85 research outputs found
Unpolarized, incoherent repumping light for prevention of dark states in a trapped and laser-cooled single ion
Many ion species commonly used for laser-cooled ion trapping studies have a
low-lying metastable 2D3/2 state that can become populated due to spontaneous
emission from the 2P1/2 excited state. This requires a repumper laser to
maintain the ion in the Doppler cooling cycle. Typically the 2D3/2 state, or
some of its hyperfine components if the ion has nuclear spin, has a higher
multiplicity than the upper state of the repumping transition. This can lead to
dark states, which have to be destabilized by an external magnetic field or by
modulating the polarization of the repumper laser. We propose using
unpolarized, incoherent amplified spontaneous emission (ASE) to drive the
repumping transition. An ASE source offers several advantages compared to a
laser. It prevents the buildup of dark states without external polarization
modulation even in zero magnetic field, it can drive multiple hyperfine
transitions simultaneously, and it requires no frequency stabilization. These
features make it very compact and robust, which is essential for the
development of practical, transportable optical ion clocks. We construct a
theoretical model for the ASE radiation, including the possibility of the
source being partially polarized. Using 88Sr+ as an example, the performance of
the ASE source compared to a single-mode laser is analyzed by numerically
solving the eight-level density matrix equations for the involved energy
levels. Finally a reduced three-level system is derived, yielding a simple
formula for the excited state population and scattering rate, which can be used
to optimize the experimental parameters. The required ASE power spectral
density can be obtained with current technology
Dark-state suppression and optimization of laser cooling and fluorescence in a trapped alkaline-earth-metal single ion
We study the formation and destabilization of dark states in a single trapped
88Sr+ ion caused by the cooling and repumping laser fields required for Doppler
cooling and fluorescence detection of the ion. By numerically solving the
time-dependent density matrix equations for the eight-level system consisting
of the sublevels of the 5s 2S1/2, 5p 2P1/2, and 4d 2D3/2 states, we analyze the
different types of dark states and how to prevent them in order to maximize the
scattering rate, which is crucial for both the cooling and the detection of the
ion. The influence of the laser linewidths and ion motion on the scattering
rate and the dark resonances is studied. The calculations are then compared
with experimental results obtained with an endcap ion trap system located at
the National Research Council of Canada and found to be in good agreement. The
results are applicable also to other alkaline earth ions and isotopes without
hyperfine structure
The Discursive Paradox of Environmental Conflict : Between Ecologism and Economism in Ecuador
Ecuador in times of the Rafael Correa government constitutes a prime example of the paradox of environmental conflict, in which all involved actors claim to represent the true vanguard concerning safeguarding of the environment and human conditions. The country presents the ecologically most progressive constitution in the world and also incorporates far-reaching recognition of indigenous peoples’ rights. Notwithstanding, the economy remains reliant on extractivism and the government argues that the revenues of extractive industries benefit the common good. Anchored in a distinction between environmentalism and ecologism, this article identifies and problematizes dominant narratives among the actors of the contentious discursive scenarios, and analyses how the state and its ecological-indigenous opposition aim to position themselves within the political conflict. The central questions are: How are eco-progressive politics perceived, defined and expressed in this setting of an intercultural and plurinational society economically reliant on natural resource extraction? Which values, interests and ontological assumptions are at stake and how are these expressed in the discursive struggle? The research is based on several years of ethnographic fieldwork, combined with critical reading of the previous literature and discourse analysis. The article contributes to politico-environmental debates in Ecuador and beyond and shows that environmental struggle is entangled in broader political disputes conditioned by global economic structures. It likewise communicates with debates on argumentative discourse and illustrates that the same core arguments can constitute the argumentative basis of rivalling actors in political struggles, thus emphasizing the centrality of the contextual framing amid ontological divides in contentious discursive settings. © 2018, © 2018 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.Peer reviewe
Broadband, unpolarized repumping and clearout light sources for Sr single-ion clocks
Future transportable optical clocks require compact and reliable light
sources. Here, broadband, unpolarized repumper and state clearout sources for
Sr+ single-ion optical clocks are reported. These turn-key devices require no
frequency stabilization nor external modulators. They are fiber based,
inexpensive, and compact. Key characteristics for clock operation are
presented, including optical spectra, induced light shifts and required
extinction ratios. Tests with an operating single-ion standard show a clearout
efficiency of 100%. Compared to a laser-based repumper, the achievable
fluorescence rates for ion detection are a few tens of per cent lower. The
resulting ion kinetic temperature is 1--1.5 mK, near the Doppler limit of the
ion system. Similar repumper light sources could be made for Ca+ (866 nm) and
Ba+ (650 nm) using semiconductor gain media.Comment: 4 pages, 6 figure
Large negative and positive delay of optical pulses in coherently prepared dense Rb vapor with buffer gas
We experimentally study the group time delay for a light pulse propagating
through hot Rb vapor in the presence of a strong coupling field in a
configuration. We demonstrate that the ultra-slow pulse propagation is
transformed into superluminal propagation as the one-photon detuning of the
light increases due to the change in the transmission resonance lineshape.
Negative group velocity as low as -c/10^6=-80 m/s is recorded. We also find
that the advance time in the regime of the superluminal propagation grows
linearly with increasing laser field power.Comment: 5 pages, 6 figure
Metamorfosa Radikalisme pada Lembaga Pendidikan di Sulawesi Tenggara
Research on the metamorphosis of radicalism in educational institutions in Southeast Sulawesi has been conducted and focused on the segregation potential to be a radical individuals and groups to preach, especially in educational institutions in the Southeast Sulawesi. Data obtained through questionnaires, structured interviews, observation, document tracking and focus group discussion.The results showed that the metamorphosis of radicalism on the knot of educational institutions in Southeast Sulawesi spreading through the penetration movement in educational institutions such as on college campuses and in schools, especially in public campuses with the goal of lecturers and students and public schools targeted teachers and students. The spread on campus through student propaganda agency involving senior students and in the school and through extra-curricular involving senior students with methods of brainwashing. Lecturer plays an important role in the growth of radicalism as teachers and leaders of radical organizations with a method of indoctrination while teachers act through the hidden curriculum. The policy of the state budget subsidies to student organizations affiliated to the radical organization helped sustain the growth of radicalism on campus.The study recommends that efforts to break the chain of radicalism in educational institutions in Southeast Sulawesi can be done by educators either individually or as an educator together with governmen
NEAT-FT: the European fiber link collaboration
The development of clocks based on optical transitions during the past three decades culminates in the availability of optical clocks with unprecedented stability and uncertainty . Simultaneously, increasing requirements for accurate time and frequency signals, e.g. for tests of fundamental physics or novel applications in relativistic geodesy, put forward new challenges. Typically, such applications rely on the comparison of two remote clocks. Thus, major challenges are how to synchronize these clocks over long distances or how to get the time or frequency signal of a clock to the location where it is required. It is generally agreed that optical fiber links are an excellent alternative to established satellite based distant clock comparison and synchronization techniques. A European joint research project called Network for European Accurate Time and Frequency Transfer (NEAT-FT) has been initiated in 2011 to lay the foundations for a novel approach to disseminate high-precision timing and ultrastable frequency signals by using existing fiber infrastructure. Since Europe has a large number of modern ultra-precise clocks, special emphasis is put on the development of new techniques for time transfer and phase-coherent comparison of remotely located optical clocks and the feasibility of a European fibre network connecting optical clocks in Europe. This talk highlights recent achievements and discusses some applications and prospects
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