Engineering the structural, plasmonic, and optical properties of multilayered aluminum-doped zinc oxide metamaterial grown by pulsed laser deposition

We engineer a tunable multilayered aluminum-doped zinc oxide metamaterial with low-loss and high-carrier concentration using the pulsed laser deposition. The results of the scanning probe microscopy study show excellent surface quality with a root mean square roughness value of 1.88±0.07  nm. The transmission electron microscopy measurements indicate a clear layer-by-layer structure of the multilayered samples. The optical permittivity results, obtained using the ellipsometry approach, show that the hyperbolic dispersion of the dielectric constant [Re (ε_‖)>0, Re (ε_⊥)<0] is achieved in the near-IR spectral range. The low imaginary part of the optical permittivity Im (ε_⊥)=0.003 and Im (ε_‖)=0.011 is achieved for the optimized sample at the epsilon-near-zero spectral point [Re (ε_⊥)=0 at 1885 nm]. The results of the ellipsometry analysis show that the systematic variation of different fabrication conditions, such as the AZO/ZnO ratio, the thickness of an individual layer, the film's total thickness, and the deposition temperatures, allows for tuning the plasma frequency ω_p and damping frequency γ_p of the investigated samples, which is a promising approach for the future precise engineering of linear and nonlinear optical properties of multilayered aluminum-doped zinc oxide metamaterial.

Designing optical metamaterial with hyperbolic dispersion based on an Al:ZnO/ZnO nano-layered structure using the atomic layer deposition technique

Nano-layered Al:ZnO/ZnO hyperbolic dispersion metamaterial with a large number of layers was fabricated using the atomic layer deposition (ALD) technique. Experimental dielectric functions for Al:ZnO/ZnO structures are obtained by an ellipsometry technique in the visible and near-infrared spectral ranges. The theoretical modeling of the Al:ZnO/ZnO dielectric permittivity is done using effective medium approximation. A method for analysis of spectroscopic ellipsometry data is demonstrated to extract the optical permittivity for this highly anisotropic nano-layered metamaterial. The results of the ellipsometry analysis show that Al:ZnO/ZnO structures with a 1:9 ALD cycle ratio exhibit hyperbolic dispersion transition change near 1.8 μm wavelength.

The Interplay of manganese and nitrate in hydroxyapatite nanoparticles as revealed by pulsed EPR and DFT

The interplay of oppositely charged substitutions in the structure of hydroxyapatite (HAp) nanopowders is investigated on the atomic level by pulsed electron paramagnetic resonance (EPR) technique and ab initio density functional theory calculations. Benefits of EPR to determine Mn(2+) ions in nano-HAp samples are demonstrated. A simple approach based on the measurements of electron spin relaxation times allowed observing the strong influence of fast-relaxing Mn(2+) ions on the relaxation characteristics of the nitrate ions (NO3(-)/NO3(2-)) incorporated in trace amounts. Based on the results of ab initio calculations, we show the propensity of Mn(2+) and NO3(-)/NO3(2-) to associate within the HAp crystal lattice. This could have a direct impact on the functional properties of the material especially to resorption and ion exchange. Furthermore, such an effect can increase a propensity of undesired impurities to incorporate into the doped nanocrystals.

Dynamics of actively mode-locked Quantum Cascade Lasers

The impact of upper state lifetime and spatial hole burning on pulse shape and stability in actively mode locked QCLs is investigated by numerical simulations. It is shown that an extended upper state lifetime is necessary to achieve stable isolated pulse formation per roundtrip. Spatial hole burning helps to reduce the pulse duration by supporting broadband multimode lasing, but introduces pulse instabilities which eventually lead to strongly structured pulse shapes that further degrade with increased pumping. At high pumping levels gain saturation and recovery between pulses leads to suppression of mode locking. In the absence of spatial hole burning the laser approaches single-mode lasing, while in the presence of spatial hole burning the mode locking becomes unstable and the laser dynamics does not reach a steady state anymore.

