Isotope shifts of 6s5d 3^3D-states in neutral Barium

Laser spectroscopy of the low lying $^1$P and $^3$D states in atomic barium has been performed. This work contributes substantially to the development of an effective laser cooling and trapping for heavy alkaline earth elements and aims in particular for a better understanding of the atomic wave function of these systems. Isotope shifts and hyperfine structures are ideal probes for the wave functions at the position of the nucleus. This is essential input for a theoretical evaluation of the sensitivity to fundamental symmetry breaking properties like permanent electric dipole moments. We report the first isotope shift measurements of the $^3$D$_{1,2}$-$^1$P$_1$ transitions. A deviation of the King plot from its expected behavior has been observed. Further we have optically resolved the hyperfine structure of the $^3$D$_{1,2}$ states.Comment: 7 pages, 7 figure

Magneto optical trapping of Barium

First laser cooling and trapping of the heavy alkaline earth element barium has been achieved based on the strong 6s$^2$ $^1$S$_0$ - 6s6p $^1$P$_1$ transition for the main cooling. Due to the large branching into metastable D-states several additional laser driven transitions are required to provide a closed cooling cycle. A total efficiency of $0.4(1) \cdot 10^{-2}$ for slowing a thermal atomic beam and capturing atoms into a magneto optical trap was obtained. Trapping lifetimes of more than 1.5 s were observed. This lifetime is shortened at high laser intensities by photo ionization losses. The developed techniques will allow to extend significantly the number of elements that can be optically cooled and trapped.Comment: 4 pages, 5 figure

Absolute frequency measurement of the 7s2^2 1^1S0_0 −- 7s7p 1^{1}P1_1 transition in 225^{225}Ra

Transition frequencies were determined for transitions in Ra in an atomic beam and for reference lines in Te$_2$ molecules in a vapor cell. The absolute frequencies were calibrated against a GPS stabilized Rb-clock by means of an optical frequency comb. The 7s^2\,^1S$_0$(F = 1/2)-7s7p\,^1P$_1$(F = 3/2) transition in $^{225}$Ra was determined to be $621\,042\,124(2)\,$MHz. The measurements provide input for designing efficient and robust laser cooling of Ra atoms in preparation of a search for a permanent electric dipole moment in Ra isotopes.Comment: Accepted for publication in the rapid communication of Physical review

Radium single-ion optical clock

We explore the potential of the electric quadrupole transitions 7s\,^2S_{1/2} - 6d\,^2D_{3/2}, 6d\,^2D_{5/2} in radium isotopes as single-ion optical frequency standards. The frequency shifts of the clock transitions due to external fields and the corresponding uncertainties are calculated. Several competitive $^A$Ra$^+$ candidates with $A=$ 223 - 229 are identified. In particular, we show that the transition 7s\,^2S_{1/2}\,(F=2,m_F=0) - 6d\,^2D_{3/2}\,(F=0,m_F=0) at 828 nm in $^{223}$Ra$^+$, with no linear Zeeman and electric quadrupole shifts, stands out as a relatively simple case, which could be exploited as a compact, robust, and low-cost atomic clock operating at a fractional frequency uncertainty of $10^{-17}$. With more experimental effort, the $^{223,225,226}$Ra$^+$ clocks could be pushed to a projected performance reaching the $10^{-18}$ level.Comment: 20 pages, 1 figur

Investigation of transcriptional targeting and DNA lesion resolution of Activation Induced Deaminase by cofactor analysis

Activation Induced Deaminase (AID) is a crucial protein in B cells, required for a functional humoral immune system. The regulation and the molecular mechanism of AID is the focus of my thesis. As an enzyme, AID induces mutations and recombination in immunoglobulin genes, leading to increased antibody affinity for antigen and alterations in antibody-effector function. Catalytically, AID deaminates cytosine to uracil in single-stranded DNA, a DNA lesion that leads to a mismatch in double-stranded DNA. AID can be controlled via multiple pathways, including: a) targeting AID to the correct locus and b) regulating the processing of the AID-induced lesion. Proteins proposed to be involved in targeting AID include members of the transcription and chromatin regulation machinery, whereas a variety of DNA repair and DNA metabolism proteins have been shown to be involved in AID-induced lesion-processing. The physical and functional interactions of AID with these co-factors are not well characterised. In this thesis I determined the molecular details and biology of candidates for AID interaction. First, I used a novel technique to uncover and characterise interacting partners of endogenous chromatin-bound AID from B cells. The presented work shows that the RNA polymerase II elongation associated protein PAF1 binds directly to AID, while knocking down members of the PAF complex in B cells inhibits AID-induced immunoglobulin diversification. Secondly, I was able to identify a novel interaction of the DNA repair regulator PCNA with AID, both in vitro and in vivo. Importantly, PCNA function was proven to be susceptible to interference by AID and thus influencing lesion resolution. Taken together, this thesis highlights the importance of cofactors for defining the AID molecular pathway, relevant to all known functions of AID within and possibly beyond the B cell reaction

Determination of transition frequencies in a single 138^{138}Ba+^{+} ion

Transition frequencies between low-lying energy levels in a single trapped $^{138}$Ba$^{+}$ ion have been measured with laser spectroscopy referenced to an optical frequency comb. By extracting the frequencies of one-photon and two-photon components of the line shape using an eight-level optical Bloch model, we achieved 0.1 MHz accuracy for the 5d $^{2}$D$_{3/2}$ - 6p $^{2}$P$_{1/2}$ and 6s $^{2}$S$_{1/2}$ - 5d $^{2}$D$_{3/2}$ transition frequencies, and 0.2 MHz for the 6s $^{2}$S$_{1/2}$ - 6p $^{2}$P$_{1/2}$ transition frequency.Comment: 5 pages, 7 figures, submitted to Phys. Rev.

Multiparametric Spectroscopic Photoacoustic Imaging of Breast Cancer Development in a Transgenic Mouse Model

licenses/by-nc-nd/3.0/). Reproduction is permitted for personal, noncommercial use, provided that the article is in whole, unmodified, and properly cited. Received: 2014.06.16; Accepted: 2014.07.29; Published: 2014.08.15 Objective: To evaluate the potential of multiparametric spectroscopic photoacoustic imaging using oxygen saturation, total hemoglobin, and lipid content to differentiate among four different breast histologies (normal, hyperplasia, ductal carcinoma in situ (DCIS), and invasive breast carcinoma) in a transgenic mouse model of breast cancer development. Materials and Methods: Animal studies were approved by the Institutional Administrative Panel on Laboratory Animal Care. Mammary glands (n=251) of a transgenic mouse model of breast cancer development (FVB/N-Tg(MMTV-PyMT)634Mul) were imaged using B-mode ultrasound and spectroscopic photoacoustic imaging, analyzed for oxygen saturation, total hemoglobin, and lipid content, and processed for histological analysis. Statistical analysis was performed using one-way ANOVA, two-sample t-tests, logistic regression, and ROC analysis. Results: Eighty-two normal, 12 hyperplastic, 96 DCIS, and 61 invasive breast carcinoma mammary glands were analyzed. Based on spectroscopic photoacoustic imaging, the oxygen saturation o