SECOND EDITION
`S E C O N D E D I T I O N
`
`T h e o r y a n d T e c h n i q u e s
`
`Cael
`L a s e r B e a m
`ant
`S h a p i n g
`
`IPR2022-01291
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`Nad ea
`E D I T E D B Y
`F R E D M . D I C K E Y
`
`Clete
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`APPLE 1077
`Apple v. Masimo
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`1
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`APPLE 1077
`Apple v. Masimo
`IPR2022-01291
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`

`

`SECOND EDITION
`S E C O N D E D I T I O N
`
`LASER DEAN
`L a s e r B e a m
`DHAPING
`S h a p i n g
`Theory and Techniques
`
`T h e o r y a n d T e c h n i q u e s
`
`2
`
`

`

`3
`
`

`

`S E C O N D E D I T I O N
`
`L a s e r B e a m
`S h a p i n g
`
`T h e o r y a n d T e c h n i q u e s
`
`E D I T E D B Y
`F R E D M . D I C K E Y
`
`Boca Raton London New York
`
`CRC Press is an imprint of the
`Taylor & Francis Group, an informa business
`
`4
`
`

`

`CRC Press
`Taylor & Francis Group
`6000 Broken Sound Parkway NW, Suite 300
`Boca Raton, FL 33487-2742
`
`© 2014 by Taylor & Francis Group, LLC
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`No claim to original U.S. Government works
`Version Date: 20140402
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`International Standard Book Number-13: 978-1-4665-6101-4 (eBook - PDF)
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`5
`
`

`

`Dedication
`
`I would like to dedicate this book to Alexander,
`Ryan, Adrian, Miles, and Leo.
`
`6
`
`

`

`7
`
`

`

`Contents
`
`Preface.......................................................................................................................ix
`Editor ........................................................................................................................xi
`Contributors ........................................................................................................... xiii
`
`Chapter 1
`
`Introduction .......................................................................................... 1
`
`Todd E. Lizotte and Fred M. Dickey
`
`Chapter 2 Mathematical and Physical Theory of Lossless Beam Shaping ............13
`
`Louis A. Romero and Fred M. Dickey
`
`Chapter 3 Laser Beam Splitting Gratings ......................................................... 103
`
`Louis A. Romero and Fred M. Dickey
`
`Chapter 4 Vortex Beam Shaping ....................................................................... 127
`
`Carlos López-Mariscal and Julio C. Gutiérrez-Vega
`
`Chapter 5 Gaussian Beam Shaping: Diffraction Theory and Design ............... 151
`
`Fred M. Dickey and Scott C. Holswade
`
`Chapter 6 Geometrical Methods ....................................................................... 195
`
`David L. Shealy and John A. Hoffnagle
`
`Chapter 7 Optimization-Based Designs............................................................ 283
`
`Alexander Laskin, David L. Shealy, and Neal C. Evans
`
`Chapter 8 Beam Shaping with Diffractive Diffusers........................................ 333
`
`Jeremiah D. Brown and David R. Brown
`
`Chapter 9 Engineered Microlens Diffusers ...................................................... 367
`
`Tasso R. M. Sales
`
`vii
`
`8
`
`

`

`viii
`
`Contents
`
`Chapter 10 Multi-Aperture Beam Integration Systems ...................................... 405
`
`Daniel M. Brown, Fred M. Dickey, and Louis S. Weichman
`
`Chapter 11 Axicon Ring Generation Systems .................................................... 441
`
`Fred M. Dickey, Carlos López- Mariscal, and Daniel M. Brown
`
`Chapter 12 Current Technology of Beam Pro!le Measurement......................... 463
`
`Kevin D. Kirkham and Carlos B. Roundy
`
`Chapter 13 Classical (Nonlaser) Methods .......................................................... 525
`
`David L. Shealy
`
`9
`
`

