研究目的
Investigating the extrinsic chirality in GaAs-based nanowires partially covered with gold through second harmonic generation measurements.
研究成果
SHG with circularly polarised light reveals the effective (or extrinsic) chiral behaviour of GaAs nanowires partially covered by an asymmetric gold nanolayer. The efficiency in detecting such geometrical features is possible in the limit of a good resonant response of the nanostructures at the first and second harmonic frequency of the incident field.
研究不足
The SHG efficiency is affected by the lack of resonant modes in NWs with larger diameters, making the difference between LCP and RCP signal less evident.
1：Experimental Design and Method Selection:
SHG measurements were performed using a linearly polarised Ti:Sapphire fs laser at 800 nm, with a pulse duration of 100 fs and a repetition rate of 80 MHz. A quarter waveplate was used to obtain either left circularly (LCP) or right circularly (RCP) polarized light.
2：Sample Selection and Data Sources:
Different samples of NWs were produced, with lengths of approximately 5 microns, and diameters ranging between 138 nm and 197 nm. Part of each sample was coated by a thin film of Au (10-20 nm) at a glancing angle.
3：List of Experimental Equipment and Materials:
Ti:Sapphire fs laser, quarter waveplate, short pass filter, narrow bandpass filter centered at 400 nm, photomultiplier tube.
4：Experimental Procedures and Operational Workflow:
The SHG signal was detected in reflection after passing through a short pass filter that removes the first harmonic pump. The SHG was analysed in the ‘s’ or ‘p’ polarisation state by an analyser.
5：Data Analysis Methods:
The signal was filtered by a narrow bandpass filter and finally detected by a photomultiplier tube in a gated photon counting regime.
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