24 research outputs found
Femtosecond-laser pumped CdSiP<sub>2</sub> optical parametric oscillator producing 100 MHz pulses centered at 6.2 μm
Broadband mid-IR frequency comb with CSP and AGS from a Er,Tm:Ho fiber laser
We report on the generation of a 2500 nm bandwidth frequency comb at 6.5 μm central wavelength based on critically phase-matched parametric down-conversion in the nonlinear crystal
CdSiP
2
CdSiP2
(CSP), driven by a compact Er,Tm:Ho fiber laser. The generated ultra-broadband pulses show a transform-limited duration of 2.3 optical cycles and carry up to 150 pJ of energy at a 100 MHz pulse repetition rate. For comparison, the spectrum generated in
AgGaS
2
AgGaS2
(AGS) spans from 6.2 to 7.4 μm at full-width at half-maximum (FWHM) with a pulse energy of 3 pJ. A full 3D nonlinear wave propagation code is used for optimization of the noncollinear angle, propagation direction, and crystal thickness.Peer ReviewedPostprint (author's final draft
Variable-range hopping in quasi-one-dimensional electron crystals
We study the effect of impurities on the ground state and the low-temperature
dc transport in a 1D chain and quasi-1D systems of many parallel chains. We
assume that strong interactions impose a short-range periodicicity of the
electron positions. The long-range order of such an electron crystal (or
equivalently, a charge-density wave) is destroyed by impurities. The 3D
array of chains behaves differently at large and at small impurity
concentrations . At large , impurities divide the chains into metallic
rods. The low-temperature conductivity is due to the variable-range hopping of
electrons between the rods. It obeys the Efros-Shklovskii (ES) law and
increases exponentially as decreases. When is small, the metallic-rod
picture of the ground state survives only in the form of rare clusters of
atypically short rods. They are the source of low-energy charge excitations. In
the bulk the charge excitations are gapped and the electron crystal is pinned
collectively. A strongly anisotropic screening of the Coulomb potential
produces an unconventional linear in energy Coulomb gap and a new law of the
variable-range hopping . remains
constant over a finite range of impurity concentrations. At smaller the
2/5-law is replaced by the Mott law, where the conductivity gets suppressed as
goes down. Thus, the overall dependence of on is nonmonotonic.
In 1D, the granular-rod picture and the ES apply at all . The conductivity
decreases exponentially with . Our theory provides a qualitative explanation
for the transport in organic charge-density wave compounds.Comment: 20 pages, 7 figures. (v1) The abstract is abridged to 24 lines. For
the full abstract, see the manuscript (v2) several changes in presentation
per referee's comments. No change in result
Scaling slowly rotating asteroids with stellar occultations
Context. As evidenced by recent survey results, the majority of asteroids are slow rotators (spin periods longer than 12 h), but lack spin and shape models because of selection bias. This bias is skewing our overall understanding of the spins, shapes, and sizes of asteroids, as well as of their other properties. Also, diameter determinations for large (>60 km) and medium-sized asteroids (between 30 and 60 km) often vary by over 30% for multiple reasons.
Aims. Our long-term project is focused on a few tens of slow rotators with periods of up to 60 h. We aim to obtain their full light curves and reconstruct their spins and shapes. We also precisely scale the models, typically with an accuracy of a few percent.
Methods. We used wide sets of dense light curves for spin and shape reconstructions via light-curve inversion. Precisely scaling them with thermal data was not possible here because of poor infrared datasets: large bodies tend to saturate in WISE mission detectors. Therefore, we recently also launched a special campaign among stellar occultation observers, both in order to scale these models and to verify the shape solutions, often allowing us to break the mirror pole ambiguity.
Results. The presented scheme resulted in shape models for 16 slow rotators, most of them for the first time. Fitting them to chords from stellar occultation timings resolved previous inconsistencies in size determinations. For around half of the targets, this fitting also allowed us to identify a clearly preferred pole solution from the pair of two mirror pole solutions, thus removing the ambiguity inherent to light-curve inversion. We also address the influence of the uncertainty of the shape models on the derived diameters.
Conclusions. Overall, our project has already provided reliable models for around 50 slow rotators. Such well-determined and scaled asteroid shapes will, for example, constitute a solid basis for precise density determinations when coupled with mass information. Spin and shape models in general continue to fill the gaps caused by various biases
Nonlinear Optical Measurements of CdSiP\u3csub\u3e2\u3c/sub\u3e at Near and Mid-infrared Wavelengths
We measure the birefringence of the nonlinear optical (NLO) properties of cadmium silicon phosphide via the Z-scan technique at near and mid-infrared wavelengths. We discuss the implications of the NLO properties on optical parametric amplifier performance. We find that the nonlinear absorption does reduce the conversion efficiency, while the nonlinear refraction has a negligible effect
Observation of a two level thermal conductivity in the low-dimensional materials
International audienc
Broadband mid-IR frequency comb with CSP and AGS from a Er,Tm:Ho fiber laser
We report on the generation of a 2500 nm bandwidth frequency comb at 6.5 μm central wavelength based on critically phase-matched parametric down-conversion in the nonlinear crystal
CdSiP
2
CdSiP2
(CSP), driven by a compact Er,Tm:Ho fiber laser. The generated ultra-broadband pulses show a transform-limited duration of 2.3 optical cycles and carry up to 150 pJ of energy at a 100 MHz pulse repetition rate. For comparison, the spectrum generated in
AgGaS
2
AgGaS2
(AGS) spans from 6.2 to 7.4 μm at full-width at half-maximum (FWHM) with a pulse energy of 3 pJ. A full 3D nonlinear wave propagation code is used for optimization of the noncollinear angle, propagation direction, and crystal thickness.Peer Reviewe
Magnetic fields and fluctuations in weakly Mn doped ZnGeP 2
We report on our measurements of local and bulk magnetic features in weakly Mn doped ZnGeP2. Utilizing muon spin rotation and relaxation measurements, we identify local ferromagnetic order and fluctuations in the local fields as sampled by an implanted muon (mu(+)). We also report on field induced ferromagnetism occurring above the claimed paramagnetic to ferromagnetic transition temperature (T-c - 312 K)
Narrow-bandwidth, mid-infrared, seeded optical parametric generation in 90° phase-matched CdSiP2 crystal pumped by diffraction limited 500-ps pulses at 1064 nm
Low-threshold, efficient optical parametric generation at 6100 nm is demonstrated with CdSiP2 at 1 to 10 kHz repetition rates with seeding at the signal wavelength employed for narrowing of the idler spectral bandwidth