Patent Description:
<CIT> is an example of a laser drilling device which includes a laser beam source and a laser drilling head. The laser drilling head includes a beam manipulator system, in which a moving mirror is provided which is dynamically and reciprocally translatable along the direction of the incoming laser beam and tiltable about an axis, as well as a compensation system comprising wedges. The drilling head also includes a spinnable laser beam rotating system, which comprises rotation elements which permit the laser beam to traverse the surface of the work piece. This drilling device, however, is complicated in that multiple stages including multiple translatable/rotatable components are required to direct the laser beam to be incident on the surface of the work piece as appropriate. Further, adjustment of the size of the area to be drilled requires adjustment of multiple components such as the mirror in the beam manipulator system and the wedges in the compensation system.

<CIT> discloses a laser welding system and method. The system for welding a target and has an optical axis including a source of a laser beam, a rotatable diffraction grating converting the laser beam to a pair of laser spots rotating about the optical axis, and a lens focusing the pair of laser spots on the target.

<CIT> discloses a laser processing apparatus including an ultra-short pulse laser, a focusing optical system and a processing of a work piece by projecting a beam delivered through the focusing optical system onto the work piece. The focusing optical system has at least a pair of diffractive surface and a refractive surface.

<CIT> describes an apparatus for drilling vias or holes in a circuit board, wherein the apparatus includes an excimer laser and a Fresnel zone plate positioned parallel to the circuit board, with the distance between the Fresnel zone plate and the circuit board being the focal length of the Fresnel zone plate.

Therefore, it is desired to provide a simpler drilling device which is configured to rotate to drill a hole in a work piece and is simpler and easier to manufacture and adjust.

According to an aspect of the present invention, a drilling device is provided which comprises a light source configured to provide a light beam and a diffractive beam propagation device having a substantially planar surface. The light source is configured such that the light beam is incident on the planar surface of the diffractive beam propagation device. The diffractive beam propagation device is configured to propagate the light beam as one or more propagated beams such that the one or more propagated beams directly surround an area with a substantially circular shape by forming one or more cones. The drilling device further comprises a focusing system for focusing the one or more propagated beams on a substantially ringlike area. The one or more propagated beams are incident on the focusing system and thereby become one or more direction-changed beams. The substantially ringlike area which is surrounded by the one or more propagated beams is perpendicular to an optical axis of the diffractive beam propagation device and/or an optical axis of the focusing system.

According to one embodiment, the diffractive beam propagation device may be further configured to rotate around a rotation axis substantially normal to the planar surface of the beam propagation device. Due to the rotation of the diffractive beam propagation device also the one or more propagated beams rotate. Thus, the one or more propagated beams surround an area with a substantially circular shape when being integrated over time.

The diffractive beam propagation device according to the present invention comprises a circular diffraction grating. Due to the circular diffraction grating the one or more propagated beams directly, i.e. also when being not integrated over time, surround an area with a substantially circular shape. For the circular diffraction grating, the one or more propagated beams forms one or more cones. In particular, the one or more propagated beams forms one cone in case that only +/-<NUM> order occurs, and two cones in case that +/-<NUM> order and +/-<NUM> order occur. The cone is composed of the overlap of the diffracted beams at different azimuths.

"Planar" in the context of this application may describe a surface which closely resembles or is aligned with a plane. Such a surface may be characterized by relatively small "imperfections" or deviations from a truly perfect planar surface. For example, real-word a planar surface may contain ridges or crevices which have nonzero heights compared to the "perfect" planar surface. A three-dimensional object extends has dimensions in each of an X direction, a Y direction, and a Z direction (in a right-handed Cartesian coordinate system). A particular object, such as for example a diffractive beam propagation device, may have at least one surface which is substantially aligned with a plane, as an example with the Y-Z plane. The object may for example have the shape of a rectangular prism, having a length in the Y direction, a width in the Z direction, and a thickness in the X direction. In a real-world object, the planar surface aligned with the Y-Z plane will, as described above, have imperfections which, when compared to the thickness of the objection in the X direction, may be relatively small. For example, heights of ridges and crevices constituting imperfections/deviations in a "planar surface" may have values which are orders of magnitudes smaller than the thickness of the object, for example less than <NUM>/<NUM>th or less than <NUM>/<NUM>th of the thickness.

The light source is configured to provide a light beam. The light source is configured to provide a light beam which is incident on the planar surface of the diffractive beam propagation device, the light beam having characteristics appropriate for the particular application of the drilling device. The light source may, in an exemplary embodiment, be a laser light source configured to provide a laser beam with the appropriate power, coherence, wavelength, pulse length, and pulse cycle for a particular drilling application. For example, the laser light source may be configured to provide a laser beam with a wavelength within the visible spectrum of light, for example a green laser beam with a wavelength of <NUM> or <NUM> for drilling holes or curves with a width of <NUM> to <NUM>. In another example, the light source may be configured to provide a laser beam with a wavelength within the infrared spectrum of light, for example a laser beam with a wavelength in the range of about <NUM> to <NUM>. In another example, the light source may be configured to provide a laser beam with a wavelength within the ultraviolet spectrum of light, for example a laser beam with a wavelength in the range of about <NUM> to <NUM>.

The diffractive beam propagation device is configured to propagate the light beam as one or more propagated beams. The diffractive beam propagation device may be of any type suitable for propagating the light beam as the one or more propagated beams. Advantageously, the drilling device can be small in size.

In some embodiments, the diffractive beam propagation device may comprise or consist of a diffraction grating. A diffraction grating may generally comprise grooves which are, for example, etched onto a planar surface of the grating. The term "planar" here refers to the characteristic of the surface before any such etching operation. That is, after etching grooves on a surface, the surface profile has necessarily changed since the grooves have nonzero depths. Nevertheless, the term "planar surface" is stilled used in this application to refer to that same surface as the non-etched portion of the surface is still substantially aligned with a plane.

