26 research outputs found
Chirality sensing employing PT-symmetric and other resonant gain-loss optical systems
Molecular chirality detection and enantiomer discrimination are very
important issues for many areas of science and technology, prompting intensive
investigations via optical methods. However, these methods are hindered by the
intrinsically weak nature of chiro-optical signals. Here, we investigate and
demonstrate the potential of gain materials and of combined gain-loss media to
enhance these signals. Specifically, we show that the proper combination of a
thin chiral layer with a gain-loss bilayer can lead to large enhancements of
both the circular dichroism (CD) response and the dissymmetry factor, g,
compared to the chiral layer alone. The most pronounced enhancements are
obtained in the case of a Parity-Time (PT) symmetric gain-loss bilayer, while
deviations from the exact PT symmetry lead to only moderate deterioration of
the CD and g response, demonstrating also the possibility of tuning the system
response by tuning the gain layer properties. In the case of PT-symmetric
gain-loss bilayers we found that the largest CD enhancement is obtained at the
system lasing threshold, while the g-enhancements at the anisotropic
transmission resonances of the systems. Our results clearly demonstrate the
potential of gain materials in chirality detection. Moreover, our
gain-involving approach can be applied in conjunction with most of the
nanophotonics/nanostructures-based approaches that have been already proposed
for chirality sensing, further enhancing the performance/output of both
approaches.Comment: 15 pages, 8 figure
Simulation of Polarized Beams from Laser-Plasma Accelerators
The generation of polarized particle beams still relies on conventional
particle accelerators, which are typically very large in scale and budget.
Concepts based on laser-driven wake-field acceleration have strongly been
promoted during the last decades. Despite many advances in the understanding of
fundamental physical phenomena, one largely unexplored issue is how the
particle spins are influenced by the huge magnetic fields of plasma and, thus,
how highly polarized beams can be produced. The realization of laser-plasma
based accelerators for polarized beams is now being pursued as a joint effort
of groups from Forschungszentrum J\"ulich (Germany), University of Crete
(Greece), and SIOM Shanghai (China) within the ATHENA consortium. As a first
step, we have theoretically investigated and identified the mechanisms that
influence the beam polarization in laser-plasma accelerators. We then carried
out a set of Particle-in-cell simulations on the acceleration of electrons and
proton beams from gaseous and foil targets. We could show that intense
polarized beams may be produced if pre-polarized gas targets of high density
are employed. In these proceedings we further present that the polarization of
protons in HT and HCl gas targets is largely conserved during laser wake-field
acceleration, even if the proton energies enter the multi-GeV regime. Such
polarized sources for electrons, protons, deuterons and He ions are now
being built in J\"ulich. Proof-of-principle measurements at the (multi-)PW
laser facilities PHELIX (GSI Darmstadt) and SULF (Shanghai) are in preparation.Comment: submitted to IO
Optical control of ground-state atomic orbital alignment: Cl(P-2(3/2)) atoms from HCl(v=2,J=1) photodissociation
H(35)Cl(v=0,J=0) molecules in a supersonic expansion were excited to the H(35)Cl(v=2,J=1,M=0) state with linearly polarized laser pulses at about 1.7 microm. These rotationally aligned J=1 molecules were then selectively photodissociated with a linearly polarized laser pulse at 220 nm after a time delay, and the velocity-dependent alignment of the (35)Cl((2)P(32)) photofragments was measured using 2+1 REMPI and time-of-flight mass spectrometry. The (35)Cl((2)P(32)) atoms are aligned by two mechanisms: (1) the time-dependent transfer of rotational polarization of the H(35)Cl(v=2,J=1,M=0) molecule to the (35)Cl((2)P(32)) nuclear spin which is conserved during the photodissociation and thus contributes to the total (35)Cl((2)P(32)) photofragment atomic polarization] and (2) the alignment of the (35)Cl((2)P(32)) electronic polarization resulting from the photoexcitation and dissociation process. The total alignment of the (35)Cl((2)P(32)) photofragments from these two mechanisms was found to vary as a function of time delay between the excitation and the photolysis laser pulses, in agreement with theoretical predictions. We show that the alignment of the ground-state (35)Cl((2)P(32)) atoms, with respect to the photodissociation recoil direction, can be controlled optically. Potential applications include the study of alignment-dependent collision effects
CAVITY-ENHANCED PARITY-NONCONSERVING OPTICAL ROTATION IN Hg, Xe, AND I
Author Institution: Department of Physics, University of Crete, and Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas 71110 Heraklion-Crete, GreeceAtomic parity-nonconservation (PNC) experiments provide a low-energy test of the Standard Model. However, atomic PNC experiments have proved to be very difficult, typically taking at least 10-20 years to complete. In addition, the measurements of anapole moments in Cs and Tl (the only such measurements to date, performed in the mid 1990s) appear to be inconsistent with each other. Atomic PNC experiments on radioactive isotopes of Fr and Ra are underway at collider facilities (TRIUMF and KVI Groningen, respectively), for which larger experimental signals are expected and several isotopes are available. Here, we describe our recent proposals for the measurement of PNC optical rotation in metastable Hg and Xe [1], and ground state I atoms [2]. A novel optical cavity is proposed which amplifies the optical rotation by about , and allows two signal reversals, therefore allowing room-temperature, table-top PNC experiments with large experimental PNC signals, and rapid signal reversals. We discuss the experimental sensitivity to anapole moments for odd-proton nuclei (in I) and odd-neutron nuclei (in Hg and Xe). \begin{itemize} \item[1] L. Bougas, G. E. Katsoprinakis, W. von Klitzing, J. Sapirstein, and T. P. Rakitzis, Phys. Rev. Lett {\bf 108}, 210801 (2012). \item[2] G. E. Katsoprinakis, L. Bougas, T. P. Rakitzis, V. A. Dzuba and V. V. Flambaum, Phys. Rev. A ({\it submitted}) http://arxiv.org/abs/1301.6947. \end{itemize
Oriented O(3P2), Ne(3P2), and He(3S1) atoms emerging from a bent magnetic guide
We describe our observation of strongly oriented total electronic angular momentum J in O(P-3(2)), Ne(P-3(2)), and He(S-3(1)) atoms emerging from a bent magnetic multipole guide, as measured by resonant multiphoton ionisation. This was contrary to our expectation because no additional (uniform) magnetic fields were applied to orient the atoms behind the exit of the guide. Two- and three-photon ionisation techniques were employed to determine the degree of J polarisation, from which we infer that atoms become oriented as a result of a combination of weak fringe fields, possible stray fields, and the fact that molecular beam packets do not oscillate around the geometric center of the bent multipole guide. We conclude that similar effects may exist in other, related experiments and that a detailed characterisation of the degree of orientation is required prior to any study of chemical dynamics or spectroscopy. This paper should serve as a warning for anybody using similar devices not to assume isotropic angular momentum distributions of atoms and molecules emerging from a magnetic guide or a decelerator, particularly when it is bent; whenever possible, the possibility for a J anisotropy should be experimentally checked. [GRAPHICS