Bright Linearly and Circularly Polarized Extreme Ultraviolet and Soft X-Ray High Harmonics for Absorption Spectroscopy

High harmonic generation (HHG) is an extreme nonlinear optical process. When implemented in a phase-matched geometry, HHG coherent upconverts femtosecond laser light into coherent “X-ray laser” beams, while retaining excellent spatial and temporal coherence, as well as the polarization state of the driving laser. HHG has a tabletop footprint, with femtosecond to attosecond time resolution, combined with nanometer spatial resolution. As a consequence of these unique capabilities, HHG is now being widely adopted for use in molecular spectroscopy and imaging, materials science, as well as nanoimaging in general. In the first half of this thesis, I demonstrate high flux linearly polarized soft X-ray HHG, driven by a single-stage 10-mJ Ti:sapphire regenerative amplifier at a repetition rate of 1 kHz. I first down-converted the laser to 1.3 μm using an optical parametric amplifier, before up-converting it into the soft X-ray region using HHG in a high-pressure, phase-matched, hollow waveguide geometry. The resulting optimally phase-matched broadband spectrum extends to 200 eV, with a soft X-ray photon flux of > 10^6 photons/pulse/1% bandwidth at 1 kHz, corresponding to > 10^9 photons/s/1% bandwidth, or approximately a three orders-of-magnitude increase compared with past work. Using this broad bandwidth X-ray source, I demonstrated X-ray absorption spectroscopy of multiple elements and transitions in molecules in a single spectrum, with a spectral resolution of 0.25 eV, and with the ability to resolve the near edge fine structure.In the second half of this thesis, I discuss how to generate the first bright circularly polarized (CP) soft X-ray HHG and also use them to implement the first tabletop X-ray magnetic circular dichroism (XMCD) measurements. Using counter-rotating CP lasers at 1.3 μm and 0.79 μm, I generated CPHHG with photon energies exceeding 160 eV. The harmonic spectra emerge as a sequence of closely spaced pairs of left and right CP peaks, with energies determined by conservation of energy and spin angular momentum. I explain the single-atom and macroscopic physics by identifying the dominant electron quantum trajectories and optimal phase matching conditions. The first advanced propagation simulations for CPHHG reveal the influence of the finite phase matching temporal window on the spectrum, as well as the unique polarization-shaped attosecond pulse train. The first tabletop XMCD measurements at the N4,5 absorption edges of Gd using this light source validate the high degree of circularity, brightness, and stability of this light source. These results demonstrate the feasibility of manipulating the polarization, spectrum and temporal shape of soft X-ray HHG by manipulating the driving laser waveform.Finally, I present the first bright phase-matched CPHHG driven by lasers at wavelengths of 2 μm and 0.79 μm, which extends CPHHG to a broader wavelength combination and confirms the universal nature of this generation scheme. By analyzing the helicity dependent intensity asymmetry of CPHHG generated using different wavelengths and different gas targets, I show that the helicity dependent intensity asymmetry was mostly caused by the helicity dependent single-atom physics, which exhibits different behaviors for different gas targets. Moreover, the asymmetry can reverse and very interestingly, CPHHG from Ar exhibits a single helicity in the high-photon-energy region of the spectrum, which provide a convenient way to generate CPHHG with a single helicity and CP attosecond pulse trains. Finally, simple simulations and cutoff analysis of CPHHG provide guidance for generating CPHHG at higher photon energies

Decreasing the uncertainty of atomic clocks via real-time noise distinguish

The environmental perturbation on atoms is the key factor restricting the performance of atomic frequency standards, especially in long term scale. In this letter, we demonstrate a real-time noise distinguish operation of atomic clocks. The operation improves the statistical uncertainty by about an order of magnitude of our fountain clock which is deteriorated previously by extra noises. The frequency offset bring by the extra noise is also corrected. The experiment proves the real-time noise distinguish operation can reduce the contribution of ambient noises and improve the uncertainty limit of atomic clocks.Comment: 5 pages, 4 figures, 1 tabl

Molecular characterization of a novel thermostable laccase PPLCC2 from the brown rot fungus Postia placenta MAD-698-R

