研究目的
Investigating the selective excitation of one Raman peak among three excited states in tip‐enhanced Raman spectroscopy (TERS) by shaping the pump and Stokes femtosecond laser pulses to suppress noise and improve detection sensitivity and accuracy.
研究成果
The enhanced selective excitation of one Raman transition among the three excited states was achieved simultaneously in the TERS nanostructure by shaped femtosecond laser pulses, increasing the probability of the selectively excited Raman transition by several hundred times in amplitude while depressing the others to zero. This method has important applications for depressing noise and improving detection sensitivity and accuracy in TERS.
研究不足
The study is theoretical, and practical implementation may face challenges in precisely shaping the laser pulses and aligning the TERS structure for optimal excitation and detection.
1：Experimental Design and Method Selection:
The study involves shaping the pump and Stokes femtosecond laser pulses to selectively excite one Raman peak among three in a TERS structure. The shaped pulses are transformed into the time domain, discretized, and reconstructed before irradiating the TERS structure obliquely.
2：Sample Selection and Data Sources:
A single molecular layer with a thickness of 0.5 nm covering an entire silver film is used as the sample. The complex permittivity of Ag is taken from Johnson and Christy.
3：5 nm covering an entire silver film is used as the sample. The complex permittivity of Ag is taken from Johnson and Christy.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: A silver conical tip with a full cone angle of 40° over an Ag film, COMSOL Multiphysics software for numerical calculations.
4：Experimental Procedures and Operational Workflow:
The shaped pump and Stokes pulses are used to irradiate the TERS structure, and the impulse responses at probe points are calculated followed by a Fourier transform.
5：Data Analysis Methods:
The spectra of the response pulses are obtained using Fourier transformation, and the phase differences between the input and response pulses are calculated.
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