Probing nonadiabatic molecular alignment by spectral modulation.

We investigated molecular alignment wakes of femtosecond laser pulses. Evolution of nonadiabatic molecular alignment in nitrogen gas has been measured via its nonlinear interaction effects with a variably delayed probe pulse. The induced rotational wave packet was mapped as a function of the angular difference between polarization directions of femtosecond pump and probe pulses as well as their relative delay and the plot of the variations of the rotational wave packet, i.e. "quantum carpet", was found to be in good agreement with the calculated angular and temporal dependencies of molecular alignment parameter.

Pressure optimization of high harmonic generation in a differentially pumped Ar or H2 gas jet.

We experimentally studied the dependence of high harmonic generation in argon and molecular hydrogen on pressure changes in a gas jet that cause variations of the phase matching conditions and absorption. The study was performed at a peak laser intensity of ∼1.5 × 10(14) W/cm(2). To enable measurements over a wide range of pressures, we employed differential pumping with an additional cell (∼20 cm(3) volume) enclosing the gas jet. By increasing the pressure in the gas jet up to a maximum of 1.5 bars with argon or 0.5 bars with hydrogen, we observed an increase in the high harmonic (HH) yield until an optimum pressure of 0.2 bars was reached for Ar, beyond which the output began decreasing. For H2, we observed an increase of the HH output up to the maximum pressure of 0.5 bars. This pressure-dependence study allowed us to achieve a tenfold enhancement in the high harmonic yield at the optimum pressure.

High-throughput beamline for attosecond pulses based on toroidal mirrors with microfocusing capabilities.

We have developed a novel attosecond beamline designed for attosecond-pump/attosecond probe experiments. Microfocusing of the Extreme-ultraviolet (XUV) radiation is obtained by using a coma-compensated optical configuration based on the use of three toroidal mirrors controlled by a genetic algorithm. Trains of attosecond pulses are generated with a measured peak intensity of about 3 × 10(11) W/cm(2).

Ultrafast electron dynamics in phenylalanine initiated by attosecond pulses.

In the past decade, attosecond technology has opened up the investigation of ultrafast electronic processes in atoms, simple molecules, and solids. Here, we report the application of isolated attosecond pulses to prompt ionization of the amino acid phenylalanine and the subsequent detection of ultrafast dynamics on a sub-4.5-femtosecond temporal scale, which is shorter than the vibrational response of the molecule. The ability to initiate and observe such electronic dynamics in polyatomic molecules represents a crucial step forward in attosecond science, which is progressively moving toward the investigation of more and more complex systems.

Micro-focusing of attosecond pulses by grazing-incidence toroidal mirrors.

The design of optical systems for micro-focusing of extreme-ultraviolet (XUV) attosecond pulses through grazing-incidence toroidal mirrors is presented. Aim of the proposed configuration is to provide a micro-focused image through a high demagnification of the XUV source with the following characteristics: i) almost negligible aberrations; ii) long exit arm to easily accommodate at the output the experimental setups required for the applications of the focused attosecond pulses; iii) possibility to have an intermediate region where the XUV beam is collimated, in order to insert a plane split-mirror for the generation of two XUV pulse replicas to be used in a XUV-pump/XUV-probe setup. We present the analytical and numerical study of two optical configurations characterized by two sections based on the use of toroidal mirrors. The first section provides a demagnified image of the source in an intermediate focus that is free from defocusing but has a large coma aberration. The second section consists of a relay mirror that is mounted in Z-shaped geometry with respect to the previous one, in order to give a stigmatic image with a coma that is opposite to that provided by the first section. An example is provided to demonstrate the capability to achieve spot sizes in the 5-15 µm range with a demagnification higher than 10 in a compact envelope.

Ultra-short echo-time MRI detects changes in bone mineralization and water content in OVX rat bone in response to alendronate treatment.

In this work we hypothesize that bisphosphonate treatment following ovariectomy manifests in increased phosphorus and decreased water concentration, both quantifiable nondestructively with ultra-short echo-time (UTE) (31)P and (1)H-MRI techniques. We evaluated this hypothesis in ovariectomized (OVX) rats undergoing treatment with two regimens of alendronate. Sixty female four-month-old rats were divided into four groups of 15 animals each: ovariectomized (OVX), OVX treatment groups ALN1 and ALN2, receiving 5 microg/kg/day and 25 microg/kg/day of alendronate, and a sham-operated group (NO) serving as control. Treatment, starting 1 week post-surgery, lasted for 50 days at which time animals were sacrificed. Whole bones from the left and right femora were extracted from all the animals. (31)P and (1)H water concentration were measured by UTE MRI at 162 and 400 MHz in the femoral shaft and the results compared with other measures of mineral and matrix properties obtained by (31)P solution NMR, CT density, ash weight, and water measured by dehydration. Mechanical parameters (elastic modulus, EM, and ultimate strength, US) were obtained by three-point bending. The following quantities were lower in OVX relative to NO: phosphorus concentration measured by (31)P-MRI (-8%; 11.4+/-0.9 vs. 12.4+/-0.8%, p<0.005), (31)P-NMR (-4%; 12.8+/-0.4 vs. 13.3+/-0.8 %, p<0.05) and micro-CT density (-2.5%; 1316+/-34 vs. 1349+/-32 mg/cm(3), p=0.005). In contrast, water concentration by (1)H-MRI was elevated in OVX relative to NO (+6%; 15.5+/-1.7 vs. 14.6+/-1.4 %, p<0.05). Alendronate treatment increased phosphorus concentration and decreased water concentration in a dose-dependent manner, the higher dose yielding significant changes relative to values found in OVX animals: (31)P-MRI (+14%; p<0.0001), (31)P-NMR (+9%; p<0.0001), ash content (+1.5%; p<0.005), micro-CT mineralization density (+2.8%; p<0.05), and (1)H-MRI, (-19%, p<0.0001). The higher dose raised phosphorus concentration above and water concentration below NO levels: (31)P-MRI (+6%; p<0.05), (31)P-NMR (+5%; p=0.01), ash content (+1.5%; p=0.005), (1)H-MRI (-14%; p<0.0001), and drying water (-10%; p<0.0005). Finally, the group means of phosphorus concentration were positively correlated with EM and US (R(2)> or =0.98, p<0.001 to p<0.05) even though the pooled data from individual animals were not. The results highlight the implications of estrogen depletion and bisphosphonate treatment on mineral composition and mechanical properties and the potential of solid-state MR imaging to detect these changes in situ in an animal model of rat ovariectomy.