In some embodiments, the diffractive beam propagation device may comprise or consist of a reflective diffraction grating. The light beam may be incident on a "front" side of the planar surface of the diffractive beam propagation device such that the light beam is propagated as one or more propagated beams which are reflected away from the front side of the planar surface of the diffractive beam propagation device. In some embodiments, exactly one propagated beam of the one or more propagated beams comprises most of the total energy of the light beam, e.g. <NUM>-<NUM>%, <NUM>% or more, <NUM>% or more, or, more preferably, <NUM>% or more. In other embodiments, exactly two of the one or more propagated beams together comprise most of the total energy of the light beam. In these embodiments, the two propagated beams may each comprise approximately the same amount of energy.

The reflective diffraction grating may be one as known in the state of the art. For example, the reflective diffraction grating may comprise or consist of a grating waveguide mirror (GWM) comprising a fused silica substrate, a waveguide layer, and a grating with a period. The GWM may be characterized by a Littrow angle, the Littrow angle being determined based on the wavelength of the light beam and the period of the grating. The Littrow angle refers to the angle with respect to the normal of the planar surface of the GWM at which a light beam incident at this angle results in a -<NUM>st-order (or other order) diffracted beam at that same angle. The Littrow angle will be explained in more detail below along with the description of the figures.

In other embodiments, the diffractive beam propagation device may comprise or consist of a transmissive diffraction grating. The light beam may be incident on a "reverse" side of the planar surface of the transmissive diffraction grating such that the light beam is propagated from the reverse side of the planar surface through the "front" side of the planar surface of the grating. For example, the light beam may be split into one or more, particularly at least two, propagated beams, e.g. two, four or six propagated beams, which together comprise most of the total energy of the light beam, e.g. at least <NUM>%, particularly <NUM>-<NUM>%, <NUM>% or more, <NUM>% or more, or, more preferably, <NUM>% or more. A plurality of the propagated beams (e.g., exactly two of the propagated beams) may each comprise approximately the same amount of energy. Under normal incidence in the transmissive or transmission grating, there may be two (+/-<NUM>) or four (+/-<NUM>, +/-<NUM>), or six (+/-<NUM>, +/-<NUM>, +/-<NUM>), etc., diffracted orders. This is due to the symmetry of the configuration. However, it is also possible to design a transmission grating which has only one diffracted beam in transmission. For this purpose, the angle of incidence and/or the grating parameters need to be adapted correspondingly.

For example, the light beam is incident on the diffractive beam propagation device at an angle substantially normal to the planar surface of the diffractive beam propagation device such that the at least two propagated beams comprise two <NUM>st-order beams (i.e., a +<NUM>st-order beam and a -<NUM>st-order beam).

In some examples, a <NUM>-order beam is substantially canceled due to the grating depth of the diffractive beam propagation device, the grating depth being determined based on at least one of the wavelength of the one or more propagated beams, an index of refraction of the diffractive beam propagation device, and a duty cycle of the diffractive beam propagation device.

In some examples, nth-order diffraction beams are substantially dampened by means of one or more apertures provided in the diffractive beam propagation device, wherein n in an integer equal to or greater than <NUM>.

In other examples, the diffraction grating may be a blazed grating having a constant line spacing along a lateral direction of the diffraction grating. The blazed grating may have a triangular, sawtooth-shaped cross section.

According to the present invention, the focusing system has an optical axis wherein the one or more propagated beams are incident on the focusing system and thereby become one or more direction-changed beams. That is, the portion(s) of the light beam which is/are diffracted but not direction-changed by the focusing system is/are referred to as propagated beams, and the portion(s) of the light beam which are diffracted and is/are direction-changed by the focusing system are referred to as direction-changed beams. Any focusing system suitable for this purpose may be employed. In some embodiments, the focusing system may consist of a single lens with a defined focal length to its focal plane. In some embodiments, the focusing system comprises further optical elements such as one or more of: lenses, mirrors, diffraction or other gratings, Fresnel lenses, and/or prisms.

In some examples, the diffractive beam propagation device may be provided such that an origin area of the one or more propagated beams may be substantially located at a focal plane of the focusing system, thereby changing the propagation directions of the propagated beams by the focusing system such that the propagated beams become direction-changed beams which are substantially parallel to each other. The origin area may correspond substantially to a single point or a small area. In some examples, the origin area may be substantially located at a focal point of the focusing system, the focal point corresponding to a point where all light beams originating or passing through this point which are incident on the focusing system become direction-changed beams which are substantially parallel to each other and to the optical axis of the focusing system. The focal point may correspond to an intersection of the optical axis with the focal plane.

In some examples, the diffractive beam propagation device may be provided such that the origin area of the propagated beams may be substantially located away from a focal plane of the focusing system, thereby changing the propagation directions of the propagated beams resulting in direction-changed beams which are substantially not parallel. The focal length of the focusing system may be in the range of <NUM> to <NUM>, and particularly in the range of <NUM> to <NUM>.

In this embodiment, propagated beams originate at the origin area which is either closer to the focusing system than the focal plane of the focusing system or farther away from the focusing system than the focal plane of the focusing system. In some examples, the origin area is located along the optical axis, though not in the focal plane of the focusing system.

In another embodiment, the diffractive beam propagation device and/or focusing system are further configured to translate relative to each other, relative to a work piece, or relative to other components of the drilling device including the light source. That is, some components of the drilling device may be fixed in location while other components may be configured to translate relative to the fixed components, for example substantially along the optical axis of the focusing system. In another embodiment, translation of the diffractive beam propagation device and/or focusing system from a first position to a second position may change a first distance and angle between the direction-changed beams when the diffractive beam propagation device is at the first position, to a second distance and angle between the direction-changed beams when the diffractive beam propagation device is at the second position.

In some examples, the distance between the direction-changed beams is set at least in part based on at least one of a grating period of the diffractive beam propagation device, a grating depth of the diffractive beam propagation device, the focal length of the focusing system, a wavelength of the light beam and the one or more propagated beams, and the origin area of the one or more propagated beams. In other words, the distance between the direction-changed beams may be determined at least in part by characteristics of the diffraction grating and the light beam.

