Method and apparatus for hybrid photoacoustic compression machining in transparent materials using filamentation by burst ultrafast laser pulses
An apparatus, system and method for the processing of orifices in materials by laser filamentation that utilizes an optical configuration that focuses the incident laser light beam in a distributed manner along the longitudinal beam axis. This distributed focusing method enables the formation of filaments over distances, and the laser and focusing parameters are adjusted to determine the filament propagation and termination points so as to develop a single/double end stopped orifice, or a through orifice. Selected transparent substrates from a stacked or nested configuration may have orifices formed therein/therethrough without affecting the adjacent substrate. These distributed focusing methods support the formation filaments with lengths well beyond ten millimeters in borosilicate glass and similar brittle materials and semiconductors.
1. A method of laser processing a target, comprising the steps of:
providing a beam having bursts of laser pulses, the target being made of a material that is transparent to the laser beam, each burst having between 2 and 50 laser pulses, each laser pulse having a pulse width of less than 10 nanoseconds;
passing the laser beam through an aberrated focusing lens;
focusing the laser beam using the aberrated focusing lens, the laser beam focused in a distributed manner along a longitudinal beam axis, the aberrations in the aberrated focusing lens developing the distributed focus;
positioning the distributed focus with respect to the target;
delivering the focused laser beam to the target, the focused laser beam having sufficient fluence to initiate Kerr effect self-focusing of the laser beam, thereby generating a laser filament that propagates along the longitudinal beam axis; and
adjusting the pulse energy and distributed focusing to guide and maintain the laser filament between a desired point of initiation and a desired point of termination in the target, the laser filament creating a void coincident with the laser filament by annularly compressing the transparent material about the longitudinal beam axis.
2. The laser processing method of claim 1 , wherein the distributed focus has a plurality of foci, including a principal focus, the principal focus located below the target.
3. The laser processing method of claim 1 , wherein the laser beam has a burst repetition rate in the range of 1 hertz to 2 megahertz and a temporal spacing between the laser pulses within a burst is in the range of 0.1 femtosecond to 10 microseconds.
4. The laser processing method of claim 1 , wherein the transparent material is one of a ceramic, a glass, a crystal, and a semiconductor.
5. The laser processing method of claim 1 , wherein the laser beam has a wavelength less than 5 micrometers.
6. The laser processing method of claim 1 , wherein each laser pulse has an energy in the range of 0.5 microjoules to 1000 microjoules.
7. The laser processing method of claim 1 , wherein the filament has a length longer than 1 millimeter in the target.
8. The laser processing method of claim 1 , wherein the focusing lens is an aspheric lens.
9. The laser processing method of claim 1 , wherein the focusing lens is a focusing assembly that includes an aspheric plate.
10. The laser processing method of claim 1 , wherein the focusing lens includes an optical element tilted with respect to the laser beam.
11. The laser processing method of claim 1 , wherein the target includes two or more layers and the adjusting of the distributed focus selectively generates the laser filament within at least one of the layers.
12. The laser processing method of claim 1 , wherein the void has an average sidewall roughness of less than 5 micrometers.
13. The laser processing method of claim 1 , wherein the void is linearly symmetric, having substantially constant diameter along the length of the void.
14. The laser processing method of claim 1 , wherein the void is created in the target without removing any of the transparent material from the target.
15. The laser processing method of claim 1 , wherein the void extends to a surface of the target to form an orifice.
16. The laser processing method of claim 15 , wherein a tapered entrance to the orifice is made by adjusting the pulse energy and distributed focusing to ablate material to a desired depth in the material.
17. The laser processing method of claim 15 , wherein a sacrificial layer is applied to the surface of the target prior to making the orifice and removed from the surface after making the orifice.
18. The laser processing method of claim 1 , including the additional step of translating the target laterally relative to the longitudinal beam axis, whereby a plurality of holes are drilled into the target by repeating the delivering and translating steps.