determines the refractive behaviour of the blank and the optical system.
If, for example, the outer shell regions of a cylinder have an optical density that differs from that of the core region, radiation incident on the plane face of the cylinder is deflected in accordance with the optical density of the material, without the surface having to be of a curved design. Thus in the case of a circular lens the density gradient in the radial direction enables a reduction of the curvature of the surface. This has the consequence that the processing of the less curved surface with a laser beam is facilitated, since as a result of the lower curvature, the laser beam can more easily be guided approximately at right angles to a normal on the curvature of the surface. However, the blank can already have a refractive behaviour that is close to the desired target shape of the lens. By this means the processing effort on the lens is reduced.
Therefore, it is further proposed that a blank with a circular cross-section is used, which has an optical density towards the centre that differs from that towards the edge.
A density gradient on the lens enables the lens to be manufactured with less curvature, or even with no curvature. This leads to a lens that can be manufactured such that it is flexible and can be rolled up. By this means it is possible to fold up or roll up a lens such that it is very small, and can be inserted into the eye through a particularly small opening. Thus, a very small incision in the cornea is sufficient to remove the old destructible lens, and to insert a new lens into the eye, which then only unfolds or rolls out in the eye.
The statements regarding the different materials and the density gradient are each essential to the invention per se, also independently of the pulse duration specified in patent claim 1.
It is advantageous if the pulse energy is varied during the ablation and/or polishing. Thus, it is proposed that the energy of the laser be varied over time. This makes it possible to ablate or polish certain surface regions with a higher pulse energy than in other surface regions. If, for example, the laser beam is guided along a meandering line over the surface of the blank, the energy input can be reduced in the turning regions, for example.
If the ablation of matter is the primary mechanism for altering the shape of the blank, reference is made to an ablative process, or an ablative laser. If, on the other hand, the shape is to remain unaltered, and the surface is only to be smoothed, reference is made to a polishing process, or a polishing laser.
It is particularly advantageous if the shape of the processed optical system in the region of the processed surface is measured after each laser pulse. Either the total ablation per surface region can be determined, or the actual crater shape can be determined. Optical coherence tomography preferably serves this purpose. This enables the location data to be stored, and for this data to be taken into account in subsequent processing of the surface, or processing of an adjacent surface. The measurement is carried out either immediately after a pulse, or in the time until processing of the measured surface is repeated, or until the processing of an adjacent surface. This enables a precision in the micron range, or even in the sub-micron range.
In addition to the measurement of the processed surface, it is advantageous if, during processing, the process temperature is monitored with a measuring system, preferably with a pyrometer or a thermal camera. This also makes it possible to control the process temperature so as to keep it within a defined bandwidth.
The laser pulse usually has a Gaussian distribution of intensity over the surface. However, a particular precision is achieved in the processing of surfaces if the pulse energy distribution of a pulse is locally asymmetric. In a deviation from a rectangular pulse, the edges of the rectangle can thus be formed differently. In particular, on one side the pulse can rise more sharply towards the centre than it falls away from the centre on the other side. This allows the energy distribution over the surface of the laser beam to be varied, such that when the beam hits a curved surface, a vaporisation is achieved that is matched to the curved surface. In particular, the depth of the crater created by the laser pulse can also be reduced, without reducing the volume vaporised during the pulse.
This enables an almost constant ablation over the surface that is to be treated. In addition, the ablation profile can be varied and manipulated as required.
Moreover, the crater depth should be essentially constant over the entire surface that is to be processed. Essentially, this has the consequence that the intensity distribution of the laser beam is adjusted such that, for example, when irradiating a circular region with a radius r, the average crater depth on a circular region with a radius r/2 is at most twice as deep as the average crater depth in an annular region in the region r/2 to r. The deviation is preferably even in the sub-μm range.