In some examples, the diffraction grating is configured to split the light beam into four split beams in a two-dimensional arrangement. To this end, the diffraction grating may comprise a circular grating or a Fresnel lense. According to these examples, a cone of light can be obtained.

In some embodiments, the drilling device further comprises a work piece, wherein the one or more propagated beams or the one or more direction-changed beams are configured to be incident on a surface of the work piece.

In some examples, the drilling device may be configured to drill a hole in the work piece by rotation of the diffractive beam propagation device around the rotation axis. In some examples, rotation of the diffractive beam propagation device around the rotation axis may be configured to cause the propagated beams or the direction-changed beams to drill one substantially circular, cylindrical, or conical hole.

Preferably, the drilling device comprises a beam splitter for splitting the light beam into a plurality of individual light beams. Further, the drilling device preferably comprises for each of the individual light beams a corresponding individual diffractive beam propagation device, wherein the individual diffractive beam propagation devices are configured and aligned such that each of the individual light beams is incident on the corresponding individual diffractive beam propagation device. Thereby, a predetermined arrangement of holes can be created, e.g. in a circular design.

Another aspect of the invention relates to use of a drilling device according to the preceding description for drilling a hole in a work piece.

Another aspect of the invention relates to a method for drilling a hole in a work piece, comprising the steps of providing a light source, a diffractive beam propagation device having a substantially planar surface, and a focusing system; wherein the light source provides a light beam incident on the planar surface of the diffractive beam propagation device, the diffractive beam propagation device comprises a circular diffraction grating that propagates the light beam as one or more propagated beams such that the one or more propagated beams directly surround an area with a substantially circular shape by forming one or more cones; the one or more propagated beams are incident on the focusing system and thereby become one or more direction-changed beams, and wherein the one or more propagated beams are focused by the focusing system on a substantially ringlike area which is surrounded by the one or more propagated beams and which is perpendicular to an optical axis of the diffractive beam propagation device and/or an optical axis of the focusing system. For example, the diffractive beam propagation device may rotate around a rotation axis substantially normal to the planar surface of the diffractive beam propagation device. Incidence of the rotating split beams on a surface of a work piece may result in drilling of the work piece.

In preferred embodiments of the above method, the result of the step of providing a light source and a diffractive beam propagation device may be any drilling device according to the invention including the above embodiments, i.e. according to the claims.

According to an example, a drilling device is provided which comprises a light source configured to provide a light beam and a diffractive beam propagation device having a substantially planar surface. The light source is configured such that the light beam is incident on the planar surface of the diffractive beam propagation device. The diffractive beam propagation device is configured to propagate the light beam as one or more propagated beams. The diffractive beam propagation device is further configured to rotate around a rotation axis substantially normal to the planar surface of the beam propagation device. Due to the rotation of the diffractive beam propagation device also the one or more propagated beams rotate. Thus, the one or more propagated beams surround an area with a substantially circular shape when being integrated over time.

According to the present invention, the diffractive beam propagation device comprises (and particularly is) a circular diffraction grating. Due to the circular diffraction grating the one or more propagated beams directly, i.e. also when being not integrated over time, surround an area with a substantially circular shape.

Unless otherwise indicated, the following figures are schematic diagrams. Any reference to the Cartesian coordinate system in the figures relates to a right-handed Cartesian coordinate system in which, by convention, the depicted arrows illustrate a "positive" direction.

The following detailed description relates to examples and an exemplary embodiment of the present invention. Other embodiments of the invention are possible within the scope of the invention as defined by the appended claims.

<FIG> illustrates a drilling device <NUM> according to an example not claimed but helpful for understanding the present invention. The drilling device <NUM> comprises a light source <NUM>, which is configured to provide a light beam <NUM>, and a diffractive beam propagation device <NUM> having a substantially planar surface <NUM>. The light source <NUM> is configured such that the light beam <NUM> is incident on the planar surface <NUM> of the diffractive beam propagation device <NUM>. The diffractive beam propagation device <NUM> is configured to propagate the light beam <NUM> as one or more propagated beams <NUM> and to rotate around a rotation axis <NUM> substantially normal to the planar surface <NUM> of the diffractive beam propagation device <NUM>. In some embodiments, the drilling device <NUM> may be used to direct the propagated beams <NUM> to be incident on a surface <NUM> of a work piece <NUM>. Incidence of the propagated beams <NUM> on the work piece <NUM> may heat and/or melt and/or vaporize and/or expel material of the work piece <NUM> to produce or extend holes and/or cuts in the work piece <NUM>.

The diffractive beam propagation device <NUM> extends along a length direction (aligned with the Y direction), along a width direction (aligned with the Z direction) and along a thickness direction (aligned with the X direction) and has a substantially planar surface <NUM> (aligned with an Y-Z plane). "Substantially planar surface" in this application may, as explained above, refer to a surface of an object (for example a diffractive beam propagation device) which is substantially flat in profile compared to an overall thickness of the object. For example, a substantially planar surface may be one in which deviations in heights (e.g. in the X direction) of ridges/crevices on the surface compared to the plane (e.g. the Y-Z plane) of the surface of a component are small compared to an overall thickness of the component in the direction (X direction) perpendicular to the planar surface (Y-Z plane). As an example, ridges and/or craters on a planar surface may have heights whose magnitudes are less than <NUM>/<NUM>th of the thickness of the component, or preferably less than <NUM>/<NUM>th of the thickness of the component. A "substantially planar surface" may also refer to a surface of a component which is substantially planar according to the above definition before material is added or removed. As will be explained below, the diffractive beam propagation device <NUM> may comprise or consist of a diffraction grating having grooves. The grooves may for example be etched on a surface which was substantially planar before the etching process was carried out. In this application, the surface of the diffractive beam propagation device may still be referred to as a planar surface. The grooves may alternatively be made by means of an index modification using, e.g., a femtosecond laser.

