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  • 1
    Online Resource
    Online Resource
    Ultrafast polarization modulation of laser pulses at terahertz frequencies via optical Kerr effect
    Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences ; 2018
    In:  Acta Physica Sinica Vol. 67, No. 23 ( 2018), p. 237801-
    Details
    In: Acta Physica Sinica, Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences, Vol. 67, No. 23 ( 2018), p. 237801-
    Abstract: Polarized light has already been widely used for photography and display technologies. Magneto-optical Faraday effect, i.e., the light polarization rotates in the magnetic field applied to the material in the direction of light propagation, plays a crucial role in the interaction between light and spin. Faraday effect allow us to understand the nature of magnetization in condensed materials. As an effect opposite to the Faraday effect, the magnetization can be induced in a transparent medium exposed to a circularly polarized electromagnetic wave, which is called inverse Faraday effect. Knowledge of the mechanism provides the opportunities of modulation devices in photonics, ultrafast opto-magnetism and magnonics. In this paper, we experimentally demonstrate a proof-of-concept ultrafast polarization modulation by employing circularly polarized light to demonstrate a strengthened terahertz (THz) frequency Kerr modulation signal, at room temperature. By using the transient pumpprobe spectroscopy with the reflected geometry, we are able to demonstrate the feasibility of such an ultrafast magneto-optical polarization modulation at 0.19 THz in a paramagnetic Li:NaTb (WO〈sub〉4〈/sub〉)〈sub〉2〈/sub〉 crystal with a thickness of 3 mm. The time-resolved modulation signal is explained by the interaction between two counter-propagating laser pulses (central photon energy of 1.55 eV) within the crystal via the optical Kerr effect. We find that the amplitude of the modulation increases with the pump fluence increasing, while the modulation frequency is dependent neither on the pump fluence nor on polarization of pump beam. However, it can further be found that the phase and amplitude of the transient Kerr modulation are strongly dependent on the helicity of the circularly polarized pump pulses. Indeed, these oscillating signals may be mistaken for spin excitation modes. The present findings allow us to get an insight into the transient magneto-optical dynamical process in transparent medium. In addition, the polarization modulation of ultrashort laser pulse on a picosecond time scale will facilitate all-optical data processing, as well as the polarization-dependent ultrafast dynamics in various material systems, which span from condensed matter to molecular spectroscopy. In this regard, our experimental results provide a possibility for designing novel all-optical (magneto-optical) modulators operating at THz clock frequencies. The magneto-optical polarization response modulated at THz frequencies may have new possibilities for designing all-optical devices, such as ultrafast modulators.
    Type of Medium: Online Resource
    ISSN: 1000-3290 , 1000-3290
    URL: Journal
    URL: Article
    DOI: 10.7498/aps
    DOI: 10.7498/aps.67.20181450
    Language: Unknown
    Publisher: Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences
    Publication Date: 2018
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  • 2
    Online Resource
    Online Resource
    Photoinduced charge carrier dynamics and spectral band filling in organometal halide perovskites
    Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences ; 2019
    In:  Acta Physica Sinica Vol. 68, No. 1 ( 2019), p. 018401-
    Details
    In: Acta Physica Sinica, Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences, Vol. 68, No. 1 ( 2019), p. 018401-
    Abstract: In recent years, the solution-processed organic-inorganic perovskite solar cells have attracted considerable attention because of their advantages of high energy conversion efficiency, low cost, and easily processing. Organometallic halide perovskite solar cells have gradually demonstrated particular superior properties in energy field due to their excellent photoelectric properties. This has been triggered by the unprecedented increase in its overall power conversion efficiency reaching 23% in just a few years, and it is becoming a direct competitor against the existing leading technology silicon. In this paper, 5-AVA-doped organometal halide perovskite films, (5-AVA)〈sub〉0.05〈/sub〉(MA)〈sub〉0.95〈/sub〉PbI〈sub〉3〈/sub〉 and (5-AVA)〈sub〉0.05〈/sub〉(MA)〈sub〉0.95〈/sub〉PbI〈sub〉3〈/sub〉/Spiro-OMeTAD, are prepared by the two-step method. The generation and recombination mechanism of charge carriers in two kinds of film samples are discussed in detail. The bivalent band structure of perovskite film material CH〈sub〉3〈/sub〉NH〈sub〉3〈/sub〉PbI〈sub〉3〈/sub〉 is determined by ultraviolet-visible absorption spectra of perovskite film (5-AVA)〈sub〉0.05〈/sub〉(MA)〈sub〉0.95〈/sub〉PbI〈sub〉3〈/sub〉 and (5-AVA)〈sub〉0.05〈/sub〉(MA)〈sub〉0.95〈/sub〉PbI〈sub〉3〈/sub〉/Spiro-OMeTAD. We investigate the photocarrier dynamics and band filling effects in these two organometal halide perovskite films by using femtosecond transient absorption spectroscopy. For (5-AVA)〈sub〉0.05〈/sub〉(MA)〈sub〉0.95〈/sub〉PbI〈sub〉3〈/sub〉, the photoinduced bleach recovery at 760 nm reveals that band-edge recombination follows second-order kinetics, indicating that the dominant relaxation pathway is via the recombination of free electrons and holes. With regard to the perovskite film (5-AVA)〈sub〉0.05〈/sub〉(MA)〈sub〉0.95〈/sub〉PbI〈sub〉3〈/sub〉 and (5-AVA)〈sub〉0.05〈/sub〉(MA)〈sub〉0.95〈/sub〉PbI〈sub〉3〈/sub〉/Spiro-OMeTAD, the signal is photoinduced absorption from 550 nm to 700 nm. As the delay time increases, the electrons and holes are recombined, which results in a red shift of absorption spectrum in (5-AVA)〈sub〉0.05〈/sub〉(MA)〈sub〉0.95〈/sub〉PbI〈sub〉3〈/sub〉. This can be referred to as Moss-Burstein band filling model. In contrast, the electrons and holes of (5-AVA)〈sub〉0.05〈/sub〉(MA)〈sub〉0.95〈/sub〉PbI〈sub〉3〈/sub〉/Spiro-OMeTAD perovskite film sample are separated after photoexcitation. The holes rapidly transfer to the hole transport layer of Spiro-OMeTAD. It will lead to an increase in sample absorbance and a rapid recovery of bleaching signals. Consequently, electron-hole recombination is no longer a dominant pathway to the relaxation of photocarriers and the band filling effect is not significant in the composite film. Our findings provide a valuable insight into the understanding of the charge carrier dynamics and spectral band filling in mixed perovskites. These results conduce to the understanding of the intrinsic photo-physics of semiconducting organometal halide perovskites with direct implications for photovoltaic and optoelectronic applications, and provide a reference for the future research of perovskite solar cells.
    Type of Medium: Online Resource
    ISSN: 1000-3290 , 1000-3290
    URL: Journal
    URL: Article
    DOI: 10.7498/aps
    DOI: 10.7498/aps.68.20181854
    Language: Unknown
    Publisher: Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences
    Publication Date: 2019
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  • 3
    Online Resource
    Online Resource
    Dynamics of A-exciton and spin relaxation in WS〈sub〉2〈/sub〉 and WSe〈sub〉2〈/sub〉 monolayer
    Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences ; 2019
    In:  Acta Physica Sinica Vol. 68, No. 1 ( 2019), p. 017201-
    Details
    In: Acta Physica Sinica, Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences, Vol. 68, No. 1 ( 2019), p. 017201-
    Abstract: Two-dimensional transitional metal dichalcogenide (2D TMD) emerges as a good candidate material in optoelectronics and valleytronics due to its particular exciton effect and strong spin-valley locking. Owing to the enhancement of quantum confinement effect and the decline of dielectric shielding effect, the optical excitation of electron-hole pair is enhanced substantially, which makes large TMD exciton binding energy and makes excitons observed easily at room temperature or even higher temperature. Optical response of 2D TMD is dominated by excitons at room temperature, which provides an ideal medium for studying the generation, relaxation and interaction of excitons or trions. By employing ultrafast time resolved spectroscopy, we investigate experimentally the dynamic behaviors of A-exciton and spin relaxations for two types of TMDs, i.e. WS〈sub〉2〈/sub〉 and WSe〈sub〉2〈/sub〉 monolayers, respectively. By tuning the excitation wavelength of the degenerate pump and probe laser beam, the WS〈sub〉2〈/sub〉 monolayer and WSe〈sub〉2〈/sub〉 monolayer are excited at their A-exciton resonance transition position or near their A-exciton resonance transition position in order to compare the dynamical evolutions of band structure and exciton polarization of the two similar WS〈sub〉2〈/sub〉 and WSe〈sub〉2〈/sub〉 monolayer structures. Our experimental results reveal that the relaxation of A exciton in WS〈sub〉2〈/sub〉 shows biexponential decay, while that of WSe〈sub〉2〈/sub〉 shows triexponential decay, and the A-exciton life time in WSe〈sub〉2〈/sub〉 is much longer than that of WS〈sub〉2〈/sub〉 counterpart. The spin relaxation of A exciton in WS〈sub〉2〈/sub〉 shows a monoexponential feature with a lifetime of 0.35 ps, which is dominated by the electron-hole exchange interaction. For the case of WSe〈sub〉2〈/sub〉, the spin relaxation can be well fitted with biexponential function, the fast component has a lifetime of 0.5 ps and the slow one has a lifetime of 28 ps. The fast relaxation is dominated by the electron-hole exchange interaction, and the slow one comes from the formation of dark exciton via spin-lattice coupling. By tuning the excitation wavelength around A-exciton transition, the formation of dark exciton in WSe〈sub〉2〈/sub〉 is demonstrated to be much more effective than that in WS〈sub〉2〈/sub〉 monolayer. Our experimental results provide qualitative physical images for an in-depth understanding of the relationship between exciton and TMD structure, and also provide reference for further designing and regulating the TMDs based optoelectronic devices.
    Type of Medium: Online Resource
    ISSN: 1000-3290 , 1000-3290
    URL: Journal
    URL: Article
    DOI: 10.7498/aps
    DOI: 10.7498/aps.68.20181769
    Language: Unknown
    Publisher: Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences
    Publication Date: 2019
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