研究目的
To generate pure Laguerre-Gaussian vector beams on the higher-order Poincaré sphere using hollow Gaussian beams through dielectric metasurfaces, overcoming diffraction limitations in extracavity generation.
研究成果
The study successfully demonstrates the theoretical and experimental generation of pure Laguerre-Gaussian vector beams using hollow Gaussian beams and dielectric metasurface q-plates. When the HGB order is twice the q-plate topological charge, pure LG modes are achieved, and any polarization state on the higher-order Poincaré sphere can be realized. The method provides high mode purity, with potential applications in high-precision measurements and quantum information. Future work could focus on improving HGB generation techniques to enhance VB quality.
研究不足
The quality of the generated VB depends on the perfection of the incident HGB; imperfections in the HGB (e.g., non-zero intensity at the center) can lead to diffracted rings and reduced purity. Larger ring radii in HGBs yield purer VBs, but lower-order HGBs are more prone to errors. Experimental errors in polarization measurements (e.g., Stokes parameters) can cause deviations from theoretical predictions.
1：Experimental Design and Method Selection:
The experiment involves using a He-Ne laser to produce a fundamental Gaussian beam, which is transformed into a hollow Gaussian beam (HGB) using a spatial light modulator (SLM) and spiral phase plate (SPP). This HGB is then passed through a q-plate implemented with dielectric metasurfaces to generate vector beams (VBs) with pure Laguerre-Gaussian (LG) modes. The theoretical basis includes deriving a general expression for VBs from HGBs and using vector diffraction theory.
2：Sample Selection and Data Sources:
The samples are the fabricated dielectric metasurface q-plates with topological charges q=0.5 and q=1. Data sources include intensity and polarization measurements from a CCD camera.
3：5 and q=Data sources include intensity and polarization measurements from a CCD camera. List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: He-Ne laser (Thorlabs HNL210L-EC), spatial light modulator (Holoeye Pluto-Vis), spiral phase plates, q-plates (dielectric metasurfaces fabricated in fused silica), polarizers (Glan laser polarizers, Thorlabs), quarter-wave plates, beam splitters, mirrors, and a CCD camera (Coherent LaserCam HR).
4：Experimental Procedures and Operational Workflow:
The beam from the laser is expanded, collimated, and linearly polarized. It is modulated by the SLM to add a helical phase, then passed through an SPP to cancel the phase and form an HGB. The polarization is adjusted using polarizers and waveplates before incidence on the q-plate. The output VB is analyzed for intensity and polarization using additional waveplates, polarizers, and the CCD.
5：Data Analysis Methods:
Stokes parameters are measured to retrieve polarization states. Intensity distributions are compared with theoretical LG modes. Radial intensity profiles are analyzed to verify mode purity.
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He-Ne laser
HNL210L-EC
Thorlabs
Emits a fundamental Gaussian beam used as the light source in the experiment.
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Charge coupled device
LaserCam HR
Coherent
Records the intensity of the exit light beam for analysis.
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Spatial light modulator
Pluto-Vis
Holoeye
Modulates the beam to add a helical phase, transforming it into a vortex beam.
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Glan laser polarizer
Thorlabs
Polarizes the light beam; used as GLP0, GLP1, GLP2 in the setup for controlling polarization.
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Quarter-wave plate
Adjusts the polarization state of the light beam; used as QWP1 and QWP2 in the setup.
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Beam splitter
Splits the light beam in the experimental setup.
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Mirror
Reflects the light beam; used to reverse the helical phase in the setup.
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Spiral phase plate
Cancels the helical phase to help form the hollow Gaussian beam.
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q-plate
Converts the hollow Gaussian beam into a vector beam with Laguerre-Gaussian mode; implemented with dielectric metasurfaces.
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