Polarization-Dependent Ultrafast Carrier Dynamics in GaAs with Anisotropic Response

The transient dynamics of anisotropic properties of GaAs is systematically studied by polarization-dependent ultrafast time-resolved transient absorption. Our findings revealed that the anisotropy of reflectivity was enhanced in both pump-induced and probe-induced processes, suggesting an extraordinary resonance absorption of photon-phonon coupling (PPC) with intrinsic anisotropic characteristic in carrier relaxation, regardless of the concrete crystallinity and orientation of GaAs sample. The results, delivering in-depth cognition about the polarization-dependent ultrafast carrier dynamics, also proved the paramount importance of interaction between polarized laser and semiconductor.

Crucial Factors for Lyα Transmission in the Reionizing Intergalactic Medium: Infall Motion, H ii Bubble Size, and Self-shielded Systems

Using the CoDa II simulation, we study the Lyα transmissivity of the intergalactic medium (IGM) during reionization. At z > 6, a typical galaxy without an active galactic nucleus fails to form a proximity zone around itself due to the overdensity of the surrounding IGM. The gravitational infall motion in the IGM makes the resonance absorption extend to the red side of Lyα, suppressing the transmission up to roughly the circular velocity of the galaxy. In some sight lines, an optically thin blob generated by a supernova in a neighboring galaxy results in a peak feature, which can be mistaken for a blue peak. Redward of the resonance absorption, the damping-wing opacity correlates with the global IGM neutral fraction and the UV magnitude of the source galaxy. Brighter galaxies tend to suffer lower opacity because they tend to reside in larger H ii regions, and the surrounding IGM transmits redder photons, which are less susceptible to attenuation, owing to stronger infall velocity. The H ii regions are highly nonspherical, causing both sight-line-to-sight-line and galaxy-to-galaxy variation in opacity. Also, self-shielded systems within H ii regions strongly attenuate the emission for certain sight lines. All these factors add to the transmissivity variation, requiring a large sample size to constrain the average transmission. The variation is largest for fainter galaxies at higher redshift. The 68% range of the transmissivity is similar to or greater than the median for galaxies with M UV ≥ −21 at z ≥ 7, implying that more than a hundred galaxies would be needed to measure the transmission to 10% accuracy.

Absorption properties of bromide photo-thermo-refractive glasses doped with Ytterbium

In this work bromide photo-thermo-refractive glasses with different Ytterbium concentration were explored. It is shown that UV irradiation and subsequent heat treatment of samples with Yb 2 mol.% causes significant red-shift absorption line from 410 nm with temperature lower than Tg to 517 nm with temperature Tg +60 °C. For small concentration of Yb (0,1 mol. %) maximum red-shift in plasmon resonance absorption band is shown as 485 nm and it is the same for heat treatment temperatures from Tg +20 °C to Tg +60 °C.

Does the wall sound different? Variable acoustics in rehearsal rooms using small resonator structures in an acoustic panel.

As the name already states, multipurpose rooms are often used from various people for different intentions like meetings or musical practicing. One example are musical rehearsal rooms, where the acoustic specifications have to meet the requirements of musicians playing different instrument groups. To meet the desire for variable acoustics in a rehearsal room, musicians often like to adjust the room to there personal preferences, what is mostly done by adjusting the frequency dependent room decay curve (T60). Hence, a variable acoustic panel has been developed which consists of several small adjustable resonator structures. In a closed state, the structure acts like a resonator. Although Helmholtz resonators are mostly used at low frequencies, the acoustic panel can address acoustic resonance absorption in the mid-frequency range between 500 Hz and 1.500 Hz. The paper highlights especially the dimensioning of the resonators and its measurements in an impedance tube, a reverberation cabin and a reverberation room. Finally, the prototype of the acoustic panel has been analysed in different rehearsal rooms where musicians examine the panel and T60 differences between the open and closed state of the panel were measured.

Small-Angle Ultra-Narrowband Tunable Mid-Infrared Absorber Composing from Graphene and Dielectric Metamaterials

We report a small-angle ultra-narrowband mid-infrared tunable absorber that uses graphene and dielectric metamaterials. The absorption bandwidth of the absorber at the graphene Fermi level of 0.2 eV is 0.055 nm, and the absorption peaks can be tuned from 5.14803 to 5.1411 μm by changing the graphene Fermi level. Furthermore, the resonance absorption only occurs in the angle range of several degrees. The simulation field distributions show the magnetic resonance and Fabry–Pérot resonance at the resonance absorption peak. The one-dimensional photonic crystals (1DPCs) in this absorber act as a Bragg mirror to efficiently reflect the incidence light. The simulation results also show that the bandwidth can be further narrowed by increasing the resonance cavity length. As a tunable mid-infrared thermal source, this absorber can possess both high temporal coherence and near-collimated angle characteristics, thus providing it with potential applications.