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Laser Beam “Clean-Up” with Spatial Filter Abstract 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. 2 Modeling Task How does the size of the pinhole, located at the intermediate focal plane, influence the output beam? ? input field - wavelength lens #1 lens #2 632.8 nm feff = 25 mm feff = 25 mm - multimode laser D = 12.5 mm D = 12.5 mm with “noise” pinhole circular opening Fourier plane 3 Spatial Filter with 7.5µm-Diameter Opening A relatively large pinhole does not filter out much noise on the Fourier plane. 7.5 µm behind pinhole in front of pinhole input field pinhole 7.5 µm diameter lens #1 lens #2 4 Spatial Filter with 7.5µm-Diameter Opening 7.5 µm behind pinhole in front of pinhole input field output field pinhole 7.5 µm diameter lens #1 lens #2 5 Spatial Filter with 5.0µm-Diameter Opening 5.0 µm behind pinhole in front of pinhole input field output field pinhole 5.0 µm diameter lens #1 lens #2 6 Spatial Filter with 2.5µm-Diameter Opening 2.5 µm behind pinhole in front of pinhole input field output field pinhole 2.5 µm diameter lens #1 lens #2 7 Output Beam Profile and Power Comparison lens #1 lens #2 pinhole varying diameter Spatial filter in the Fourier plane helps reduce the higher-frequency noise, therefore leads to better output beam profiles. pinhole diameter 7.5µm pinhole diameter 5.0µm pinhole diameter 2.5µm 8 Output Beam Profile and Power Comparison lens #1 lens #2 pinhole varying diameter Relatively small pinhole limits the transmitted light and, as a consequence, leads to relatively large loss of power. pinhole diameter 7.5µm pinhole diameter 5.0µm pinhole diameter 2.5µm 9 Peek into VirtualLab Fusion flexible consideration of diffraction via Fourier transform settings real lens modeling for laser beams 10 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 11 VirtualLab Fusion Technologies nonlinear free crystals & components space prisms, anisotropic plates, components cubes, ... 1 waveguides lenses & & fibers freeforms 1 1 2 1 1 apertures & 3 scatterer Field 3 boundaries Solver diffusers gratings 2 2 diffractive diffractive, beam Fresnel, meta splitters lenses SLM & micro lens & HOE, CGH, adaptive freeform DOE components arrays # idealized component 12 Document Information title Laser Beam “Clean-Up” with Spatial Filter document code MISC.0082 version 1.0 edition VirtualLab Fusion Basic software version 2020.1 (Build 1.202) category Application Use Case - Pinhole Modeling in a Low-Fresnel-Number System further reading - Automatic Selection of Fourier Transform Techniques in Free-Space Propagation Operator 13 www.LightTrans.com.
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