WO2002042828A1

WO2002042828A1 - Method of marking an optical element

Info

Publication number: WO2002042828A1
Application number: PCT/AU2001/001516
Authority: WO
Inventors: Wayne Olsen
Original assignee: Sola International Holdings Limited
Priority date: 2000-11-24
Filing date: 2001-11-23
Publication date: 2002-05-30
Also published as: AU2002223274A1; AUPR168000A0

Abstract

The invention provides a system and method for making an optical element (7) using a neodymium-doped yttrium-aluminium-garnet (Nd:YAG) laser (1) to provide a mark (S) that is normally visible. The marking is performed by focussing (5) and steering (2, 3, 4) the Nd:YAG laser beam on and cross the optical element, and forming on, or within, the optical element a series of discreet sub-marks wherein the combination of the sub-marks provide the mark.

Description

METHOD OF MARKING AN OPTICAL ELEMENT

Field of the Invention

The present invention relates to a method for providing desired markings on optical elements, particularly on or within ophthalmic lenses or lens wafers, but also on or within moulds for such lenses or lens wafers.

Background of the Invention

It is advantageous to mark optical elements with an identifying or functional mark that does not damage the desirable optical properties of the element and also is not able to be easily removed. Such marks may be a manufacturer's trade mark or product code (for anti-counterfeiting, authenticity or product branding reasons), an alignment mark for use by opticians (in the case of an ophthalmic lens), or even a bar code.

Typically, efforts to mark optical elements such as ophthalmic lenses have centred on providing marks on a surface of the lens, using physical processes such as engraving or acid etching, or using radiation processes such as those that use lasers such as carbon dioxide or pulsed gas-discharge (Excimer) lasers.

However, it has been found that the physical processes generally cause undesirable damage to the optical surfaces, whilst also being complex and time consuming processes. In particular, engraving is generally unable to provide a mark of consistent form or shape, particularly on optical elements with a steep surface curvature, and causes undesirable microfractures on the surface, whilst acid etching is a time consuming process (often taking up to 13 hours) and usually requires the use of dangerous chemicals. On the other hand, the radiation processes have generally required the use of a mask having the desired marking cut into it, which introduces complexity and mask availability constraints. For instance, the use of a mask limits flexibility as there must be a different mask for each mark to be applied, so the marking of unique labels such as serial numbers is quite problematic. Additionally, lasers such as the CO₂ laser, have relied on the generation of heat at the surface of the optical element, or (as in the case of an Excimer laser) upon the use of undesirably toxic gases such as argon or fluorine.

The present invention thus aims to provide a method of marking an optical element, which method is relatively simple, does not require the use of masks or undesirably toxic chemicals, and will not cause unacceptable damage to the optical properties of the optical element. It is also an aim to produce an optical element with a desired marking that is normally visible, rather than one that would require the aid of special instruments or apparatus in order to be viewed.

Summary of the Invention

The present invention is characterised by the use of a neodymium-doped yttrium-aluminium-garnet (Nd:YAG) laser to provide an optical element (such as an ophthalmic lens or lens wafer, or a mould therefore) with a mark that is normally visible.

The present invention provides a method of providing an optical element with a mark that is normally visible, the method including the steps of:

- focussing a laser beam from a neodymium-doped yttrium-aluminium-garnet (Nd:YAG) laser at the optical element; and

- forming on or within the optical element a series of discrete sub-marks that, in combination, provide the mark.

The present invention also provides an optical element having a mark either therewithin or on a surface thereof, wherein the mark is normally visible and is defined by a series of discrete sub-marks provided by a neodymium-doped yttrium-aluminium-garnet (Nd:YAG) laser.

Before turning to a discussion of further advantageous forms of the present invention, reference will firstly be made to the meaning of various terms that are used throughout this specification.

In particular, the term Optical element' means lenses for optical devices such as spectacles, sunglasses, goggles, cameras, microscopes, telescopes and the like, or for the refracting or reflecting of light in any scientific or medical device, and of course includes ophthalmic lenses of all types. The term Optical element' also includes a part of any such lens, such as a lens wafer used in multiples to form a lens, and also moulds used for the manufacture of such lenses or lens wafers.

Additionally, the term 'normally visible' means visible to an unaided or naked eye, without the essential need to utilise instruments or apparatus such as magnifying devices, nor special techniques such as the application of polarised or ultraviolet light, for detection.

