Cavity-enhanced single frequency synthesis via DFG of mode-locked pulse trains

We show how to synthesize a CW, single-frequency optical field from the frequency-dispersed, pulsed field of a mode-locked laser. This process, which relies on difference frequency generation in an optical cavity, is efficient and can be considered as an optical rectification. Quantitative estimates for the output power and amplitude noise properties of a realistic system are given. Possible applications to optical frequency synthesis and optical metrology are envisaged

Testing the Dirac equation

The dynamical equations which are basic for the description of the dynamics of quantum felds in arbitrary space--time geometries, can be derived from the requirements of a unique deterministic evolution of the quantum fields, the superposition principle, a finite propagation speed, and probability conservation. We suggest and describe observations and experiments which are able to test the unique deterministic evolution and analyze given experimental data from which restrictions of anomalous terms violating this basic principle can be concluded. One important point is, that such anomalous terms are predicted from loop gravity as well as from string theories. Most accurate data can be obtained from future astrophysical observations. Also, laboratory tests like spectroscopy give constraints on the anomalous terms.Comment: 11 pages. to appear in: C. L\"ammerzahl, C.W.F. Everitt, and F.W. Hehl (eds.): Gyros, Clocks, Interferometers...: Testing Relativistic Gravity in Space, Lecture Notes in Physics 562, Springer 200

Sub-Hz line width diode lasers by stabilization to vibrationally and thermally compensated ULE Fabry-Perot cavities

We achieved a 0.5 Hz optical beat note line width with ~ 0.1 Hz/s frequency drift at 972 nm between two external cavity diode lasers independently stabilized to two vertically mounted Fabry-Perot (FP) reference cavities. Vertical FP reference cavities are suspended in mid-plane such that the influence of vertical vibrations to the mirror separation is significantly suppressed. This makes the setup virtually immune for vertical vibrations that are more difficult to isolate than the horizontal vibrations. To compensate for thermal drifts the FP spacers are made from Ultra-Low-Expansion (ULE) glass which possesses a zero linear expansion coefficient. A new design using Peltier elements in vacuum allows operation at an optimal temperature where the quadratic temperature expansion of the ULE could be eliminated as well. The measured linear drift of such ULE FP cavity of 63 mHz/s was due to material aging and the residual frequency fluctuations were less than 40 Hz during 16 hours of measurement. Some part of the temperature-caused drift is attributed to the thermal expansion of the mirror coatings. High-frequency thermal fluctuations that cause vibrations of the mirror surfaces limit the stability of a well designed reference cavity. By comparing two similar laser systems we obtain an Allan instability of 2*10-15 between 0.1 and 10 s averaging time, which is close to the theoretical thermal noise limit.Comment: submitted to Applied Physics

Information Literacy Competencies of Library and Information Science Postgraduate Students in South East Nigeria Universities: A Focus on the Knowledge and Skill Level

The study investigated the information literacy competencies possessed by Library and Information Science (LIS) postgraduate students in Federal Universities in South East Zone Nigeria with a focus on the Knowledge and skill level. Descriptive survey design was adopted for the study. Seventy two students which included all 2011/2012 PhD and Masters degree students from the Departments of LIS in Nnamdi Azikiwe University, Awka and University of Nigeria, Nsukka. Data was collected using Achievement Test and Questionnaire. Percentages, frequencies and mean rating were used to answer research questions. T-test was used to test hypotheses. The major findings of the study include:  LIS postgraduate students in Federal Universities in South East Zone Nigeria possessed information literacy knowledge since the  measure based on understanding the need for information, how to locate, evaluate and use information have average percentage scores of 95%, 87%, 82% and 88% respectively. However, the information literacy knowledge possessed by LIS Postgraduate students in Nnamdi Azikiwe University, Awka (NAU) differed significantly from those possessed by LIS Postgraduate students in University of Nigeria, Nsukka (UNN); LIS postgraduate students possessed moderate level of information literacy skills as their level of information literacy skills as measured based on ability to locate and access, evaluate and use information has general mean rating of 3.34. However, the skills differed significantly between LIS Postgraduate students in NAU and UNN. Based on the findings, it was recommended that more practical aspect of information literacy should be employed through students industrial training and internship, and  LIS curriculum should be enhanced especially with reference to skill acquisition. Keywords: Literacy, Competency, Skills, Knowledge , Nigeria , Library and Information Science, Nnamdi Azikiwe University Awka, University of Nigeria Nsukka, Student

