Higher index focus–focus singularities in the Jaynes–Cummings–Gaudin model: Symplectic invariants and monodromy

We study the symplectic geometry of the Jaynes–Cummings–Gaudin model with $n=2m-1$ spins. We show that there are focus–focus singularities of maximal Williamson type $(0,0,m)$. We construct the linearized normal flows in the vicinity of such a point and show that soliton type solutions extend them globally on the critical torus. This allows us to compute the leading term in the Taylor expansion of the symplectic invariants and the monodromy associated to this singularity.     

Synthesis of ZrSiN composite films using a plasma focus device

ZrSiN thin films are synthesized by using plasma focus through various numbers of focus shots （10, 20, and 30）, with samples placed at 9 cm away from the tip of the anode. Crystal structures, surface morphologies, and elemental compositions of ZrSiN films are characterized by an X-ray diffractometer （XRD） and scanning electron microscope （SEM） attached with energy dispersive X-ray spectroscopy （EDS）. XRD patterns confirm the formations of polycrystalline ZrSiN films. Crystallinity of nitride increases with the increase of focus shot number. The average crystallite size of zirconium nitride increases from 27 ± 3 nm to 73±8 nm and microstrain decreases from 2.28 to 1.0 with the increase of the focus shot number. SEM results exhibit the formations of granular and oval-shaped microstructures, depending on the number of focus shots. EDS results confirm the presences of silicon, zirconium, nitrogen, and oxygen in the composite films. The content values of Zr and N in the composite films increase with the increase of the focus shot number.     

The focus of light – theoretical calculation and experimental tomographic reconstruction

We present numerical calculations on the field distribution in the focus of an optical system with high numerical aperture. The diffraction integrals which are based on the Debye approximation are derived and evaluated for a radially polarized input field with a doughnut-shaped intensity distribution. It is shown that this mode focusses down to a spot size significantly smaller as compared to the case of linear polarization. An experimental setup to measure the three-dimensional intensity distribution in the focal region is presented, which is based on the knife-edge method and on tomographic reconstruction. Received: 14 July 2000 / Published online: 30 November 2000     

Effect of pre-ionization on Cu Kα emission from a small plasma focus

One of the most important factors for optimizing the X-ray emission from a plasma focus device is the use of pre-ionization before triggering the device. In this paper, we investigated the effect of pre-ionization on Cu Kα and total X-ray emission from a Mather-type plasma focus device. The Cu Kα and total X-ray yield is measured as a function of the deuterium-filling pressure by using PIN-diode detectors. The maximum Cu Kα emission is found to be 1.95 J for the α-source and 1.62 J without the α-source, with corresponding average efficiencies of 0.049 and 0.06% without and with the α-source, respectively. The maximum total X-ray yield in 4π geometry is estimated to be about 2.64 and 2.12 J, with corresponding efficiencies of about 0.08 and 0.064% with and without the α-source, respectively.     

Can spatial coherence effects produce a local minimum of intensity at focus?

It is demonstrated that, for high-Fresnel-number focusing systems illuminated by certain classes of partially coherent light, it is possible to produce a local minimum of intensity at the geometrical focus. Such an effect is possible even though the average intensity in the entrance plane of the lens is uniform. An explanation is offered for this effect, and potential applications are considered.     

Energy spectrum of multi-radiation of X-rays in a low energy Mather-type plasma focus device

The multi-radiation of X-rays was investigated with special attention to their energy spectrum in a Mather-type plasma focus device （operated with argon gas）. The analysis is based on the effect of anomalous resistances. To study the energy spectrum, a four-channel diode X-ray spectrometer was used along with a special set of filters. The filters were suitable for detection of medium range X-rays as well as hard X-rays with energy exceeding 30 keV. The results indicate that the anomalous resistivity effect during the post pinch phase may cause multi-radiation of X-rays with a total duration of 300 ± 50 ns. The significant contribution of Cu-Kα was due to the medium range X-rays, nonetheless, hard X-rays with energies greater than 15 keV also participate in the process. The total emitted X-ray energy in the forms of Cu-K and Cu-K/3 was around 0.14 ± 0.02 （J/Sr） and 0.04 ±0.01 （J/Sr）, respectively. The total energy of the emitted hard X-ray （〉 15 keV） was around 0.12± 0.02 （J/Sr）.     

Three-dimensional optical data storage using a solid immersion lens to focus a femtosecond laser pulse

A solid immersion lens (SIL) has been applied to the writing and reading of three-dimensional optical data storage in transparent materials. Using a SIL with n=1.516 to focus a 150-fs, 800-nm Tiisapphire laser, the 5-layer reading and writing of data are achieved in fused silica and polyethylene methacrylate at a density of 1.1×10 2 b/cm3. Some advantages of the employment of SIL have been discussed.     

On the use of lenses to focus few-cycle pulses with controlled carrier–envelope phase

From a model of focusing with lenses that includes the effects of the lens variable thickness, material dispersion, aperture, spherical and chromatic aberrations, we characterize the conditions under which a lens can focus to few-cycle, transform-limited pulses propagating without distortion along the focal region. A lens also allows to control the carrier?Cenvelope phase shift along the focus. The carrier?Cenvelope phase shift is drastically reduced by focusing with specific focal lengths and input spot sizes, which are of the same order as those typically used in experiments involving focusing for phase-sensitive, light-matter interactions.     

Anomalous long-range propagation of femtosecond laser pulses through air: moving focus or pulse self-guiding?

Self-guided propagation of femtosecond laser pulses is studied for a converging-beam configuration. Channeling of the pulse energy through various gases is observed over distances well beyond the lens focal point, a fact that cannot be explained by the moving-focus model. The results are in good agreement with three-dimensional numerical simulations.     

Structural and mechanical properties of Al–C–N films deposited at room temperature by plasma focus device

The Al–C–N films are deposited on Si substrates by using a dense plasma focus(DPF) device with aluminum fitted central electrode(anode) and by operating the device with CH_4/N_2 gas admixture ratio of 1:1. XRD results verify the crystalline Al N(111) and Al_3CON(110) phase formation of the films deposited using multiple shots. The elemental compositions as well as chemical states of the deposited Al–C–N films are studied using XPS analysis, which affirm Al–N, C–C, and C–N bonding. The FESEM analysis reveals that the deposited films are composed of nanoparticles and nanoparticle agglomerates. The size of the agglomerates increases at a higher number of focus deposition shots for multiple shot depositions. Nanoindentation results reveal the variation in mechanical properties(nanohardness and elastic modulus)of Al–C–N films deposited with multiple shots. The highest values of nanohardness and elastic modulus are found to be about 11 and 185 GPa, respectively, for the film deposited with 30 focus deposition shots. The mechanical properties of the films deposited using multiple shots are related to the Al content and C–N bonding.     

Effect of preionization on the axial run-down velocity,focus amplitude and current sheath formation in 3.3 kJ small He plasma

The sheath dynamics is an important parameter in dense plasma focus. In this paper, the effect of preionization on sheath dynamics, pinching and its filamentary structure is studied by measuring the axial run-down velocity and its confinement time. A discharge is produced in a 3.3 kJ pure He plasma. The Rogowski and high-voltage signals reveal the formation of an axisymmetric parabolic current sheath, high focusing amplitude during collapse phase with preionization source. The working pressure effect on sheath dynamics and spatial evolution is also studied. The enlarge and symmetric pinhole images with preionization support and conform with the results obtained.