DEVICE AND METHOD FOR PROCESSING MATERIAL BY MEANS OF LASER RADIATION

Abstract

The invention relates to a method for processing material, in particular for modifying material and/or material properties, by means of laser radiation, comprising the following steps: a) generating a multiplicity of laser pulses (L); b) controlling the point of impact of the laser pulses (L) on a workpiece (100) to be processed, in particular deflecting the laser pulses (L) and/or moving the workpiece (100) to be processed, such that the laser pulses (L) are guided along a predetermined trajectory (Z) on the workpiece (100) to be processed. According to the invention, —a pulse-to-pulse time interval (Δt) between the individual laser pulses (L) generated and/or—a pulse energy (Pi) of the laser pulses (L) and/or—a beam diameter (D) of the laser pulses (D) and/or—the predetermined trajectory (Z) is/are specifically subjected to noise.

Claims

1. A method for processing material, in particular for modifying material and/or material properties, by means of laser radiation, comprising the following steps: a) generating a multiplicity of laser pulses (L); b) controlling the point of impact of the laser pulses (L) on a workpiece (100) to be processed, in particular deflecting the laser pulses (L) and/or moving the workpiece (100) to be processed, such that the laser pulses (100) are guided along a predetermined trajectory (Z) on the workpiece (100) to be processed; characterized in that a pulse-to-pulse time interval (Δt) between the individual laser pulses (L) generated, and/or a pulse energy (Pi) of the laser pulses (L), and/or a beam diameter (D) of the laser pulses (L), and/or the predetermined trajectory (Z) is/are specifically subjected to noise.

2. The method according to claim 1, characterized in that the pulse-to-pulse time interval (Δt) is varied by a pseudo random pulse interval sequence (Ppt) of a determined pulse sequence length (LI), wherein in particular the pseudo random pulse interval sequence (Ppt) is cyclically repeated.

3. The method according to claim 2, characterized in that merely a pseudo random pulse interval sequence (Ppt) is defined, which is cyclically repeated, wherein a start pulse of the repeating pseudo random pulse interval sequence (Ppt) is temporally shifted by a pseudo random value.

4. The method according to claim 1, characterized in that the pulse energy (Pi) of the laser pulses (L) is varied by a pseudo random pulse energy sequence (Ppe), wherein in particular the pseudo random pulse energy sequence (Ppe) is cyclically repeated.

5. The method according to claim 1, characterized in that the beam diameter (D) of the laser pulses (L) is varied by means of a pseudo random pulse diameter sequence (Ppd), which is in particular cyclically repeated.

6. The method according to claim 1, characterized in that points of the predetermined trajectory (Z), along which the laser pulses (L) are guided, are shifted by a pseudo random pulse trajectory sequence (Ppz), wherein in particular the pseudo random pulse trajectory sequence (Ppz) is cyclically repeated.

7. A device for processing material, in particular for modifying material and/or material properties, by means of laser radiation, preferably for executing the method according to claim 1, wherein the device includes the following: a laser unit (10) for generating a multiplicity of laser pulses (L); a unit for controlling the point of impact of the laser pulses (L) on a workpiece (100) to be processed, in particular a deflecting unit (20) for deflecting the laser pulses (L) along a predetermined trajectory (Z) on the workpiece (100) to be processed and/or a movement unit for moving the workpiece to be processed; optionally a displaying (30) unit for displaying, in particular for focusing, the laser pulses (L) along the predetermined trajectory (Z) on a workpiece (100) to be processed; as well as a system controller (40) in communicable connection with the laser unit (10) and/or the unit for controlling the point of impact of the laser pulses (L), in particular the deflecting unit (20) and/or the movement unit and/or the displaying unit (30), such that the laser unit (10) and/or the unit for controlling the point of impact of the laser pulses (L), in particular the deflecting unit (20) and/or the movement unit and/or the displaying unit (30), is/are controllable by the system controller (40) by means of control signals, wherein: a pulse-to-pulse time interval (Δt) between the individual laser pulses (L) generated, and/or a pulse energy of the laser pulses (L), and/or a beam diameter (D) of the laser pulses (L), and/or the predetermined trajectory (Z) is/are variable by specifically subjecting at least one of the control signals to noise.