Multi-modality study of the compositional and mechanical implications of hypomineralization in a rabbit model of osteomalacia.

Osteomalacia is characterized by hypomineralization of the bone associated with increased water content. In this work we evaluate the hypotheses that 1) 3D solid-state magnetic resonance imaging (MRI) of (31)P (SSI-PH) and (1)H (SSI-WATER) of cortical bone can quantify the key characteristics of osteomalacia induced by low-phosphate diet; and 2) return to normophosphatemic diet (NO) results in recovery of these indices to normal levels. Twenty female five-week old rabbits were divided into four groups. Five animals were fed a normal diet for 8 weeks (NOI); five a hypophosphatemic diet (0.09%) for the same period to induce osteomalacia (HYI). To examine the effect of recovery from hypophosphatemia an additional five animals received a hypophosphatemic diet for 8 weeks, after which they were returned to a normal diet for 6 weeks (HYII). Finally, five animals received a normal diet for the entire 14 weeks (NOII). The NOI and HYI animals were sacrificed after 8 weeks, the NOII and HYII groups after 14 weeks. Cortical bone was extracted from the left and right tibiae of all the animals. Water content was measured by SSI-WATER and by a previously reported spectroscopic proton-deuteron nuclear magnetic resonance (NMR) exchange technique (NMR-WATER), phosphorus content by SSI-PH. All MRI and NMR experiments were performed on a 9.4 T spectroscopy/micro-imaging system. Degree of mineralization of bone (DMB) was measured by micro-CT and elastic modulus and ultimate strength by 3-point bending. The following parameters were lower in the hypophosphatemic group: phosphorus content measured by SSI-PH (9.5+/-0.4 versus 11.1+/-0.3 wt.%, p<0.0001), ash content (63.9+/-1.7 versus 65.4+/-1.1 wt.%, p=0.05), ultimate strength, (96.3+/-16.0 versus 130.7+/-6.4 N/mm(2), p=0.001), and DMB (1115+/-28 versus 1176+/-24 mg/cm(3), p=0.003); SSI-WATER: 16.1+/-1.5 versus 14.4+/-1.1 wt.%, p=0.04; NMR-WATER: 19.0+/-0.6 versus 17.4+/-1.2 wt.%, p=0.01. Return to a normophosphatemic diet reduced or eliminated these differences (SSI-PH: 9.5+/-0.9 versus 10.6+/-0.8 wt.%, p=0.04; DMB: 1124+/-31 versus 1137+/-10 mg/cm(3), p=0.2; US: 95.6+/-18.6 versus 103.9+/-7.5 N/mm(2), p=0.2; SSI-WATER: 12.4+/-0.6 versus 12.2+/-0.3 wt.%, p=0.3) indicating recovery of the mineral density close to normal levels. Phosphorus content measured by SSI-PH was significantly correlated with DMB measured by micro-CT (r(2)=0.47, p=0.001) as well as with ultimate strength (r(2)=0.54, p=0.0004). The results show that the methods presented have potential for in situ assessment of mineralization and water, both critical to the bone's mechanical behavior.

Measurement of phosphorus content in normal and osteomalacic rabbit bone by solid-state 3D radial imaging.

In osteomalacia decreased mineralization reduces the stiffness and static strength of bone. We hypothesized that hypomineralization in osteomalacic bone could be quantified by solid-state (31)P magnetic resonance imaging (SS-MRI). Hypomineralization was measured with a 3D radial imaging technique at 162 MHz (9.4T) in rabbit cortical bone of hypophosphatemic (HY) and normophosphatemic (NO) animals. The results were compared with those obtained by quantitative micro-CT (micro-CT) and (31)P solution NMR. 3D images of 277 microm isotropic voxel size were obtained in 1.7 hr with SNR approximately 9. Mineral content was lower in the HY relative to the NO group (SS-MRI: 9.48 +/- 0.4 vs. 11.15 +/- 0.31 phosphorus wet wt %, P < 0.0001; micro-CT: 1114.6 +/- 28.3 vs. 1175.7 +/- 23.5 mg mineral/cm(3); P = 0.003). T(1) was shorter in the HY group (47.2 +/- 3.5 vs. 54.1 +/- 2.7 s, P = 0.004), which suggests that relaxation occurs via a dipole-dipole (DD) mechanism involving exchangeable water protons, which are more prevalent in bone from osteomalacic animals.