Device and method for processing a workpiece along a predetermined processing line using a pulsed polychromatic laser beam and a filter

Abstract

Devices and methods for processing a workpiece along a predetermined processing line are provided. The device includes: a pulsed, polychromatic laser beam generator; an optical arrangement; and a moving device. The laser beam generator generates a laser beam along a beam direction. The optical arrangement generates a focal line along the beam direction. The optical arrangement has a chromatic aberration for wavelength-dependent focusing of the laser beam and a filter for wavelength-dependent filtering of the laser beam. The moving device generates relative movement between the laser beam and the workpiece along the predetermined processing line.

Claims

1. A method for processing a workpiece along a predetermined processing line, comprising: generating a pulsed polychromatic laser beam with a pulse duration of less than 1 ps and a wavelength in the range of 350 nm to 2400 nm; guiding the laser beam using an optical arrangement in order to generate a focal line along a beam direction of the laser beam, the optical arrangement having chromatic aberration for wavelength-dependent focusing of the laser beam; and generating a relative movement between the laser beam and the workpiece along the predetermined processing line, in order to process the workpiece by the laser beam, wherein the workpiece comprises a material selected from a group consisting of glass, glass ceramic, and plastic, wherein the material is at least partially transparent for wavelengths of the laser beam, wherein the depth ofprocessing of the workpiece along the predetermined processing line is adjusted.

2. The method of claim 1, wherein the laser beam is generated by a generator device selected from a group consisting of: a supercontinuum fiber laser, a spectral broadener, and a chirped pulse amplifier.

3. The method of claim 1, further comprising controlling the laser beam to provide an attribute selected from a group consisting of: an average laser power of 5 to 120 watts, a burst mode of 12 to 48 ns, a wavelength range of 350 nm to 2400 nm, and any combinations thereof.

4. The method of claim 1, wherein the chromatic aberration for wavelength-dependent focusing of the laser beam comprises a convex lens made of quartz glass or two diffraction gratings.

5. The method of claim 1, wherein the filter is selected from a group consisting of: a band edge filter, a highpass filter, and lowpass filter.

6. The method of claim 1, further comprising separating the workpiece along the predetermined processing line by external action.

7. The method of claim 6, wherein the external action comprises mechanical action or thermal action.

8. The method of claim 1, wherein the workpiece comprises a stack of workpieces or a workpiece laminate.

9. The method of claim 1, further comprising applying a nonlinear interaction between an electromagnetic field of the laser beam and the workpiece so that the laser beam self-focuses.

10. The method of claim 1, further comprising spectrally broadening a pulse of the laser beam as a function of the pulse width according to the equation $\frac{K}{c}\frac{{}^2}{},$ with K being 0.441 for a Gaussian pulse shape and K being 0.315 for a sech2-shaped pulse and being the pulse width.

11. The method of claim 1, further comprising a wavelength dependent filtering of the laser beam by a filter.

12. The method of claim 1, further comprising controlling the laser beam to provide an average laser power of 5 to 120 watts.

13. A method for processing a workpiece along a predetermined processing line, comprising: providing the workpiece that is at least partially transparent for a wavelength range; generating a pulsed polychromatic laser beam in the wavelength range and with a pulse duration of less than 1 ps and a wavelength in the range of 350 nm to 2400 nm; passing the pulsed polychromatic laser beam through at least one filter for wavelength-dependent filtering of the laser beam, wherein the at least one filter is located only before an optical arrangement; guiding the laser beam onto the workpiece using the optical arrangement having chromatic aberration for wavelength-dependent focusing of the laser beam such that an elongated focal line along a beam direction of the laser beam is generated and a filament is introduced within the workpiece; and generating relative movement between the pulsed polychromatic laser beam and the workpiece along the predetermined processing line, in order to process the workpiece by the laser beam, wherein the depth of processing of the workpiece along the predetermined processing line is adjusted.

14. The method of claim 13, wherein the length of the filament is at least partially dependent on the chromatic aberration.