By way of explanation, the gain medium of Nd:YAG laser is a yttrium- aluminium-garnet (YAG) crystal embedded with neodymium (Nd) such that the YAG crystal is the holding matrix and the neodymium atoms are the excitable component. In this respect, and in one form of the invention, the Nd absorbs the light energy of a pump source at, for instance, 809nm and is excited and emits light at, for instance, 1064nm.

In the present invention, such a Nd:YAG laser may be pumped using a variety of methods, as will now be described. Such a laser may be pumped by an arc lamp, which lamp preferably uses a continuos broadband fluorescent light stimulated via electrodes. Such a broadband fluorescent light preferably outputs wavelengths between 300 and 1500nm, but typically only the 809nm wavelength is used to excite the neodymium. Indeed, the other wavelengths tend to be wasted light energy that create heat as a side effect. This is known as a continuous wave (CW) laser.

Alternatively, such a laser may be pumped by a pulsed light lamp, which lamp preferably uses a pulsed flash light method, creating pulses of light to excite the medium and enable a high energy pulse. A shutter is usually also used to create a build up of power before opening to output the laser pulse (often referred to as being "Q-Switched").

In both these forms of pumping, the Nd:YAG laser may be diode pumped, wherein diodes are used to transmit at wavelengths of about 809nm. Since typically only the required wavelength is used, these lasers are very efficient. It is possible to use either a pulsed or a continuous wave diode pumped Nd:YAG laser in the method of the present invention.

Indeed, the frequency tripling and quadrupling stages of diode-pumped lasers rival the applicability of Excimer lasers by delivering comparable fluency levels and offering better beam quality at far higher pulse repetition rates. However, unlike a typical Excimer rectangular emission, the entire output beam from a Nd:YAG laser can be focused to small spot sizes with long working distances. This superior focusability assists in eliminating the need for photo-masks and permits the use of scanning mirrors mounted on computer-controlled galvanometers to direct a beam to any location on a work surface, greatly improving the ease of marking optical elements such as in the present invention.

Indeed, these lasers can ideally be reasonably tightly focussed by an operator, which means that a computer-controlled scanning system is able to rapidly focus a beam to allow for direct marking of optical elements if necessary, without the need for masks. An optical element marked in accordance with the method of the present invention preferably has, either within it or upon one of its surfaces, a mark that consists of a series of discrete sub-marks. Each sub-mark is ideally formed by the Nd:YAG laser to form, in combination with other sub-marks, the desired mark.

Where the mark is provided as a surface mark on an optical element, the sub- marks may be ablations caused on the surface by the high concentrations of energy and short pulse lengths of radiation issued from the Nd:YAG laser, which ablate and break the molecular bonds of the surface in a rapid manner. A series of overlapping or spaced ablations may thus provide the series of discrete sub-marks that, in combination, form the desired mark.

Indeed, for the surface marking of plastic and glass lenses or moulds it is preferable that the effects of the marking process do not create any problems for any secondary processing of the lens or mould (for example, for any subsequent tinting, photochromic application, or heating and the like). In this respect, lasers operating in the infrared region mark materials by the use of heat, which causes problems in secondary processing, whereas plastic and glass are effectively opaque in the ultraviolet region, as the radiation is absorbed rather than transmitted.

Thus, it is preferred for a Nd:YAG laser to operate at a wavelength of about 266nm, which is in the ultraviolet region, such that the plastic and glass absorb the laser radiation sufficiently, and directly break the long chain molecular bonds that hold the material together. As mentioned above, the typically high concentrations of energy and short pulse lengths of radiation of the Nd:YAG laser, ablates and breaks the molecular bonds of the surface in such a rapid manner that no heat is transferred to the remaining material, and thus secondary effects are eliminated. The desired mark is then created by linking together a series of single point ablations. Where the mark is provided as a mark within an optical element, the sub-marks may be small microscopic cracks created in the body of the material in a controlled manner by focussing the Nd:YAG laser radiation to a point within the body of material with the use of very short pulse lengths and high energy levels. This preferably forms a bitmapped type of image created by a pattern of a series of discrete microscopic cracks.

The wavelength to be used for this type of marking is preferably such that it is normally transmitted through the material, and the actual absorption of the radiation in the material is low. Thus, the radiation is transmitted through the surface layer and into the volume of the material where, due to the non-linear absorption properties of the transparent material, the high energy and focussed points are able to create the microscopic cracks referred to above.

