Electric heating – Metal heating – By arc
Reexamination Certificate
2001-01-25
2003-04-22
Dunn, Tom (Department: 1725)
Electric heating
Metal heating
By arc
C219S121700, C219S121670, C219S121680, C219S121690, C606S010000, C372S025000, C372S053000
Reexamination Certificate
active
06552301
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to methods of laser processing and modification of materials, and more particularly the present invention relates to laser processing and modification of a variety of materials using ultrafast laser pulses.
BACKGROUND OF THE INVENTION
Many efforts in the current generation of laser processing of materials can be described as investigating new modalities in which the laser fluence may be delivered to a workpiece, specifically the ways in which the pulse duration, wavelength or pulse-shape give significant new control over the laser-material interaction.
Various studies have shown that laser material processing in the ultrashort-pulse regime (<100 picosecond) offers numerous advantages compared with longer pulses, see for example S A. Kuper and M. Stuke, Appl. Phys. B 44, 2045 (1987); S. Press and M. Stuke, Appl. Phys. Lett 67, 338 (1995); C. Momma et al., Optics Comm., 129, 134 (1996); C. Momma et al., Appl. Surf. Sci., 109/110, 15 (1997); D. von der Linde, K. Sokolowski-Tinten, and J. Bialkowski,
Appl. Surf. Sci.
109/110, 1 (1997); X. Liu, D. Du, and G. Mourou,
IEEE J. of Quantum Electron.
33, 1706 (1997) J. X. Zhao, B. Hüttner, and A. Menschig, SPIE Proc Vol. 3618, (1999); U.S. Pat. No. 5,361,275; U.S. Pat. No. 5,656,186; U.S. Pat. No. 5,720,894; U.S. Pat. No. 6,090,507; U.S. Pat. No. 6,150,630; U.S. Pat. No. 6,043,452; and patent publication WO 89/08529. The first reported advantages in ultrafast laser processing by S A. Kuper and M. Stuke, Appl. Phys. B 44, 2045 (1987) and patent publication WO 89/08529 emphasized improvements in surface morphology, absence of thermal degradation, and reduced threshold fluence for polymers and inorganic non-metallics such as teeth when using sub-picosecond ultraviolet lasers in comparison with traditional nanosecond ultraviolet lasers. Ultrashort lasers offer high intensity to micromachine, to modify and to process surfaces cleanly by aggressively driving multi-photon, tunnel ionization, and electron-avalanche processes, see J. Ihlemann,
Appl. Surf. Sci.
54 (1992) 193; D. Du, X. Liu, G. Korn, J. Squier, and G. Mourou,
Appl. Phys. Lett.
64 (1994) 3071; P. P. Pronko, S. K. Dutta, J. Squier, J. V. Rudd, D. Du, G. Mourou,
Optics Comm.
114 (1995) 106; B. C. Stuart, M. D. Feit, S. Herman, A. M. Rubenchick, B. W. Shore, M. D Perry,
J. Opt. Soc. Am B
13 (1996) 459; and C. B. Schaffer, A. Brodeur, N. Nishimura, and E. Mazur,
SPIE
3616 (1999) 143.
Beyond the simple delivery of ‘raw’ fluence, lasers offer the parameters of intensity, wavelength, and pulse duration as factors which afford control over essential aspects of material interaction. Particularly, ultrafast laser interactions have well-defined ‘damage’ thresholds offering improved precision in processing applications, including the fabrication of hole sizes that are smaller than the beam diameter, see U.S. Pat. No. 5,656,186; X. Liu, D. Du, and G. Mourou,
IEEE J. of Quantum Electron.
33, 1706 (1997) and D. Du, X. Liu, G. Korn, J. Squier, and G. Mourou,
Appl. Phys. Lett.
64 3071 (1994). Much recent literature has been devoted to ultrafast laser damage and processing of transparent or wide-bandgap materials, see J. Ihlemann,
Appl. Surf. Sci.
54 (1992) 193, D. Du, X. Liu, G. Korn, J. Squier, and G. Mourou,
Appl. Phys. Lett.
64 (1994) 3071. Nonlinear absorption mechanisms are key to coupling laser energy into such non-absorbing media.
