The gain enhancement effect of surface plasmon polaritons on terahertz stimulated emission in optically pumped monolayer graphene

Abstract

Nonlinear carrier relaxation/recombination dynamics and the resultant stimulated terahertz (THz) photon emission with excitation of surface plasmon polaritons (SPPs) in photoexcited monolayer graphene has been experimentally studied using an optical pump/THz probe and an optical probe measurement. We observed the spatial distribution of the THz probe pulse intensities under linear polarization of optical pump and THz probe pulses. It was clearly observed that an intense THz probe pulse was detected only at the area where the incoming THz probe pulse takes a transverse magnetic (TM) mode capable of exciting the SPPs. The observed gain factor is in fair agreement with the theoretical calculations. Experimental results support the occurrence of the gain enhancement by the excitation of SPPs on THz stimulated emission in optically pumped monolayer graphene.

Negative dynamic Drude conductivity in pumped graphene

“…The emerging contribution to the optical conductivity, which we call the interband Drude conductivity, appears to be negative for the photon energies below the double quasi-Fermi energy of pumped electrons and holes. We find that for the Gaussian correlated distribution of scattering centers, the real part of the net Drude conductivity (interband plus intraband) can be negative in the terahertz and near-infrared frequency ranges, while the radiation amplification by a single graphene sheet can exceed 2.3%.Graphene under the conditions of interband pumping has attracted considerable interest [1] due to the rich physics including nonlinear photoresponse [2], collinear relaxation and recombination [3], anomalous carrier diffusion [4], and self-excitation of surface plasmons [5]. The emergence of population inversion [6-8] and negative interband dynamic conductivity in pumped graphene enables the amplification of radiation, particularly, in the terahertz (THz) range [9].…”

Исследования волноводных структур с квантовыми ямами на основе HgCdTe для получения длинноволнового стимулированного излучения

“…Квантовые ямы HgTe/CdHgTe обладают рядом уни-кальных свойств, обусловленных, в частности, тем, что при уменьшении ширины КЯ можно осуществить пере-ход от инвертированной зонной структуры (наследуемой в широких КЯ от объемного HgTe), к нормальной через возникающий при некоторой критической толщине КЯ " графеноподобный" закон дисперсии [16]. Преимущества графена для создания лазера терагерцового диапазона активно обсуждаются в литературе, и уже получены первые экспериментальные результаты в этом направ-лении [17][18][19]. Даже в материале с очень малой щелью определенная симметрия законов дисперсии носителей позволяет подавить оже-рекомбинацию, которая являет-ся одним из важнейших факторов, ограничивающих воз-можность получения инверсии населенностей.…”

Graphene materials and devices for terahertz science and technology

“…unique features in their response to THz electromagnetic radiation, such as extremely high absorption as well as giant terahertz gain [4,16]. As compared with the lasing associated with the stimulated emission of the electromagnetic modes (i.e., photons), the stimulated emission of plasmons by the interband transitions in population inverted graphene can be much stronger emission process [17,18]. Non-equilibrium plasmons in graphene can be coupled to the TM modes of THz photon radiation resulting in formation and propagation of SPPs [17].…”

“…Non-equilibrium plasmons in graphene can be coupled to the TM modes of THz photon radiation resulting in formation and propagation of SPPs [17]. It is theoretically shown in [17] and experimentally verified in [18] that the plasmon gain in pumped graphene can be very high due to small group velocity of the plasmons in graphene and strong confinement of the plasmon field in the vicinity the graphene layer.…”