Description

[0059] Hereinafter, the invention will be described also with respect to further features and advantages on the basis of exemplary embodiments, which will be explained in more detail by means of the Figures. Shown are in:

[0060] FIG. 1: a schematic representation of the device according to an exemplary embodiment of the invention for processing material of a workpiece;

[0061] FIG. 2: a schematic representation of the pulse sequence according to an exemplary embodiment of the invention;

[0062] FIG. 3: a top view of a workpiece during processing according to the state of the art;

[0063] FIG. 4: a top view of a workpiece during a processing method according to an exemplary embodiment according to the invention; as well as

[0064] FIG. 5: a schematic flow chart according to an exemplary embodiment of the invention.

[0065] In FIG. 1, a laser unit 10 is shown, which includes a seed laser unit 11 designed to emit light pulses in the direction of an amplifier area 12, wherein a first optical modulator 13, in particular an electro-optical modulator (EOM), is inferior to the amplifier area 12, which modulator has a first state causing light pulses to be able to leave the amplifier area, and a second state in which the light pulses circulate within the amplifier area so as to be amplified there per circulation.

[0066] Furthermore, the laser unit 10 comprises, downstream of the first optical modulator 13, a second optical modulator 14, in particular an acousto-optical modulator (AOM), which has a first state causing light pulses to be emitted from the laser unit 10, and a second state causing light pulses of the laser unit 10 not to be emitted and remaining in it.

[0067] Light pulses emitted from the laser unit 10 are displayed by a displaying unit 30, in particular of a focusing unit arranged downstream of the laser unit 10, along a predetermined trajectory Z in the direction of a workpiece 100 to be processed. The displaying unit 30 may in this case be a telescope, a lens, a lens array, a parabolic mirror or a spherical mirror, or a combination of two or more of these elements.

[0068] For influencing the beam position or the point of impact on the workpiece 100, a deflecting unit 20 is located between the displaying unit 30 and the workpiece. The deflecting unit 20 serves the purpose of deflecting the laser pulses L along a predetermined trajectory Z on the workpiece 100 to be processed. In FIG. 1, the average angle of deviation of the beam is approximately 90°. According to the invention, the device, however, is not restricted to this average angle of deviation.

[0069] Furthermore, a coordinate system x, y and z is illustrated in FIG. 1, wherein the x-axis and y-axis span the plane of the workpiece 100, and the z-axis runs orthogonally to the workpiece plane.

[0070] A system controller 40 determines via the first modulator 13 and the second modulator 14, at which points in time a laser pulse is emitted from the laser unit, controls the displaying unit 30 with respect to a focus position relative to the workpiece 100, and controls the predetermined trajectory Z of the laser pulses via the deflecting unit 20, and thus controls the beam position with respect to the workpiece 100.

[0071] In doing so, the system controller is able to specifically subject parameters of the pulse interval between the individual generated laser pulses and/or a pulse energy of the laser pulses and/or a beam diameter of the laser pulses and/or the predetermined trajectory to noise so as to avoid the problems in processing material mentioned before.

[0072] In a further exemplary embodiment, it is also possible for the system controller to subject the temporal emission of the light pulses of the seed laser 11 to noise.

[0073] In FIG. 2, a schematic representation of a pulse sequence according to one exemplary embodiment of the invention is illustrated. The pulse energy Pi over time t is depicted. The individual pulses are at least substantially Gauss pulses having a constant energy level in the present example. Furthermore, a repetition rate T is delineated in FIG. 2, which represents the period duration in which the individual laser pulses are repeated. In the exemplary embodiment shown in FIG. 2, the pulse intervals are varied by means of a pseudo random pulse interval sequence such that the single pulse intervals Δt are varied from pulse to pulse.

[0074] In FIG. 4, a top view of a workpiece 100 during processing of the workpiece 100 according to the inventive method is represented. In the exemplary embodiment shown, a pulsed laser beam is guided along a trajectory Z on a surface of the workpiece 100.

[0075] In this exemplary embodiment, trajectory Z runs along an x-axis of a coordinate system (x, y, z), wherein the x-axis and the y-axis span a workpiece plane of the workpiece and the z-axis runs orthogonally to the x-axis and the y-axis. Depending on focussing and quality of the material of the workpiece, it is possible for the pulsed laser beam to be guided along a trajectory Z within the workpiece.

[0076] In FIG. 4, the processing points L generated by the laser pulses are moreover shown, which have a diameter D. Since the pulsed laser beam is guided and/or deflected continuously along trajectory Z, but the time intervals between the laser pulses vary temporally, an irregular pattern of processing points L results on the workpiece.

[0077] Likewise, further parameters of the laser pulses can be specifically varied, in particular additionally, for example by means of pseudo random pulse energy sequences, pulse diameter sequences and/or pulse trajectory sequences.