The light source <NUM> is configured to provide a light beam <NUM>. The light source <NUM> is configured to provide the light beam <NUM> incident on the planar surface <NUM> of the diffractive beam propagation device <NUM> with characteristics appropriate for the particular application of the drilling device <NUM>. The light source <NUM> may, in an exemplary embodiment, be a laser light source configured to provide a laser beam with the appropriate power, coherence, wavelength, pulse length, and pulse cycle or repetition rate for a particular application. For example, the laser light source may be configured to provide a laser beam with a wavelength within the visible spectrum of light, for example a green laser beam with a wavelength of <NUM> or <NUM> for drilling holes or lines with a width of <NUM> to <NUM>. In another example, the light source may be configured to provide a laser beam with a wavelength within the infrared spectrum of light, for example a laser beam with a wavelength in the range of about <NUM> to <NUM>. In another example, the light source may be configured to provide a laser beam with a wavelength within the ultraviolet spectrum of light, for example a laser beam with a wavelength in the range of about <NUM> to <NUM>.

The diffractive beam propagation device <NUM> has a substantially planar surface <NUM>. The diffractive beam propagation device <NUM> generally has a length extending along a length direction, for example the Y direction as depicted in <FIG>; a width extending along a width direction, the Z direction; and a thickness extending alone a thickness direction, the X direction. With the sheet of paper on which <FIG> is printed considered to be a cross-section of an X-Y plane with no Z component, the Z direction is thus the direction perpendicular to the sheet of paper "into" and "out of" the sheet of paper. The length direction (Y) and the width direction (Z) characterize the two dimensions of the planar surface <NUM> (Y-Z plane).

In the example of <FIG>, the diffractive beam propagation device <NUM> comprises or consists of a reflective diffraction grating, for example such as the grating waveguide mirror (GWM) <NUM> depicted in <FIG>, having grooves <NUM> in a grating layer <NUM> each of substantially uniform width L in a Y direction (i.e. substantially parallel to the length direction of the diffractive beam propagation device <NUM>). In another example, the widths L of the grooves <NUM> may not be uniform along the diffraction grating. The grooves <NUM> are further characterized by a substantially uniform depth σ in an X direction substantially parallel to the width direction of the diffractive beam propagation device <NUM>. In another example, the depths σ of the grooves <NUM> may not be uniform along the lateral direction (the Y direction). Further, the grooves <NUM> are characterized by a groove period A substantially along the Y direction, one period along the Y direction being defined as the distance from the side of one groove <NUM> to the corresponding side of an adjacent groove <NUM>, as indicated in <FIG>. The groove period A may be, in an example, substantially uniform along the Y direction. In another example, the groove period A may not be uniform along the Y direction. A duty cycle of the diffraction grating may be given by the widths L of the grooves <NUM> divided by the period A. The grooves <NUM> are also characterized by a length in the Z direction (i.e. parallel to the width direction of the diffractive beam propagation device <NUM>). The grating parameters depend on many factors such as the laser wavelength or the diffraction angle relating to the desired size of holes to be drilled. However, for typical lasers and in case that the grating is used as a transmission grating, the grating period A can be, for example, in the range of <NUM>,5λ to 100λ or 1λ to 100λ, where λ is the wavelength of the laser. The depth σ of the grating corresponds or is typically in the range of the wavelength λ, so that the <NUM>th transmitted order can be canceled. In case of a reflective grating, the grating period A can be, for example, in the range of <NUM>-<NUM>, but also in this case, the value may depend on many factors such as the laser wavelength or a separation angle.

The grating layer <NUM> of the GWM <NUM> may be stacked on a waveguide layer <NUM>, which may in turn be stacked on highly reflective (HR) mirror <NUM>. HR mirror <NUM> itself may comprise alternating layers of materials with a high refractive index (HRI) and materials with a low refractive index (LRI). HRI materials may be considered to be those with a refractive index between <NUM> and <NUM>, such as for example (but not limited to) Ta<NUM>O<NUM>, HfOs, Nb<NUM>O<NUM>, TiO<NUM>, Al<NUM>O<NUM>, and Si<NUM>Ni<NUM>. LRI materials may be considered to be those with a refractive index between <NUM> and <NUM>, such as for example (but not limited to) SiO<NUM> and MgF<NUM>. The HR mirror may then be stacked on a substrate, such as fused silica. In this respect, reference is made to <NPL> and to the International Patent Application <CIT> which is included by reference.

Referring again to <FIG>, the diffractive beam propagation device <NUM> is configured to propagate the light beam <NUM> as one or more propagated beams <NUM>. The diffractive beam propagation device <NUM> may be of any type suitable for propagating the light beam <NUM> as the one or more propagated beams <NUM>.

The diffractive beam propagation device <NUM> may be configured to diffract the light beam <NUM> such that one propagated beam <NUM> comprises most, e.g. <NUM>% or more, of the total energy of the light beam <NUM>. In the example of <FIG>, the propagated beam <NUM> is a -<NUM>st-order diffracted beam. The light beam <NUM> is propagated (i.e. diffracted) substantially at an origin area <NUM> at the diffractive beam propagation device <NUM>. The origin area <NUM> may, in some examples, be located substantially at an intersection between the rotation axis <NUM> and the planar surface <NUM> of the diffractive beam propagation device <NUM>. This situation is illustrated in <FIG>, for example. In some examples, the diffractive beam propagation device <NUM> may also diffract the light beam <NUM> into <NUM> and/or <NUM>nd or higher-order beams.

The diffractive beam propagation device <NUM> is provided such that the rotation axis <NUM> is substantially perpendicular to the planar surface <NUM> of the diffractive beam propagation device <NUM> (i.e., the rotation axis <NUM> is parallel to the X direction). The planar surface <NUM> of the diffractive beam propagation device <NUM> is substantially aligned with an Y-Z plane (with no X component) in <FIG>, the Z direction considered to be the direction perpendicular to the X-Y plane in the figure. In other words, the sheet of paper on which <FIG> is printed may be considered to be a cross-section of a X-Y plane with no Z component, and the Z direction is thus the direction perpendicular to the sheet of paper "into" and "out of" the sheet of paper.

