Time-Resolved Coherent Anti-Stokes Raman Scattering of Graphene: Dephasing Dynamics of Optical Phonon

Abstract

We report dynamics of the G-mode in graphene probed with time-resolved coherent anti-Stokes Raman scattering measurements. By applying BOXCARS excitation geometry with three different excitation wavelengths, various nonlinear processes can be selectively detected due to energy and momentum conservation and temporal sequence of the pulses. The Raman signal due to resonant coherent excitation of the G-mode shows exponential decay with lifetime of ∼325 ± 50 fs. This decay time is shorter than expected based on the line width of the G-mode in the Raman spectrum. We propose that the unexpectedly short dephasing time is a result of dynamic variation of nonadiabatic coupling of the photoexcited electron distribution and the G-mode.

Nonlinear Optical Characterization of 2D Materials

“…This technology has been well applied in the detection of biological and polymer materials [ 38 , 115 ], so the technology can be used for the characterization of 2D materials, and it also has great advantages in its chemical specific detection. The measurement of multiple characteristic peaks by tuning the spectrally narrow wavelength can be achieved, but the introduction of the supercontinuum makes the operation of detection easier and able to achieve rapid spectral characterization [ 22 , 108 ].…”

“…The system instrument can be further improved in other aspects. For example, if you need to use the CARS system to detect the dynamics of electrons and phonons in 2D materials, the time-resolved method can be used in CARS to detect the phase movement mechanics of specific modes of electrons and phonons in 2D materials [ 108 ]. At the same time, it can be considered to improve the NLO characterization platform in the inherent performance of the instrument itself.…”

“…The signal reflected by the nonlinear interaction between the incident laser light and the micro-nano structure sample is reflected through the dichroic mirror and received by the scientific complementary Metal-Oxide-Semiconductor detector and CCD in the imaging spectrometer to detect the spectrum and image. A bandpass filter is added between the spectrometer, CCD, and dichroic mirror, which is used to filter the excitation light to obtain the signal [ 108 ]. Compared with the optical path introduced earlier, a broadband spectrum detection function is added to detect multiple fingerprints of a sample at the same time.…”

“…The introduction of the concept of phonons makes many complex physical problems easy to handle. Phonons not only have an important influence on the thermal properties of crystals such as specific heat, thermal expansion, and thermal conduction, but they also are closely related to the electrical, optical, and dielectric properties of the crystal [ 108 ]. Using the interaction of three laser pulses with different wavelengths, a time delay ( Figure 14 b) between the two pulses is set to generate a CARS signal with time resolution.…”

“…( b ) Schematic diagram of time-resolved CARS principle and decay graph of CARS signal with delay time. Reproduced from [ 108 ], with permission from American Chemical Society, 2017.…”