Ultrafast generation of optical and acoustic phonons in nanocrystallites

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We report on the impulsive generation of optical and acoustic phonons in CdTe0.68Se0.32 nanocrystallites embedded in glass, at room temperature. Using ultrafast laser pulses in a pump-probe configuration, we were able to generate coherent vibrations. The energy of our laser was tuned to the absorpti...

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Autores principales:	Bragas, A.V., Aku-Leh, C., Merlin, R.
Formato:	CONF
Materias:	Coherent phonon Confined acoustic phonon Laser pulse Semiconductor quantum dot Stimulated Raman Excitons Frequencies Laser pulses Nanostructured materials Raman scattering Semiconductor quantum dots Spectrum analysis Coherent phonons Confined acoustic phonons Ultrafast phonons Phonons
Acceso en línea:	http://hdl.handle.net/20.500.12110/paper_0277786X_v5725_n_p126_Bragas
Aporte de:	Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires

id	todo:paper_0277786X_v5725_n_p126_Bragas
record_format	dspace
spelling	todo:paper_0277786X_v5725_n_p126_Bragas2023-10-03T15:16:33Z Ultrafast generation of optical and acoustic phonons in nanocrystallites Bragas, A.V. Aku-Leh, C. Merlin, R. Coherent phonon Confined acoustic phonon Laser pulse Semiconductor quantum dot Stimulated Raman Excitons Frequencies Laser pulses Nanostructured materials Raman scattering Semiconductor quantum dots Spectrum analysis Coherent phonons Confined acoustic phonons Stimulated Raman Ultrafast phonons Phonons We report on the impulsive generation of optical and acoustic phonons in CdTe0.68Se0.32 nanocrystallites embedded in glass, at room temperature. Using ultrafast laser pulses in a pump-probe configuration, we were able to generate coherent vibrations. The energy of our laser was tuned to the absorption edge of the nanocrystals so as to resonantly excite the quantum dots. We identified two longitudinal optical phonons, an optical mode of mixed longitudinal-transverse nature and a longitudinal-like acoustic mode. The frequency, amplitude, decay and phase as a function of excitation energy were determined for the optical modes. These results clearly identify impulsive stimulated Raman scattering as the underlying mechanism of the coherent field generation. The acoustic oscillations are associated with the lowest confined acoustic mode with pseudo angular momentum l=0. We find that the frequency of this mode increases as the laser central energy increases. Since the energy of the exciton at the fundamental gap depends strongly on the particle size, such a behavior is attributed to resonant size-selective excitation of the nanocrystallites. In contrast, spontaneous Raman measurements obtained from the same sample do not show size selectivity and, in addition, the resonant spectra show l=1 and l-2 modes, which are not seen in the pump-probe data. Possible explanations and comparison with other reports are discussed. Fil:Bragas, A.V. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. CONF info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/2.5/ar http://hdl.handle.net/20.500.12110/paper_0277786X_v5725_n_p126_Bragas
institution	Universidad de Buenos Aires
institution_str	I-28
repository_str	R-134
collection	Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
topic	Coherent phonon Confined acoustic phonon Laser pulse Semiconductor quantum dot Stimulated Raman Excitons Frequencies Laser pulses Nanostructured materials Raman scattering Semiconductor quantum dots Spectrum analysis Coherent phonons Confined acoustic phonons Stimulated Raman Ultrafast phonons Phonons
spellingShingle	Coherent phonon Confined acoustic phonon Laser pulse Semiconductor quantum dot Stimulated Raman Excitons Frequencies Laser pulses Nanostructured materials Raman scattering Semiconductor quantum dots Spectrum analysis Coherent phonons Confined acoustic phonons Stimulated Raman Ultrafast phonons Phonons Bragas, A.V. Aku-Leh, C. Merlin, R. Ultrafast generation of optical and acoustic phonons in nanocrystallites
topic_facet	Coherent phonon Confined acoustic phonon Laser pulse Semiconductor quantum dot Stimulated Raman Excitons Frequencies Laser pulses Nanostructured materials Raman scattering Semiconductor quantum dots Spectrum analysis Coherent phonons Confined acoustic phonons Stimulated Raman Ultrafast phonons Phonons
description	We report on the impulsive generation of optical and acoustic phonons in CdTe0.68Se0.32 nanocrystallites embedded in glass, at room temperature. Using ultrafast laser pulses in a pump-probe configuration, we were able to generate coherent vibrations. The energy of our laser was tuned to the absorption edge of the nanocrystals so as to resonantly excite the quantum dots. We identified two longitudinal optical phonons, an optical mode of mixed longitudinal-transverse nature and a longitudinal-like acoustic mode. The frequency, amplitude, decay and phase as a function of excitation energy were determined for the optical modes. These results clearly identify impulsive stimulated Raman scattering as the underlying mechanism of the coherent field generation. The acoustic oscillations are associated with the lowest confined acoustic mode with pseudo angular momentum l=0. We find that the frequency of this mode increases as the laser central energy increases. Since the energy of the exciton at the fundamental gap depends strongly on the particle size, such a behavior is attributed to resonant size-selective excitation of the nanocrystallites. In contrast, spontaneous Raman measurements obtained from the same sample do not show size selectivity and, in addition, the resonant spectra show l=1 and l-2 modes, which are not seen in the pump-probe data. Possible explanations and comparison with other reports are discussed.
format	CONF
author	Bragas, A.V. Aku-Leh, C. Merlin, R.
author_facet	Bragas, A.V. Aku-Leh, C. Merlin, R.
author_sort	Bragas, A.V.
title	Ultrafast generation of optical and acoustic phonons in nanocrystallites
title_short	Ultrafast generation of optical and acoustic phonons in nanocrystallites
title_full	Ultrafast generation of optical and acoustic phonons in nanocrystallites
title_fullStr	Ultrafast generation of optical and acoustic phonons in nanocrystallites
title_full_unstemmed	Ultrafast generation of optical and acoustic phonons in nanocrystallites
title_sort	ultrafast generation of optical and acoustic phonons in nanocrystallites
url	http://hdl.handle.net/20.500.12110/paper_0277786X_v5725_n_p126_Bragas
work_keys_str_mv	AT bragasav ultrafastgenerationofopticalandacousticphononsinnanocrystallites AT akulehc ultrafastgenerationofopticalandacousticphononsinnanocrystallites AT merlinr ultrafastgenerationofopticalandacousticphononsinnanocrystallites
_version_	1807324537219448832

Ultrafast generation of optical and acoustic phonons in nanocrystallites

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