Solid State Physics Laboratory

About: Solid State Physics Laboratory is a facility organization based out in Delhi, India. It is known for research contribution in the topics: Quantum dot & Dielectric. The organization has 1754 authors who have published 2597 publications receiving 50601 citations.

Spin dephasing and photoinduced spin diffusion in a high-mobility two-dimensional electron system embedded in a GaAs-(Al,Ga)As quantum well grown in the [110] direction

Abstract: We have studied spin dephasing and spin diffusion in a high-mobility two-dimensional electron system, embedded in a GaAs/AlGaAs quantum well grown in the [110] direction, by a two-beam Hanle experiment. For very low excitation density, we observe spin lifetimes of more than 16 ns, which rapidly decrease as the pump intensity is increased. Two mechanisms contribute to this decrease: The optical excitation produces holes, which lead to a decay of electron spin via the Bir-Aronov-Pikus mechanism and recombination with spin-polarized electrons. By scanning the distance between the pump and probe beams, we observe the diffusion of spin-polarized electrons over more than 20 $\ensuremath{\mu}$m. For high pump intensity, the spin polarization in a distance of several micrometers from the pump beam is larger than at the pump spot, due to the reduced influence of photogenerated holes.

Swift heavy ion irradiation induced modifications in sapphire

Abstract: Swift heavy ion irradiation is carried out on sapphire (α-Al2O3) for controlled modification of its optical properties. Single crystals of α-Al2O3 (0 0 0 1) were irradiated at room temperature with 190 MeV Ag ions having Se∼23 keV/nm with fluences varying from 1011 to 1013 ions/cm2. The pristine as well as irradiated sapphires were characterized by photoluminescence, Fourier transform infrared spectra, optical absorption and X-ray diffraction techniques. The intensity of the PL peak observed at 2.1 eV increases with fluence. X-ray diffraction analysis shows that the surface starts getting amorphized after the fluence of 1 × 1012 ions/cm2. Structural disorder and generation of optically active defect centers (color centers) occur after a fluence of 1 × 1012 ions/cm2. At this fluence the defected zones start overlapping due to multiple ion impact giving rise to cumulative optical response of defects.

Order parameters of a nematic liquid-crystal with low optical anisotropy as determined by depolarized raman-scattering

Abstract: Depolarized Raman measurements are reported for the order parameters and of a partially hydrogenated nematic compound. Similar to the situation observed for some nematic compounds of large birefringence the value of is anomalously low compared with theoretical predictions. Furthermore, resonant Raman measurements are reported for coloured probe molecules dissolved in the nematic compound. The order parameters of the probe are not typical for the ordering of the host-material Mesure en diffusion Raman polarisee des parametres d'ordre et de composes nematiques partiellement hydrogenes. Comme dans le cas des composes possedant une birefringence elevee, est beaucoup plus petit que la prediction theorique. En utilisant l'effet Raman resonant, les parametres d'ordre d'une sonde coloree dissoute dans le compose nematique ne representent pas l'ordre orientationnel de l'hote

Characterization of area arrays of microbolometer-based un-cooled IR detectors without using ROIC

Abstract: We present the characterization of microbolometer area arrays being developed for IR imaging applications. Here, we propose a technique that does not use readout integrated circuit for accessing detector array elements for characterization, which is useful for initial detector technology development. The technique is based on a connection scheme that uses two levels of metal lines in a row–column fashion, thereby, reducing the number of pads and therefore the fan-out complexity from N × M to N + M for an array of N × M detectors. The resulting networked structure has been analyzed and the technique has been developed for extracting back the actual signal and noise values from the measured data. We have implemented this technique on a set of 16 × 16 arrays of Ti-microbolometers developed at our laboratory. However, it may be extended to other types as well. The measurement on these arrays and extraction of various performance parameters are discussed here. The results of detailed characterization show that the average detectivity is about 1.44 × 10 8 Jones, TCR is 0.27%, thermal time constant is 9.91 ms and thermal conductivity is 0.16 μW/K in these arrays. These values are very close to the design values.