One form of embodiment envisages that the pulse energy distribution during a pulse on a circular or an oval surface has at least one maximum in the radial direction. The intensity distribution of the pulse can, for example, be represented as the shape of a volcanic crater, so that a higher intensity acts in the edge regions of the circular oval surface than in the central region. This makes it possible, depending on the task, to vary the intensity distribution of the pulse over the surface impinged upon by the pulse in an individual manner. This pulse shape can be set once, or can be altered during the processing. It is therefore proposed that the pulse energy distribution be varied transverse to the direction of irradiation during the processing.
The statements regarding the local and temporal energy distributions are each essential to the invention per se, also independently of the pulse duration specified in patent claim 1.
The effect of a laser beam varies, depending on whether the laser beam impinges onto the surface to be processed at right angles, or at another angle. As a result, the alignment of the laser beam relative to the processed surface also influences the ablation result. In order to limit these differences, it is proposed that during the processing of a curved optical system, the alignment of the laser beam is maintained essentially at right angles to a tangent plane at the intersection of the laser beam and the optical system. Here “essentially” means with a deviation of less than 40% and preferably less than 10%. Since “at right angles” describes an angle of the laser beam of 90° to the tangent plane, “essentially at right angles” describes, for example, an angle of the laser beam to the tangent plane of greater than 70°. Alternatively or cumulatively, the intensity or the intensity distribution of the laser beam can also be varied as a function of the angle of incidence.
In order to ensure that the laser beam impinges onto the surface to be processed as far as possible at right angles, the beam can be deflected via mirrors. However, the positions of the laser and the optical system to be processed can also be altered relative to each other. It is therefore proposed that the position and/or the alignment of the blank or the laser be moved during processing.
The processing effort can be greatly reduced by using a blank that already has a defined shape on one side or a plurality of sides, such as, in particular, a convex or concave shape, and is only processed with the laser on one side. A preferred variant of embodiment envisages that the blank is to be symmetrically formed on one side, and on another side is to be processed asymmetrically, or in a free-form manner.
The statements regarding the alignment of the laser beam and the shape of the blank are each essential to the invention per se, also independently of the pulse duration specified in patent claim 1.
The precise processing of optical systems makes it possible to produce a visual aid, such as an intraocular lens or a contact lens, for a patient in an individual manner. For this it is proposed that an eye of a patient is first measured, and that thereby a data set is created, and that the ablative laser and/or the polishing laser is subsequently controlled on the basis of the data of this data set.
The eye can be measured by means of biometry and/or topometry so as to determine the axial length of the eyeball, the anterior corneal surface, the posterior corneal surface, the corneal thickness, and/or the refractive index of the cornea. Topometry allows the peripheral corneal radii to be measured with an ophthalmometer or keratometer, in addition to the central radii, in order to obtain meaningful surface parameters, for example, for the customisation of contact lenses or intraocular lenses. Topometry provides individual measured values, from which the surface character can be approximated, and keratography delivers a complete surface profile. This results in a data set for the target shape, which enables the individual manufacture of a lens or other visual aid. The visual defects can originate from all elements of the eye. A measurement of the individual elements or the use of ray tracing to determine the diffraction of a radiation beam passing through an eye makes it possible to define a visual correction in order to compensate for these errors with a visual correction medium.
It is advantageous if a data set is already created in the course of measurement, which can easily be converted into a computer control program for the production of a lens.
Various individually manufactured visual aids or vision correction aids can be used, or standard visual aids can be combined with individually manufactured vision correction aids. However, it is also possible to replace just the lens with a corrected intraocular lens, in order to correct as many of the errors of the eye as possible.
Such a method has been described in EP 0 954 255 B1. It has been proposed that an artificial lens should be cut with a laser. This method is not economically feasible, because it is time-consuming to cut a lens with a laser such that it corresponds exactly to a specific target shape, and is so smooth that no unwanted refractions of light occur. Only the combination of the method with a plastic material such as, in particular, an acrylate, and a plastic-vaporising laser, has led to an economical method. This method is essential to the invention, also independently of the above-cited method steps, in particular as a two-stage method, with an ablative laser used for material ablation, and a polishing laser used for a polishing operation.
