More Like this

1. Ultrafast transverse and longitudinal response of laser-excited quantum wires

   https://doi.org/10.1364/OE.448934  

   Gulley, Jeremy_R; Huang, Danhong (March 2022, Optics Express)

   We couple 1D pulse propagation simulations with laser-solid dynamics in a GaAs quantum wire, solving for the electron and hole populations and the interband and intraband coherences between states. We thus model not only the dynamical dipole contributions to the optical polarization (interband bound-charge response) but also the photo-generation and back-action effects of the net free-charge density (intraband free-charge response). These results show that solving for the dynamic electron and hole intraband coherences leads to plasma oscillations at THz frequencies, even in a 1D solid where plasma screening is small. We then calculate the transverse and longitudinal response of the quantum wire and characterize the dispersion relation for thee-hplasma. This approach allows one to predict the optoelectronic response of 1D semiconductor devices during and after exposure to resonant ultrashort pulses. 

   more » « less
2. Explicit formula for high-order sideband polarization by extreme tailoring of Feynman path integrals

   https://doi.org/10.1103/PhysRevB.107.174308  

   Wu, Qile; Sherwin, Mark S. (May 2023, Physical Review B)

   High-order sideband generation (HSG), as an analog of the interband processes in high-harmonic generation (HHG) in solids, is a nonperturbative nonlinear optical phenomenon in semiconductors that are simultaneously driven by a relatively weak near-infrared (NIR) laser and a sufficiently strong terahertz (THz) field. We derive an explicit formula for sideband polarization vectors in a prototypical two-band model based on the saddle-point method. Our formula connects the sideband amplitudes with the laser-field parameters, electronic structures, and nonequilibrium dephasing rates in a highly nontrivial manner. Our results indicate the possibility of extracting information on band structures and dephasing rates from high-order sideband generation experiments with simple algebraic calculations. We also expect our approach to be useful on the quantitative understanding of the interband HHG. 

   more » « less
3. Ultrafast Dynamics of Colloidal Copper Nanorods: Intraband versus Interband Excitation

   https://doi.org/10.1002/smsc.202100103  

   Diroll, Benjamin T.; Jeong, Soojin; Ye, Xingchen (December 2021, Small Science)

   Colloidal copper nanorods (NRs) display transverse and longitudinal localized surface plasmon resonances. The longitudinal localized surface plasmon modes are tunable through the near‐infrared electromagnetic radiation energies with NR aspect ratios. Visible and near‐infrared transient optical response of the copper NRs is investigated under excitation conditions spanning intraband and interband excitation (0.79−3.50 eV). In both the visible and near‐infrared regions, the spectral response of the samples under intraband excitation (<2 eV) differs substantially from their response under interband excitation (>2 eV). However, the timescale of the electron−phonon coupling estimated from pump fluence‐dependent measurements (τ_ep) is less sensitive to excitation conditions than reports for gold.τ_epshortens slightly from ≈616 fs with intraband excitation (at visible probe energies) to ≈565 fs with interband excitation. The observed dynamics correspond to an average sample electron−phonon coupling parameter varying across all conditions from 4.4 × 10¹⁶to 6.4 × 10¹⁶ J m⁻³ K⁻¹, which is similar to bulk copper. Furthermore, coherent acoustic phonons are observed for the longitudinal localized surface plasmon resonance with a range of oscillatory periods reflecting sample size dispersion. 

   more » « less
4. Interband Transitions and Critical Points of Single‐Crystal Thoria Compared with Urania

   https://doi.org/10.1002/pssb.202200238  

   Dugan, Christina; Wang, Lu; Zhang, Kai; Mann, James_Matthew; Kimani, Martin_M; Mei, Wai-Ning; Dowben, Peter_A; Petrosky, James (August 2022, physica status solidi (b))

   The interband transitions of UO₂are validated independently through cathode luminescence. A picture emerges consistent with density functional theory. While theory is generally consistent with experiment, it is evident from the comparison of UO₂and ThO₂that the choice of functional can significantly alter the bandgap and some details of the band structure, in particular at the conduction band minimum. Strictly ab initio predictions of the optical properties of the actinide compounds, based on density functional theory alone, continue to be somewhat elusive. 

   more » « less
5. High-temperature and low-threshold interband cascade lasers at wavelengths longer than 6  μm

   https://doi.org/10.1117/1.OE.57.1.011021  

   Rassel, S.M.Shazzad; Li, Lu; Li, Yiyun; Yang, Rui Q.; Gupta, James A; Wu, Xiaohua; Aers, Geof C. (January 2018, Optical Engineering)

   InAs-based interband cascade (IC) lasers with improved optical confinement have achieved high-temperature operation with a threshold current density as low as 333 A/cm2 at 300 K for emission at 6003 nm. The threshold current density is the lowest ever reported among semiconductor mid-infrared lasers at similar wavelengths. These InAs-based IC devices lased in pulsed mode at temperatures up to 357 K near 6.28 μm. A narrow-ridge device was able to operate in continuous-wave mode at temperatures up to 293 K at 6.01 μm. 

   more » « less