`

`Preface
`
`At the time of the publication of the !rst edition of this book, there was a signi!cant
`interest in laser beam shaping for industrial applications and research. A signi!cant
`amount of this work was not published for proprietary reasons. At that time, people
`began to publish their work on beam shaping. The interest in laser beam shaping
`increased dramatically in the following years. This is due to the increase in the
`number of laser applications that can bene!t from shaping the beam, the increase in
`research in laser beam shaping techniques and the corresponding increase in the lit-
`erature, and the advances in optical component fabrication technology. The purpose
`of this edition is to update the book to include signi!cant developments in laser beam
`shaping theory and techniques.
`After the Introduction chapter, Chapter 2 presents the underlying electromagnetic
`theory and mathematical techniques applicable to beam shaping. This chapter is very
`fundamental and has one minor correction or change. Chapter 3 is a new chapter that
`presents the theory of optimal beam splitting gratings (fan-out gratings). Chapter 4 is
`a new chapter that addresses the theory and application of vortex beams. Chapter 5
`(former Chapter 3) presents the diffraction approach to single-mode Gaussian beam
`shaping and includes experimental results. The major changes in this chapter are the
`inclusion of a new section on wavelength dependence of the problem and an expan-
`sion of Appendix B. The methods, theory, and application of geometrical optics are
`discussed in Chapter 6 (former Chapter 4). This chapter is expanded signi!cantly to
`include the author’s research that was not available at the time of the !rst edition.
`Optimization-based techniques are presented in Chapter 7 (former Chapter 5). This
`chapter is greatly revised around the techniques based on the use of current opti-
`cal software packages. Beam shaping using diffractive diffusers is introduced in
`Chapter 8 (former Chapter 6). This chapter is signi!cantly revised. Chapter 9 is a
`new chapter that presents the theory of beam shaping based on the use of microlens
`diffusers. Multiaperture beam integration systems, including experiment and design,
`are presented in Chapter 10 (former Chapter 7). The major change in this chapter is
`the addition of a new section on channel integrators. Chapter 11 is a new chapter that
`discusses the generation of light ring patterns using axicons. This chapter includes
`a technique for the generation of rectangular line light patterns. Beam pro!le mea-
`surement technology is addressed in Chapter 12 (former Chapter 9). This chapter
`is signi!cantly updated. Chapter 13 (former Chapter 8) discusses the application of
`geometrical optics methods to classical (nonlaser) shaping problems.
`The material in these chapters gives the reader a working understanding of the
`fundamentals of laser beam shaping techniques. It also provides insight into the
`potential application of laser beam pro!le shaping in laser system design.
`The book is intended primarily for optical engineers, scientists, and students
`who have a need to apply laser beam shaping techniques to improve laser pro-
`cesses. It should be a valuable asset to someone who researches, designs, procures,
`
`ix
`
`10
`
`

`

`x
`
`Preface
`
`or assesses the need for beam shaping with respect to a given application. Due to
`the broad treatment of theory and practice in the book, we think that it should also
`appeal to scientists and engineers in other disciplines.
`I express my gratitude to the contributing authors whose efforts made the book
` possible. It was a pleasure working with the staff of Taylor & Francis Group books.
`Finally, I express my appreciation to the very helpful project coordinator, Laurie
`Schlags.
`
`Fred M. Dickey
`FMD Consulting, LLC
`
`11
`
`

`

`Editor
`
`Fred M. Dickey received his BS (1964) and MS (1965) degrees from Missouri
`University of Science and Technology, Rolla, Missouri, and his PhD degree (1975)
`from the University of Kansas, Lawrence, Kansas. He started and chaired the SPIE
`Laser Beam Shaping Conference, which is in its !fteenth year, for the !rst 8 years,
`and is currently a committee member. He heads FMD Consulting, LLC, Spring!eld,
`Missouri. He is a fellow of the International Optical Engineering Society (SPIE) and
`the Optical Society of America, and a senior member of the Institute of Electrical
`and Electronic Engineers. Dr. Dickey is also the author of over 100 papers and book
`chapters, and holds 9 patents.
`
`xi
`
`12
`
`