15. The method of claim 1, wherein the pulsed polychromatic laser beam further has an average laser power of 5 to 120 watts.

16. The method of claim 1, wherein the pulsed polychromatic laser beam further has a burst mode of 12 ns to 48 ns.

17. A method for processing a workpiece along a predetermined processing line, comprising: providing the workpiece that is at least partially transparent for a wavelength range of an ultrashort pulsed polychromatic laser beam with a pulse duration of less than 1 ps and a wavelength in the range of 350 nm to 2400 nm, wherein the laser beam has a pulse that is spectrally broadened as a function of the pulse width according to the equation $\frac{K}{c}\frac{{}^2}{},$ with K being 0.441 for a Gaussian pulse shape and K being 0.315 for a sech2-shaped pulse and T being the pulse width; passing the pulsed polychromatic laser beam through at least one filter for wavelength-dependent filtering of the laser beam; guiding the laser beam onto the workpiece using the optical arrangement having chromatic aberration for wavelength-dependent focusing of the laser beam so that an elongated focal line along a beam direction of the laser beam is generated and a filament is introduced within the workpiece; and generating relative movement between the pulsed polychromatic laser beam and the workpiece along the predetermined processing line, in order to process the workpiece by the laser beam.

18. The method according to claim 17, wherein the pulsed polychromatic laser beam is passed through at least one filter for wavelength-dependent filtering of the laser beam, and wherein the length or depth of processing of the workpiece along the predetermined processing line is adjusted.

19. The method according to claim 17, wherein the workpiece is selected from the group consisting of glass, glass-ceramics, and plastics.

20. The method according to claim 1, further comprising, between the first generating step and the guiding step, the step of passing the pulsed polychromatic laser beam through at least one filter for wavelength-dependent filtering of the laser beam, wherein the at least one filter is located only before an optical arrangement.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the spectral power density of a typical white fiber laser;

(2) FIG. 2 shows spectral broadening of a pulse as a function of pulse width;

(3) FIG. 3 shows shaping of a pulsed polychromatic laser beam with an optical arrangement having chromatic aberration, which comprises a convex lens made of quartz glass.

(4) FIG. 4 shows an enlarged view of the focal line with the different foci;

(5) FIG. 5 shows the effective focal length of the system shown in FIG. 3;

(6) FIG. 6 shows a pulsed laser beam converted into a ring beam;

(7) FIG. 7 shows a device for processing a workpiece according to the present disclosure; and

(8) FIG. 8 shows the processing of a workpiece along a predetermined processing line.

DETAILED DESCRIPTION

(9) The inventors have been able to show that, by means of the device according to the invention, the processing depth in a workpiece may be adjusted selectively and accurately. The device is highly suitable, in particular, for processing workpieces made of glass or glass ceramic, or workpieces which comprise glass or glass ceramic, for example stacks of glass or glass ceramic sheets, stacks of glasses and glass ceramics of different chemical composition, glass-plastic laminates.

(10) With a pulsed polychromatic laser beam, having in particular a certain pulse duration and having certain wavelengths of the laser beam, by means of the optical arrangement having chromatic aberration for wavelength-dependent focusing of the laser beam and having at least one filter for wavelength-dependent filtering of the laser beam, it is possible to produce a focal line along the beam direction of the workpiece, with which the processing depth of the workpiece may be adjusted selectively and accurately. In particular, the length of the focal line may be adjusted by generating different foci.

(11) By means of a filter, at least one wavelength of the laser beam may be selectively filtered, so that selectively no focus is formed at least at a particular position in the focal line. In particular, by unilateral or bilateral limiting of the optical spectrum (introduction of a band edge filter, or bandpass filter), it is possible to define a start or end point of the focal line. In a separate embodiment, in particular the endpoint (on the side facing away from the laser) is adjusted in a defined way, for example to avoid processing of a support on which the workpiece is resting.

