Electric heating – Metal heating – By arc
Reexamination Certificate
2002-10-08
2004-03-23
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
By arc
C219S121610, C219S121700, C219S121710, C219S121770, C219S121830, C700S166000
Reexamination Certificate
active
06710293
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to laser drilling and particularly relates to microfilter design for laser drilling systems producing multiple sub-beams for parallel drilling operations.
BACKGROUND OF THE INVENTION
Material ablation by pulsed light sources has been studied since the invention of the laser. Etching of polymers by ultraviolet (UV) excimer laser radiation in the early 1980s led to further investigations and developments in micromachining approaches using lasers—spurred by the remarkably small features that can be drilled, milled, and replicated through the use of lasers. A recent article entitled “Precise drilling with short pulsed lasers” (X. Chen and F. Tomoo, High Power Lasers in Manufacturing, Proceedings of the SPIE Vol. 3888, 2000) outlines a number of key considerations in micromachining. Other recent patents of interest include the following:
U.S. Pat. No. 6,252,714, “Diffractive homogenizer with compensation for spatial coherence,” describes a diffractive homogenizer for receiving a beam of laser energy and producing a desired illumination pattern in a target plane. The homogenizer is made up of a plurality of diffractive sub-elements, each of which contributes to all or a portion of the desired image. By combining the contributions of many sub-elements to form the final image, a homogenizing effect is realized. In preferred embodiments, the sub-elements are designed to compensate for the finite spatial coherence of the incident laser beam and to control the numerical aperture distribution of the transmitted light. Each sub-element is composed of a large number of discrete pixels, each of which alters the phase of radiation passing therethrough by a selected amount. The pixel arrangement is chosen; using computer modeling and optimization techniques, such that the interference pattern created by the collective pixels in a sub-element makes up the desired image (or a portion thereof). A technique is also provided for reducing the intensity of the image formed by a selected sub-element, which may be located in a laser “hot spot”, by randomizing a selected percentage of the pixels located in that sub-element. This diffractive homogenizer is useful in various laser ablation and annealing, and other laser material processing applications.
U.S. Pat. No. 6,243,209, “Method and apparatus for providing rectangular shape array of light beams,” describes a linear array of equal intensity optical beams transformed into a rectangular array of equal intensity optical beams, while the intensity of each beam is kept nearly constant. The transformation is performed using an optical element that has two coatings on the front surface and a reflective coating on the opposing back surface. The front surface is partially coated with a reflective coating and partially coated with an anti-reflective coating. The beams are incident upon the front surface, with some of the beams incident on each of the two different coatings on the front surface. The beams incident on the front surface are specularly reflected. The remaining beams are transmitted through the optical element to the back surface, reflected from the back surface, and transmitted back up through the optical element and exit from the front surface. The exiting beams are thus shifted laterally and transversely to define the desired rectangular array. The index of refraction, thickness of the optical element, and the incident angle of the beam are selected to achieve the desired arrangement of beams.
U.S. Pat. No. 6,236,509, “Diffractive optical system with synthetic opening and laser cutting device incorporating this system,” describes an optical device for focusing a light beam. The device includes a Fourier diffractive element that can separate an incident beam into n beams along n directions that are symmetric about an optical axis. The device also includes a diffractive element including a Fresnel lenses capable of refocusing the n beams onto the optical axis. The device may be used with lasers and laser cutting devices.
U.S. Pat. No. 6,025,938, “Beam homogenizer,” describes a beam homogenizer that minimizes undesired intensity variations at the output plane caused by sharp breaks between facets in previous embodiments. The homogenizer includes a hologram made up of irregularly patterned diffractive fringes. An input beam illuminates at least part of the hologram. The hologram transmits a portion of the input beam onto an output plane. In doing so, the energy of the input beam is spatially redistributed at the output plane into a homogenized output beam having a pre-selected spatial energy distribution at the output plane. Thus, the illuminated portion of the output plane has a shape predetermined by the designer of the homogenizer.
U.S. Pat. No. 5,566,024, “Beam separation control and beam splitting by single blazed binary diffraction optical element,” describes two sets of two single blazed binary diffractive optical elements that form a beam separation control apparatus for expanding two closely spaced parallel beams into two wider spaced parallel beams or for contracting two wider spaced parallel beams into two closely spaced parallel beams. Four sets of two single blazed binary diffractive optical elements form a beam separation control apparatus for separating two closely spaced parallel beams into two wider spaced parallel beams for possible modulation or other optical effect, then returning the two beams to be closely spaced and parallel. A set of two adjacent and opposite single blazed binary diffractive optical elements can form a beam splitting apparatus or a beam combining apparatus.
Ultrafast lasers generate intense laser pulses with durations from roughly 10
−11
seconds (10 picoseconds) to 10
−14
seconds (10 femtoseconds). Short pulse lasers generate intense laser pulses with durations from roughly 10
−10
seconds (100 picoseconds) to 10
−11
seconds (10 picoseconds). Along with a wide variety of potential applications for ultrafast and short pulse lasers in medicine, chemistry, and communications, short pulse lasers are also useful in milling or drilling holes in a wide range of materials. In this regard, hole sizes in the sub-micron range are readily drilled by these lasers. High aspect ratio holes are also drilled in hard materials; applications in this regard include cooling channels in turbine blades, nozzles in ink-jet printers, and via holes in printed circuit boards.
Parallel processing of laser-milled holes is a key technique for increasing throughput in laser micromachining. Beamsplitting devices (beamsplitters) such as diffractive optical elements (DOEs) are used in laser micromachining to divide a single beam into multiple beams and thereby achieve parallel machining. However, such use of beamsplitters introduces technical challenges in hole geometry requirements and in the ability to produce consistent results. Such challenges need to be overcome in order to maintain consistency and repeatability in laser milling.
lnkjet nozzle design, construction, and operation are all important factors in providing high quality inkjet print resolution. Inkjet nozzle designs, which typically include specific patterns of many ink jet holes, which in turn are also specific defined geometries, provide the templates for nozzle holes drilled in a thin foil or polymer to a particular shape. Each nozzle hole includes an input section, a shaped section and an exit hole section, and each exit hole section is preferably cut with a high degree of precision respective to the design pattern. In a particular nozzle inconsistency in nozzle hole shape leads to inconsistent expulsion of inks among the individual holes in an inkjet nozzle, which negatively affects print resolution. Therefore, imperfections in the shape of the inkjet nozzle holes respective to the design pattern negatively impact print quality.
When a DOE is used to produce multiple sub-beams for parallel machining, generally there is variation in beam strengths among the sub-beams, i.e., some sub-
Cheng Chen-Hsiung
Liu Xinbing
Evans Geoffrey S.
Harness Dickey & Pierce PLC
Matsushita Electric - Industrial Co., Ltd.
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