Search results for "Ultrafast laser"
showing 10 items of 100 documents
Time-resolved spectroscopy of ZnWO4
2001
The luminescence spectra of ZnWO 4 excited by a pulsed electron beam, pulsed nitrogen laser and X-ray are studied. The luminescence decay kinetics are compared with transient absorption relaxation kinetics. Broad band transient absorption spectra are observed and it is shown that the slow decay component (∼14 μs at RT) of the transient absorption matches well with the luminescence decay therefore this absorption is due to the excited state absorption of the luminescence center.
Induced optical absorption and ITS relaxation in LiNbO3
1999
Abstract Electron pulse induced absorption spectra and their decay kinetics have been investigated in LiNbO3 crystals with various Li/Nb ratios rasnging from congruent to stoichiometric composition. It is shown that the absorption spectra, the optical density and the decay kinetics depend on the Li/Nb ratio. The rising front of the induced absorption is too fast to be resolved. The room temperature decay, characterized by the half-lifetime Δt, is faster in the stoichiometric crystal (∼ 750 ns) than in the congrruent crystal (∼ 3.5 μs).
Pulsed electron beam excited transient absorption in SrTiO3
2002
Abstract Transient absorption (TA) spectra and optical density relaxation kinetics in SrTiO3 (STO), STO–Nb and STO–V were studied. The electron polaron free or bound at intrinsic defect is suggested to be responsible for the TA band at ∼1.4 eV observed in STO. The band peaking below 0.75 eV in STO–Nb is proposed to be from Nb4+. The electron center V3+ or electron polaron bound in the vicinity of V4+ is responsible for the absorption band at 1.0 eV in STO–V. The absorption from hole polarons is suggested to be in the range 1.8–2.3 eV. It is shown that TA in pure STO at room temperature decays due to electron–hole polaron recombination.
Experimental and theoretical studies of polaron optical properties in KNbO3 perovskite
2004
Time-resolved absorption and luminescence spectra have been measured in KNbO3 perovskite crystals after pulsed band-gap excitation by 200 fs laser pulses and 10 ns electron pulses. Quantum chemical calculations using the large unit cell periodic model support the interpretation of the observed transient absorption bands at 0.8 and 1.1 eV as the self-trapped electron polarons and bound hole polarons, respectively. The activation energy for the 2.2 eV green luminescence quenching is 0.05 eV. We suggest that the short lifetime (,15 ns) of the luminescence at RT is caused by the radiative recombination of nearest electron and hole polarons. q 2003 Elsevier Ltd. All rights reserved.
X‐ray and pulsed electron beam excited luminescence and optical absorption in KTaO 3 crystals
2005
Pulsed electron beam excited time-resolved transient absorption and luminescence have been studied in nominally pure and Li-doped KTaO3 single crystals. It is found that under electron beam excitation in nominally pure KTaO3 the absorption bands peaks at ∼0.8 eV, ∼1.1 eV and 1.7 eV whereas in KTaO3:Li at ∼1.1 eV and ∼1.7 eV. The transient absorption decay varies over the spectrum thus revealing several short-lived centers. The main luminescence peak is centred at ∼2.7 eV in all KTaO3 specimens. Luminescence decay kinetics observed for the two bands slightly differ indicating different kinds of excited states are involved. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Size-And Wavelength-Dependent Two-Photon Absorption Cross-Section of CsPbBr3 Perovskite Quantum Dots
2017
All-inorganic colloidal perovskite quantum dots (QDs) based on cesium, lead, and halide have recently emerged as promising light emitting materials. CsPbBr3 QDs have also been demonstrated as stable two-photon-pumped lasing medium. However, the reported two photon absorption (TPA) cross sections for these QDs differ by an order of magnitude. Here we present an in-depth study of the TPA properties of CsPbBr3 QDs with mean size ranging from 4.6 to 11.4 nm. By using femtosecond transient absorption (TA) spectroscopy we found that TPA cross section is proportional to the linear one photon absorption. The TPA cross section follows a power law dependence on QDs size with exponent 3.3 +- 0.2. The …
Strong Exciton-Coherent Phonon Coupling in Single-Layer MoS2
2020
Broadband transient absorption with sub-20fs temporal resolution, supported by ab-initio calculations, quantitatively provides the strength of exciton-coherent phonon coupling in 1L-MoS2, showing a resonant profile around the C exciton.
Transient absorption of polarons in KNbO3
2002
Abstract Transient absorption spectra have been measured in a number of undoped KNbO 3 crystals following two kinds of electronic excitation: two-photon absorption of 200 fs laser pulses and 10 ns pulsed electron beam. A band peaking at 0.8 eV and broad, poorly resolved absorption in the range 1.3–3.3 eV were observed. Based on similarity to the 1 eV band in LiNbO 3 previously identified as the intrinsic electron polaron (electron self-localized on niobium in the regular lattice site), we suggest that the transient absorption band at 0.8 eV in KNbO 3 is also associated with the intrinsic electron polaron.
Optical investigations of TlBr detector crystals
2004
Shift of fundamental absorption edge, the position of main luminescence bands, the luminescence decay and transient absorption spectra in three TlBr crystals were studied. The γ-quanta detector made from TlBr crystals with similar transient absorption and luminescence parameters shows similar detector properties. The iodine impurity in TlBr was detected by optical methods. The role of impurities and crystal defects in γ-quanta detectors manufactured is discussed.
Laser driven parametric amplification of xuv and soft-x-rays in neutral gases
2010
We present the first theoretical description and also experimental evidence for the amplification of XUV and soft-X-ray radiation by parametric stimulated emission in neutral gases driven by near-IR laser pulses reaching small-signal-gain up to 8000.