`

`13
`
`13
`
`

`

`Contributors
`
`Daniel M. Brown
`Optosensors Technology, Inc.
`Gurley, Alabama
`
`Alexander Laskin
`AdlOptica GmbH
`Berlin, Germany
`
`David R. Brown
`JENOPTIK Optical System, LLC
`Huntsville, Alabama
`
`Todd E. Lizotte
`Via Mechanics USA, Inc.
`Londonderry, New Hampshire
`
`Jeremiah D. Brown
`JENOPTIK Optical Systems, LLC
`Huntsville, Alabama
`
`Carlos López-Mariscal
`US Naval Research Laboratory
`Washington, DC
`
`Louis A. Romero
`Department of Computational
`and Applied Mathematics
`Sandia National Laboratories
`Albuquerque, New Mexico
`
`Carlos B. Roundy
`Logan, Utah
`
`Tasso R.M. Sales
`RPC Photonics Inc.
`Rochester, New York
`
`David L. Shealy
`Department of Physics
`University of Alabama at Birmingham
`Birmingham, Alabama
`
`Louis S. Weichman
`Sandia National Laboratories
`Albuquerque, New Mexico
`
`Fred M. Dickey
`FMD Consulting, LLC
`Spring!eld, Missouri
`
`Neal C. Evans
`PointClear Solutions, Inc.
`Innovation Depot
`Birmingham, Alabama
`
`Julio C. Gutiérrez-Vega
`Photonics and Mathematical Optics
`Group
`Tecnológico de Monterrey
`Monterrey, Mexico
`
`John A. Hoffnagle
`Picarro, Inc.
`Santa Clara, California
`
`Scott C. Holswade
`Sandia National Laboratories
`Albuquerque, New Mexico
`
`Kevin D. Kirkham
`Ophir-Spiricon, LLC
`North Logan, Utah
`
`xiii
`
`14
`
`

`

`15
`
`15
`
`

`

`1 Introduction
`
`Todd E. Lizotte and Fred M. Dickey
`
`Beam shaping is the process of redistributing the irradiance and phase of a beam
`of optical radiation. The beam shape is de!ned by the irradiance distribution. The
`phase of the shaped beam is a major factor in determining the propagation proper-
`ties of the beam pro!le. For example, a reasonably large beam with a uniform phase
`front will maintain its shape over a considerable propagation distance. Beam shaping
`technology can be applied to both coherent and incoherent beams.
`Arguably, there exists a preferred beam shape (irradiance pro!le) in any laser
`application. In industrial applications, the most frequently used pro!le is a uniform
`irradiance with steep sides, $at-top beam. This is due to the fact that the same inter-
`action (physics) is accomplished over the illuminated area. Flat-top beams also have
`applications in laser printing. However, this is not the only pro!le of interest. Laser
`disk technology uses a focused beam with minimized side lobes to eliminate cross
`talk. Other patterns of interest in applications include shaped lines, rings, and array
`patterns. Some of the major applications of laser beam shaping are discussed in
`detail in Laser Beam Shaping Applications.1
`Although the laser was invented in 1960, there were only about eight papers
`on laser beam shaping that appeared in the literature before 1980. A brief history
`and overview of laser beam shaping is given in the 2003 Optics & Photonics News
`paper “Laser Beam Shaping.”2 The rate of the appearance of laser beam shaping
`papers grew linearly, but slowly, until about 1995 when the rate increased dramati-
`cally. There is evidence that considerable research and development work on laser
`beam shaping was done in the period before 1995, but was not published for propri-
`etary reasons. Starting in 2000 and continuing to the present, there have been 14
`International Society for Optics and Photonics (SPIE) laser beam shaping confer-
`ences.3–16 The history of laser beam shaping is treated by Shealy in Chapter 9 of
`Laser Beam Shaping Applications.
`A $at-top laser irradiance pro!le can be obtained by expanding the beam to obtain
`a pattern with the desired degree of uniformity. This approach intrudes very large
`losses in energy throughput. In almost all beam shaping applications, it is desirable
`to minimize the losses. The two major beam shaping techniques for producing a
`uniform beam are !eld mapping and beam integrators (homogenizers). These tech-
`niques can be designed to have very low losses.
`Field mapping is the technique of using a phase element to map the laser beam
`into a uniform beam (or other pro!le) in a given plane. Field mappers are appli-
`cable to single-mode (spatially coherent) lasers. Producing vortex beams is also an
`
`1
`
`16
`
`

