SYSTEM FOR PERFORMING LASER FILAMENTATION WITHIN TRANSPARENT MATERIALS
Systems and methods are described for forming continuous laser filaments in transparent materials. A burst of ultrafast laser pulses is focused such that a beam waist is formed external to the material being processed without forming an external plasma channel, while a sufficient energy density is formed within an extended region within the material to support the formation of a continuous filament, without causing optical breakdown within the material. Filaments formed according to this method may exhibit lengths exceeding up to 10 mm. In some embodiments, an aberrated optical focusing element is employed to produce an external beam waist while producing distributed focusing of the incident beam within the material. Various systems are described that facilitate the formation of filament arrays within transparent substrates for cleaving/singulation and/or marking. Optical monitoring of the filaments may be employed to provide feedback to facilitate active control of the process.
1 . A system for laser processing a transparent material, comprising:
a laser source configured to provide a laser beam comprising bursts of laser pulses;
one or more focusing elements configured to externally focus said laser beam relative to said transparent material to form a beam waist at a location that is external to said transparent material while avoiding the formation of an external plasma channel, and,
said laser beam and said one or more focusing elements produce a sufficient energy density within said transparent material to form a continuous laser filament therein without causing optical breakdown of said transparent material.
2 . A system for laser processing a transparent material as claimed in claim 1 , further comprising:
a motorized mechanism for varying a relative position between said laser beam and said transparent material; and
a control and processing unit operatively coupled to means for varying said relative position between said laser beam and said transparent material.
3 . A system for laser processing a transparent material as claimed in claim 2 , further comprising:
said control and processing unit is configured to control the relative position between said laser beam and said transparent material for the formation of an array of continuous laser filaments within said transparent material.
4 . The system according to claim 1 wherein said one or more focusing elements comprise one or more aberrated optical elements.
5 . The system according to claim 4 wherein said one or more aberrated optical elements comprise a normal field-corrected scan lens and a corrective window configured to produce an aberrated laser beam.
6 . The system according to claim 1 , further comprising:
said laser beam has an incident spot diameter on said transparent material and a continuous laser filament diameter within said transparent material;
a critical ratio defined as the ratio of said incident spot diameter of said laser beam on said transparent material to said continuous laser filament diameter within said transparent material;
said laser being focused such that said critical ratio is between approximately 1 and 1000.
7 . The system according to claim 1 , further comprising:
means for varying a relative orientation between said laser beam and said transparent material; and,
a control and processing unit is further operatively coupled to said means for varying said relative orientation between said laser beam and said transparent material.
8 . The system according to claim 1 , further comprising:
a control and processing unit for controlling said laser source.
9 . The system according to claim 8 , further comprising:
said control and processing unit varies the pulse wavelength of said laser source.
10 . The system according to claim 8 , further comprising:
said control and processing unit varies pulse-to-pulse separation within a burst of said laser source.
11 . The system according to claim 8 , further comprising:
said control and processing unit varies pulse energy of said individual pulses within a burst of said laser source.
12 . The system according to claim 8 , further comprising:
said control and processing unit varies the burst repetition rate of said laser source.
13 . The system according to claim 8 , further comprising:
said control and processing unit varies pulse energy of said laser source.
14 . The system according to claim 8 , further comprising:
said control and processing unit varies polarization of said laser source.
15 . The system according to claim 7 wherein said means for varying the relative position between said laser beam and said transparent material is configured to maintain constant spacing between continuous filaments formed within said transparent material.
16 . The system according to claim 1 further comprising a means for auto-focusing of said laser beam in real-time.
17 . The system according to claim 15 further comprising:
at least one optical monitoring device configured for optically monitoring said continuous laser filaments;
said control and processing unit is operatively coupled to said at least one optical monitoring device;
said control and processing unit is configured to determine one or more parameters associated with formation of said continuous laser filaments based on images or signals provided by said at least one optical monitoring device; and
said control and processing unit is configured to actively control the formation of the continuous laser filaments according to at least one of the parameters.
18 . The system according to claim 17 wherein said imaging device is located above, below, adjacent to said transparent material.
19 . The system according to claim 17 wherein said at least one optical monitoring device comprises:
an optical detector configured to detect optical radiation emitted during said filament formation process;
said control and processing unit is configured to process signals from said optical detector to determine one or more parameters associated with said continuous laser filaments.
20 . The system according to claim 17 wherein said one or more of said parameters are selected from the group consisting of filament depth, filament size, filament position, and pattern fidelity.
21 . The system according to claim 1 further comprising the steps of:
said transparent material has a surface with a complex spline profile in two, two and half or three dimensions;
controlling said relative position between said laser beam and said transparent material and controlling the orientation of said laser beam such that said array of continuous laser filaments is formed within said transparent material singulating or cleaving said transparent material results in formation of a tilted, straight or chamfered edge.
22 . The system according to claim 1 further comprising the steps of:
said transparent material has a surface with a complex spline profile in two, two and half or three dimensions;
controlling said relative position between said laser beam and said transparent material and controlling the orientation of said laser beam such that said array of continuous laser filaments is formed within said transparent material for purpose of singulation, said laser pulses are controlled to do laser ablation for material removal on the same substrate in a second beam delivery.
23 . The system according to claim 1 further comprising the steps of:
providing a second laser source to release the array of continuous laser filaments by application of a heat source having a sufficient temperature differential from the substrate material to cause separation at the scribed/cut location.
24 . The system according to claim 23 further comprising, said laser source can be CO 2 , solid state or fiber laser.