Fast Analysis for the Focusing of a Laser Beam with Amplitude Modulation and Phase Fluctuation Through an Aperture Lens

1　Ｉｎｔｒｏｄｕｃｔｉｏｎ　　Ｌａｓｅｒｂｅａｍｓｗｉｔｈａｍｐｌｉｔｕｄｅｍｏｄｕｌａｔｉｏｎｓ(ＡＭｓ)ａｎｄｐｈａｓｅｆｌｕｃｔｕａｔｉｏｎｓ (ＰＦｓ) ｐｒｏｐｏｓｅｄｂｙｔｈｅＬａｗｒｅｎｃｅ ＬｉｖｅｒｍｏｒｅＮａｔｉｏｎａｌＬａｂｏｒａｔｏｒｙ (ＬＬＮＬ)ｉｓａｔｙｐｉｃａｌｐｈｙｓｉｃａｌｍｏｄｅｌｆｏｒｈｉｇｈ ｐｏｗｅｒｌａｓｅｒｓ[1] .Ｉｎｈｉｇｈ ｐｏｗｅｒｌａｓｅｒｓｙｓｔｅｍｓ,ｓｕｃｈａｓｌａｒｇｅＮｄ∶ｇｌａｓｓｌａｓｅｒｆｕｓｉｏｎｄｒｉｖｅｒｓ,ｈｉｇｈ ｐｏｗｅｒｌａ…     

Finite element analysis of the dynamic response of clamped sandwich beams subject to shock loading

The finite element (FE) method is employed to analyse the response of clamped sandwich beams subject to shock loadings. Pressure versus time histories representative of shock loadings are applied uniformly to the outer face of the sandwich beam; an impulse applied uniformly to the outer face of the sandwich beam is shown to model adequately shock loadings. Material elasticity and strain hardening representative of structural steels have only a minor effect upon the beam response. Further, the magnitude of the compressive strength of the core has only a limited influence upon the dynamic response of the sandwich beam for the representative range of core strengths considered. The FE results for the deflections and structural response time agree well with the rigid ideally-plastic analytical predictions of Fleck and Deshpande (J. Appl. Mech. (2003), in press).     

Development of a Detector System for Transient Magnetic Field Experiments with Radioactive-Isotope Beams and a Test Experiment

For g-factor measurements of excited states of unstable nuclei, we have been developing a setup for the transient field experiment at RIKEN Accelerator Research Facility. For the preparation of ferromagnetic material, thick Gd foils have been annealed. In a test experiment using a ²²Ne beam, the projectile Coulomb excitation to the first excited state has been observed. This revised version was published online in September 2006 with corrections to the Cover Date.     

Status report on the folded tandem ion accelerator at BARC

The folded tandem ion accelerator (FOTIA) facility set up at BARC has become operational. At present, it is used for elemental analysis studies using the Rutherford backscattering technique. The beams of¹H, ⁷Li, ¹²C, ¹⁶O and ¹⁹F have been accelerated up to terminal voltages of about 3 MV and are available for experiments. The terminal voltage is stable within ±2 kV. In this paper, present status of the FOTIA and future plans are discussed.     

Changes in the polarization ellipse of random electromagnetic beams propagating through the turbulent atmosphere

During the last few years, changes in the state of polarization of a class of random electromagnetic beams (so-called electromagnetic Gaussian Schell-model beams), propagating in free space have been investigated. In the present paper, we extend the analysis to propagation of such beams in homogeneous, isotropic, non-absorbing atmospheric turbulence. We find that the effects of turbulence on the state of polarization are most significant when the atmospheric fluctuations are weak or moderate, whereas in a strong regime of atmospheric fluctuations the state of polarization of the beam returns to its original state. Our results might find possible useful applications for sensing, imaging and communication through the atmosphere.     

The refined theory of transversely isotropic piezoelectric rectangular beams

The problem of deducing one-dimensional theory from two-dimensional theory for a transversely isotropic piezoelectric rectangular beam is investigated. Based on the piezoelasticity theory, the refined theory of piezoelectric beams is derived by using the general solution of transversely isotropic piezoelasticity and Lur’e method without ad hoc assumptions. Based on the refined theory of piezoelectric beams, the exact equations for the beams without transverse surface loadings are derived, which consist of two governing differential equations: the fourth-order equation and the transcendental equation. The approximate equations for the beams under transverse loadings are derived directly from the refined beam theory. As a special case, the governing differential equations for transversely isotropic elastic beams are obtained from the corresponding equations of piezoelectric beams. To illustrate the application of the beam theory developed, a uniformly loaded and simply supported piezoelectric beam is examined.     

Propagation of off-axial cosine-Gaussian beams passing through an apertured and misaligned optical system

A closed-form expression for the one-dimensional off-axial cosine-Gaussian beams passing through an apertured and misaligned paraxially ABCD optical system is derived. As special cases, the corresponding closed-forms for the off-axial or non off-axial cosine-Gaussian beams passing through apertured or unapertured and misaligned or aligned optical systems are also given. The obtained results could be straightforward to the two-dimensional case or sine-Gaussian beams.     

Dynamics of free and embedded lead clusters in intense laser fields

Lead clusters are exposed to strong femtosecond light pulses. The dependence of the recoil energy on the charge state of the atomic ion is now investigated using a new detection setup, i.e., a Thomson analyser. First results show that in contrast to laser-induced overdense plasmas at surfaces the recoil energy distribution appears much narrower. Comparing free lead clusters with lead clusters embedded in large helium droplets, the charging dynamics show distinct differences on the femtosecond time scale. In the embedded case the maximum ionization enhancement is reached earlier.