Mode-selective phonon excitation in gallium nitride using mid-infrared free-electron laser

Abstract

The single-phonon mode was selectively excited in a solid-state sample. A mid-infrared free-electron laser, which was tuned to the target phonon mode, was irradiated onto a crystal cooled to a cryogenic temperature, where modes other than the intended excitation were suppressed. An A 1 (LO) vibrational mode excitation on GaN(0001) face was demonstrated. Anti-Stokes Raman scattering was used to observe the excited vibrational mode, and the appearance and disappearance of the scattering band at the target wavenumber were confirmed to correspond to on and off switching of the pump free-electron laser and were fixed to the sample vibrational mode. The sum-frequency generation signals of the pump and probe lasers overlapped the Raman signals and followed the wavenumber shift of the pump laser.

Orbital facilitated charge transfer originated phonon mode in Cr‐substituted PrFeO3: A brief Raman study

“…The absorption coefficient (C VC ) is ideally zero for photon energy; E < E g (E g is CT gap), which scales with the photon energy E. [ 2,32 ] From Equation , it is clear that with the increase in the energy (C V → C ) and density of photon (ρ(ω)), the rate of electronic transition scales systematically, which is in good conformance with the laser excitation energy and power‐dependent investigations on the prepared samples. It is interesting to note that by exciting a particular Raman mode, electron–phonon interactions even induce metal–insulator transitions and changes in the magnetic order, [ 43 ] which makes these phenomena further very interesting. At this point, it is important here to note that with changing the laser excitation energy, penetration depth also changes, which contributes to the change in the relative intensity of phonon modes.…”

“…Present results demonstrate the case of selective phonon mode excitation and the magnitude of the observed Franck-Condon scattering (shown in Figure S6) should prove useful for fundamental studies of the relation between global and local effects in correlated systems in general and electron-phonon interactions in particular, as well as for the study of transient phenomena such as electron-phonon interactions induced metal-insulator transitions, changes in the magnetic interactions, and so forth. [43,44]…”

Two-photon selective excitation of phonon-mode in diamond using mid-infrared free-electron laser

“…In one-photon mode-selective phonon excitation [20,21], the excitation part with pump light is one-photon (linear) absorption from the excitation light. The transition rate, R (1) , for this process is given as…”

“…In previous reports, some of the present authors have proposed an alternative method with a simpler and straightforward approach, involving the direct pumping of the phonon energy through the irradiation of mid-infrared (MIR) free-electron-laser (FEL) whose photon energy is equal to that of the target phonon [20,21]. Selective excitation of the particular phonon in 6H-SiC and GaN were demonstrated.…”

Mode-selective excitation of an infrared-inactive phonon mode in diamond using mid-infrared free electron laser

“…22,23) The mode-selective lattice vibration excitation using KU-FEL has been performed for a specific phonon mode of SiC and GaN in previous studies. 24,25) In these researches, the excitation of a particular phonon mode which is infrared and Raman active in SiC or GaN was demonstrated by ASRS. However, due to the infrared-Raman selection principle, the one photon selective excitation of a particular phonon mode in diamond cannot be detected by ASRS spectroscopy.…”