(12) In further embodiments, workpieces, in particular glass-metal laminates, processed from the glass side without modification or ablation of the metal. In a further embodiment, the microchannels produced along the focal line are used for direct through-contacting onto the metal layer, whichdepending on the process sequencemay be structured before or after the through-contacting. Typical diameters of the microchannels are preferably less than 1 m, particularly preferably less than 500 nm, more particularly preferably less than 300 nm.

(13) By means of the optical arrangement, the filament may be converted by a chromatically induced transformation of the incident light beam into a Bessel-like beam. DE 103 25 942 A1 and DE 10 2008 029 459 A1 present special optics, or lenses, the chromatic aberration of which has been deliberately increased in order, as a function of the wavelength, to induce focusing of the beam components over a region of the focal line thereby formed. The foci of these systems may be extended over ranges of up to 30 cm. These systems are employed in the field of high-precision distance and contour measurement or, in the case of transparent bodies, also for thickness measurement of monolayer or multilayer substrates (as the difference of a plurality of distance measurements). In principle, these optics or lenses may also be used as optical arrangements having chromatic aberration for the present invention.

(14) In the device according to the invention, a pulsed polychromatic laser beam may be converted by the chromatic aberration of the imaging optics (optical arrangement) wavelength-selectively into a corresponding intensity distribution along the focal line. By combining a spectral energy distribution of a laser source and a filter (filter functions), the intensity distribution in the working volume may be exactly adjusted along the focal line.

(15) Particularly advantageous embodiments of the device according to the invention will be described below.

(16) The means for generating a pulsed polychromatic laser beam preferably comprise at least one supercontinuum fiber lasers, or they comprise means for spectral broadening of the laser pulse, in particular means for amplifying chirped pulses (chirped pulse amplification).

(17) In the case of amplifying chirped pulses, the laser pulse is spatially spread along the wavelength by means of gratings and then amplified. A thin-film transistor display (TFT display) before a grating may (with an energy loss) sharply block individual wavelength ranges. In this way, individual zones of the focal line may be blocked (filtered) in the laser beam direction. During amplification after the shadowing, the amplification power may be applied to the remaining wavelength ranges, so that the laser beam power decreases proportionally less than as originally shadowed in the case of a seeder. Injection seeding is a technique which is usually applied to pulsed lasers and optical parametric oscillators, usually with the main aim of achieving a narrower optical bandwidth (line width). This essentially means that the light from a seed laser, which is usually a single-frequency in continuous-wave operation, is fed into a Q-switched slave laser or into a nanosecond optical parametric oscillator at the start of a pulse buildup phase. Without this seed laser, the slave laser or OPO would normally emit on multiple resonator moments with optical amplification of comparable size, and the power distribution in the case of a plurality of modes may fluctuate from pulse to pulse. If the optical frequency of the seed laser light is close enough to the resonant frequency of a particular resonator mode of the slave apparatus, this mode may start with a much higher power than a very high power and may therefore greatly dominate in the output pulse. In this way, the emission bandwidth is drastically reduced compared with unimpeded (freely running) emission, and the temporal pulse profile may be smoother since mode collision is avoided.

(18) The means for generating a pulsed polychromatic laser beam preferably provide at least the following: average laser power 5 to 120 watts, pulse duration of the laser beam less than 1 ns, preferably less than 1 ps, burst mode 12 to 48 ns, and wavelength range of the laser beam 350 nm to 2400 nm.

(19) In one embodiment, the wavelength of the laser source (means for generating a pulsed polychromatic laser beam) is in this case restricted to a region in which the number of photons for bridging the bandgap remains constant.

(20) Suitable means for generating a pulsed polychromatic laser beam, in particular laser sources, may be provided in a very wide variety of ways.

(21) Known supercontinuum fiber lasers emit, for example, pulses in the range of less than 10 ps with an average power of the laser of 20 watts over a wavelength range of from 350 nm 2400 nm. Power spectra distributed in such a way make it possible to process workpieces which, in the visible or near-infrared range, are transparent. FIG. 1 shows the spectral power density of a typical white fiber laser. The upper curve shows the profile for an average power of the laser of 20 watts. The lower curve shows the profile for an average power of the laser of 10 watts. The average power of the laser is given by integration.