Here the lens can also have multi-focal functions. Moreover, the lens can be used to correct errors caused by scattering in the eye, such as that caused, in particular, by age-related scattering centres in the vitreous humour. In addition, reflections in the eye, local absorption, alterations in polarisation in the eye, and individual visual impairments, can be corrected such that the quality of the correction attains or even exceeds the optical resolution of the retina (retina quality IOL).
Furthermore, it is proposed to alter systematically the optical density of the surface of the optical system, by ablation and/or polishing, such that the altered refractive index prevents reflections. In particular, extreme polishing can minimise light refractions, such as the Fabry-Pérot effect, and multiple reflections. The polish then acts like an anti-reflection coating. In particular this can be achieved by altering the refractive index in different layers.
In particular, to eliminate scattered radiation and to be able to manufacture lenses with an increased depth of field and multi-focal IOLs, it is proposed to modify the material of the blank with the laser radiation such that the finished lens has an optical density gradient. An alteration of the density gradient can be achieved by ablative and additive methods. For example, a density gradient can be achieved by a radially co-rotated orientation of the laser light spot or the laser focus. In particular, a density gradient can also be achieved by means of a defined beam distribution. Thus, processing can take place with a higher intensity of the laser beam in a radially inner region than in a radially outer region in order to achieve a density gradient or regions of different density. Correspondingly, processing can also take place with a lower intensity of the laser beam in a radially inner region than in a radially outer region in order to achieve a density gradient or regions of different density. This gradient or density difference can be taken into account when calculating the refraction behaviour of a transmissive optical system. An optical density difference between two regions of the lens of at least 0.01 is advantageous, allowing any, preferably radially symmetrical, refractive index gradient to be generated as a step change in density, or as a continuous density transition.
A particularly important field of application for this method is therefore the manufacture of the optical system of an intraocular lens.
Technically, it has proved to be advantageous if the ablative laser is operated such that it effects a material ablation of 0.01 to 10 μm per pulse, and preferably of 0.02 μm to 5 μm per pulse, and particularly preferably of 0.02 μm to 0.5 μm per pulse. Depending on the required material ablation, the ablation can also be carried out in a plurality of layers, whereby the ablation per layer should be less than 20 μm, preferably less than 2 μm, and particularly preferably less than 1 μm. At first it is possible to work with the ablation of a larger amount of material, and when approaching the target shape the ablation per layer can be reduced. The result is that firstly greater ablation is effected with greater intensities or also larger irradiated regions, and subsequently a smaller ablation per pulse is effected, so that the surface becomes as smooth as possible, and requires less polishing.
It has been shown that it is advantageous if the ablative laser is operated with a laser wavelength of 100 to 1,200 nm, and preferably less than 400 nm, such as in particular between 193 nm and 370 nm. Preferred wavelengths are 193, 248, 266, 343 and 355 nm.
During the ablation, the focal diameter of the ablative laser should be between 5 and 50 μm, and preferably approx. 20 μm.
The scanning rate of the ablative laser lies between 100 and 5,000 mm/s, and preferably between 500 and 5,000 mm/s, and particularly preferably at approx. 1,000 mm/s.
The pulse energy of the ablative laser can lie between 0.1 μJ and 10 μJ, and preferably at approx. 1 μJ.
The repetition rate of the ablative laser can lie between 5 kHz and 5,000 kHz, and preferably between 50 and 200, or between 10 and 500 kHz.
An advantageous variant of the method envisages that the laser beam of the ablative laser firstly removes material at some distance from the target shape, until at least 50% of the material has been removed, and only then is material removed in a region closer to the target shape. Here the laser can be guided upwards and downwards. With guidance of the laser upward, only one element is firstly ablated radially on the very outside, and then, as a rule, a smaller element, reaching further radially inwards. “Downwards” means that firstly a large element is ablated radially from the outside as far as the final shape, and then a smaller element is ablated underneath.