`

`2
`
`Laser Beam Shaping
`
`example of !eld mapping. The individual lenslets in beam integrators function as
`!eld mappers.
`Beam integrators break up the input beam into smaller beamlets that are directed
`to overlap in the output plane with the desired shape. They frequently consist of a
`lenslet array and a primary lens. Beam integrators can also be implemented using
`a re$ective tube and focusing the laser beam on the input aperture of the tube. This
`approach is called a channel integrator. Beam integrators are especially applicable to
`low spatial coherence beams. The low spatial coherence of the input beam reduces the
`speckle pattern that is inherent in the output of beam integrators. There cases when it
`is useful to apply beam integrators to spatially coherent beams when the speckle can
`be tolerated. It is interesting to note that optical con!gurations that can be considered
`beam integrators were introduced long before the advent of the laser.17,18
`The ability to do beam shaping is limited by uncertainty principle of quantum
`mechanics, or equivalently the time–bandwidth product inequality associated with
`signal processing. Mathematically, the uncertainty principle is a constraint on the
`lower limit of the product of the root-mean-square width of a function and its root-
`mean-square bandwidth. It can be directly applied to the beam shaping problem
`because of the Fourier transform relation in the Fresnel integral used to describe
`the beam shaping problem. In fact, the uncertainty principle is generally applicable
`to diffraction theory. Applying the uncertainty principle to the general diffraction
`problem associated with laser beam shaping, one obtains a parameter β of the form
`
`
`
`β
`
`= C
`
`r y
`0 0
`λ
`z
`
`(1.1)
`
`where:
`r0 is the input beam half-width
`y0 is the output beam half-width
`C is a constant that depends on the exact de!nition of beam widths
`z is the distance to the output plane
`
`The parameter β is also obtained when applying the method of stationary phase to
`diffraction problems.
`The value of β must be suf!ciently large for successful beam shaping to be accom-
`plished. It should be noted that the system designer has some design control over β
`by specifying r0 or, possibly, the other three parameters in Equation 1.1. Because of
`its fundamental nature, β is applicable to !eld mappers and beam integrators.
`It is commonly stated that when β is large the problem can be treated using geo-
`metrical optics. This is true for !eld mapping systems designed to produce $at-top
`pro!les. However, techniques such as diffractive diffusers inherently require the use
`of diffraction theory in the design process. In addition, diffraction theory is useful in
`determining some general properties of beam shapers. An example is the wavelength
`independence of some !eld mapping con!gurations (see Chapter 5).
`In no case can quality beam shaping be accomplished if β is small. It is suggested
`that this parameter be considered in the initial stage of any beam shaping system
`design.
`
`17
`
`

`

`Introduction
`
`3
`
`As stated earlier and clearly de!ned in the subsequent chapters, the theory,
` calculations, and strategies for designing laser beam shaping systems have come a
`long way. Although success in the application of beam shaping does not only come
`from knowing how to calculate a design and understanding the guiding parameters
`such as β, it simply provides a working baseline of knowledge.
`When an engineer or a development team considers the integration of optics into
`a process, they need to take into account a number of primary as well as ancillary
`variables that start at the process and work backward through the optical system to
`the laser source itself. Failure is inevitable if beam shaping is considered simply as
`an off-the-shelf product that is easy to integrate. Consideration of a new beam shaper
`design or the purchase of an off-the-shelf beam shaping product must be approached
`carefully since the beam shaper’s performance is dependent on the stability of the
`laser source itself. Offering a considerable number of challenges due to the dynamic
`nature of laser processes simple changes to duty cycle often result in pointing insta-
`bility, divergence shifts, beam intensity distribution, and power $uctuations, to name
`a few. All of the variables identi!ed need to be scrutinized and prioritized so that the
`beam shaper can be designed and con!gured with an appropriate set of precondition-
`ing optics or enough axes of adjustment to provide !ne-tuning if required.19 These
`items are only part of what it takes to be successful; a willingness to tackle the hard-
`est problems !rst is the only true guarantee.
`Since the introduction of lasers into the industrial marketplace, those of us
`involved in its application have been in a technology race, whether we like it or not.
`Driving innovation is the key to success for technologists, but that innovation in
`many cases is found by simply searching for insight from existing successes within
`the scienti!c community or other markets where similar technology is applied. That
`insight can take many forms such as exposure to existing and past technologies or
`merely taking calculated risks by blazing a new trail by pulling together various
`technologies and integrating them into a new solution. Whether applying old or new
`ideas, innovation of beam shaping technology requires identifying the parameters
`within the context of a laser process that matter and moving through them systemati-
`cally to deliver an elegant solution.
`Below are two examples that highlight the development of “diffractive and refrac-
`tive” laser beam shaping technology over the past 20 years and hit upon this theme.
`From a historical perspective, the examples were selected to illustrate the progres-
`sion and impact of laser beam shaping on the industrial laser system marketplace. No
`attempt has been made to select speci!c technological milestones of equal impor-
`tance nor should the reader consider these items critical in terms of a grand historical
`record. These examples are simply moments in time where insight gained by early
`adopters led to experimentation and the evolution of laser beam shaping within the
`industrial laser and laser materials processing !eld. Let us explore a few exemplar
`beam shaper solutions that were brought to market, which is the point where true
`innovation ends, as well as demonstrated.
`As mentioned earlier, !eld mappers are phase elements that redistribute laser light
`to form a new desired irradiance and phase pro!le. These phase elements commonly
`take two highly ef!cient forms, either traditional refractive phase elements, such as cus-
`tom aspheric lenses (>96% ef!cient), or diffractive elements, such as diffractive lenses
`
`18
`
`