The light beam <NUM> may be incident on the planar surface <NUM> of the diffractive beam propagation device <NUM> at a light source angle θs with respect to the rotation axis <NUM> (again, the rotation axis <NUM> being substantially perpendicular to the planar surface <NUM> of the diffractive beam propagation device <NUM>), as illustrated in <FIG>. Based on the properties of the diffraction grating of the diffractive beam propagation device <NUM>, the -<NUM>st-order beam (the propagated beam <NUM>) may be diffracted at a diffraction angle θD with respect to the direction perpendicular to the surface of the diffractive beam propagation device <NUM> (the direction perpendicular to the surface of the diffractive beam propagation device <NUM> being parallel to the rotation axis <NUM> in this example). The propagated beam <NUM> may be incident on a work piece <NUM>.

<FIG> illustrates another example not claimed but helpful for understanding the present invention. The diffractive beam propagation device <NUM> of <FIG> may be similar or the same as the one in <FIG> and/or <NUM>. In <FIG>, the light source angle θS approaches (i.e., is close but not equal to) the Littrow angle θLitt of the configuration. The Littrow angle θLitt of a configuration including a diffraction grating refers to the angle of incidence of a light beam on a diffraction grating at which a diffracted beam of a particular order m is diffracted back at the same angle. In the example of <FIG>, if the light beam <NUM> were incident on the diffractive beam propagation device <NUM> at the (-<NUM>st-order) Littrow angle θLitt (i.e. θS = θLitt), the -<NUM>st-order propagated beam <NUM> would be diffracted back toward the light source <NUM> at the same angle, the Littrow angle θLitt, (i.e. θD = θS = θLitt). In other words, for example, a light beam incident on a diffraction grating in a Littrow configuration (i.e. at the Littrow angle) may have the result that a -<NUM>st-order beam diffracted from the light beam is counter-propagated at that same angle, the Littrow angle. The Littrow configuration is known in the state of the art and is characterized by the following equation: <MAT> where θLitt is the Littrow angle, m is the grating diffraction order, λ is the wavelength of the light beam (the incident beam), and A is the grating period. Since the grating diffraction order m, the wavelength λ of the light beam, and the grating period A may be known, θLitt may be determined and thus also known for a particular configuration.

In <FIG>, the light source angle θS is "close" to but not equal to the Littrow angle θLitt (which is indicated in <FIG> by the dotted and dashed line) such that the -<NUM>st-order beam 18a of the propagated beams <NUM> (18a, 18b) is diffracted at an angle θD slightly smaller than θLitt. In other words, <FIG> illustrates a configuration, where the Littrow condition is not (but almost) met. In general, the light source angle θS may depend on the size of the hole to be drilled and/or a lens <NUM> (which is shown in <FIG>). Specifically, the light source angle θS is slightly larger than (e.g. less than <NUM>° larger than) the Littrow angle θLitt and the -<NUM>st-order beam 18a is diffracted at a diffraction angle θD slightly smaller than (e.g. less than <NUM>° smaller than) the Littrow angle θLitt. The <NUM>-order beam 18b corresponds to reflection of the light beam <NUM> and has a reflection angle θR substantially equal to the light source angle θS. In this example, rotation of the diffractive beam propagation device <NUM> around the rotation axis <NUM> results in the drilling of a slightly elliptical-shaped hole in the work piece <NUM> since diffraction angle θD is slightly larger than reflection angle θR.

<FIG> illustrates another example not claimed but helpful for understanding the present invention, in which the diffractive beam propagation device <NUM> comprises or consists of a transmissive diffraction grating, wherein the diffractive beam propagation device <NUM> is configured to split the light beam <NUM> into at least two propagated beams <NUM> (<NUM>+, <NUM>-, collectively referred to as "propagated beams <NUM>"), wherein two of the propagated beams <NUM> together preferably comprise at least <NUM>%, more preferably at least <NUM>% and most preferably at least <NUM>% (or further preferably at least <NUM>%) of the total energy of the light beam <NUM>. The two propagated beams <NUM> may each comprise approximately the same amount of energy. The diffractive beam propagation device <NUM> may, for example, comprise or consist of a diffraction grating comprising fused silica.

Like the diffractive beam propagation device <NUM> of <FIG> and <FIG>, diffractive beam propagation device <NUM> is characterized by grooves <NUM> having widths L, depths σ, and a period A, each of which may or may not be uniform along the diffraction grating. The diffractive beam propagation device <NUM> also has a planar surface <NUM> substantially aligned with the Y-Z plane of <FIG>. For example, the light beam <NUM> is incident along an incidence direction <NUM> on one side (along the X direction) of the diffractive beam propagation device <NUM>, which may be referred to as the "reverse" side, at an angle perpendicular to the planar surface <NUM> of the diffractive beam propagation device <NUM> (i.e. perpendicular to the Y-Z plane). In some examples, the incidence direction <NUM> may substantially corresponds to the rotation axis <NUM>, as shown in <FIG>. The diffractive beam propagation device <NUM>, comprising or consisting of a transmissive diffraction grating, is configured to allow the light beam to be transmitted through the diffractive beam propagation device <NUM> toward the other side (along the X direction) of the diffractive beam propagation device <NUM>, which may be referred to as the "front" side. The diffraction grating may be arranged on the "front" and/or the opposite side, i.e. the "back" side, of the diffractive beam propagation device <NUM>.

The diffractive beam propagation device <NUM> is configured to diffract/split the light beam <NUM> substantially at an origin area <NUM> into the at least two propagated beams <NUM>. The origin area <NUM> may, in some examples, be located substantially at an intersection between the rotation axis <NUM> and the surface of the diffractive beam propagation device <NUM>. This situation is illustrated in <FIG>, for example. For example, the at least two propagated beams <NUM> comprise a +<NUM>st-order diffracted beam <NUM>+ and a -<NUM>st-order diffracted beam <NUM>-. The +<NUM>st-order diffracted beam <NUM>+ is diffracted at a positive diffraction angle θD+ with respect to the incidence direction <NUM> of the light beam <NUM>, while the -<NUM>st-order diffracted beam <NUM>- is diffracted at a negative diffraction angle θD-with respect to the incidence direction <NUM> of the light beam <NUM>. The magnitudes of the positive diffraction angle θD+ and the negative diffraction angle θD- may be substantially equal. That is, the following equation may be substantially fulfilled: <MAT>.