Moreover, it has proved to be advantageous if the distance between the ablation craters created by the individual laser pulses on the surface within one ablation layer is not constant. This distance can also be varied so as to adjust the mean ablated layer density. By this means the ablation per surface is altered by the distance between the pulse footprints on the optical system that is to be processed. Closely spaced pulse footprints result in greater ablation, while widely spaced pulse footprints result in less ablation.
For polishing, it is proposed that the polishing laser be operated in a pulsed or modulated manner with a pulse duration of more than 1 μs. By this means an optimum polishing of, for example, plastics, can be achieved.
Preferred laser wavelengths for the polishing process lie in the range between 0.1 μm and 100 μm, and preferably between 9 μm and 11 μm, or between 0.1 μm and 0.4 μm, or between 1 and 12 μm.
A particular form of method management envisages that the polishing laser is operated continuously. The laser is therefore not pulsed during the polishing process, but rather the beam is moved relative to the surface of the optical system, preferably with a varying intensity. In contrast to a pulsed laser, in this case a particular laser power is always present.
For the polishing process, it has proved to be advantageous if the polishing laser has a beam diameter at the workpiece of less than 10 mm, and preferably of between 0.1 mm and 8 mm. The polishing process can be simplified, in that the polishing laser has a beam diameter at the workpiece that is greater than or equal to that of the surface to be polished. By this means it is possible to polish the said surface all at once, without moving the laser backwards and forwards over the surface.
An advantageous feed rate of the polishing laser lies between 1 and 100 mm/s.
Furthermore, it is advantageous if the polishing laser is formed into a “quasi-line” by means of a scanning movement with a scanning rate of 500 mm/s to 20,000 mm/s. By moving the laser beam backwards and forwards, even a pulsed laser does not produce individual craters, but rather a deepened surface or a groove.
The polishing laser can be operated with an average laser power of 1 to 500 W, preferably of approx. 100 to 300 W. It is advantageous if less than 30, and preferably only 1 to 10, passes are carried out with the polishing laser in order to polish the optical system.
The polishing laser can also be operated with a line length that is at least as long as an extent of the surface to be polished. The laser beam is thus guided as a line over the surface to be polished, and at the same time care is taken to ensure that the entire surface is covered by the laser beam.
The object underlying the invention is also achieved by a lens, which has a density in one region that is 1% lower than in another region of the lens. Such a density gradient leads to a particular refractive behaviour, whereby the lens causes a different refraction of light not only by virtue of its shape, but also, and in particular, by virtue of its density in diverse regions. It is advantageous if the difference is between 2 and 5% or even higher, such as, for example, more than 10%.
It is furthermore advantageous if the lens has a surface region and a core region, and the density in the surface region is higher than in the core region. Cumulatively or alternatively, the lens can have a circular cross-section and a radial density gradient.
Depending on the application, it can be advantageous if the lens reflects less than 5%, and preferably less than 1%, of the incident radiation.
The statements regarding the parameters of the laser in the course of ablation and polishing are each essential to the invention per se, also independently of the pulse duration specified in patent claim 1 and the other features cited above.
Inventive examples of embodiment are illustrated in the figures and are described in what follows. Here:
After ablation, the blank 2 has the shape shown in
The blank is a plastic and in the present case is an acrylate 8. The said blank can also comprise other materials, such as other plastics, or glass. However, the surface of the blank to be reworked is made of plastic.
By the arrangement of a plurality of craters of this type in close proximity to each other, a planar material ablation 4 is achieved. The resulting surface structure is rough as a result of the linking together of the craters. By minimising the depth of the crater, and minimising the distances between the craters, the roughness of the plastic surface can be reduced.