`

`4
`
`Laser Beam Shaping
`
`FIGURE 1.1 Gaussian to round $at-top diffractive !eld mapping beam shaper element.
`
`(>85% ef!cient), where the phase coef!cients are compressed into 2Π surface reliefs.
`Figure 1.1 shows a Gaussian to round $at-top diffractive !eld mapping beam shaper ele-
`ment. In many cases, these diffractive optics are based upon an aspheric phase design. It
`should be stated that fabrication plays a major role in the ef!ciency of such !eld mappers
`and during the early 1990s the costs for fabricating these elements were signi!cant; 20
`years later, these elements are now manufactured at scale with competitive pricing that
`has made them available for lower cost laser marking applications.
`Although numerous far- and near-infrared (FIR/NIR) lasers such as CO2 and
`Nd:YAG have bene!ted from more traditional beam shaping and !eld mapping
`aspheric systems, frequency tripled and quadrupled diode-pumped solid-state (UV
`DPSS) lasers (355 and 266 nm, respectively) have bene!ted from !eld mappers to
`a greater degree. As UV DPSS lasers began to be adopted into larger volume laser
`system markets, it quickly became necessary to begin employing !eld mappers to
`improve process performance. Immediate gains in process stability and overall
`material removal quality were demonstrated. Finding a home within high volume
`microelectronics packaging manufacturing, industrial ultraviolet (UV) laser tools
`utilizing !eld mappers led to the rapid level of microminiaturization of numerous
`consumer electronics and commercial products. By providing uniform intensities,
`very small features can be produced.
`As !eld mapper-based beam shapers were employed, the UV DPSS laser system
`began shifting from a traditional focal point machining technique to a higher precision
`imaging technique.20 Optical imaging is the most widely used beam delivery technique
`in the laser micromachining world. Optical imaging is the preferred method because it
`offers a high-!nesse process that creates accurate and controllable structures into the
`surfaces of a wide variety of organic and inorganic materials. De!ned by an image
`placed on a mask, the desired structures are optically transferred from the mask to
`the surface. The design of the beam delivery system is based on the lens imaging
`equation; however, the calculation of most importance, is the demagni!cation required
`to achieve the optimum energy density on target for the material being processed to
`
`19
`
`

