Terahertz-driven, all-optical electron gun

Ultrashort electron beams with narrow energy spread, high charge, and low jitter are essential for resolving phase transitions in metals, semiconductors, and molecular crystals. These semirelativistic beams, produced by phototriggered electron guns, are also injected into accelerators for x-ray light sources. The achievable resolution of these time-resolved electron diffraction or x-ray experiments has been hindered by surface field and timing jitter limitations in conventional RF guns, which thus far are <200 MV/m and >96 fs, respectively. A gun driven by optically-generated single-cycle THz pulses provides a practical solution to enable not only GV/m surface fields but also absolute timing stability, since the pulses are generated by the same laser as the phototrigger. Here, we demonstrate an all-optical THz gun yielding peak electron energies approaching 1 keV, accelerated by 300 MV/m THz fields in a novel micron-scale waveguide structure. We also achieve quasimonoenergetic, sub-keV bunches with 32 fC of charge, which can already be used for time-resolved low-energy electron diffraction. Such ultracompact, easy to implement guns driven by intrinsically synchronized THz pulses that are pumped by an amplified arm of the already present photoinjector laser provide a new tool with potential to transform accelerator based science.Comment: 24 pages, 9 figure

Overcoming Bifurcation Instability in High-Repetition-Rate Ho:YLF Regenerative Amplifiers

We demonstrate a Ho:YLF regenerative amplifier (RA) overcoming bifurcation instability and consequently achieving high extraction energies of 6.9 mJ at a repetition rate of 1 kHz with pulse-to-pulse fluctuations of 1.1%. Measurements of the output pulse energy, corroborated by numerical simulations, identify an operation point that allows high-energy pulse extraction at a minimum noise level. Complete suppression of the onset of bifurcation was achieved by gain saturation after each pumping cycle in the Ho:YLF crystal via lowering the repetition rate and cooling the crystal. Even for moderate cooling, a significant temperature dependence of the Ho:YLF RA performance was observed

A Novel Spice: Pickled Pepper Powder and Some Quality Aspects

An alternative pepper powder with better sensory quality was produced from some pickled pepper species. The peppers pickled via traditional and quick methods were dried at 65±1°C, ground and physical, chemical and sensory characteristics of the samples were compared to those of commonly consumed pepper powders (control). Capsicum species grown in Turkey including Chili, Kapia, Jordan, Biberiye, Frenk and etc. were used. The results are expected to contribute to the development of new products, to provide more alternatives for consumers in the market and to satisfy consumer expectations. Along with typical pickled aroma, hotness and colour, pickled pepper powders may be a valuable food additive especially for ready-to-eat and fast foods

1 kHz, Multi-mJ Yb:KYW Bulk Regenerative Amplifier

We report on a high energy Yb:KYW dual-crystal regenerative amplifier, delivering 6 mJ at 1 kHz. The pulses entered at 1030 nm, stretched with chirped fiber Bragg gratings, can sustain a sub-ps duration after recompression

Power and energy scaling of rod-type cryogenic Yb:YLF regenerative amplifiers

We numerically investigate the power and energy scaling potential of cryogenic Yb:YLF regenerative amplifiers in rod geometry. Our approach is based on solving the coupled set of equations describing thermal behavior of the material and its effect on spectroscopic properties, gain, and overall amplification. The approach is first benchmarked with earlier experimental data. By carefully analyzing the sensitivity of the system to operation parameters, we see that the relatively low gain nature of the Yb:YLF and the onset of thermal effects are the main factors that limited the performance in earlier experimental work. We show that usage of dual-rod geometry promises much improved performance. Specifically, we demonstrate that sub-250 fs pulses with an average power of up to 270 W and a peak power above 500 GW can be extracted directly from a single-stage Yb:YLF regenerative amplifier employing dual Yb:YLF rods. We further show that by adjusting the spot size in the regenerative amplifier, one can operate the amplifier in either high-energy mode (>100mJ at 1 kHz) or high-average-power mode (>25mJ at 10 kHz, with >250W). We also discuss pros and cons of Yb:YLF with respect to Yb:YAG, and underline the need for measurement of population and photo-elastic-effect-induced lensing in Yb:YLF to obtain a better understanding of Yb:YLF systems. The findings presented in this work can be used for the design and development of next-generation high-average and peak-power Yb:YLF amplifier systems

Effect of learning approaches of pre-service science teachers on the argument create skills

The aim of this study is to investigate the relationship between science teacher candidates’ ability to construct an argument and learning approaches. For this purpose, the “Learning Approach Scale” was applied to Inonu University Educational Faculty Science teachers ‘first grade students’, and the results were compared with the arguments which were created by the same students. The findings shows that there is a significant relationship between their argument create skills and learning approaches

Front-End of Yb-based High-Energy Optical Waveform Synthesizer

We demonstrate a front-end of an Yb-based passively CEP-stable, two-octave wide, two-channel optical parametric synthesizer driven by slightly sub-picosecond pump pulses from a multi-mJ regenerative amplifier at 1 kHz

Highly efficient broadband sum-frequency generation in the visible wavelength range

We report on efficient broadband sum-frequency generation, converting a 140 THz near-infrared bandwidth to the visible regime with photon conversion efficiency greater than 90%. Using a 20-mm-long aperiodically adiabatively poled KTP crystal, the spectral range 660–990 nm was converted to 405–500 nm using a strong pump wave at 1030 nm. The photon conversion efficiency was confirmed to be 92±0.5% when pumped with an intensity of 0.94  GW/cm2. Our experimental results agreed very well with analytic predictions and numerical simulations

Is there a relationship between basilar artery tortuosity and vertigo?

alpua, murat/0000-0002-0951-5962WOS: 000460832100018PubMed: 30771568Objective: The aim of this study was to investigate the relationship between basilar artery (BA) tortuosity, hypogenesis/agenesis of the vertebral artery (VA), and vertigo, with the use of magnetic resonance imaging (MRI). Patients and methods: This case-control study included patients admitted to the outpatient clinics, who were aged 18-80 years, without any known systemic diseases. All patients were evaluated with a 1.5-tesla MRI system. BA Tortuosity, VA agenesis, and VA asymmetry were noted. BA diameter (central) and length (longitudinal) were measured. Results: A total of 154 vertigo patients (46 M, 108 F; mean age of 48.95 +/- 17.3 years) and 346 control subjects (112 M, 234 F; mean age of 45.12 +/- 17.0 years) were included. The mean age of the vertigo patients was significantly higher than that of the control group (48.95 vs 45.12 years) (p = 0.021). The rate of BA tortuosity was higher in patients with vertigo (p = 0.030). When the participants were divided into two groups according to median age ( = 45 years) there was no statistically significant difference between the groups in terms of VA asymmetry (p = 0.070) and hypogenesis/agenesis (p = 0.577). There was a statistically significant difference between the groups in respect of BA tortuosity (p = 0.033), BA diameter (p < 0.001), and BA length (p < 0.001). When the study populations were divided into two groups according to the presence of vascular tortuosity, the mean age, BA diameter, and BA length values were higher in the tortuosity ( + ) group (all p < 0.001). Conclusion: These results demonstrated that vertigo and BA tortuosity rates seem to increase with age. Likewise, BA diameter and length increased with age, although there was no significant relationship with vertigo. Patients with tortuosity were significantly older, and had higher rates of VA asymmetry/agenesis, and increased BA diameter compared to subjects without tortuosity