In some examples, the propagated beams <NUM> may be incident on a surface of a work piece <NUM>. In the case that a surface <NUM> of the work piece <NUM> is aligned substantially parallel to the planar surface <NUM> of the diffractive beam propagation device <NUM> (i.e. along the Y-Z plane), angles of incidence θI+, θI- of the respective propagated beams <NUM>+, <NUM>- with respect to the surface <NUM> of the work piece may be substantially equal to the respective positive and negative diffraction angles θD+, θD-. The propagated beams <NUM> may be incident on the surface <NUM> of the work piece <NUM> separated by a distance D, as illustrated in <FIG>.

In some examples, it may be desired to substantially reduce a <NUM>-order beam which would otherwise be incident on the work piece <NUM> (or on a focusing system, which will be described later). A <NUM>-order beam <NUM> may be present at an angle of substantially zero from the incidence direction <NUM> of the light beam <NUM> on the diffractive beam propagation device <NUM>, as shown in <FIG>. The grating depth σ of the diffractive beam propagation device <NUM> may be configured based on the wavelength of the light beam <NUM> and/or an index of refraction ns of the diffraction grating and may be configured to reduce the <NUM>-order beam <NUM>. In order to cancel the <NUM>th transmitted order, the grating structure is preferably configured to introduce a π-phase shift. In a scalar approximation, this phase shift is equal to <NUM>·σ·(n-<NUM>), where n is the refractive index of the material in which the grating is integrated. In case of a grating with a high aspect-ratio and for a grating period in the range of the wavelength, then a more precise formula would take into account the indices of modes excited in the grating region and σ = λ / <NUM>·(ne<NUM> - ne<NUM>), where ne<NUM> and ne<NUM> are the refrective indices of the excited modes.

In some examples, it may additionally or alternatively be desired to substantially reduce <NUM>nd or higher-order split beams which would otherwise be incident on the work piece <NUM> (or on a focusing system, which will be described later). For example, <NUM>nd-order split beams <NUM>+ and <NUM>- (which may be collectively referred to as "<NUM>nd-order split beams <NUM>") may be present respectively at <NUM>nd-order diffraction angles of θD2+ and θD2- from the incidence direction <NUM>, as shown in <FIG>. The magnitudes of the <NUM>nd-order diffraction angles θD2+, θD2- of the <NUM>nd-order split beams <NUM> from the optical axis <NUM> may be respectively smaller than the magnitudes of the <NUM>st-order diffraction angles θD1+, θD1- of the <NUM>st-order propagated beams <NUM> as shown in <FIG>. To reduce the effects of the <NUM>nd-order (or higher) beams <NUM>, an aperture <NUM> as shown in <FIG> may be provided integrally, attachably, or separately from the diffractive beam propagation device <NUM> such that <NUM>nd or higher-order split beams <NUM> of angles θD2, each respectively greater in magnitude than those θD1 of the <NUM>st-order propagated beams <NUM>, are substantially not able to exit the aperture <NUM> where they would otherwise eventually be incident on the work piece <NUM> (or on a focusing system, as described below).

According to the invention, a drilling device <NUM> including a light source <NUM> and a diffractive beam propagation device <NUM> further includes a focusing system <NUM>, the focusing system <NUM> having an optical axis <NUM>, wherein the one or more propagated beams <NUM> are incident on the focusing system <NUM> thereby becoming one or more direction-changed beams <NUM>. That is, the focusing system <NUM> is provided to change the direction of the propagated beams <NUM>, such that they are further propagated as direction-changed beams <NUM>+ and <NUM>- (hereby collectively referred to as "direction-changed beams <NUM>"). Any focusing system <NUM> suitable for this purpose may be employed. For example, focusing system <NUM> consists of a single lens with a focal length f to its focal plane <NUM>, as shown in <FIG>. In the example of <FIG>, a drilling device <NUM> comprises a focusing system <NUM> and a diffractive beam propagation device <NUM> comprising or consisting of a transmissive diffraction grating such as those depicted in <FIG> and described above. However, it is to be understood that the drilling device <NUM> may also comprise a focusing system <NUM> and a diffractive beam propagation device comprising or consisting of a reflective diffraction grating such as one of those depicted in <FIG> and <FIG> and described above.

Propagated beams <NUM> originating from substantially the same origin area <NUM> when the origin area <NUM> is located substantially at a point along the focal plane <NUM> of the focusing system <NUM> which are incident on the focusing system <NUM> may result in direction-changed beams <NUM> which are substantially parallel to each other. The term "origin area" in this application refers to a substantially single and substantially small location or point which may in practice be small and disc or sphere-shaped. For example, a diameter of such a small disc of sphere-shaped "origin area " may be on the order of millimeters or micrometers.

Propagated beams <NUM> originating from an origin area <NUM> farther than the focal length f away from the focusing system <NUM> which are incident on the focusing system <NUM> may result in direction-changed beams <NUM> which propagate toward each other (i.e. converge) along the component of their propagation direction parallel to the optical axis <NUM> (i.e. along the X direction), as shown in <FIG>, which corresponds to an example of a drilling device <NUM> comprising a focusing system <NUM>.

Propagated beams <NUM> originating from a location <NUM> closer than the focal length f to the focusing system <NUM> which are incident on the focusing system <NUM> may result in direction-changed beams <NUM> which propagate away from each other (i.e., diverge) along the component of their propagation direction parallel to the optical axis (along the X direction).