`

`Introduction
`
`5
`
`FIGURE 1.2 An assembled beam shaping and imaging beam delivery for a UV DPSS
`marking application installed on an automation system.
`
`produce precision ablated microstructures. The demagni!cation ratio determines the
`conjugate distances of the optical imaging system, that is to say the object (mask) dis-
`tance to the lens and the image distance to the target plane. The optical system reduces
`the mask design by this factor; therefore, when generating the mask artwork, the fea-
`ture desired on target is multiplied by the magni!cation factor. Figure 1.2 shows an
`assembled beam shaping and imaging beam delivery for a UV DPSS marking appli-
`cation installed on an automation system. The UV beam delivery systems geared for
`UV DPSS laser micromachining applications have four basic functions once the laser
`beam exits the laser itself: (1) improve the uniformity of the laser beam, (2) illuminate
`a !xed aperture or mask plane, (3) reduce/demagnify and project the mask image onto
`the target material, and (4) control the energy density at the target.
`In most cases, the output intensity pro!le of the UV DPSS laser is Gaussian or
`TEM00 mode. For precision micromachining such as drilling or thin-!lm pattern-
`ing, the transformation of the Gaussian laser beam into a $at-top intensity pro!le
`was the watershed moment, where the quality and accuracy of laser-based processes
`
`20
`
`

`

`6
`
`Laser Beam Shaping
`
`truly began to be demonstrated. Microvias that are laser-drilled into microelectronic
` packaging and laser thin-!lm patterning for solar cells and $at panel displays were
`key markets where the bene!ts of laser beam shaping were initially realized in the
`late 1990s and continue even today.
`Two examples of common designs include !eld mappers for transforming
` single- mode Gaussian laser beams into a round or square $at-top intensity distribu-
`tion pro!le. Figure 1.3 shows a Gaussian and super Gaussian pro!le. Within the !eld
`of microvia drilling of printed circuit boards (PCBs), the Gaussian output of a UV
`DPSS laser beam is shaped into a round $at-top intensity distribution and demagni-
`!ed by using an optical imaging system to achieve the appropriate energy density
`to either ablate a thin metal !lm or polymer dielectric layers that make up a PCB
`assembly. Figure 1.4 shows a 30, 40, and 50 μm blind microvia in a PCB. Conversely,
`a square $at-top intensity pro!le can be used to pattern thin !lms to form struc-
`tures such as pixel arrays or to precisely cut circuits for repairing advanced displays.
`Figure 1.5 shows an electrical grounding strap that was laser deleted using a square
`
`2N
`
`r w
`
`0
`
`2
`I ∝ e
`
`N = 1
`
`N = 10
`
`Gaussian
`
`Super Gaussian
`
`FIGURE 1.3 A Gaussian and super Gaussian pro!le distribution as an example of the
`desired transformation for many industrial beam shaping applications.
`
`FIGURE 1.4 Microvia hole drilling on a PCB with 30, 40, and 50 μm diameters (left to
`right). These are possible using a UV DPSS $at-top laser beam.
`
`21
`
`

`

`Introduction
`
`7
`
`FIGURE 1.5 A grounding strap deletion using a square $at-top laser beam.
`
`$at-top beam and the energy density was tailored so that only the strap was removed
`leaving the underlying material undamaged.
`Depending on the laser system setup, the imaged beam can precisely drill or
`pattern materials with such !nesse as to minimize or negate any thermal damage
`to the surrounding material. Therefore, precise and tailored to the material being
`processed, !eld mappers have enabled new opportunities for precision micromanu-
`facturing that could not have been possible 20 years ago.
`The arrival of integrator technology for laser materials processing was under
`the radar and developed in earnest when major challenges were encountered
`with the introduction of excimer lasers into the marketplace. During these early
`years, integrator development was kept secret until patent !lings revealed their
` implementation. Many of these innovations were championed by laser system devel-
`opers who were seeking solutions to improve excimer laser beam uniformity for
`large !eld size high-precision laser processes. In nearly all applications, excimer
`laser output uniformity is critical for high-precision applications.21 During the early
`1980s, to create a uniform irradiance beam pro!le, engineers were limited to either
`improving the performance of the laser itself, at a hefty price, or utilizing optical
`techniques. Modi!cation of the laser meant trade-offs; increased uniformity at the
`sacri!ce of pulse energy or power and that still did not guarantee the best uniformity.
`At this time the excimer laser was !nding new applications within semiconduc-
`tor processing such as lithography and gaining ground in the promising !eld of laser
`micromachining. These early adopters were exposed to similar integrator designs
`used within illumination systems for lamp-based exposure tools, such as those pro-
`duced by Oriel Instruments Corporation (Stratford, CT), which were generally simple
`lens array integrator designs.22 The earliest and relatively successful example of an
`industrial excimer laser application that would not have been possible without the use
`of beam integrators, besides the semiconductor lithography market, was laser anneal-
`ing of silicon. Patented by XMR, Inc. (Houston, TX) in 1986 and issued in 1988 as
`
`22
`
`