The thermal impact of picosecond and femtosecond laser interactions is highly limited, confining laser energy dissipation to small optical penetration depths with minimal collateral damage. This precisely confined laser ‘heating’ minimizes the energy loss into the underlying bulk material, providing for an efficient and controllable ablation process, see U.S. Pat. No. 5,656,186; U.S. Pat. No. 5,720,894; U.S. Pat. No. 6,150,630; S. Preuss, A. Demchuk, and M. Stuke, Appl. Phys. A, 61, 33 (1995); and T. Götz and M. Stuke, Appl. Phys. A, 64, 539 (1997). Because the laser-matter interaction is so brief, there is a shift in the partition of absorbed energy. Relatively thin layers of near-solid density material are heated, during ultrafast-laser interaction, and this enhances evaporative cooling: though the speed of expansion of the volume of heated material is largely fixed by the temperature, the factor increase in volume of a thin layer is much greater. The volume of tenuous heated material more quickly decouples thermally from the bulk, in the case of ultrafast laser-matter interaction, and in this brief time less heat is transferred from the laser-absorption zone to the underlying bulk material. A greater proportion of absorbed energy is carried away in the evaporated material than is the case for longer-duration pulses.
Collectively, these ultrafast laser effects in small volumes minimize thermal transport, mechanical shocks, cracks, charring, discolouration, and surface melting in the nearby laser interaction zone. Ultrafast laser machining permits repair of ultrafine (sub-mircron) defects on photomasks, see U.S. Pat. No. 6,090,507. Such interactions also reduce pain during medical procedures (see U.S. Pat. No. 5,720,894) and enable the microshaping of explosive materials without deflagration or detonation (see U.S. Pat. No. 6,150,630). The short duration further ensures that, all of the laser energy arrives at the surface before the development of a significant ablation plume and/or plasma; such efficient energy coupling is not available with longer duration (>10's ps) laser pulses because of plasma reflection, plasma and plume scattering, and plume heating. Such ultrafast-processing features are highly attractive for the precise microprocessing of good heat conductors such as metals; at the same time, nonlinear absorption of these intense ultrafast pulses also reduces the ablation threshold for wide-bandgap or “transparent” optical materials such as silica glasses.
Ultrafast lasers also offer the means to internally process transparent glass. Microexplosions provide opportunities for 3-D optical storage (C. B. Schaffer, A. Brodeur, N. Nishimura, and E. Mazur,
SPIE
3616
(1999) 143) while refractive index structures such as volume gratings and waveguides (K. M. Davis, K. Miura, N. Sugimoto, and K. Hirao,
Opt. Lett.
21 (1996)1729) have been formed, by the permanent alteration of the local index of refraction.
These prior studies and developments of ultrashort-laser processing of materials have centered on ultrafast systems with pulse rates typically operating in the ~1 Hz to 10,000 kHz regime. A high-repetition rate three-pulse laser system is described by Opower in U.S. Pat. No. 5,361,275 with pulse separations of 0.5 to 5 ns (200 to 2000 MHz); each pulse is a different wavelength, delivered such that a subsequent pulse arrives soon enough to still interact with the expanding plume of the previous pulse, thereby to benefit from more uniform heating of the plasma plume.
While ultrafast lasers offer exciting prospects for processing materials, at present undesirable effects exist and processing windows are poorly defined. Effects requiring more control in laser processing and modification of materials includes, for example, incubation (defect generation) effects that change etching rates, self-focusing and clouding effects, ‘gentle’ and ‘strong’ ablation phases developing with increasing number of pulses, pre-pulse or pedestal effects, poor morphology,: periodic surface structures, melt, debris, surface swelling, shock-induced microcracking, slow processing rates and saturation of hole depth in via/hole formation.
It is advantageous to provide a method of laser processing of materials that addresses the aforementioned difficulties present in present processing methods.
SUMMARY OF THE INVENTION
The present invention provides a method of processing and/or modifying materials based on high repetition-rate (continuous or pulsetrain-burst) application of ultrafast laser pulses to materials. The high-repetition rate provides a new control over laser interactions by defining
Herman Peter R.
Marjoribanks Robin
Oettl Anton
Dunn Tom
Edmondson L.
Hill & Schumacher
Schumacher Lynn C.
LandOfFree
Burst-ultrafast laser machining method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Burst-ultrafast laser machining method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Burst-ultrafast laser machining method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3061775