In the example of <FIG>, the light source <NUM> is configured to provide a light beam <NUM> along an incidence direction <NUM> which is substantially parallel to and aligned with the optical axis <NUM>. The propagated beams <NUM> originate at an origin area <NUM> slightly farther from the focal plane <NUM> of the focusing system <NUM> such that the direction-changed beams <NUM> are incident on a work piece <NUM> at respective incidence angles θI+, θI- not equal to zero with respect to the optical axis <NUM>. For example, direction-changed beams <NUM> may be incident on a surface <NUM> of the work piece <NUM> at an angle of <NUM>° to <NUM>° (or - <NUM>° to <NUM>°) with respect to the optical axis <NUM> (the X direction), or from the perpendicular of the surface <NUM> of the work piece <NUM> in the case that the surface <NUM> of the work piece <NUM> is substantially planar and is substantially parallel to the planar surface <NUM> of the diffractive beam propagation device <NUM>. The propagation direction of the propagated beams <NUM> and the direction-changed beams <NUM> may comprise a horizontal component in an X direction and a vertical component in a Y direction in <FIG>. For example, depending on the desired hole size, the diffractive beam propagation device <NUM> can be distanced from the focal plane <NUM> by a value in the range of <NUM> to <NUM>.

The terms "horizontal" and "vertical" may be used with respect to the earth; that is, "horizontal" may refer to a direction or a plane substantially parallel or tangent to the surface of the earth while "vertical" may refer to a direction or a plane substantially perpendicular the surface of the earth. In some examples, the X direction may correspond to horizontal and the Y direction may correspond to vertical. In other examples, the X direction may correspond instead to vertical and the Y direction may correspond to horizontal. In still other examples, the X and Y directions may not correspond to horizontal or vertical, and the drilling device may be configured at a particular angle with respect to the surface of the earth. As a convention, a positive angle may refer to a clockwise direction from a reference axis while a negative angle may refer to a counterclockwise direction form a reference axis.

For example, the propagated beams <NUM> substantially consist of two <NUM>st-order beams, a positive and a negative <NUM>st-order beam <NUM>+, <NUM>-, separated from each other by a diffraction angle θD + θD-. A <NUM>-order beam and <NUM>nd or higher order beams may be substantially suppressed as explained above, e.g. in the example illustrated in <FIG>. In the case that the incidence direction <NUM> of the light beam <NUM> is provided substantially along the optical axis <NUM> of the focusing system <NUM>, as shown in <FIG>, the propagated beams <NUM> will each be provided substantially at a same magnitude of a diffraction angle from the optical axis <NUM>, i.e. |θD+|=|θD-|. In other examples, the light beam <NUM> may be provided in an incidence direction <NUM> substantially parallel to but not substantially the same as the optical axis <NUM> or may instead not be provided substantially parallel to the optical axis <NUM>.

In another example, origin area <NUM> of the propagated beams <NUM> is provided substantially at a point along the focal plane <NUM> of the focusing system <NUM>. Thus, as explained above, the propagated beams' <NUM> incidence on the focusing system <NUM> results in substantially parallel direction-changed beams <NUM>. The direction-changed beams <NUM> may be incident on a work piece <NUM>. For a work piece <NUM> with a substantially planar surface <NUM> substantially parallel to the planar surface <NUM> of the diffractive beam propagation device <NUM> (i.e. aligned with a Y-Z plane), the direction-changed beams <NUM> may be incident on the work piece <NUM> at points located along the Y plane at the surface <NUM> of the work piece <NUM> separated by a distance D. In the case of direction-changed beams <NUM> which are parallel, as in this example, the distance between the direction-changed beams <NUM> may remain substantially constant along the X direction from the focusing system <NUM>.

This diffraction angle θ = θD+ + θD- and the distance D between the parallel direction-changed beams <NUM> may be determined by the following equations: <MAT> <MAT>.

However, for improved drilling in certain applications, it may be desired to provide direction-changed split beams <NUM> which are not substantially parallel, as explained above. Such an example is shown in <FIG>.

The diffractive beam propagation device <NUM> may be configured to rotate around a rotation axis <NUM> which is substantially normal to the planar surface <NUM> of the diffractive beam propagation device <NUM>. For example, the rotation axis <NUM> is substantially the same as the incidence direction <NUM> of the light beam and the optical axis <NUM> of the focusing system <NUM>. For example, the diffractive beam propagation device <NUM> and, optionally, the focusing system <NUM> are configured to rotate at a rate of approximately <NUM> to <NUM>,<NUM>, such as at about <NUM>. In other words, the rotation speed can be up to <NUM> rounds per minute, or even higher. Rotation of the diffractive beam propagation device <NUM> may result in rotation of the propagated beams <NUM> (and thus the direction-changed beams <NUM>). When the light source <NUM> and diffractive beam propagation device <NUM> are used in a drilling device, rotation of the diffractive beam propagation device <NUM> may melt and/or vaporize and/or expel material of the work piece <NUM> to produce or extend holes and/or cuts in the work piece <NUM>. For example, the diffractive beam propagation device <NUM> rotates while the focusing system <NUM> is stationary. In another example, the diffractive beam propagation device <NUM> and the focusing system <NUM> are coupled to a shared rotary stage and rotate together with the same frequency.

<FIG> illustrates the result of a drilling operation of a drilling device <NUM> according to an example of the present invention. The drilling device <NUM> is configured with a focusing system <NUM> such that direction-changed beams <NUM> are provided which converge in the horizontal component (along the X direction) of the propagation direction at a convergence point <NUM>. For example, the direction-changed beams <NUM> may correspond to those in the example of <FIG>. The direction-changed beams <NUM> intersect at the convergence point <NUM> since in this example the direction-changed beams <NUM> are provided both substantially in the same plane (the Z plane). In this example, the convergence point <NUM> is configured to correspond to a location outside of the work piece <NUM>, i.e. at a distance in the X direction farther than a thickness t of the work piece <NUM> from the surface <NUM> of the work piece <NUM>, as shown in <FIG>. Configuration of the location of the convergence point <NUM> may depend on at least one of the focusing system <NUM>, the focal length f of the focusing system <NUM>, the location of the origin area <NUM> of the propagated beams <NUM>, and/or the diffraction angles θD+, θD- of the propagated beams <NUM>. In such a configuration, rotation of the diffractive beam propagation device <NUM> substantially about the rotation axis <NUM> (in this example being substantially aligned with the optical axis <NUM> and the propagation direction <NUM> of the light beam <NUM>) heats and/or melts and/or vaporizes and/or expels the material of the work piece <NUM> in a way which results in a substantially truncated cone-shaped hole, as shown in <FIG>. The diameter D<NUM> of the base of the truncated cone-shaped hole at the surface <NUM> may be set according to the above parameters. Diameter D<NUM> of the truncated end of the truncated cone-shaped hole at an opposite surface <NUM> of the work piece <NUM> than the surface <NUM> of incidence of the direction-changed beams <NUM> is based on the angles of incidence θI+, θI- of the direction-changed beams <NUM> and the thickness t of the work piece <NUM>. It is noted, however, that the geometry, particularly the diameter D<NUM>, may also be based on other process parameters such as the drilling time and the pulse energy.