`

`8
`
`Laser Beam Shaping
`
`FIGURE 1.6 A beam integrator design from the mid-1980s manufactured by XMR, Inc.
`
`US Patent 4,733,944, the design is one of a handful of instances of an imaging beam
`integrator for a high-volume industrial laser process requiring absolute stability and
`uniformity. What was unique about the design at the time was the fact that the spot
`size produced could be selectively adjusted in size at the working plane. Adjustability
`allowed variation of the energy density on target, tailoring it to an optimum setting
`and process area. Figure 1.6 is an example of an XMR design from the actual system.
`From this point, the design of laser beam integrators began to take the form of
`specialized optical con!gurations with further enhancements and re!nements to
`meet the needs of ever-demanding laser micromachining processes. In 1994 the
`integration of UV excimer lasers for laser micromachining of $uidic structures
`was being exploited for consumer and medical device products. One such prod-
`uct was the production of nozzle plates and $uidic channels for inkjet printers.
`Although personal inkjet printers had entered the marketplace in 1988, it was
`not until 1991 when inkjet printer manufacturers had begun to seriously consider
`excimer lasers as a means to reduce the costs of forming precision inkjet nozzle
`plates, which were upward of $4.00 each to manufacture. Figure 1.7 shows an
`example of an inkjet nozzle plate with integrated $uidic channels imaged and
`ablated into polyimide.
`At that time, manufacturing nozzle plates to micron accuracies was not an easy
`task and they were costly to manufacture using traditional lithography and nickel
`electroforming techniques. It was clear in the early days of process development that
`the design of excimer beam delivery optics, physical system con!guration, methods
`of optical beam shaping, and laser material interaction would play signi!cant roles
`in producing inkjet nozzle plates. Due to higher demands for quality and the criti-
`cal nature of providing consumers with exceptionally reliable products, the excimer
`processes needed to be robust and repeatable to a 3σ or better level.23
`
`23
`
`

`

`Introduction
`
`9
`
`FIGURE 1.7 An inkjet nozzle plate with integrated $uidic channels imaged and ablated
`into polyimide.
`
`Matching the laser process optics to resolve the nozzle and $uidic channel features
`to micron tolerances within the desired material was the goal. To complicate matters,
`inkjet nozzle arrays have dimensional requirements upward of 15  × 2 mm in size
`(L × W), which made the selection of beam shaping technology to provide uniformity
`across the entire image plane at a uniform energy density the most critical aspect of
`the excimer micromachining system. Figure 1.8 shows how the implementation of an
`imaging lens array beam integrator evolved in less than 10 years (ca. 1994). Larger
`in size and its zooming feature allowing larger illumination !eld sizes at the mask
`plane demonstrates how the integrator design had progressed into a useful and ver-
`satile tool for large-!eld ablation applications. Incorporating beam preconditioning
`optics, in this case an anamorphic cylindrical lens telescope, the output beam of the
`excimer was shaped from a rectangular shape into an optimized square con!gura-
`tion for illuminating the zoomable cross-cylindrical lens beam integrator. The beam
`integrator design was also more advanced than earlier designs, with an adjustable
`zoom for both axes of the beam, allowing the illumination !eld at a mask plane to be
`both uniform in intensity and dimensionally optimum. The shaped beam illuminated
`a mask that de!ned the features being produced. The numerical aperture of the beam
`integrator was designed to match the numerical aperture of the !nal imaging lens
`system allowing the mask design to be imaged onto the material to be processed. As
`the !rst excimer laser inkjet nozzle drilling system came online, the cost of inkjet
`nozzle plates had dropped to less than $0.20 a unit—a signi!cant milestone for that
`industry that would not have been achieved without an integrator-based beam shaper
`design.
`Since that time, further advancements have made it possible to take an excimer
`beam with a beam s