AbstractBackgroundLaccase has been considered important for the degradation of lignocellulose by wood rot fungi. The properties and functions of laccase in white rot fungi have been investigated extensively, but those from brown rot fungi remain largely unknown. In this paper, a laccase isoform Pplcc2 from the brown rot fungus Postia placenta MAD-698-R was expressed heterologously in Pichia pastoris GS115, purified and the properties of the enzyme were determined.ResultsThe molecular weight of the protein was determined to be 67kDa using SDS-PAGE. It cannot oxidize syringaldazine (SGZ), but it can oxidize 2,2′-azino-di-(3-ethylbenzothialozin-6-Sulfonic acid) (ABTS) and 2,6-dimethoxyphenol (DMP). Specific activity for ABTS was 1960±19Unit/mg. The catalytic constant (kcat) was 1213±18.3s-1 for ABTS and 293.2±21.9s-1 for DMP. Km was 22.08μM for ABTS and 11.62μM for DMP. The optimal pH for the oxidation of ABTS and DMP was 3.5 and 5.0 respectively. The optimal temperature for the oxidation of ABTS and DMP was 60°C.ConclusionsThis is the first identified thermo activated and thermostable laccase in brown rot fungi. This investigation will contribute to understanding the roles played by laccases in brown rot fungi

FC2 stabilizes POR and suppresses ALA formation in the tetrapyrrole biosynthesis pathway

During photoperiodic growth, the light-dependent nature of chlorophyll synthesis in angiosperms necessitates robust control of the production of 5-aminolevulinic acid (ALA), the rate-limiting step in the initial stage of tetrapyrrole biosynthesis (TBS). We are interested in dissecting the post-translational control of this process, which suppresses ALA synthesis for chlorophyll synthesis in dark-grown plants. Using biochemical approaches for analysis of Arabidopsis wild-type (WT) and mutant lines as well as complementation lines, we show that the heme-synthesizing ferrochelatase 2 (FC2) interacts with protochlorophyllide oxidoreductase and the regulator FLU which both promote the feedback-controlled suppression of ALA synthesis by inactivation of glutamyl-tRNA reductase, thus preventing excessive accumulation of potentially deleterious tetrapyrrole intermediates. Thereby, FC2 stabilizes POR by physical interaction. When the interaction between FC2 and POR is perturbed, suppression of ALA synthesis is attenuated and photoreactive protochlorophyllide accumulates. FC2 is anchored in the thylakoid membrane via its membrane-spanning CAB (chlorophyll-a-binding) domain. FC2 is one of the two isoforms of ferrochelatase catalyzing the last step of heme synthesis. Although FC2 belongs to the heme-synthesizing branch of TBS, its interaction with POR potentiates the effects of the GluTR-inactivation complex on the chlorophyll-synthesizing branch and ensures reciprocal control of chlorophyll and heme synthesis.Chinese Scholarship CouncilDeutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Peer Reviewe

Current status and influential factors associated with adherence to self-monitoring of blood glucose with type 2 diabetes mellitus patients in grassroots communities: a cross-sectional survey based on information-motivation-behavior skills model in China

ObjectiveSelf-monitoring of blood glucose (SMBG) plays a vital role in the maintenance of blood glucose with type 2 diabetes mellitus(T2DM) and pre-diabetes patients. The study was intended to describe the current status of SMBG with T2DM and pre-diabetes patients in grassroots communities, explore the relationship between SMBG frequency and blood glucose level and apply information-motivation-behavior(IMB) model to analyze the potential influencing factors of SMBG compliance based on electronic questionnaires.MethodsA cross-sectional study was conducted with 1388 T2DM and pre-diabetes patients who completed electronic questionnaires composed of demographics and IMB model content. Chi-square test, Mann-Whitney U test and multivariable logistic regression model analysis were utilized to explore deeply causes of SMBG compliance.ResultsThe results of this study showed that among 1388 T2DM patients, only 26.2% (363/1388) patients reached SMBG standard, indicating low compliance with SMBG. Given that SMBG is one of the individual predictors of type 2 risk in prediabetes patients, this result suggests that the SMBG compliance rate needs to be improved. Patients with fixed occupation (OR=1.989, P=0.035), BMI in normal range (OR=1.336, P=0.049), smoking habit(OR=1.492, P=0.019), understanding SMBG frequency (OR=1.825, P<0.001), understanding control goal of blood glucose (OR=1.414, P<0.001), knowing all the functions of the blood glucose meter (OR=1.923, P<0.001), buying a blood glucose meter/test paper conveniently(OR=2.329, P=0.047), taking supplementary measurement when forgetting blood glucose test(OR=2.044, P=0.005), rotating all the fingers when measuring blood glucose (OR=1.616, P<0.001) and less pain at the needling site(OR=2.114, P<0.001)were independently promoting factors of adherence to SMBG. However, the lack of accessibility and convenience of blood glucose meter or heavy financial burden were blocking factors of adherence to SMBG. Moreover, there were still bottlenecks such as lack of health care knowledge and needle pricking pain.ConclusionThis study verified the practicability of applying IMB model to SMBG with T2DM and pre-diabetes patients. Adherence to SMBG still remained to improved, and putting more emphasis in improvement of individual information, motivation and behavioral skills with patients might be beneficial to maintain better adherence to SMBG in long-term routine of diabetes self-management