Frequency Metrology on single trapped ions in the weak binding limit: The 3s1/2-3p3/2 transition in 24-Mg+

We demonstrate a method for precision spectroscopy on trapped ions in the limit of unresolved motional sidebands. By sympathetic cooling of a chain of crystallized ions we suppress adverse temperature variations induced by the spectroscopy laser that usually lead to a distorted line profle and obtain a Voigt profile with negligible distortions. We applied the method to measure the absolute frequency of the astrophysically relevant D2 transition in single 24-Mg+ ions and find 1072082934.33(16)MHz, a nearly 400fold improvement over previous results. Further, we find the excited state lifetime to be 3.84(10) ns.Comment: 4 pages, 5 figure

Injection Locking of a Trapped-Ion Phonon Laser

We report on injection locking of optically excited mechanical oscillations of a single, trapped ion. The injection locking dynamics are studied by analyzing the oscillator spectrum with a spatially selective Fourier transform technique and the oscillator phase with stroboscopic imaging. In both cases we find excellent agreement with theory inside and outside the locking range. We attain injection locking with forces as low as 5(1)×10^(-24)  N so this system appears promising for the detection of ultraweak oscillating forces

Interference of an array of atom lasers

We report on the observation of interference of a series of atom lasers. A comb-like array of coherent atomic beams is generated by outcoupling atoms from distinct Bose-Einstein condensates confined in the independent sites of a mesoscopic optical lattice. The observed interference signal arises from the spatial beating of the overlapped atom laser beams, which is sampled over a vertical region corresponding to 2 ms of free fall time. The average relative de Broglie frequency of the atom lasers was measured.Comment: 3 figure

Sub-milliKelvin spatial thermometry of a single Doppler cooled ion in a Paul trap

We report on observations of thermal motion of a single, Doppler-cooled ion along the axis of a linear radio-frequency quadrupole trap. We show that for a harmonic potential the thermal occupation of energy levels leads to Gaussian distribution of the ion's axial position. The dependence of the spatial thermal spread on the trap potential is used for precise calibration of our imaging system's point spread function and sub-milliKelvin thermometry. We employ this technique to investigate the laser detuning dependence of the Doppler temperature.Comment: 5 pages, 4 figure

Hypolipidemic activity of the methanolic extract of Ficus thonningii (Blume) leaves in hypercholesterolemic-induced rats

Ficus thonningii has been reported to have nutritional and ethno-rnedical uses especially by the Igede-speaking people of Benne State, Nigeria. Therefore, this study: was carried out to assess effects of methanolic leaf extract of Ficus thonningii (MEFT) against cholesterol-induced hyperlipidaemia in rats. Adult rats were divided into 6 groups of 5 rats each. Group 1 and 2 were orally administered 5 nil/kg/day of distilled water. Groups 3-6 received 10 rug/kg/day of simvastatin, 50, 100 and 200 mg/kg/day of extract respectively, for 30 days. Cholesterol (400' mg/kg/ day) was also given to allthe groups except group 1for 30 days. On day 31, blood samples were collected for the determination of serum triglycerides (TG), total cholesterol (TC), low density lipoprotein (LDL-c), very low density lipoprotein (VLDL-c), and high density lipoprotein (HDL-c). MEFI' (200 rug/kg) significantly lowered TG, TC, LDL-c and VLDL-c levels. At this dose the extract also significantly increased HDL-c levels when compared with the cholesterol treated group. These suggest the extract to possess preventive or therapeutic effects on dietinduced hyperlipidaemia.KEYWORDS: hyperlipidaemia, lipoproteins, athrogenic index, cardiovascular disease

Astronomical spectrograph calibration with broad-spectrum frequency combs

Broadband femtosecond-laser frequency combs are filtered to spectrographically resolvable frequency-mode spacing, and the limitations of using cavities for spectral filtering are considered. Data and theory are used to show implications to spectrographic calibration of high-resolution, astronomical spectrometers