type-II Phase Research Articles

Noncollinear parametric amplification in the near-infrared based on type-II phase matching

Noncollinear parametric amplification based on type-II phase matching for the generation of ultrabroadband and tunable spectra in the near infrared is investigated. In a noncollinear geometry the group velocity matching condition between signal and idler can be obtained in frequently used crystals such as β-barium borate (BBO) even for wavelengths fully located in the anomalous dispersion region. The extremely broadband operation, peculiar tuning possibilities and straightforward experimental implementation with the standard BBO crystal pave the way for a versatile NIR source in ultrafast spectroscopy.

Polarisation analysis of optimal conditions for stationary second-harmonic generation in a solid-state laser

The Jones matrix method is used to study the optimal conditions for steady-state generation through intracavity frequency conversion in a solid-state laser under type-II phase matching based on a weakly anisotropic model of an active medium (amplitude and phase anisotropy) and a nonlinear element. The optimal rotation angles of the nonlinear element are found.

Parametric generation of broadband biphotons in a periodic sequence of thin crystals

Collinear parametric scattering of light under type-II phase matching is considered in a periodic sequence of nonlinear cells made of BBO crystals. The possibilities of reducing the duration of the wave packets of biphotons and increasing their intensity under monochromatic pumping are studied. The analysis is based on the account of dispersion of the refractive indices using Sellmeier equations. The obtained results allow one to conclude that at an appropriate choice of the crystal thicknesses and the number of cells, it is possible to significantly increase the flux of broadband biphotons and obtain extremely short quantum packets. It is shown that for sufficiently small thicknesses of individual crystals (layers), this system exhibits a fine structure in the spectrum of biphotons: with an increase in the number of cells (layers) the broadband spectrum is divided into a number of narrow bands and the number of these bands increases. When use is made of a nonlinear BBO crystal, this method allows one to obtain ultrashort packets of biphotons with duration . Compared with a different method of generation of broadband biphotons, which is based on the use of quasi-phase-matched periodically poled crystals, the method studied in this paper does not necessitate the need for the phase modulation of a biphoton to be converted into the amplitude modulation.

An ab initio study of oxide ion dynamics in type-II Bi3NbO7

Oxide ion dynamics in the type-II phase of Bi3NbO7have been studied using a series of DFT molecular dynamics calculations.

Direct visualization of vortex pattern transition inZrB12with Ginzburg-Landau parameter close to the dual point

In nature, many systems exhibit modulated phases with periodic macroscopic patterns and textures mainly due to the competitive interactions of different phases. Vortex systems in superconductors, which are easy to access, offer the possibility of tuning the ratio between the competitive interactions, providing a unique tool to study the evolution and equilibrium of similar patterns. The $\ensuremath{\kappa}\ensuremath{-}T$ phase diagram of clean superconductors shows the transition from type-I to type-II superconductivity via a narrow $\ensuremath{\kappa}$ range near the dual point $\ensuremath{\kappa}=1/\sqrt{2}$ where the vortices attract each other at long distances and repel each other at short distances. This $\ensuremath{\kappa}$ range, which is termed the type-II/1 phase, becomes larger with decreasing temperature. The direct imaging at the scale of individual vortices of the vortex pattern transition would provide valuable information. Therefore, by using scanning Hall probe microscopy, we have performed direct visualization of the vortex pattern transition in a ${\mathrm{ZrB}}_{12}$ single crystal across the type-II and type-II/1 phases. By gradually lowering the temperature, and thereby tuning vortex interactions, a transition is observed from the ordered Abrikosov vortex lattice to a disordered vortex pattern with large areas of Meissner phase, vortex chains, and vortex clusters. The formation of vortex chains and clusters has been found to arise from the combined effect of quenched disorder and the attractive vortex-vortex interaction in the type-II/1 phase. The clusters and chains serve as the vortex reservoir to enable the formation of a triangular vortex lattice of the type-II phase at high temperatures.

