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The optical feedback mechanisms in coherently tunable lasers are investigated and the relation to an electromagnetically induced transparency process that happens in the conduction intersubband transitions is discussed. Results show that the sign of the tuning process, red or blue shift, is decided by the frequency of this field, after proper choice of the corrugation periods.

A method is proposed to coherently generate uniform and phase-shifted complex-coupled (CC) semiconductor distributed feedback (DFB) lasers based on intersubband transitions in n-doped quantum-well structures. Results reveal that gain- and index-coupled DFB lasers are associated, respectively, with gain without inversion and laser-induced transparency in the conduction intersubband transitions of quantum-well structures.

The effects of hole dispersion and mixing in the conduction intersubband transitions and infrared dressing of undoped quantum wells (QWs) is studied. This is done by considering transitions of photo-excited electrons from one conduction subband (e1) to another (e2) in the presence of Coulomb interaction with the photo-excited holes.

Multilevel mixing of 1s and 2s states of excitons in quantum-well semiconductors is examined.

A Bragg multiquantum well active photonic gap structures along with infrared laser are used to design optical materials with fundamentally unique features that serves as the cornerstone of many optical devices and photonic systems. The applications of the coherent formation of optically homogeneous periodic structure within a frequency range around the Bragg wavelength for ultrafast switching and time delay control are also discussed.

An inversionless intrinsically single-mode distributed feedback laser structure is studied. The results have shown that under a lasing condition, the laser might develop a mechanism to resist against side effects of spatial hole burning and become increasingly coherent.

The exciton capture and escape in shallow quantum wells including the effects of valence subband mixing are reported. The mixing processes have significant impacts on the various functionalities of optoelectronic devices, such as their speed and leakage currents.

The quantum interference effects in the conduction intersubband transitions of n-doped quantum wells (QWs) are used for proposing a functional one-dimensional functional photonic band gap (PBG) structure. The phase associated with electromagnetically induced optical defects is adjusted by the control field, thus allowing the generation of tunable electromagnetically induced transmission resonances within the band gap.

We propose tunable midinfrared laser systems based on dynamic formation of electromagnetically induced optical defect sites. Such defects occur in a waveguide structure having a uniformly corrugated quantum well structure in the absence of any structural defect or phase slip. In the absence of a control laser field, such a corrugated structure causes a uniform perturbation of refractive index along the waveguide. However, when a relatively small region of such a waveguide structure is illuminated from the side by the control laser field, electromagnetically induced transparency occurs in this region while its refractive index corrugation is removed. We also show that such a coherently induced defect can be dynamically moved along the waveguide structure by just steering the control laser beam to illuminate different locations. We utilize the fact that the phase associated with this defect site can be adjusted via changing the length of the illuminated region to present a tunable distributed feedback laser where its lasing wavelength can be continuously varied within the stop-band. We study the case where two coherently induced defect sites happen along the waveguide structure and discuss the impacts of illumination of the whole waveguide structure with the control laser field. We show that the latter can either make the waveguide coherently transparent by destroying its refractive index perturbation and stop-band, or generate a gain-without-inversion grating. Formation of such a grating allows the waveguide to act as a tunable partly gain-coupled distributed feedback laser. [ABSTRACT FROM PUBLISHER]

The Persian oak, Quercus brantii, trees in the Zagros region of Western Iran have been in decline since 2000. The decline is assumed to be highly connected with changes in meteorological parameters. Our objectives were to quantify the long-term trends in meteorological parameters and reference evapotranspiration (ET0) in the Zagros region and estimate ecohydrological parameters highly affected by climate variability and related to rainfall interception (I) process (i.e., canopy storage capacity (S), the ratio of mean evaporation rate from the wet canopy to the mean rainfall intensity (E/R), and the free throughfall coefficient (p)). Long-term (1961-2010) changes in air temperature (T), precipitation (P), and wind speed (WS) were obtained from six synoptic meteorological stations located in the region. Throughfall (TF) was measured using the sixteen rain gauges randomly located underneath the crown of the five individual trees. P was measured using rain gauges fixed in an open space nearby to the oak trees .I was computed as the difference between P and TF. From 2000 to 2010, meteorological parameters and ET0 changed slightly; T, WS, and ET0 increased (+0.6 ˚C, +0.4 m.s -1, +0.25 mm.day-1, respectively), while P decreased (-60 mm).When climate patterns between 1961-2010 were analyzed for 6 synoptic weather stations, P significantly decreased significantly at one station, whereas T significantly increased at two stations and significantly decreased at another. I was estimated to be 40% and 25% within in-leaf and leaf-less periods, respectively. During the in-leaf period, the mean values of S, E/R, and p were roughly estimated to be 1 mm, 0.22, and 0.23, respectively. Our results indicate that the Zagros region is getting warmer and oak trees will indisputably experience reduction in the available water because of increased evaporative loss.