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Multiple-Reflection And Focussing Apparatus for Concentrating Laser Radiation at an Array of Sites

IP.com Disclosure Number: IPCOM000101207D
Original Publication Date: 1990-Jul-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 6 page(s) / 261K

Publishing Venue

IBM

Related People

Linsker, R: AUTHOR [+3]

Abstract

A technique is described whereby a multiple-reflection and focussing apparatus provides the ability to selectively concentrate and focus the fluence and incident radiation of a laser beam onto a set of desired locations or regions. Two methods are discussed, multiple-reflection and focussing, to enable the apparatus to provide an increase in the fluence delivered to the laser target. This results in a significant increase in product throughput at a given output power per laser pulse.

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Multiple-Reflection And Focussing Apparatus for Concentrating Laser Radiation at an Array of Sites

       A technique is described whereby a multiple-reflection
and focussing apparatus provides the ability to selectively
concentrate and focus the fluence and incident radiation of a laser
beam onto a set of desired locations or regions. Two methods are
discussed, multiple-reflection and focussing, to enable the apparatus
to provide an increase in the fluence delivered to the laser target.
This results in a significant increase in product throughput at a
given output power per laser pulse.

      In laser actuated applications, such as drilling of via holes
or laser etching of line segments, much of the laser energy
concentration at the illuminated portions of masked areas is absorbed
by the mask.  The concept described herein provides a method of
concentrating the incident radiation only to those sites which lie in
a regular array.  This allows faster processing of the laser
operation.

      The apparatus includes focussing and masking elements, and a
cavity of uniform cross sections having some or all of the inner
walls coated with reflective material, so as to form a "light
tunnel".  If the cavity is square or hexagonal and all walls are
reflecting, the apparatus will concentrate the power from the laser
beam onto a plurality of sites lying on a regular grid.  If the
cavity has only two opposite walls reflecting, the incoming beam can
be concentrated onto a plurality of regular spaced parallel line
segments.  Masking of the beam allows a selection of a desired subset
of sites and to provide prescribed fluences at each of these sites.

      To illustrate the principle, consider the problem of
concentrating a beam of uniform illumination onto three parallel
equally-spaced lines, as shown in Fig.  1.  The "light tunnel" in
this case is reflective on the top and bottom surfaces, such that the
beam enters at the left and is defined by stops at the top and
bottom, and by optional mask M1, focussed by cylinder lens L0.
Central beam portion 12 fills output window W without undergoing any
reflections. Top peripheral beam 14 is reflected once off the bottom
wall of the tunnel, so as to fill output window W.  Bottom peripheral
beam 15 is similarly reflected off the top wall. Observing the output
beyond window W, the illumination comes from three apparent line
sources, such that lens L1 will focus the illumination from  these
apparent sources onto the target.  The control of the relative
intensities of the three beams is performed by mask M1, such that the
fraction of the beam transmitted through mask M1 is different for the
three beam regions.  This is desirable so as to equalize the final
beam intensities.  For example, region 12 can be partially masked to
compensate for the reflective losses incurred by the final beams
corresponding to regions 14 and 15.  If it is required to block out
one of the lines completely, the...