Abstract: Ultrafast carrier dynamics and terahertz emission in optically pumped graphene at room temperature

http://prb.aps.org/abstract/PRB/v85/i3/e035443

Received 5 April 2011; revised 11 November 2011; published 26 January 2012

We report, within a picosecond time scale, fast relaxation and relatively slow recombination dynamics of photogenerated electrons and holes in an exfoliated graphene under infrared pulse excitation. We conduct time-domain spectroscopic studies using an optical pump and terahertz probe with an optical probe technique and show that graphene sheet amplifies an incoming terahertz field. The graphene emission spectral dependency on laser pumping intensity shows a threshold-like behavior, testifying to the occurrence of the negative conductivity and the population inversion. The phase behavior of the measured terahertz electric field also shows clear Lorentzian-like normal dispersion around the gain peak, testifying to the amplification that can be attributed to stimulated emission of photocarriers in the inverted states. The emission spectra clearly narrow at a longer terahertz probe delay time, giving evidence that the quasi-Fermi energy moves closer to the equilibrium at this longer terahertz probe delay time.

©2012 American Physical Society

URL:

http://link.aps.org/doi/10.1103/PhysRevB.85.035443

DOI:

10.1103/PhysRevB.85.035443

PACS:

78.45.+h, 78.47.D-, 78.66.Tr, 78.70.-g

^*stephanealbon@hotmail.com

Abstract:Ultrafast carrier dynamics and terahertz emission in optically pumped graphene at room temperature

S. Boubanga-Tombet, S. Chan, A. Satou, V. Ryzhii, and T. Otsuji

http://prb.aps.org/accepted/B/8d071Y6cQf41b62629da6ff57cc914dfee7cb4880

We report within picosecond time scale, fast relaxation and relatively slow recombination dynamics of photogenerated electrons/holes in an exfoliated graphene under infrared pulse excitation. We conduct time domain spectroscopic studies using an optical pump/terahertz probe and optical probe technique and show that graphene sheet amplifies an incoming terahertz field. The graphene emission spectral dependency on laser pumping intensity shows a threshold like behavior, testifying the occurrence of the negative conductivity and the population inversion. The phase behavoir of the measured Terahertz electric field also show clear Lorentzian-like normal dispersion around the gain peak, testifying the occurrence of amplification that can be attributed to stimulated emission of photo-carriers in the inverted states. The emission spectra also show a clear narrowing at longer terahertz probe delay time giving a clear evidence of the quasi-fermi energy moving closer to the equilibrium at this longer terahertz probe delay time.