The invention relates to a method for machining a surface.

The invention relates particularly to the machining of a surface with a light beam, for instance from a laser. Radiating the beam of light onto a surface enables removal of particles from the surface. The size of the removed particles will substantially correspond here to the wavelength of the light beam and hereby lies between about 300 and 1500 nm.

It is an object of the invention to provide a method of the type stated in the preamble with which it is possible to remove from a surface particles with a size differing from the wavelength of the light used, and in particular being smaller than the wavelength of the light used.

The method of the type stated in the preamble according to the invention has for this purpose the steps of:

a) providing the surface for machining;

b) disposing at a determined distance from the surface a light source which is configured to emit an annular light beam;

c) the light source emitting the light beam in the direction of the surface, wherein the annular l ight beam causes an annular wave displacing inwardly in the outer face of the surface facing toward the light source, this wave coming together in a centre thereof, thus forming a peak for the purpose of removing a particle from the surface.

The amplitude of the annular wave which displaces inwardly in the outer face of the surface will increase in inward direction until it forms a peak in the centre of the wave, or in the centre of the annular light beam where it impinges upon the surface. This peak has an intensity such that it removes a particle from the surface, which particle has a size which depends on the energy, and so on the wavelength, of the light but is not limited to the wavelength itself. The particle can be both smaller and larger than the wavelength of the light beam.

For the purpose of forming the annular light beam the light source can be a circular light source covered in the centre by a circular cover element disposed coaxially therewith, which cover element has a diameter smaller than the diameter of the circular light source, so that an annular edge is left clear and the light source emits annular light.

The annular light beam emitted by the light source can for instance be a parallel light beam.

The light source is alternatively configured in step b) to emit a converging annular light beam, wherein the method further comprises the step, to be performed prior to step c), of:

d) focussing the light source relative to the surface such that the surface is not located at the focal point of the light beam to be emitted.

By focussing the light source such that the surface is not located at the focal point of the light beam to be emitted, the light beam impinges annularly upon the surface for the purpose of creating the wave displacing inwardly in the outer face of the surface. Focussing of the light source in this way can for instance take place by using optical elements such as lenses, but also by selecting a suitable distance of the light source relative to the surface.

The focussing in step d) preferably takes place such that the surface is disposed between the focal point of the light beam and the light source, i.e. at a distance from the light source shorter than the focal distance.

In an embodiment of the method according to the invention the light source emits light beams in step c) at a determined frequency in the direction of the surface.

By emitting a number of light beams at a determined frequency the waves will lie an increasingly shorter distance from each other toward the centre so that the travelling wave is amplified in the outer face and the peak formed in the centre acquires a very high intensity. The particles will in this way be removed from the surface in effective manner.

The number of light beams in step c) are in each case emitted particularly toward the same point or location on the surface. Once the number of light beams have been emitted at the determined frequency, a subsequent number of light beams which is the same or optionally different can be emitted at the same or optionally a different frequency to another point or location on the surface.

The number of light beams emitted to the same location is greater here than 50, preferably greater than 100. In a practical though not exclusive manner the number of light beams will lie between about 100 and 2000.

The frequency at which the number of light beams is emitted lies for instance between 100 kHz and 20 MHz, preferably between 1 and 15 MHz, more preferably between 5 and 10 MHz.

The light source is preferably an annular laser which emits light at a wavelength lying between 300 nm and 1500 nm.

According to the invention the energy per pulse is less than the amount of energy necessary to damage the surface of the material. Material will hereby not be removed directly from the surface by the laser beam, but only by the oscillation or wave created in the surface. The desired size of the particles can hereby be relatively small, in particular smaller than the size of the light beam. The energy per pulse is preferably less here than 5 microjoules.

The pulse duration is preferably shorter than a picosecond.

In another embodiment of the method according to the invention the method comprises the step of:

e) periodically displacing the light source relative to the surface for the purpose of removing a particle in each case at a different location in the surface.

The light source is displaced here such that the distance from the light source to the surface remains substantially the same. The light source and focussing thereof need hereby not be reset, and the removal of particles from the surface at different locations thereon can take place in simple manner.

The light source is preferably displaced here in each case after a number of light beams have been emitted at a determined frequency in step c).

The surface machined after step c) or d) is for instance suitable for the growth of bone structures.

Such surfaces have a surface structure characterized by very small dimensions, in particular smaller than the wavelength of light. Now that the method according to the invention is suitable for removing particles from a surface of a size which can be smaller than the wavelength of the light beam used, such a surface can be manufactured in very suitable manner using the method according to the invention.

The invention also relates to a machined surface which has been machined with the method according to the invention as described above, the method comprising the steps of:

a) providing the surface for machining;

b) disposing at a determined distance from the surface a light source which is configured to emit an annular light beam;

c) the light source emitting the light beam in the direction of the surface, wherein the annular light beam causes an annular wave displacing inwardly in the surface, this wave coming together in a centre thereof, thus forming a peak for the purpose of removing a particle from the surface.

A surface machined with the method according to the invention can be applied for diverse purposes for which a fine surface structure is required. The machined surface is for instance suitable for growth of bone structures.

The invention will be further elucidated with reference to figures shown in a drawing, in which:

figure 1 is a side view of the light source and the surface;

figure 2 is a perspective top view of the waves created in the outer face of the surface, figure 3 shows a cross-section of figure 2; and

figure 4 shows a machined surface which has been machined with the method according to the invention.

Figure 1 shows an annular laser 1 disposed a determined distance from a surface 2 for machining. Annular laser 1 is focussed on surface 2 such that surface 2, particularly the outer face 5 of surface 2 facing toward annular laser 1 , is located between the focal point 4 of the converging annular laser beam 3 emitted by annular laser 1 and the annular laser I, so that laser beam 3 is radiated annularly onto surface 2. Annular laser 1 emits laser beams 3 at a chosen frequency.

As shown in figures 2 and 3, each laser beam 3 causes an annular wave 6 displacing inwardly in outer face 5 of surface 2. The amplitudes of waves 6 will increase in inward direction until waves 6 form a peak 7 in the centre of the wave, i.e. in the centre of the annular laser beam 3 where it impinges upon surface 2. This peak 7 has an intensity such that particles of a determined size, which can be both larger and smaller than the wavelength of laser beam 3, are removed from surface 2.

Referring to figure 1, annular laser 1 can for instance be displaced laterally in direction 8, wherein the distance between annular laser 1 and surface 2 remains substantially the same so that a particle is removed in each case from surface 2 at a different location thereon. A surface machined in this way is shown in figure 4, which clearly shows the particles 9 removed from surface 2. The machined surface of figure 4 is for instance suitable for growth of bone structures.

The parameters affecting the size of the removed particles include:

- Energy per pulse;

- Wavelength;

- Pulse duration;

- Pulse frequency;

- Write pattern;

- Polarization of beam; and

- The material of the surface.

It is noted that the invention is not limited to the shown embodiments, but also extends to variants within the scope of the appended claims.