International Journal of Modern Physics B

Conventional lasers consist of two components: a gain material that is pumped in order to provide amplification of light and a cavity to provide feedback. Random lasers replace the traditional laser cavity with a random, multiple-scattering medium. This can give rise to complex lasing behavior, such as unpredictable multidirectional and multifrequency output. Controlling these systems has proved difficult and, until now, has consisted of material and structural manipulations. In random lasers, the most common pumping mechanism is an optical field, which can be applied uniformly or partially across the scattering medium. Partial pumping, referring to the restricted spatial extent of the pump applied to the gain material, is therefore quite ubiquitous in such systems. In contrast to conventional lasers, however, the impact of partial pumping can be significant in random lasers as a subset of the scattering medium is probed. In this review, we discuss state-of-the-art investigations of partially pumped random lasers. Numerical and experimental investigations of how even a simple spot profile of the pump can dramatically alter random laser output are presented. First, the simple case of partial pumping in strongly scattering systems where laser modes are spatially confined is described. Then the most common but more difficult case of weakly scattering random lasers is considered. Here, modes are spatially extended, forcing greater mode interaction and making the random laser output more difficult to predict. Finally, we review recent works that show how the pumping degree of freedom allows a general increase in control over random lasers.

In order to investigate the effects of Ba doping BiFeO₃ on multiferroic properties, Bi_1-xBa_xFeO₃(0≤x≤1)(Ba_xBFO) ceramics were fabricated via rapid solid phase sintering method, and material's structures and electrical properties were investigated. The phase transitions from rhombohedral to pseudo-cubic (x = 10%) and then to tetragonal (x = 40%) were confirmed by X-ray diffraction investigation. Although the electrical conductivity of Ba_xBFO (x = 10%, 20% and 30%) ceramics was low, which is a similar trend to previous reports, an abnormal enhancement of electrical conductance was observed in Ba_xBFO (x = 1%, 3% and 5%) ceramics. Such as, the electrical conductivity of Ba_0.03BFO is calculated to be ~10⁶ Ω⋅cm that is five orders of magnitude higher than that of the BiFeO₃. This has been discussed and ascribed to more percent of oxygen vacancies and Fe²⁺ ions in Ba_xBFO ceramics, as confirmed by X-ray photoelectron spectroscopy investigation.

We propose a protocol for realizing two entanglement concentration scheme with cross-Kerr nonlinearity and double cross-phase modulation method. In our protocols, two remote parties do not require the accurate information of the less entangled state and the double cross-phase modulation is introduced to overcome the errors caused by the imperfect Kerr interaction. By this way, a single-photon entanglement is concentrated, and a three-photon polarized GHZ state is also achieved. Furthermore this protocol can be scaled to multiphoton polarized GHZ state concentration and the giant Kerr media is not needed, which makes our protocols more feasible in experiment.

Synchronization of the Genesio–Tesi chaotic system is investigated via back-stepping method. Based on the Lyapunov stability theory, a novel scheme is designed. A global asymptotical synchronization can be realized via two simpler controllers, each controller involving only one state variable. Furthermore, the convergence speed can be adjusted by control coefficient. Finally, some numerical simulations are employed to verify the effectiveness of the proposed methods.

In this paper, active control and adaptive control methods are applied, respectively. Adaptive control method is implemented when system parameters are unknown and active control method is applied when system parameters are known. Based on the Lyapunov stability theory, the controllers are designed to realize anti-synchronization, meanwhile, the update laws of parameters are proposed. The theoretical proof is given. And two groups of examples are shown to verify the effectiveness of the proposed schemes.

This paper reports the enhancement in the sensing properties of organic dye methyl orange (MO) by introducing TiO₂ nanoparticles. For this purpose, two surface type Ag/MO/Ag and Ag/MO:TiO₂/Ag multifunctional sensors were fabricated by spin coating a 3.0 wt.% solution of MO and 3.0:0.3 wt.% of MO:TiO₂ composite on pre-patterned silver (Ag) electrodes. The gap between Ag electrodes was 40 μm. The Ag/MO/Ag and Ag/MO:TiO₂/Ag structures were characterized to investigate their response towards humidity and temperature variations. The Ag/MO:TiO₂/Ag sensor exhibited better sensitivity and response time than Ag/MO/Ag sensor. The large surface to volume ratio of TiO₂ nanoparticles is the primary reason for the higher sensitivity of Ag/MO:TiO₂/Ag sensor. The sensors can be used to detect humidity variations from 30% to 95% RH and temperature variation from 30°C to 200°C with good stability. Surface morphologies of the film were investigated by scanning electron microscope (SEM).

Solution cast technique has been used to prepare films of PVA and its blend with PVP. Moreover, cobalt chloride (CoCl₂) has been doped in PVA and also PVA/PVP 90/10 as a host matrix for it. Also, UV/VIS optical analysis has been used to drop more light on the structural modification that occurs due to doping CoCl₂ with different levels in different polymeric matrixes. Indeed, UV–Vis spectra is a useful tool for studying the absorption spectra and estimating the values of absorption edge, E_g, and band tail, E_u, for all samples. The optical absorption measurements have been carried out in the wavelength region from 200 nm to 900 nm. In addition, the ligand field parameters and optical energy gaps have been calculated and discussed. X-ray diffraction (XRD) and fourier transform infrared (FTIR) spectroscopy have been used to characterize the studied samples which illustrates that PVA is strongly affected by mixed fillers.

One of the main shortcomings in a field effect diode (FED) is its scaling. Use of an oxide layer in the channel is proposed to enhance the control of the gate on the channel carriers. This is the so-called silicon on raised insulator FED (SORI-FFD) structure. The Shockley–Read–Hall (SRH) mechanism is one of the main components of leakage current in FED devices. The potential induced by the gates in the OFF-state of a SORI-FFD, is larger than that induced by the gates of a regular FED. This reduces, SRH recombination rate. Hence, OFF-state characteristics of the SORI-FED device improves. We evaluate the impact of band-to-band tunneling (BTBT) on the electrical characteristics of Modified FED (M-FED).We show that for channel lengths of 35 nm and lower this device does not turn off. While, the proposed structure makes device channel length scaling possible down to 15 nm. We will also compare electrical characteristics of SORI-FED and M-FED using three metrics: gate delay time versus channel length, gate delay time versus I_ON/I_OFF ratio and energy-delay product versus channel length. Benchmarking results show the proposed FED structure provides improvement in I_ON/I_OFF ratio and holds promise for future logic transistor applications.

It has been empirically known that the disordered system exhibits a power-law behavior. We show from calculation the power law t^-1-α for the pausing-time distribution of thermal diffusion of hydrogen in the exponential density of states. This power law of the pausing-time distribution is examined by the Monte Carlo simulation. The results agree with those obtained by analytical calculation. We discuss the power law in terms of random walk in fractal structure (Cantor ensemble).