Mode-locked pulses from mid-infrared quantum cascade lasers

In this study, we report the unequivocal demonstration of midinfrared mode-locked pulses from quantum cascade lasers. The train of short pulses was generated by actively modulating the current and hence the gain of an edge-emitting quantum cascade laser (QCL). Pulses with duration of about 3 ps at full-width-at-half-maxima and energy of 0.5 pJ were characterized using a second-order interferometric autocorrelation technique based on a nonlinear quantum well infrared photodetector. The mode-locking dynamics in the QCLs was modeled based on the Maxwell-Bloch equations in an open two-level system. Our model reproduces the overall shape of the measured autocorrelation traces and predicts that the short pulses are accompanied by substantial wings as a result of strong spatial hole burning. The range of parameters where short mode-locked pulses can be formed is found.

Scaling of femtosecond Yb-doped fiber amplifiers to tens of microjoule pulse energy via nonlinear chirped pulse amplification

We demonstrate that the compensation of self-phase modulation by third-order dispersion can be exploited in the design of fiber amplifiers with tens of microjoules pulse energy. At the highest energies, the amplified pulse accumulates nonlinear phase shift as large as 17 pi. Gain-narrowing occurs in the final amplifier stage, but shorter pulses are still generated with larger nonlinear phase shifts. A large-mode-area Yb-doped photonic crystal fiber amplifier generates diffraction-limited 30 microJ pulses, which are compressed to 240 fs duration. These are converted to the second harmonic with 48% conversion efficiency, as expected theoretically, which confirms the pulse quality.

Interplay of nonlinearity and gain shaping in femtosecond fiber amplifiers

A study of chirped-pulse amplification in the presence of large nonlinear phase shifts (as large as approximately 12pi) and finite gain bandwidth is presented. Numerical simulations that include the effect of nonlinearity, group-velocity dispersion, higher-order dispersion, and finite gain bandwidth predict the spectral signature of the interplay of nonlinearity with gain shaping. Experimental results obtained for up to approximately 0.4 microJ pulse energies from a Yb fiber amplifier agree with the numerical calculations.

Compensation of nonlinear phase shifts with third-order dispersion in short-pulse fiber amplifiers

We show that nonlinear phase shifts and third-order dispersion can compensate each other in short-pulse fiber amplifiers. This compen-sation can be exploited in any implementation of chirped-pulse amplification, with stretching and compression accomplished with diffraction gratings, single-mode fiber, microstructure fiber, fiber Bragg gratings, etc. In particular, we consider chirped-pulse fiber amplifiers at wavelengths for which the fiber dispersion is normal. The nonlinear phase shift accumulated in the amplifier can be compensated by the third-order dispersion of the combination of a fiber stretcher and grating compressor. A numerical model is used to predict the compensation, and experimental results that exhibit the main features of the calculations are presented. In the presence of third-order dispersion, an optimal nonlinear phase shift reduces the pulse duration, and enhances the peak power and pulse contrast compared to the pulse produced in linear propagation. Contrary to common belief, fiber stretchers can perform as well or better than grating stretchers in fiber amplifiers, while offering the major practical advantages of a waveguide medium.

Manipulation of in vitro toxicant sensors in an ultrasonic standing wave

Multi-cellular spheroids are increasingly employed as in vitro sensors of toxicants and a single spheroid can be used as a test object. An ultrasonic standing wave trap (USWT) can hold small particles in a medium-flowing system. This study investigated the conditions for holding HepG2 spheroids in an USWT and its relevance to use in toxicity testing. It can take many hours to reach a detectable end point of cell damage in a standard cellular in vitro toxicant assay and the process might be accelerated through increased sample flow past the spheroid. A USWT was employed here to levitate and hold HepG2 spheroids stationary against a flow of 3 mm s(-1) when the acoustic pressure amplitude is 1.9 MPa. The ultrasonic drive frequency was 1.64 MHz. Acoustic microstreaming in the standing wave chamber generated 1 mm s(-1) flow past a levitated spheroid-scale (80 microm diameter) latex particle in the absence of sample through-flow. The conditions required to form aggregates of cells of a HepG2 cell line in a single half wavelength ultrasonic standing wave mini-chambers are also described here. It is argued that the manipulation capabilities demonstrated may have potential in increasing the efficiency of in vitro toxicant detection by spheroids. Preliminary, visual (unquantified) fluorescence microscopy observations of spheroids levitated in the standing wave in the presence of the toxicant DL-propranolol do suggest accelerated loss of viability compared with controls.

Generation of 36-femtosecond pulses from a ytterbium fiber laser

By optimizing the cavity dispersion map, 1.5-nJ pulses as short as 36 fs are obtained from a Yb-doped fiber laser. Residual higher-order dispersion currently limits the pulse duration, and it should be possible to generate pulses as short as 25-30 fs with Yb-doped fiber.

