RESUMO
Samples of energetic material TEX (C6H6N4O8) are studied using Raman spectroscopy and X-ray diffraction (XRD) up to 27 GPa pressure. There are clear changes in the Raman spectra and XRD patterns around 2 GPa related to a conformational change in the TEX molecule, and a phase transformation above 11 GPa. The molecular structures and vibrational frequencies of TEX are calculated by density functional theory based Gaussian 09W and CASTEP programs. The computed frequencies compare well with Raman spectroscopic results. Mode assignments are carried out using the vibrational energy distribution analysis program and are also visualized in the Materials Studio package. Raman spectra of the high pressure phases indicate that the sensitivity of these phases is more than that of the ambient phase.
RESUMO
Self-induced transparency is reported for circularly polarized light in the R1(-3/2) line of a 30 ppm ruby (α-Al2O3:Cr3+) at 1.7 K in a magnetic field of Bâc=4.5 T. In such a field and temperature, a 30 ppm ruby is in the so-called superhyperfine limit resulting in a long phase memory time, TM=50 µs, and a thousand-fold slower pulse propagation velocity of â¼300 m/s was observed, compared to the â¼300 km/s measured in the first observation of self-induced transparency (SIT) â¼50 years ago, that employed a ruby with a 500 ppm chromium concentration in zero field and at 4.2 K. To date, this is the slowest pulse propagation ever observed in a SIT experiment.
RESUMO
Alloyed nanocrystalline Ba0.5Sr0.5FCl0.5Br0.5 doped with Sm(3+) ions was prepared by a facile ball milling method at room temperature. Spectral hole-burning properties of Sm(2+) ions from X-irradiated sample were investigated in the (7)F0-(5)D0 transition between 2.5 K and room temperature. The alloying allows a "chemical" broadening of the inhomogeneous width of the (7)F0-(5)D0 f-f transition to 40 cm(-1); spectral holes with a homogeneous width of 5 cm(-1) can be burnt, yielding a figure-of-merit of Γinh/Γhom = 8. Mechanochemical preparation methods have a significant potential for the preparation of functional materials for applications in frequency domain optical data storage and as X-ray storage phosphors by allowing the preparation of tailored solid solutions.
RESUMO
Slow light based on transient spectral hole-burning is reported for emerald, Be(3)Al(2)Si(6)O(18):Cr(3+). Experiments were conducted in π polarization on the R(1)(± 3/2) line (E2 â A(2)4) at 2.2 K in zero field and low magnetic fields B||c. The hole width was strongly dependent on B||c, and this allowed us to smoothly tune the pulse delay from 40 to 154 ns between zero field and B||c = 15.2 mT. The latter corresponds to a group velocity of 16 km/s. Slow light in conjunction with a linear filter theory can be used as a powerful and accurate technique in time-resolved spectroscopy, e.g., to determine spectral hole-widths as a function of time.
Assuntos
Silicatos de Alumínio/química , Berílio/química , Luz , Campos Magnéticos , Modelos Químicos , Refratometria/métodos , Simulação por Computador , Espalhamento de RadiaçãoRESUMO
In this letter, we investigate the circular differential deflection of a light beam refracted at the interface of an optically active medium. We show that the difference between the angles of deviation of the two circularly polarized components of the transmitted beam is enhanced manyfold near total internal reflection, which suggests a simple way of increasing the limit of detection of chiro-optical measurements.
RESUMO
The angles at which a light beam gets diffracted by a grating depend strongly on the direction of incidence for diffraction angles close to a right angle. Accordingly, it is possible to amplify small beam deflections by placing a grating at an optimal orientation to the light path. We use this principle to amplify small beam deviations arising out of a light beam refracting at the interface of an optically active medium, and demonstrate a new technique of enhancing the limit of detection of chiro-optical measurements.