Laser Machining a Transparent Workpiece

Abstract

The invention relates to a method for machining a transparent workpiece (4) by generating non-linear absorption of laser radiation in a laser beam focus located in a volume of the workpiece (4). The object of the invention is that of providing a method of improved precision and quality, and a corresponding device, for laser machining of workpieces. In particular, it is also intended for it to be possible for workpieces made of composite materials or of other special materials, such as filter glass, to be machined at an improved level of quality. For this purpose, the method according to the invention comprises the following steps: spectroscopic measurement of the linear absorption of the laser radiation in the workpiece (4), selecting a working wavelength at which the linear absorption is low, and machining the workpiece (4) by means of application of laser radiation at the working wavelength. The invention furthermore relates to a corresponding device for machining a transparent workpiece (4).

Claims

1. Method for machining a transparent workpiece by generating non-linear absorption of laser radiation in a laser beam focus located in a volume of the workpiece, comprising the following steps: spectroscopic measurement of the linear absorption of the laser radiation in the workpiece, selecting a working wavelength at which the linear absorption is low, and machining the workpiece by means of application of laser radiation at the working wavelength.

2. Method according to claim 1, wherein the working wavelength is selected in accordance with the stipulation that, at the working wavelength, the linear absorption in the laser beam direction is less than 20% per centimeter.

3. Method according to claim 1, wherein the transmission curve resulting from the measurement of the linear absorption exhibits a minimum at the working wavelength.

4. Method according to claim 1, wherein the machining of the workpiece is performed using a laser, the wavelength of which can be tuned.

5. Method according to claim 4, wherein the spectroscopic measurement is also performed using a laser, the wavelength of which can be tuned.

6. Method according to claim 5, wherein, during measurement of the workpiece, the intensity of the laser radiation remains below a threshold at which ionization processes occur in the volume of the workpiece.

7. Method according to claim 1, wherein the laser radiation is pulsed, wherein the pulse duration of the laser pulse is from 10 fs to 100 ps.

8. Method according to claim 1, wherein the working wavelength is selected in accordance with the secondary condition that the non-linear absorption should be as high as possible, at a harmonic of the working wavelength.

9. Use of the method according to claim 1 for separating glass workpieces, wherein the position of the laser focus is guided, during the machining, between two or more connected glass workpieces, along a separation plane or a predetermined breaking point.

10. Device for machining a transparent workpiece, comprising a laser that emits a laser beam at an adjustable working wavelength, coupling optics that couples the laser beam into the volume of the workpiece and focuses said beam in a laser beam focus located in the volume of the workpiece, a measuring device that measures the linear absorption of the laser radiation in the workpiece, a controller that is connected to the laser, the measuring device and the coupling optics, which controller is designed to set the working wavelength to a value at which the linear absorption is low, and to vary the position of the laser beam focus during the machining of the workpiece.

11. Device according to claim 10, wherein, during the machining, the laser emits the laser beam at an intensity at which non-linear absorption, in particular ionization, occurs in the laser beam focus.

12. Method according to claim 1, wherein the working wavelength is selected in accordance with the stipulation that, at the working wavelength, the linear absorption in the laser beam direction is preferably less than 10% per centimeter.

Description

[0026] Further features, details and advantages of the invention can be found from the wording of the claims and from the following description of an embodiment with reference to the figure, in which:

[0027] FIG. 1: is a schematic block diagram of a device according to the invention.

[0028] The device shown in FIG. 1 comprises a laser 1 that emits laser radiation 2. The laser 1 can be tuned with respect to the wavelength of the laser radiation. The laser radiation 2 is directed, by means of an objective 3, towards a workpiece 4.

[0029] The workpiece 4 consists for example of a special glass. This can for example be an optical filter glass. A separation plane 5 is intended to be introduced into the workpiece 4 by means of laser machining. The objective 3 focuses the laser radiation 2 such that the focus position inside the volume of the workpiece 4 is located on the separation plane 5. In this case, a controllable optical assembly 6 is provided, in order to vary the beam position in a plane perpendicular to the direction of the laser beam 2 (i.e. in the x- and y-direction). The objective 3 and the assembly 6 together form a coupling optics that couples the laser beam 2 into the volume of the workpiece 4. The focal length of the objective 3 is also variably controllable. Overall, it is thus possible for the focus position to be varied in three dimensions, i.e. in the x-, y- and z-direction. In an alternative embodiment, it is possible to move the position of the workpiece 4 relative to the optics. The coupling optics is connected to a program-controlled controller 7. The program-controlled controller 7 actuates the objective 3 and the deflection device 6 in order to vary the focus position during the machining. In this case, the program-controlled controller 7 is designed to generate a specified modification profile within the workpiece 4 by means of non-linear absorption of the laser beam 2 in the focus, said profile specifically being along the separation plane 5. The program-controlled controller 7 also actuates the laser 1 in order to switch it on and off, respectively, for generating the laser radiation. Furthermore, the device comprises a photo detector 8 as a measuring device, which photo detector is connected to the controller 7. The controller 7 can actuate the objective 3 such that the laser beam 2 is not focused inside the workpiece 4, but is instead transmitted through the workpiece 4. The transmitted laser beam 2 then strikes the photo detector 8. Varying the wavelength of the laser 1, by means of corresponding actuation using the controller 7, makes it possible to record a transmission curve of the workpiece 4, in order to carry out a spectral measurement of the linear absorption of the laser radiation in the material of the workpiece 4 prior to the actual machining, in a manner according to the invention. The controller 7 then adjusts the working wavelength of the laser 1, i.e. the wavelength to be used during the machining, in accordance with the measured transmission curve, to a value at which the linear absorption is less than 10% per centimeter, in the direction of the laser beam 2. For the purpose of spectroscopic measurement of the linear absorption, the laser 1 can be actuated so as to emit in a manner having reduced intensity, e.g. by reducing the power of a pump light source. In an alternative embodiment, the spectroscopic measurement is carried out ex situ, e.g. by means of a separate white light spectrometer. During the machining, the laser 1 then emits the laser beam 2 at a higher intensity, at which non-linear absorption, in particular ionization, occurs in the laser beam focus.