[0078] FIG. 5 shows a flowchart according to one exemplary embodiment of the invention. In step S0, a control signal is generated, which is specifically subjected to temporal noise, in particular so-called jitter. The control signal may be a TTL signal, for example, which has low voltage values, for example below 0.2 V, and high voltage values, for example above 2 V.

[0079] The control signal specifically subjected to jitter is transmitted to the laser unit 10 in step S1. In step S2, it is decided in the laser unit 10 by means of the control signal whether a laser pulse should be applied. This may be triggered by a threshold value comparison, for example when the voltage value of the control signal is above 1.8 V.

[0080] When in step S2 a decision has been made that a laser pulse should be triggered, the EOM of the laser unit 10 is closed in step S3. Thereby, an inversion, i.e. a reinforcement of the laser signal of the seed laser unit 11 builds up in the laser unit 10. If, on the contrary, in step S2, for example when the voltage value of the control signal is below 1.8 V, a decision is made that no laser pulse should be triggered, the method returns to step S1.

[0081] In step S4, a query is made as to whether a certain inversion time has passed, so that a desired reinforcement of the laser signal of the seed leaser unit 11 has been reached.

[0082] If the certain inversion time has passed, both the EOM and the AOM are opened in step S5. Hereby, a laser pulse is now emitted from the laser unit 10 and applied to the material to be processed.

[0083] In a further step S6, the EOM is closed after the laser pulse has been emitted. After closing the EOM, the AOM will also be closed, with the closing process of the AOM, however, being slower than the closing process of the EOM.

[0084] The method returns now to step S2, in which a decision is made by means of the trigger signal, if a laser pulse should be emitted again.

[0085] Independent of the exemplary embodiments represented in FIGS. 1 to 5, reference is made to still a further possible field of application of the invention: A possible field of application of the method according to the invention and/or the device according to the invention, for example, is the treatment of the cornea of an eye, in particular a human eye, by a laser, in particular an ultrashort pulse (USP) laser.

[0086] During the methods known from the state of the art for treating the cornea of an eye, a periodic structure is hereby formed as a result. These methods are inter alia employed in the application Femto-LASIK (Laser-assisted in situ keratomileusis supported by femtosecond lasers) and the application FLEX (femtosecond laser lenticular extraction).

[0087] The laser, in particular the ultrashort pulse laser thereby generates a structure of cavitation bubbles in the tissue so that tissue parts can be subsequently separated from one another along the generated separation layers.

[0088] The diffraction effects resulting from the periodic structure of the treatment, subsequent to the treatments according to the state of the art, result for the patient in the perception of a rainbow structure when looking at bright light sources. The effect is known under the designation “rainbow glare” as a side effect of the above-mentioned methods of the state of the art.

[0089] By means of the present invention, a method and/or a device are/is provided by means of which the separation layers can be generated without forming a periodic structure in the tissue in the process. This results in suppressing the diffraction effects and thus in reducing the side effect of the above-mentioned applications.

[0090] In other words, a method for processing a cornea of an eye, in particular a human eye, by means of laser radiation, comprising the steps mentioned in method claim 1, is proposed in a possible embodiment of the invention. The eye is in this case defined to be the workpiece to be processed.

[0091] In further embodiments of the invention, the method steps mentioned in the subclaims are also applied in processing the cornea of the eye.

[0092] A further aspect of the invention relates to a device for processing a cornea of an eye, in particular a human eye, by means of laser radiation, comprising the components mentioned in claim 7. The eye is in this case defined to be the workpiece to be processed.

LIST OF REFERENCE NUMERALS

[0093] 10 laser unit [0094] 11 seed laser unit [0095] 12 amplifier area [0096] 13 first optical modulator [0097] 14 second optical modulator [0098] 20 deflecting unit [0099] 30 displaying unit (e.g. focussing unit) [0100] 40 system controller [0101] 100 workpiece [0102] D beam diameter [0103] D′ beam diameter of the laser pulses [0104] L laser pulses (processing points generated by the laser pulses) [0105] L′ laser pulses (processing points generated by the laser pulses) of the state of [0106] the art [0107] Pi pulse energy [0108] S0 generating a control signal subjected to noise [0109] S1 transmitting the control signal to the laser unit [0110] S2 querying whether a laser pulse should be applied [0111] S3 building up the reinforcement of the seed laser unit (inversion) [0112] S4 querying whether a desired inversion time has been reached [0113] S5 opening the EOM and the AOM [0114] S6 closing the EOM and (including a delay) the AOM [0115] Δt pulse interval [0116] T repetition rate [0117] Z trajectory [0118] Z′ trajectory of the state of the art