innovations in beam shaping & illumination applicationsdls/presentations/fio_moo1... · 2013....
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Innovations in beam shaping & illumination applications
David L. ShealyDepartment of Physics
University of Alabama at BirminghamE-mail: [email protected]
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Innovation
NoveltyThe introduction of something newA new idea, method, or device => patent trends?The making of a change in something established
So, what innovations are being made in laser beam shaping and illumination applications?
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Growth in US patents involving beam shaping
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1976-80 1981-85 1986-90 1991-95 1996-02
US PatentsInvolvingBeam Shaping
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What is Laser Beam Shaping?
Process of redistributing the irradiance and phaseOptical design methods based on geometrical or physical optics are available in literature.
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Examples of Laser Beam Shapers
Uniform illumination of a surface can be achieved with a 1-element beam shaper, such as, mirror, plano-aspheric lens, or DOE.Transforming beam irradiance profile (Gaussian to more uniform) while retaining the wavefront shape requires 2 beam shaping elements, such as:
2 mirrors or 2 plano-aspheric lenses 1 bi-aspheric lens2 or 3-element spherical GRIN system 2 DOEs1 DOE and 1 plano-aspheric lens
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Physical or Geometrical Optics-based Design*
0 02 2f
r Yπβλ
=λ = wavelength, r0 = waist or radius of input beam, Y0= half-width of the desired output dimensionf = focal length of the focusing optic, or the working distance from the optical system to the target plane
ββββ < 4, Beam shaping will not produce acceptable results4 < β < 32, 4 < β < 32, 4 < β < 32, 4 < β < 32, Diffraction effects are significantβ > 32,β > 32,β > 32,β > 32, Geometrical optics methods should be adequate
Beam Shaping Guidelines:
*Laser Beam Shaping: Theory and Techniques, F.M. Dickey & S.C.Holswade,eds., Mercel Dekker, 2000.
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What innovations have been made in laser beam shaping?
Consider 2 element laser beam shapers
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Selected Literature on 2-element Laser Beam Shapers
Frieden, Appl. Opt. 4.11, 1400-1403, 1965: “Lossless conversion of a plane wave to a plane wave of uniform irradiance.” Kreuzer, US Patent 3,476,463, 1969: “Coherent light optical system yielding an output beam of desired intensity distribution at a desired equi-phase surface.”Rhodes & Shealy, Appl. Opt. 19, 3545-3553, 1980: “Refractive optical systems for irradiance redistribution of collimated radiation – their design and analysis.” Jiang, Shealy, & Martin, Proc. SPIE 2000, 64-75, 1993: “Design and testing of a refractive reshaping system.” Hoffnagle & Jefferson, Appl. Opt. 39.30, 5488-5499, 2000: “Design and performance of a refractive optical system that converts a Gaussian to a flattop beam” and US Patent 6,295,168, September 25, 2001: “Refractive optical system that converts a laser beam to a collimated flat-top beam.”
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( )( )
( )
122 2
max 2 2max
1 exp 2
1 exp 2
rR r R
r
α
α
− − = ± − −
Conservation of Energy:
Frieden, Appl. Opt. 4.11, 1400-1403, 1965:“Lossless conversion of a plane wave to a plane wave of
uniform irradiance.”
• Intensity shaping leads to OPL variation of 20λλλλ• Need to shape of output wavefront when phase is important• Frieden requires rays to be parallel Z-axis• Leads to OPL variation of λ/20λ/20λ/20λ/20
2π∫ Iin(r)r dr = 2π∫ Iout(R)R dR
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•Kreuzer, US Patent 3,476,463, 1969:“Coherent light optical system yielding an output beam of desired intensity distribution at a desired equi-phase surface.”
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Kreuzer, US Patent 3,476,463, 1969.