494.5 nm generation by sum-frequency mixing of diode pumped neodymium lasers

We report a coherent radiation at 494.5nm by intra-cavity sum-frequency generation of 912nm Nd:GdVO4 laser and 1080nm Nd:CaYAlO4 laser. Blue laser is obtained by using a doubly folded cavity, type-II critical phase matching KTP (KTiOPO4) crystal sum-frequency mixing. With total pump power of 33W (13.8W pump power for 1080nm Nd:CaYAlO4 laser and 19.2W pump power for 912nm Nd:GdVO4 laser), TEM00 mode blue laser at 494.5nm of 1.6W is obtained. The power stability in 30min is better than 3.5%.

Phase-response synchronization in neuronal population

In this study, we have formulated the phase description of the neuronal oscillator with non-instantaneous synaptic inputs and external periodic stimulus by using the phase sensitivity function. By numerical simulation, we have found that the phase of a neuronal oscillator undergoes periodic evolution or locked state, which is determined by the synaptic time constant. The synaptic time constant is also an important condition under which the global network is synchronized. When the synaptic time constant is relatively small, perfectly synchronized behavior quickly occurs in the neuronal population. As the synaptic time constant becomes slightly larger, periodic synchronization emerges in the neuronal population. However, synchronized activity in the neuronal population is lost for larger synaptic time constant. The external periodic stimulus can change the synchronization patterns in the neuronal population. With a weak low-frequency stimulus, the neuronal populations quick synchronized bursting; whereas a high-frequency stimulus can produce synchronized overlapping bursting. We have also found that neuronal oscillators with type-II phase response curves are more susceptible to synchronization than those with type-I phase response curves.

Efficient yellow beam generation by intracavity sum frequency mixing in DPSS Nd:YVO4 laser

We present our studies on dual wavelength operation using a single Nd:YVO4 crystal and its intracavity sum frequency generation by considering the influence of the thermal lensing effect on the performance of the laser. A KTP crystal cut for type-II phase matching was used for intracavity sum frequency generation in the cavity at an appropriate location for efficient and stable yellow output power. More than 550 mW of stable CW yellow-orange beam at 593.5 nm with beam quality parameter (M2) ∼4. 3 was obtained. The total pump to yellow beam conversion efficiency was estimated to be 3.83%.

A Q-BAND FREQUENCY SYNTHESIZER IN 0.13 μM SIGE BICMOS

In this paper, a 42GHz frequency synthesizer fabricated with 0.13m SiGe BiCMOS technology is presented, which consists of an integer-N fourth-order type-II phase locked loop (PLL) with a LC tank VCO and a frequency doubler. The core PLL has three-stage current mode logic (CML) and flve stage true single phase clock (TSPC) logic in the frequency divider. Meanwhile, a novel balanced common-base structure is used in the frequency doubler design to widen the bandwidth and improve the fundamental rejection. The doubler shows a 41% fractional 3dB bandwidths with a fundamental rejection better than 25.7dB. The synthesizer has a maximum output power of 0dBm with a DC power consumption of 60mW. The worst phase noise at 100kHz, 1MHz and 10MHz ofiset frequencies from the carrier is i71dBc/Hz, i83dBc/Hz and i102:4dBc/Hz, respectively.

Decreased Hepcidin-25 Level as a Predictor of Poor Prognosis in Acute Coronary Syndrome Patients

Background: The peptide hormone hepcidin-25 is known as a type-II acute phase protein in patients with chronic inflammatory conditions and it has a central role in iron homeostasis as well as in anemia, inflammation and hypoxia. Atherosclerosis is widely accepted as a chronic inflammatory disease. Herein, we evaluated whether hepcidin-25 level has a prognostic role in patients with acute coronary syndromes (ACS). Material and Method: Forty-eight patients with ACS admitted to the coronary care unit of our hospital were included in Group 1, 19 patients without any significant coronary artery disease were included in Group 2 and 20 healthy subjects as control were included in Group 3. Serum hepcidin-25 levels were measured with Hepcidin ELISA kits. Results: Patients with ACS were followed-up for up to 24 months after admission with regard to cardiac events including death, myocardial infarction and revascularisa- tion. There was no significant difference between the baseline biochemical and clinical characteristics of Group 1 and Group 2. Hepcidin-25 level was lower in Group 1 when compared with other Groups (192± 74 ng/mL, 296 ±104 ng/mL, 303.8±92.1, p<0.01). Hepcidin-25 level was found significantly lower in patients who developed a cardiac event compared to those who did not (140 ± 78 ng/ml vs 208±74 ng/ml, p<0.05) but ferritin and hsCRP were similar. Conclusions. Reduced serum hepcidin-25 levels might predict poor outcome in patients with ACS.