It is advantageous for the smoothing of the surface if the laser intensity is minimised, and/or the footprint of the laser on the surface to be processed is increased, so that material is only melted, and, as far as possible, no material evaporates. A polishing laser 20 is usually used for this purpose, which is scanned along the line 21 with a scanning rate (Vscan) and a footprint width 22, 23 over the surface 24. The polishing laser 20 is moved forward at a feed rate (Vfeed) in the direction of the arrow 25, at right angles to the line 21.
As a consequence, as shown in
In the example of embodiment, the material surface shown in
During material ablation 4 with the ablative laser 3, care is taken to ensure that systematically localised material ablation is achieved by the action of ultra-short pulses of laser radiation of about 100 or 200 femtoseconds only at the point of impingement of the laser onto the surface, without any thermal damage to the surrounding material. In the example of embodiment, a laser wavelength of 343 nm is used, so that the laser radiation is absorbed near the surface as a result of the small optical penetration depth of this laser wavelength in the acrylate.
By comparing the initial shape and the target shape of the surface, the required ablation depth and thus the required number of laser pulses at each point on the surface are determined. In this manner the material ablation 4 can be determined by the number of laser pulses per unit surface area without altering the nature of the laser radiation. Here the laser beam 30 can be guided in a meandering manner over the surface to be processed, in particular for the laser material ablation. On the basis of the calculated number of laser pulses per unit surface area, the laser is switched on and off during its passage over the surface to be processed.
In the example of embodiment shown in
For the subsequent laser polishing, a laser with a wavelength of 10.6 μm is used, since this wavelength is also absorbed near the surface in the material. The laser is operated continuously and the laser power is in the range of 50 to 100 watts. As a consequence the material surface is melted by the action of the laser radiation during laser polishing, and is then smoothed by the surface tension before it solidifies once again.
In the example of embodiment shown in
The processing strategy for the iteration shown in
With a higher average laser power a higher feed rate is to be used, and with a lower average laser power the feed rate is reduced. This process can therefore be scaled. The dependence between feed rate 33 and average laser power 36 is shown in
It is advantageous if the pulse energy is varied during ablation and/or polishing. To this end
The local intensity distribution of a pulse 60 on the spatial axes 61 and 63 is shown in an exemplary manner in
In order to optimise this effect, it is proposed that the pulse energy distribution be varied transverse to the direction of radiation during processing.
In order to achieve homogeneous processing of a lenticular surface 80 of a lens 81, it is advantageous if the laser beam 82 is maintained essentially at right angles to a tangent 83 at the point of intersection 84 of the laser beam 82 and the lens 81. This can be achieved by varying the alignment of the laser beam during processing and maintaining the position of the lens 81 constant, or by altering the alignment of the lens 81 relative to the laser beam 82 by moving the lens 81 during processing. Needless to say, both the lens and laser can be moved so as to align the laser beam 82 as nearly at right angles as possible to the normal 83 on the surface of the lens. Moreover, instead of moving the laser, the laser beam can also be aligned with the aid of a mirror so that it impinges onto the lens surface as nearly at right angles as possible.
As in the example of the lens shown in
The arrangement of the ablation craters 100 on the surface 101 of a lens 102 is shown in
The lens 110 shown in
The inverted density distribution was implemented with the lens 120 shown in
In the plan view shown in
In all the examples of embodiment shown, the optical density can migrate via a gradient into an altered optical density, and, alternatively, regions of different optical densities can lie clearly bounded next to each other. Here the varying optical density can be used to influence the refractive behaviour of the lens when a light beam passes through it, and its deflection. Alternatively or cumulatively, the reflection properties, especially at the boundary surface of the lens surface, can be influenced by way of its density and the hardness that usually accompanies the latter.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2016 014 747.4 | Dec 2016 | DE | national |
| 10 2017 002 986.5 | Mar 2017 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DE2017/000337 | 10/12/2017 | WO | 00 |
