Transition from incoherent to coherent Random Lasing by Adjusting Silver Nanowires
R. A. Ejbarah, J. M. Jassim, S. F. Haddawi, S. M. Hamidi
The features of silver nanowire random laser (different sizes and concentrations)-based random lasers with a fixed concentration of laser dye rhodamine B pumped by a nanosecond pulsed laser were indicated. It was shown that the sizes and concentrations of scattering centers greatly affect the optical amplification mechanism, thresholds, narrowing the emission intensity and then the transition from the incoherent to a coherent type of random laser. The emergence of spikes and the increase in their number are also discussed under the influence of the size and concentration of silver (Ag) nanowires. The gain narrowing and the enhancement factor were calculated to reinforce obtained results.
In this days, arXiv preprint (a research-sharing platform) shares a new research entitled as “LED based photoacoustic NO2 sensor with sub-ppb detection limit”
A high-sensitivity LED based photoacoustic NO2 sensor is demonstrated. Sensitive photoacoustic gas sensors based on incoherent light sources are typically limited by background noise and drifts due to a strong signal generated by light absorbed at the photoacoustic cell walls. Here we reach a sub-ppb detection limit and excellent stability by using cantilever-enhanced photoacoustic detection and performing a two-channel relative measurement. A white-light LED is used as a light source and the spectrum is divided into two wavelength channels with a dichroic filter. The photoacoustic signals generated by the two wavelength channels are measured simultaneously and used to solve the NO2 concentration. The background signal is highly correlated between the two channels and its variations are suppressed in the relative measurement. A noise level below 1 ppb is reached with an averaging time of 70 s. This is, to the best of our knowledge, the first time a sub-ppb detection limit is demonstrated with an LED based photoacoustic NO2 sensor. As LEDs are available at wide selection of emission wavelengths, the results show great potential for development of cost-effective and sensitive detectors for a variety of other trace gasses as well.
In this days, the journal of Optics Express publishes a new paper entitled as “Switchable generation of azimuthally- and radially-polarized terahertz beams from a spintronic terahertz emitter“
We propose and demonstrate a method of generating two fundamental terahertz cylindrical vector beams (THz-CVBs), namely the azimuthally- and radially-polarized THz pulses, from a spintronic THz emitter. We begin by presenting that the spintronic emitter generates the HE21 mode, a quadrupole like polarization distribution, when placed between two magnets with opposing polarity. By providing an appropriate mode conversion using a triangular Si prism, we show both from experiment and numerical calculation that we obtain azimuthal and radial THz vector beams. The proposed method facilitates the access of CVBs and paves the way toward sophisticated polarization control in the THz regime.
The Journal of Biopolymers: Original Research on Biomolecules published a paper entitled as “Structure of Methylene Blue-DNA Complexes Studied by Linear and Circular Dichroism Spectroscopy“
Bradley et al. [(1972)Biopolyrners 11,645-6521 used electro-optical measurements to show that methylene blue (MB),like acridine orange, in its DNA complex is oriented more or less perpendicular to the helix axis as expected if intercalated. High-precision flow linear dichroism (LD) here confirms that MB is coplanar with the DNA bases at low dyeDNA binding ratios and low ionic strengths. CD shows two origins of induced optical activity for the transition of lowest energy (polarized parallel to the long-axis of the dye molecule): a t low binding ratios (r <0.05),a weak monomeric CD with the same shape as the absorption curve is observed, while at higher binding ratios, a strong exciton CD dominates due to interaction between pairs of MB ligands. The monomeric CD spectrum shows a remarkable dependence on ionic strength: it is negative in the absence of extra salt, but changes sign (at ca 20 mM NaCl or 0.15mMMgC12) and becomes essentially the positive mirror-image spectrum at high ionic strengths (>300mMNa+ or >0.4 mMMg2+). Nondegenerate coupled-oscillator theory can explain the CD in terms of interactions of transition moments of the dye and the nearest nucleotide bases and indicates a change between two intercalation geometries: a Lerman type of mode, denoted y-,and an orthogonal mode, denoted y+. This rotation of MB in the base-pair pocket is accomplished at Na+ and Mg2+concentrations when the phosphates are effectively screened and the result suggests a more localized bonding of Mg2+than is expected from simple polyelectrolyte models. The exciton effect at high binding ratios, observed both in CD and in LD, can be interpreted in terms of an interaction between an intercalated and a nonintercalated MB. The geometry of this “accidental” dimer is consistent with a location of the nonintercalated MB in the minor groove, bridging the strands by the positively charged amino groups directed towards phosphate groups. The dihedral angle of the MB pairs, corresponding to a left-handed helix, is opposite to that with acridine orange and proflavine on DNA, indicating that the latter ligands bind to DNA in a different way.
In this days, Journal of Advanced Optical Materials publishes a new paper entitled as “Electrically Switchable Color Tags Based on Active Liquid-Crystal Plasmonic Metasurface Platform”
Recent demonstrations of metasurfaces show their great potential to realize flat and multifunctional optical elements, viable for many new device applications. Yet, a major frontier in this field is to develop active, tunable, and reconfigurable metasurface platforms. These are highly desirable in modern technologies that require dynamic modulation of light. To achieve this goal, in this work an active liquid-crystal (LC) plasmonic metasurface integrated system is developed and studied. It is specifcally used to demonstrate electrically switchable plasmonic-metasurface-based color tags. The active tags utilize the ability to rotate the polarization of incident light, by application of an external electric feld on twisted nematic liquid crystal confguration. Combined with the wavelength and polarization-selective response of the metasurface, it allows to obtain electrically controlled transmission colors potentially spanning the entire visible spectrum. It is experimentally demonstrated that the dynamic wavelength shift in the devices is greater than 100 nm at a low driving voltage varying from 0 to 5 V. These experimental results indicate the potential of active LC-plasmonic metasurface platforms to realize the next-generation dynamic optical devices.
