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1.
Phys Rev Lett ; 126(6): 067402, 2021 Feb 12.
Article in English | MEDLINE | ID: mdl-33635695

ABSTRACT

Ultrafast transmission changes around the fundamental trion resonance are studied after exciting a p-shell exciton in a negatively charged II-VI quantum dot. The biexcitonic induced absorption reveals quantum beats between hot-trion states at 133 GHz. While interband dephasing is dominated by relaxation of the P-shell hole within 390 fs, trionic coherence remains stored in the spin system for 85 ps due to Pauli blocking of the triplet electron. The complex spectrotemporal evolution of transmission is explained analytically by solving the Maxwell-Liouville equations. Pump and probe polarizations provide full control over amplitude and phase of the quantum beats.

2.
Rev Sci Instrum ; 90(12): 123003, 2019 Dec 01.
Article in English | MEDLINE | ID: mdl-31893859

ABSTRACT

We present an ultrafast spectroscopy system designed for temporal and spectral resolution of transient transmission changes after excitation of single electrons in solid-state quantum structures. The system is designed for optimum long-term stability, offering the option of hands-off operation over several days. Pump and probe pulses are generated in a versatile Er:fiber laser system where visible photon energies may be tuned independently from 1.90 eV to 2.51 eV in three parallel branches. Bandwidth-limited pulse durations between 100 fs and 10 ps are available. The solid-state quantum systems under investigation are mounted in a closed-cycle superconducting magnet cryostat providing temperatures down to 1.6 K and magnetic fields of up to 9 T. The free-standing cryomagnet is coupled to the laser system by means of a high-bandwidth active beam steering unit to eliminate residual low-frequency mechanical vibrations of the pulse tube coolers. High-NA objective lenses inside the sample chamber are employed for focusing femtosecond laser pulses onto the sample and recollection of the transmission signal. The transmitted probe light is dispersed in a grating monochromator equipped with a liquid nitrogen-cooled CCD camera, enabling a frame rate of 559 Hz. In order to eliminate spurious background effects due to low-frequency changes in the thermal equilibrium of the sample, we operate with a lock-in scheme where, instead of the pump amplitude, the pump-probe timing is modulated. This feature is provided without any mechanical action by an electro-optic timing unit inside the femtosecond Er:fiber system. The performance of the instrument is tested with spectrally resolved pump-probe measurements on a single negatively charged CdSe/ZnSe quantum dot under a magnetic field of 9 T. Selective initialization and readout of charge and spin states is carried out via two different femtosecond laser pulses. High-quality results on subpicosecond intraband relaxation dynamics after single-electron excitation motivate a broad variety of future experiments in ultrafast quantum optics and few-fermion quantum dynamics.

3.
Pharmazie ; 42(7): 455-6, 1987 Jul.
Article in English | MEDLINE | ID: mdl-3671470

ABSTRACT

The present investigation deals with the microencapsulation of potassium chloride with mastic. Spherical potassium chloride crystals with a mean particle diameter of approximately 450 microns were used. It could be shown that with a layer of mastic wall material thicker than 21 microns the release of potassium chloride in the in vitro test can be controlled for more than 6 h. The thickness of the wall material over the tested range of 21 to 33 microns has only a limited effect on the kinetics of release of potassium chloride. Increasing the thickness of the layer from 21 to 33 microns merely leads to a reduction of about another 10% in the amount of drug released in 6 h.


Subject(s)
Plant Extracts , Potassium Chloride/administration & dosage , Resins, Plant , Capsules , Chemistry, Pharmaceutical , Mastic Resin , Microscopy, Electron, Scanning
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