In relation to these microscopic cracks, the shorter the wavelength, the smaller the spot size and cracks able to be created, and ultimately a clearer overall mark is produced. In this respect, it has been determined that Nd:YAG lasers operating at 1064nm, 532nm and 355nm are all able to provide marks within an optical element. However, it will be appreciated that different material types may required different wavelengths for fine tuning the quality of the mark for each material.

Furthermore, in this form of the invention, namely where a mark is provided within the optical element, the discrete sub-marks provided in the form of microscopic cracks are preferably suitably spaced so as to avoid the possibility of adjacent cracks joining to create a wider crack within the optical element.

Therefore, it can be seen that the method of the present invention allows for the marking of an optical element in a variety of ways, as dictated by the particular marking requirements. With some adaptation, the same general apparatus and method may be used to either mark the surface of the optical element or the interior of the optical element, as necessary. The method avoids the use of masks and toxic chemicals, and is able to relatively quickly produce a mark of consistent form without the need for complex apparatus. Furthermore, the marks produced by the present invention can be viewed by the naked eye without the need for specialist viewing equipment or devices.

Detailed Description of the Invention

The present invention will now be described in relation to a preferred embodiment as illustrated in the following examples. However, it is to be appreciated that the following description is not to limit the generality of the above description. In the drawings:

Figure 1 is a schematic representation of apparatus suitable for use in a first preferred embodiment of the method of the present invention, in which the parts of the apparatus are labelled as follows:

1. Nd:YAG laser source (including power supply and frequency conversion stages)

2. Beam steering optics 3. X-axis galvanometer

4. Y-axis galvanometer

5. Beam focussing optics

6. X-Y-Z table for precise component positioning

7. Component to be marked (showing sample marking in the form of the letter 'S')

Referring to Figure 1 , the Nd:YAG laser source 1 outputs a laser beam at the required marking wavelength for the type of mark and material to be marked. This component may include the power source and any frequency conversion stages required. The laser source 1 will thus be capable of adjusting the pulse energy, frequency and any other necessary parameters as required for tuning the marking. The laser beam is able to be steered downwards by a mirror 2 onto two galvanometer mirrors (3 and 4). These two mirrors are scanned together to steer the beam in both the x & y axis to create the exact mark pattern required. The beam ideally passes through one or a combination of lenses to focus the beam at the correct location.

The component to be marked will be mounted on an x-y-z table 6 that is used to precisely align the component to an exact and known position for marking. The laser source 1 , the galvanometers (3 and 4) and the x-y-z table 6 will ideally be controlled via an external computer controller. In use, the laser source will supply pulses of radiation in combination with the galvanometer scanning to create the required pattern of sub-marks to create the overall mark required.

Finally, it will be appreciated that there may be other alterations and modifications made to the methods and apparatus described above that are also within the scope of the present invention.

Claims

1. A method of marking an optical element with a mark that is normally visible, the method including: a. focussing a laser beam from a neodymium-doped yttrium-aluminium- garnet (Nd:YAG) laser at the optical element; and b. forming on or within the optical element a series of discrete sub-marks; wherein the combination of the sub-marks provide the mark.

2. A method according to claim 1 wherein the optical element is an ophthalmic lens.

3. A method according to claim 1 wherein the optical element is an ophthalmic lens wafer.

4. A method according to claim 1 wherein the optical element is a mould for an ophthalmic lens.

5. A method according to claim 1 wherein the sub-marks are formed on the optical element using a laser beam having an operating wavelength of 266nm.

6. A method according to claim 1 wherein the step of forming sub-marks within the optical element is performed using the laser beam to create microscopic cracks in the body of the optical element.

7. A method according to claim 6 wherein the laser has an operating wavelength of 1064nm.

8. A method according to claim 6 wherein the laser has an operating wavelength of 532nm.

9. A method according to claim 6 wherein the laser has an operating wavelength of 355nm.

10. An optical element having a normally visible mark which has been provided using a neodymium-doped yttrium-aluminium-garnet laser.

11. A system for marking an optical element with a mark that is normally visible, the system including: a. a neodymium-doped yttrium-aluminium-garnet laser; b. a beam steering apparatus; c. a beam focusing apparatus; and d. a table; wherein the mark is provided by focussing the output of the laser at the optical element using the beam steering apparatus and the beam focusing apparatus, the optical element being secured to the table.