Browsing by Subject "Ultrafast spectroscopy"
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Item Open Access Efficient generation of emissive many-body correlations in copper-doped colloidal quantum wells(Cell Press, 2022-09-21) Yu, Junhong; Sharma, Manoj; Li, Mingjie; Liu, Baiquan; Hernández-Martínez, Pedro Ludwig; Delikanli, Savaş; Sharma, Ashma; Altintas, Yemliha; Hettiarachchi, Chathuranga; Sum, Tze Chien; Demir, Hilmi Volkan; Dang, CuongColloidal quantum wells (CQWs) provide an appealing platform to achieve emissive many-body correlations for novel optoelectronic devices, given that they act as hosts for strong carrier Coulomb interactions and present suppressed Auger recombination. However, the demonstrated high-order excitonic emission in CQWs requires ultrafast pumping with high excitation levels and can only be spectrally resolved at the single-particle level under cryogenic conditions. Here, through systematic investigation using static power-dependent emission spectroscopy and transient carrier dynamics, we show that Cu-doped CdSe CQWs exhibit continuous-wave-pumped high-order excitonic emission at room temperature with a large binding energy of ∼64 meV. We attribute this unique behavior to dopant excitons in which the ultralong lifetime and the highly localized wavefunction facilitate the formation of many-body correlations. The spectrally resolved high-order excitonic emission generated at power levels compatible with solar irradiation and electrical injection might pave the way for novel solution-processed solid-state devices. © 2022 The AuthorsItem Open Access Investigation of the ultrafast response and saturable absorption of voltage-controlled graphene(OSA, 2018) Baylam, I.; Çizmeciyan, M. N.; Kakenov, Nurbek; Kocabaş, Coşkun; Sennaroğlu, A.Ultrafast pump-probe measurements show that at a bias voltage of 1V, voltage reconfigurable graphene supercapacitors can operate as fast saturable absorbers with adjustable insertion loss over an ultrabroad spectral range from 630 to 1100 nm.Item Open Access Ultrafast control of the optical transition in type-II colloidal quantum wells(American Chemical Society, 2023-04-21) Yu, J.; Durmusoglu, E. G.; Wang, Y.; Sharma, M.; Demir, Hilmi Volkan; Dang, C.Manipulating the optical transition in semiconductors at ultrashort timescales is of both fundamental interest and central importance for emerging photonic applications. Traditionally, this manipulation is realized by electrostatic gating via Stark effects or band-gap renormalizations. Here, we report an ultrafast and all-optical route to engineer an indirect transition in core–crown colloidal quantum wells (CQWs), namely, CdSe/CdTe, with a type-II band alignment. Following the intense laser pulse excitation, the indirect band transition energy exhibits a pronounced blueshift–redshift crossover on the picosecond timescale, stemming from the formation and dissipation of the transient electric field (E-field) that forms upon photoexcitation to compensate for the driving force provided by the band offsets. Both the energy shift and dynamics of the transient E-field can be modulated optically by tuning the laser pulse excitation fluence. Our finding demonstrates a strong analogy between the type-II heterojunction and a p–n junction with respect to carrier equilibrium processes, which holds promise to facilitate the integration of CQWs within optical switching networks.Item Open Access Ultrafast spectroscopy of voltage reconfigurable graphene saturable absorbers in the visible and near infrared(IOP, 2019-04-23) Baylam, I.; Kakenov, Nurbek; Kocabaş, Coşkun; Sennaroğlu, A.; Çizmeciyan, M. N.We describe a detailed experimental investigation of the ultrafast nonlinear response of a voltagecontrolled graphene-gold saturable absorber (VCG-gold-SA) by employing femtosecond pump probe spectroscopy. Visible and near-infrared continuum probe pulses covering the spectral range from 500nm to 1600nm were used. In the experiments, the saturation fluence, modulation depth, ultrafast relaxation times, and the saturable absorption bandwidth of the VCG-gold-SA were measured as a function of the applied bias. We observed both saturable absorption and multi-photon absorption regimes as the applied bias voltage was varied between 0 and 2 V. Measurements indicate that under bias voltages in the range of 0–2 V, it should be possible to adjust the insertion loss of the VCG-gold-SA and at the same time, maintain a sufficient amount of modulation depth as well as an attainable level of saturation fluence over an ultrabroad spectral bandwidth. In particular, at the bias voltage of 1 V, the VCG-gold-SA exhibited fast saturable absorber behavior with adjustable insertion loss from 630nm to 1100nm. These results clearly demonstrate that the VCG-gold-SA can operate as a versatile mode locker for femtosecond pulse generation from lasers operating in the visible and near-infrared wavelengths.