研究目的
To demonstrate a technique in velocity map imaging (VMI) that allows spatial gating of the laser focal overlap region in time resolved pump-probe experiments to significantly enhance signal-to-noise ratio by eliminating background signal arising outside the region of spatial overlap of pump and probe beams.
研究成果
The technique of tilting the laser beams and applying a time gate to the MCP detector significantly enhances the signal-to-noise ratio in pump-probe photo-ion imaging experiments by selecting particles born only in the overlap region of the pump and probe beams. This method is particularly beneficial for experiments involving extreme-ultraviolet light or X-rays.
研究不足
The technique introduces a possible energy smearing of the particles which could introduce uncertainties in the energy measurement. The effectiveness of the gating can be limited by the tilt angle of the laser beams and the width of the time gate applied to the MCP detector.
1：Experimental Design and Method Selection:
The technique involves tilting the laser beams with respect to the surface of the VMI electrodes to create a gradient in flight time for particles born at different points along the beam. A microchannel plate (MCP) detector is pulsed to select particles born only where the laser beams overlap.
2：Sample Selection and Data Sources:
Ethylene (C2H4) is used as a target gas, and harmonics consisting predominantly of the third harmonic (260 nm, 4.75 eV) in both pump and probe arms are used to excite and ionize ethylene.
3：75 eV) in both pump and probe arms are used to excite and ionize ethylene.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: A three stage Ti:Sapphire laser amplifier, high harmonic VUV and XUV radiation generation setup, VMI spectrometer with electrodes, microchannel plate detector coupled to a phosphor screen, and a CMOS camera.
4：Experimental Procedures and Operational Workflow:
The laser beams are focused onto the target gas in the center of the VMI spectrometer. The ions produced are accelerated towards the MCP detector, and the resulting images are recorded by the CMOS camera.
5：Data Analysis Methods:
The ion yield is analyzed as a function of pump-probe delay to determine the signal-to-noise ratio enhancement.
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