High efficiency 125 J second-harmonic generation from CsLiB_6O_10 nonlinear crystal by diode-pumped Nd:glass laser

A 12.5 J second-harmonic generation with 71.5% conversion efficiency at 0.6 Hz repetition rate from a diode-pumped Nd:glass laser system has been demonstrated by using a CsLiB(6)O(10) (CLBO) nonlinear optical crystal as a frequency doubler. The CLBO has aperture of 40 mm x 40 mm and thickness of 14 mm with Type-II phase matching. The CLBO is mounted into a housing which flows dry nitrogen gas on the CLBO's face. There is no significant reduction of conversion efficiency by exposing of over 600,000 shots for intermissive experiment during 3 years. In our knowledge, these experimental results of output energy and conversion efficiency are highest performance as second-harmonic generation of a diode-pumped solid state laser by using one CLBO nonlinear crystal. In this paper, potential of the CLBO as a frequency converter for repetitive kJ class laser is discussed.

Toward a downconversion source of positively spectrally correlated and decorrelated telecom photon pairs

Frequency correlation (or decorrelation) of photon pairs is of great importance in long-range quantum communications and photonic quantum computing. We experimentally characterize a spontaneous parametric downconversion source, based on a β-barium borate crystal cut for type-II phase matching at 1550 nm, which has the capability to emit photons with positive or no spectral correlations. Our system employs a carefully designed detection method exploiting two InGaAs detectors.

Influence of on-site Coulomb interaction U on properties of MnO(001)2 × 1 and NiO(001)2 × 1 surfaces

We investigate the non-polar and antiferromagnetic (001) surfaces of MnO and NiO crystallizing in the antiferromagnetic type-II phase by means of spin-polarized density functional theory. Results are presented for surface energy, magnetization, and electronic structure. Besides the comparison of the two materials with differently filled minority-spin t2g shells we study the influence of exchange–correlation treatment within two schemes, the generalized gradient approximation GGA and the GGA + U scheme including an effective on-site d–d interaction U.

Characterization of broadband MHD fluctuations during type-II edge localized modes as measured in 2D with ECE-imaging at ASDEX Upgrade

The characterization of a broadband fluctuation that is typical for the type-II ELM regime at ASDEX Upgrade has been improved using the 2D capabilities of ECE-imaging. During the transition from the type-I to type-II ELMy phase, it has been found that electron temperature fluctuations form a broadband peak in the 19–65 kHz range. In the type-II phase, this broadband fluctuation reaches a maximum relative amplitude of almost 20% just inside the top of the pedestal. Simultaneously, the electron temperature profile is completely flattened at this location. The 2D distribution of the amplitude of this broadband fluctuation is such that, when averaged over time, a minimum occurs around the mid-plane. From the measurements of the nearby magnetic pickup coils, a similar broadband fluctuation seems visible in the same frequency range. However, this is peaked at a slightly lower frequency and does not show a similar minimum. From the analysis of the fluctuations on small timescales, the poloidal and toroidal mode numbers are estimated to be m ∼ 100 and n ∼ 21. Furthermore, activity reminiscent of beat waves has been observed, which might partially account for the fluctuation's broadband nature and the seeming velocity variation of single fluctuation passages. Overall, similarities between the characteristics of this broadband fluctuation and various precursors to type-I ELMs suggest that this fluctuation can play an important role in regulating the ELM cycle.

Periodic Small Signal Analysis of a Wide Class of Type-II Phase Locked Loops Through an Exhaustive Variational Model

Phase-locked loops are important building blocks for several different applications. Modern design and implementation of these circuits is largely advantaged by a mixed analog/digital simulation approach since phase locked loops are stiff systems and a full analog representation is in general too large to simulate in reasonable time. Even though current algorithms, based on a mixed analog/digital representation, lead to models characterized by outstanding properties, they do not allow efficient simulations of important periodic and small signal features such as modulation/demodulation or noise effects. In this paper a novel, reliable and efficient method is proposed that overcomes those limitations and makes possible to evaluate both modulation/demodulation and noise effects in the widely adopted class of type-II phase-locked loop circuits based on a digital three-state phase-frequency detector.