Comparative study of biological activity of insulins of lower vertebrates in the novel adenylyl cyclase test-system

The biological activity of insulins of lower vertebrates (teleosts-Oncorhynchus gorbuscha, Scorpaena porcus, chondrosteans-Acipenser guldenstaedti and cyclostomates-Lamperta fluviatilis) was studied and compared with that of standard pig insulin. The determination of biological activity was made using the novel adenylyl cyclase (AC) test-system based on the adenylyl cyclase signaling mechanism (ACSM) of insulin action discovered earlier by the authors. The biological activity of insulins was estimated as EC(50), i.e. concentration leading to half-maximal activating effect of the hormone (10(-11)-10(-7) M), in vitro, on adenylyl cyclase in two types of the target tissues: in membrane fractions of the muscles of rat and mollusc Anodonta cygnea. In rat, the efficiency of insulins was found to decrease in the following order: pig insulin>scorpaena insulin>gorbuscha insulin>sturgeon insulin>lamprey insulin. In the mollusc, the order was different: sturgeon insulin>scorpaena insulin>pig insulin>gorbuscha insulin. Lamprey insulin at the same concentrations did not apparently reach the maximal adenylyl cyclase activating effect. The suggestion was made that differences in the biological activity of insulins depend on the hormone structure and a number of indexes characteristic of the adenylyl cyclase test-system in the vertebrate and invertebrate tissues. The proposed adenylyl cyclase test-system is highly sensitive to insulin at physiological concentrations, has good reproduction and is easy to apply.

On the mechanism of relaxin action: the involvement of adenylyl cyclase signalling system

The molecular mechanism of relaxin action was studied taking into account the evolutionary relationship of the peptides belonging to the insulin superfamily and using the authors' previous data on the involvement of the adenylyl cyclase (AC) signalling system in the action of insulin and related peptides. Human relaxin 2 (10(-12)-10(-8) M) has been shown to cause a dose-dependent activating effect on AC in the human myometrium (+370%), in rat skeletal muscles (+117%) and the smooth foot muscles of the bivalve mollusc Anodonta cygnea (+73%). In these tissues mammalian insulin and insulin-like growth factor-1 (IGF-1) also had the AC activating effect. The order of efficiency of the above peptides based upon their ability to induce the maximal AC activating effect was as follows: relaxin > IGF-1 > insulin (human myometrium); IGF-1 > relaxin > insulin (rat skeletal muscle); molluscan insulin-like peptide > IGF-I > insulin > relaxin (molluscan muscle). The relaxin AC activating effect was inhibited with a selective tyrosine kinase blocker tyrphostin 47 and potentiated with Gpp[NH]p providing evidence for the participation of the receptor-tyrosine kinase and G-protein of the stimulatory type (Gs) in the regulatory action of relaxin. The conclusion is that the signalling chain: receptor tyrosine kinase ==> Gs protein ==> AC is involved in the mechanism of relaxin action.

Plants transformed with a cistron of a potato virus Y protease (NIa) are resistant to virus infection

An oligonucleotide carrying signals for translation initiation in plants was engineered upstream to a cDNA clone containing nucleotides 5812-7260 of the potato virus Y (PVY) genome. This fragment contains all but the first 100 5' terminal bases of the cistron encoding one of the PVY proteases (NIa) as well as the first 251 bases of the next cistron (NIb). Nicotiana tabacum cv. SR1 plants were transformed with this fragment. The presence of the NIa sequences in transformed plants was determined by hybridization or PCR, and its expression was ascertained by reverse transcription coupled to PCR. Plants expressing NIa were self-pollinated, and the R1 kanamycin-resistant progeny were rechecked for NIa expression. Several of these plants were found to be resistant to PVY infection, inasmuch as they did not develop symptoms for at least 50 days (the duration of the experiments), and no viral accumulation could be detected in their leaves by ELISA. All of the descendents of resistant homozygous R2 plants were also resistant. Several of the plants transformed with the last three cistrons of PVY (bases 5812-9704; NIa-NIb-coat protein) were also resistant to PVY. None of the transformed plants exhibited resistance to tobacco mosaic virus. Exposure of the plants to 35 degrees C for 48 hr prior to inoculation lowered, but did not abolish, resistance.