Laser Beam “Clean-Up” with Spatial Filter · 2020. 5. 28. · Laser Beam “Clean-Up” with...
Transcript of Laser Beam “Clean-Up” with Spatial Filter · 2020. 5. 28. · Laser Beam “Clean-Up” with...
Laser Beam “Clean-Up” with Spatial Filter
Abstract
To obtain good beam quality is important for many laser applications, and a typical experimental method to obtain good beam quality is the spatial filtering. Within a spatial filtering system, a pinhole is placed on the intermediate focal plane (i.e. the Fourier plane) to get rid of the unwanted spatial frequency components. To model such systems, one must consider the diffraction from the pinhole and the diffraction property of the laser beams, and we demonstrate the spatial filtering effect in this example.
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Modeling Task
?input field
- wavelength 632.8 nm
- multimode laser with “noise”
lens #1feff = 25 mmD = 12.5 mm
pinholecircular opening
lens #2feff = 25 mmD = 12.5 mm
How does the size of the pinhole, located at the intermediate focal plane,
influence the output beam?
Fourier plane
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Spatial Filter with 7.5µm-Diameter Opening
input field
in front of pinhole
pinhole7.5 µm diameter
lens #2lens #1
behind pinhole
7.5 µm
A relatively large pinhole does not filter out much noise on the Fourier plane.
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Spatial Filter with 7.5µm-Diameter Opening
input field
in front of pinhole
pinhole7.5 µm diameter
lens #2lens #1
behind pinhole
output field
7.5 µm
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Spatial Filter with 5.0µm-Diameter Opening
input field
in front of pinhole
pinhole5.0 µm diameter
lens #2lens #1
behind pinhole
output field
5.0 µm
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Spatial Filter with 2.5µm-Diameter Opening
input field
in front of pinhole
pinhole2.5 µm diameter
lens #2lens #1
behind pinhole
output field
2.5 µm
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Output Beam Profile and Power Comparison
pinholevarying diameter
lens #2lens #1
pinhole diameter 7.5µm pinhole diameter 5.0µm pinhole diameter 2.5µm
Spatial filter in the Fourier plane helps reduce the higher-frequency
noise, therefore leads to better output beam profiles.
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Output Beam Profile and Power Comparison
pinholevarying diameter
lens #2lens #1
pinhole diameter 7.5µm pinhole diameter 5.0µm pinhole diameter 2.5µm
Relatively small pinhole limits the transmitted light and, as a
consequence, leads to relatively large loss of power.
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Peek into VirtualLab Fusion
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flexible consideration of diffraction via Fourier transform settings
real lens modeling for laser beams
Workflow in VirtualLab Fusion
• Set up input Gaussian field− Basic Source Models [Tutorial Video]
• Import lens systems from Zemax OpticStudio®
− Import Optical Systems from Zemax [Use Case]
• Set the position and orientation of components− LPD II: Position and Orientation [Tutorial Video]
• Set the Fourier transforms properly
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free space prisms,
plates, cubes, ...
lenses & freeforms
apertures & boundaries
gratings
diffractive, Fresnel, meta
lensesHOE, CGH,
DOEmicro lens &
freeform arrays
SLM & adaptive
components
diffractive beam
splitters
diffusers
scatterer
waveguides & fibers
crystals & anisotropic components
nonlinear components
VirtualLab Fusion Technologies
Field Solver
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1 1 2
1 1
2 2
# idealized component
3 3
Document Information
www.LightTrans.com13
title Laser Beam “Clean-Up” with Spatial Filterdocument code MISC.0082version 1.0edition VirtualLab Fusion Basicsoftware version 2020.1 (Build 1.202)category Application Use Case
further reading- Pinhole Modeling in a Low-Fresnel-Number System- Automatic Selection of Fourier Transform Techniques in Free-Space
Propagation Operator