Growth imperfections in oriented grown KDP crystals by X-ray topographic analysis

Potassium dihydrogen phosphate (KDP) crystals were restrained to grow in two dimensions only, using a specially designed platform. This enables us to grow the blanks of frequency conversion elements that satisfy type-II phase matching direction out of a type-II phase-matched seed crystal. Synchrotron radiation topography was used to study the growth mechanism of these profiling grown KDP crystals. It is found that both dislocation growth mechanism and layer growth mechanism were involved in the growing process. Inclusions, growth striations and dislocations were the main defects that influenced the crystalline quality of these crystals. High-resolution X-ray diffraction was employed to study the lattice integrality of the crystal.

Efficient Nd:Y0.5Gd0.5VO4-KTiOPO4 green laser under diode pumping into the emitting level 4 F 3/2

We report a green laser at 532 nm generation by intracavity frequency doubling of a continuous wave (cw) laser operation of a 1064 nm Nd:Y0.5Gd0.5VO4 laser under diode pumping into the emitting level 4 F 3/2. A KTiOPO4 (KTP) crystal, cut for critical type-II phase matching at room temperature is used for second harmonic generation (SHG) of the laser. At an incident pump power of 17.8 W, as high as 4.21 W of cw output power at 532 nm is achieved. The optical-to-optical conversion efficiency is up to 23.6%, and the fluctuation of the green output power was better than 2.8% in the given 30 min.

Comparative investigation of long-wave infrared generation based on ZnGeP2 and CdSe optical parametric oscillators

Long-wave infrared (IR) generation based on type-II (o→e+o) phase matching ZnGeP2 (ZGP) and CdSe optical parametric oscillators (OPOs) pumped by a 2.05 μm Tm,Ho:GdVO4 laser is reported. The comparisons of the bire-fringent walk-off effect and the oscillation threshold between ZGP and CdSe OPOs are performed theoretically and experimentally. For the ZGP OPO, up to 419 mW output at 8.04 μm is obtained at the 8 kHz pump pulse repetition frequency (PRF) with a slope efficiency of 7.6%. This ZGP OPO can be continuously tuned from 7.8 to 8.5 μm. For the CdSe OPO, we demonstrate a 64 mW output at 8.9 μm with a single crystal 28 mm in length.

83 W yellow-green laser at 556 nm from frequency-doubling of a Q-Switched Nd:YAG laser at 1112 nm in LBO

We demonstrate a high power 556 nm yellow-green laser by intracavity frequency doubled of the diode-pumped 1112 nm Nd:YAG laser in a symmetrical L-shaped flat-flat cavity. The coatings of the resonator mirrors were carefully designed to achieve efficient operation of fundamental wavelength of the laser at 1112 nm. By using a type-II phase matching LBO nonlinear crystal as the frequency-doubler, the maximum output power of the 556 nm laser was measured to be as high as 83 W with a pulse repetition frequency (PRF) of 10 kHz under incident pump power of 1150 W, corresponding to an optical-to-optical conversion efficiency of about 7.2%. The fluctuation of output power was less than 2% over 30 min.

Optical properties of wurtzite/zinc-blende heterostructures in GaN nanowires

The optical and structural properties of wurtzite GaN nanowires containing zinc-blende GaN inclusions of different thicknesses are investigated. Micro-photoluminescence spectra of single nanowires exhibit a series of narrow emission peaks with linewidth as low as 0.8 meV in the interval 3.1–3.42 eV. The peak energy blue-shifts with increasing excitation power following a ∼I1/3 law due to the progressive band filling and to the screening of the internal field. The quantum confinement in these type-II crystal phase heterostructures was simulated in the framework of a one-dimensional effective mass model, accounting for the internal electrical polarization of the wurtzite GaN. The predicted transition energies are in good agreement with the energy statistics realized on more than 30 single nanowire emission spectra.