Method and apparatus for laser processing of silicon by filamentation of burst ultrafast laser pulses
A method for laser processing of Silicon includes placing a Kerr material into engagement with the Silicon forming an interface therebetween. A laser beam is applied having at least one subpulse in a burst envelope operating at a first wavelength. The laser beam passes through a distributive lens focusing assembly and to the Kerr material. The first wavelength is modified to a plurality of second wavelengths, some of which are effective for processing Silicon. Photoacoustic compression processing is produced by the laser pulse energy by a portion of second wavelengths delivered through the interface and to the Silicon which initiates Kerr Effect self focusing which is propagated in the Silicon by additional energy input to the Silicon thus producing a filament within the Silicon.
1. A method for laser processing of silicon, comprising the steps of:
providing a silicon substrate, said silicon substrate includes a top surface;
providing a Kerr material and placing said Kerr material into engagement with said top surface of said silicon substrate forming an interface therebetween;
providing a laser source delivering a laser beam having between 1 and 50 subpulses in a burst envelope, said subpulses in said burst envelope having a first wavelength;
delivering said laser beam through a distributive focusing assembly to said Kerr material and said silicon substrate, said distributive focusing assembly creating a principal focal waist and a plurality of linearly-arranged secondary focal waists (foci), said secondary foci having sufficient fluence in said Kerr material and said silicon substrate to form a filament and maintain said filament by continued refocusing; and,
wherein as said subpulses travel through said Kerr material a plurality of second wavelengths are generated, said plurality of second wavelengths being white light; and,
wherein a portion of said plurality of said second wavelengths of said subpulses being greater than or equal to 1.3 μm; and,
wherein said portion of said second wavelengths being greater than or equal to 1.3 μm propagates in said silicon substrate by Kerr-effect self-focusing and additional energy input to said silicon substrate, each filament creating a void by annularly compressing silicon about said filament.
2. The method for laser processing of silicon, as claimed in claim 1 , wherein said distributive focusing assembly is a single non-ideal lens.
3. The method for laser processing of silicon, as claimed in claim 1 , wherein said distributive focusing assembly includes a plurality of optical elements arranged along the propagation axis of said laser beam.
4. The method for laser processing of silicon, as claimed in claim 1 , further comprising the step of:
selecting said Kerr material from the group consisting of glass, sapphire and water.
5. The method for laser processing of silicon, as claimed in claim 1 , further comprising the step of:
creating orifices in said silicon substrate with a consistent internal diameter.