In another example, the convergence point <NUM> is configured to correspond to a point located substantially on the opposite surface <NUM> of the work piece <NUM>. In this example, rotation of the diffractive beam propagation device <NUM> about the rotation axis <NUM> causes material of the work piece <NUM> to be heated and/or melted and/or vaporized and/or expelled in a way which results in drilling of a substantially cone-shaped hole. A diameter of a base of the cone-shaped hole at the surface <NUM> may correspond to the distance D at the surface <NUM> of the work piece <NUM>. An apex of the cone-shaped hole may, in this example, be located at a thickness t of the work piece <NUM> away from the surface <NUM> of the work piece <NUM> in the X direction.

In another example, it is also possible to configure the drilling device <NUM> such that the convergence point <NUM> is located in the X direction between the focusing system <NUM> and the surface <NUM> of the work piece <NUM>, in which case rotation of the diffractive beam propagation device <NUM> substantially about the rotation axis <NUM> would drill a substantially truncated cone-shaped hole with a wider-diameter (D<NUM>) base at the opposite surface <NUM> compared to a diameter (D<NUM>) of a truncated end at the surface <NUM> of incidence of the direction-changed beams <NUM>.

In another example, the convergence point <NUM> is configured to be located substantially at the surface <NUM> of the work piece <NUM>, and the drilled hole is substantially cone-shaped, with a wider-diameter base of the cone-shaped hole at the opposite surface <NUM> of the work piece <NUM> and an apex at the surface <NUM> of the work piece <NUM>.

In another example, the convergence point <NUM> is configured to be located inside the work piece <NUM>, i.e. between the surface <NUM> and the opposite surface <NUM> located at the thickness t from the surface <NUM> in the X direction. In this case, the hole drilled is substantially in the shape of two cones stacked on their respective apexes, the base of one cone located at the surface <NUM> of the work piece <NUM> and tapering in the X direction to its apex located at the convergence point <NUM>, at which point the apex of the second cone begins, the second cone flaring in the X direction to its base at the opposite surface <NUM>.

<FIG> illustrates an embodiment of the present invention, in which the diffractive beam propagation device <NUM> comprises a circular diffraction grating, the cross section of which is shown on the top left of <FIG>. An incident light beam <NUM> is diffracted by the diffractive beam propagation device <NUM>, i.e. by the circular diffraction grating, such that the propagated beams <NUM> form a cone. In other words, the diffractive beam propagation device <NUM> propagates the light beam <NUM> such that the propagated beam <NUM> has a substantially circular or ringlike shape, i.e. that the propagated beam <NUM> surrounds a substantially circular area. The circular area which is surrounded by the propagated light beam <NUM> is perpendicular to the optical axis of the diffractive beam propagation device <NUM> and/or to the optical axis of the focusing system <NUM>. The propagated ring shaped beam <NUM> is incident on the focusing system <NUM> and thereby becomes a direction-changed beam <NUM>. The direction-changed beam <NUM> is incident on a work piece for drilling the work piece. In <FIG>, the diffracted intensity distribution of the propagated beam <NUM> and the focused intensity distribution of the direction-changed beam <NUM> are also shown. In the illustrated example, the intensity distributions have a substantially circular shape. Thus, according to the embodiment of <FIG>, due to the circular diffraction grating, it is not necessary to rotate the diffractive beam propagation device <NUM> in order to generate a propagated beam <NUM> that surrounds a substantially circular area. Compared to the previously described examples, according to which an incident beam is focused onto a spot and rotated by rotating the diffractive beam propagation device <NUM>, the incident beam, according to the embodiment of <FIG>, is focused on a substantially ringlike area. Accordingly, since the ringlike area, on which the beam of the present embodiment is focused on, is larger than a spot, on which the beam of the previously described examples is focused on, the energy of the incident light has to be larger in the present embodiment than the energy of light used in the previously described examples in order to achieve the same drilling effect. In other words, the laser power has to be increased. However, on the other hand, according to the embodiment of <FIG>, it is not necessary to rotate the diffractive beam propagation device <NUM> so that the mechanical construction is much easier.

Claim 1:
A drilling device (<NUM>) comprising:
a light source (<NUM>) configured to provide a light beam (<NUM>); and
a diffractive beam propagation device (<NUM>) having a substantially planar surface (<NUM>); wherein:
the light source (<NUM>) is configured such that the light beam (<NUM>) is incident on the planar surface (<NUM>) of the diffractive beam propagation device (<NUM>);
the diffractive beam propagation device (<NUM>) comprises a circular diffraction grating being configured to propagate the light beam (<NUM>) as one or more propagated beams (<NUM>) such that the one or more propagated beams (<NUM>) directly surround an area with a substantially circular shape by forming one or more cones;
and wherein the drilling device (<NUM>) further comprises a focusing system (<NUM>) for focusing the one or more propagated beams (<NUM>) on a substantially ringlike area, the focusing system (<NUM>) having an optical axis (<NUM>), wherein the one or more propagated beams (<NUM>) are incident on the focusing system (<NUM>) and thereby become one or more direction-changed beams (<NUM>), and wherein the substantially ringlike area which is surrounded by the one or more propagated beams (<NUM>) is perpendicular to an optical axis of the diffractive beam propagation device (<NUM>) and/or the optical axis (<NUM>) of the focusing system (<NUM>).