(22) Generation of another type of pulsed polychromatic laser beam is given by the relationship between spectral bandwidth and pulse duration t

(23) $vK\frac{K}{v}$
where K depends on the specific pulse shape according to

(24) TABLE-US-00001 Pulse shape I(t) K Gaussian $I\left(t\right)=e^{-4\ln 2*\frac{t^2}{t}}$ 0.441 sech.sup.2 $I\left(t\right)=\sec h^2\left(\frac{1.76t}{t}\right)$ 0.315

(25) Here, t is the pulse duration, the value of which is determined as a full width at half maximum (FWHM) of the intensity distribution I (t) and Dn is the spectral bandwidth/frequency width of the pulse at FWHM.

(26) The following FIG. 2 shows the spectral broadening of the pulse as a function of the pulse width in a log-log representation with a central wavelength of 1064 nm, the following calculation formula being used as a basis:

(27) $\frac{K}{c}\frac{{}^2}{}$

(28) At the transition from ps to fs pulses, broadening of the pulse to the order of magnitude n100 nm is to be expected. Further shortening of the pulse duration to attosecond pulses in fact produces a white light distribution.

(29) A disadvantage in this case is first that the interaction of the short fs pulse or attosecond pulse with the workpiece causes less and less damage in the material of the workpiece, so that the processability or separability of the workpiece decreases further and further (because of the short interaction time of the pulse (the photons), coupling to the phonons of the material cannot occur, so that direct heating of the material does not take place). Compensation may in this case be carried out by a significant increase in the number of burst mode pulses.

(30) The optical arrangement having chromatic aberration preferably comprises at least one convex lens made of quartz glass, or it comprises at least two diffraction gratings.

(31) Shaping of a pulsed polychromatic laser beam in the wavelength range of less than 800 nm with an optical arrangement having chromatic aberration, which comprises a convex lens made of quartz glass, is depicted in FIG. 3. An enlarged view of the focal line with the different foci is shown by FIG. 4. In this embodiment, the foci for 350 nm and 1000 nm differ by about 2 mm, i.e. the focal points of the wavelengths 350 nm and 1000 nm are separated from one another by about 2 mm. The focus may thus be shifted through this distance by spectral filtering. This distance shift may be calculated for different optical arrangements with commercially available ray tracing programs. Ray tracing is an algorithm based on the emission of rays for calculating masking, i.e. for determining the visibility of three-dimensional objects from a particular point in space. Ray tracing likewise refers to several extensions of this basic method, which calculate the further path of rays after striking surfaces. In optical simulation software, for example Zemax, the path of a field of light rays, which come from an object considered to be segmented, through the imaging optical system as far as the detector is represented.

(32) FIG. 5 shows the effective focal length of the system shown in FIG. 3 in the wavelength range of from 0.30 m to 0.80 m (300 nm to 800 nm).

(33) In a further embodiment (FIG. 6), the pulsed laser beam is converted by two diffraction gratings (BG1 and BG2) into a ring beam, in which the shorter wavelength of the beam spectrum .sub.1 lies at the outer ring and the longer wavelength of the beam spectrum .sub.2 lies at the inner ring. If this ring beam is then focused with axicon or similar optics, a plurality of foci F1 and F2 will be formed, the position of which depends on the wavelength.

(34) The filter is preferably a band edge filter, in particular a highpass or lowpass filter.

(35) The filter is preferably arranged before the optical arrangement having chromatic aberration in the beam path of the laser beam. It may, however, also be arranged after the optical arrangement having chromatic aberration in the beam path of the laser beam (it is, however, necessary to ensure that the filter does not protrude into the focal line). An arrangement of a plurality of filters before and/or after the optical arrangement is also possible.

(36) By a plurality of filters, a plurality of wavelengths may be selectively filtered so that the focal line selectively does not have a focus at a plurality of positions.