( )
( )
20
2m a x 0
122
m ax 2
1( , ) s in 01
θ−
−
−+ − = −
r r
r r
er s S Re
R
( ) ( )1 1 cos 0d n n θ− + − =R
( )
( ) ( )( )
20 2 11
r drz rn dnR r
= −− + −
∫ ( )( ) ( )
( )
= −− + −
∫ 20 2 11
R dRZRn dnR r
•Conservation of Energy & Ray Trace Equations:
•Constant OPL:
Mirror Surface Equations:
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Laser Beam Shaping Equations
Conservation of energy within a bundle of rays – geometrical optics intensity law.Ray trace equations.Constant optical path length condition.
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Optical Design of Laser Beam Shapers
Geometrical optics (Frieden, Kreuzer, Rhodes, & Shealy) leads to equations of two optical surfaces:
Hoffnagle and Jefferson note the importance of output beam uniformity; efficient utilization of input beam power; propagation of beam over useful region; and using surfaces which can be fabricated
Gaussian Super-Gaussian or Fermi-Dirac distribution
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Jiang, Ph.D. Dissertation, UAB, 1993
First work to build and test a 2-element beam shaper for operation with HeCdlaser at 441.57nm.
Optics fabricated in 1992 by Janos Optics by diamond turning of CaF2.
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Input and Output Beam Profile
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Illustrates the relationship λ and d.
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Input and output intensity profiles of an HeNelaser use with HeCd beam shaping optics.
Increased the lens spacing from 150.0 mm to 152.2mm
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J.A. Hoffnagle & C. M. Jefferson, “Design and performance of a refractive optical system that converts a Gaussian to a flattop beam,” Appl. Opt. 39.30, 5488-5499, 2000.
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Gaussian to Flat Top
• High Efficiency – Accepts 99.7% of the input beam while minimizing diffraction by using a Fermi-Dirac output beam profile
•High Uniformity - 78% incident power is within region with 5% rms power variation
•Good Propagation features•Large Bandwidth from 257 to 1550nm
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Collimated Output Beam
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Cover Graphics for Nov 2003 issue of Optical EngineeringIrradiance of Gaussian beam propagating through beam shaper developed by Hoffnagle & Jefferson, who contributed this graphics for the special section on laser beam shaping.
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Newport - Refractive Beam Shaper*
*Based on New Product Concept literature distributed at SPIE 2002, Seattle.
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GRIN Beam Shapers
Can a spherical-surface GRIN beam shaping system be designed using catalog GRIN materials?System would have practical applications.
Literature:• Wang & Shealy, Appl. Opt. 32.25, 4763-4769, 1993 – design of 2
spherical surface GRIN lenses where GRIN materials are determined from beam shaping equations, but are not from glass catalogs.
• N. C. Evans, D. L. Shealy, Proc. SPIE 4095, pp. 27-39, 2000 –design of 3 spherical surface GRIN beam shaper using catalog glasses. This problem is well suited for Genetic Algorithms (GAs) using both discrete parameters (small # of GRIN glasses, # elements) and continuous parameters (radii, thickness).
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Optical Design of Laser Beam Shapers
We know that geometrical optics leads to equations of two aspherical optical surfaces.Global Optimization works well with discrete & continuous variables:
Beam shaping merit function
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( )
( )
22
Target N1Diameter Collimation
Uniformityout out
1 1
exp exp 1 cos ( )
1 1( )
NQ
ii
N N
i ki k
s R RM MM
MI R I R
N N
γ=
= =
− − − − = = −
∏
∑ ∑
Beam Shaping Merit Function
Rtarget = Output Beam RadiusRN = Marginal Ray Height on Output Planeγi = Angle ith Ray Make with the Optical AxisQ and s = Convergence Constants
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3-Element GRIN Shaping System
Element 1
Element 2Element 3
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3-Element GRIN Shaping System•Average evaluation time for a generation: 7.80s
•Total execution time: 26.8 hrs
•Integrating Output Profile over Output Surface yields 21.9 units; integrating Input Profile over Input Surface yields 21.7 units
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Innovations in laser beam shaping using geometrical optics
Theory – laser beam shaping equations; trade-off between efficiency, uniformity & propagation losses; and merit function for use with GA optimizationAnalysis – better software for graphics, ray tracing aspherics and computing irradianceFabrication of aspherics has improvedTesting of beam shaping (afocal) opticsSome applications are revolutionary