The all-inorganic perovskite nanocrystals are currently in the research spotlight owing to their physical stability and superior optical properties—these features make them interesting for optoelectronic and photovoltaic applications. Here, we report on the observation of highly efficient carrier multiplication in colloidal CsPbI3 nanocrystals prepared by a hot-injection method. The carrier multiplication process counteracts thermalization of hot carriers and as such provides the potential to increase the conversion efficiency of solar cells. We demonstrate that carrier multiplication commences at the threshold excitation energy near the energy conservation limit of twice the band gap, and has step-like characteristics with an extremely high quantum yield of up to 98%. Using ultrahigh temporal resolution, we show that carrier multiplication induces a longer build-up of the free carrier concentration, thus providing important insights into the physical mechanism responsible for this phenomenon. The evidence is obtained using three independent experimental approaches, and is conclusive.
We report quasi-one-optical-cycle pulse compression of the ultrabroadband white-light continuum generated using both induced-phase modulation (IPM) and self-phase modulation (SPM) in a 3.0 atom Ar-gas-filled hollow fiber. Fundamental and second harmonic waves of amplified 30 fs Ti:sapphire laser pulses were irradiated into a 37 cm hollow fiber with an inner diameter of 140 m. When the two pulses were temporally overlapped in the hollow fiber, the white-light continuum with the wavelength range of 350-1050 nm was generated. The spectral phase of the white-light continuum was measured by a modified spectral interferometry for direct electric-field reconstruction, and quasi-automatic feedback chirp compensation was carried out using a programmable liquid-crystal spatial light modulator placed on the Fourier plane of a 4-f system. As a result, 2.6 fs, 3.6 J, 1.3 cycle transform-limited (TL) pulses with a peak power up to 1.4 GW at a 1 kHz repetition rate were generated in the visible to near-infrared region (the over-one-octave bandwidth of 450-975 nm). The fact that the IPM+ SPM light was compressed to the TL duration is important toward the generation of a single, intense one-optical-cycle pulse in the visible region.
We generated an ultrabroadband infrared pulse ranging from far infrared to 200 THz through a plasma by focusing a hollow-fiber compressed intense 10-fs pulse and its second harmonic in air. We coherently detected the signal up to 100 THz with electro-optic sampling and clarified its drastic dependence on the orientation of the second harmonic crystal in a range of 100–200 THz with an HgCdTe detector. From these, we confirmed the whole frequency components originated from the AC biased plasma and were phase locked. This result opens the possibility of a pump-probe spectroscopy which covers the whole infrared range.
We demonstrate Fourier synthesis of multiple coherent anti-Stokes Raman scattering signals in a LiNbO 3 crystal at room temperature. The signals up to the 20th order ͑470-800 nm͒ were generated by two crossing femtosecond Ti:sapphire laser pulses. Angle dispersion of the signals was compensated into one white-continuum beam by modifying a conventional 4f configuration. Spectral phase of the signal was measured by spectral phase interferometry for direct electric-field reconstruction. Isolated pulses with 25 fs duration at 1 kHz were generated only by appropriately aligning the angle-dispersion compensator. This result opens the possibility of the generation of subfemtosecond pulses in the visible region.
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