(37) Use of edge filters (highpass and lowpass) limits the outer positions of the focal line, and band-stops make it possible to block or inactivate individual regions of the focal line. The combination of spectral intensity distribution of the laser source with the filter curve of the filters used determines the intensity distribution of the laser beam on the entry side of the optical arrangement having chromatic aberration (mathematically: calculation of the convolution integral of the light intensity distribution and the filter curve). On the beam exit site, the chromatic aberration of the optical arrangement determines the intensity distribution reached.

(38) The workpiece to be processed is preferably at least partially transparent for the laser wavelength range used, the transmission of the workpiece being in this more than 85%, preferably more than 90%, particularly preferably more than 95%.

(39) The workpiece to be processed comprises in particular glass, glass ceramic or plastic.

(40) The device is, in particular, a device for introducing a separating line along which the workpiece can be separated by external action, in particular by mechanical or thermal action.

(41) The device is, in particular, a device for processing a workpiece stack or a workpiece laminate made of the same or different materials.

(42) The object is also achieved by a method for processing a workpiece along a predetermined processing line, comprising at least the steps: generating a pulsed polychromatic laser beam, guiding the laser beam using an optical arrangement in order to generate a focal line along the beam direction of the laser beam, the optical arrangement having chromatic aberration for wavelength-dependent focusing of the laser beam and at least one filter for wavelength-dependent filtering of the laser beam, generating a relative movement between the laser beam and the workpiece along the predetermined processing line, in order to process the workpiece by means of action of the focused laser beam.

(43) The method for processing a workpiece along a predetermined processing line thus comprises at least the following steps: generating a pulsed polychromatic laser beam, guiding the laser beam using an optical arrangement having chromatic aberration for wavelength-dependent focusing of the laser beam and at least one filter for wavelength-dependent filtering of the laser beam, in order to generate a focal line along the beam direction, generating a relative movement between the laser beam and the workpiece along the predetermined processing line, in order to process the workpiece by means of action of the focused laser beam (laser beam focal line).

(44) Preferably, the pulsed polychromatic laser beam is generated by means of a supercontinuum fiber laser or by means of spectral broadening of the laser pulse, in particular by means of amplifying chirped pulses.

(45) At least the following are preferably adjusted during the generation of the laser beam: pulse duration of the laser beam less than 1 ns, preferably less than 1 ps; burst mode 12 to 48 ns; wavelength range of the laser beam 350 nm to 2400 nm.

(46) At least one convex lens made of quartz glass or at least two diffraction gratings may preferably be used as an optical arrangement having chromatic aberration.

(47) A band edge filter, in particular a highpass or lowpass filter, may preferably be used as the filter.

(48) A workpiece which is at least partially transparent for wavelengths of the laser, and comprises glass, glass ceramic or plastic, is preferably processed.

(49) The method is preferably a method for introducing a separating line along which the workpiece can be separated by external action, in particular by mechanical or thermal action.

(50) The method is preferably a method for processing a workpiece stack or a workpiece laminate made of the same or different materials.

(51) The present invention will be further clarified with the aid of the following exemplary embodiments.

(52) FIG. 7 shows a device (1) for processing a workpiece (2) along a predetermined processing line (3) the device (1) comprising the following means: means (4) for generating a pulsed polychromatic laser beam (5), an optical arrangement (6) having chromatic aberration for wavelength-dependent focusing of the laser beam (5) and having at least one filter (7) for wavelength-dependent filtering of the laser beam (5), in order to generate a focal line (8) along the beam direction (Z direction) of the laser beam, means for generating a relative movement (not represented) between the laser beam (5) and the workpiece (2) along the predetermined processing line (3), in order to process the workpiece (2) by means of action of the focal line (8) of the laser beam (5).

(53) The advantage of the present invention is represented in FIG. 8: the processing of a workpiece along a predetermined processing line by means of pulsed laser beams, the processing depth being selectively adjusted.