Grating-assisted phase matching in extreme nonlinear optics

We propose a new technique for phase matching high harmonic generation that can be used for generating bright, tabletop, tunable, and coherent x-ray sources at keV photon energies. A weak quasi-cw counterpropagating field induces a sinusoidal modulation in the phase of the emitted harmonics that can be used for correcting the large plasma-induced phase mismatch. We develop an analytical model that describes this grating-assisted x-ray phase matching and predicts that very modest intensities (<10(10) W/cm2) of quasi-cw counterpropagating fields are required for implementation.     

Development of perfluorocarbon (PFC) primary standards for monitoring of emissions from aluminum production

An EPA Voluntary Aluminum Industrial Partnership (VAIP) program has been formed to help US primary producers focus on reducing the emissions of two perfluorocarbons (PFCs), tetrafluoromethane (CF4) and hexafluoroethane (C2F6), during the production of aluminum. To ensure comparability of measurements over space and time, traceability to national sources was desirable. Hence, the EPA approached the NIST to develop a suite of primary standards to cover a mole fraction (concentration) range of 0.1 to 1400 micromol mol(-1) for CF4 and 0.01 to 150 micromol mol(-1) of C2F6. A total of eight gravimetric PFC gas standards were prepared with relative expanded uncertainties of < or = 0.52% (approximately 95% confidence level). These primary standards were ultimately used to assign values to a series of secondary gas standards at three mole-fraction levels with relative expanded uncertainties ranging from +/- 0.7% to 5.3% (approximately 95% confidence level). This series of secondary standards was used within the aluminum industry to calibrate instruments used to make emission measurements. Assignment of values to the secondary standards was performed by use of gas chromatography with flame-ionization detection (GC-FID) and Fourier transform infrared spectrometry (FTIR). Real time pot-line and stack samples from a local aluminum plant were also obtained and sub-samples sent to each participating facility for analysis. The data generated from each facility were sent to NIST for analysis. The maximum difference between the NIST and individual facilities' values for the same sub-sample was +/- 26%.     

The application of pattern recognition to the identification of pathogens by laser-excited fluorimetry

The k-nearest neighbor (kNN) approach to pattern recognition was used to evaluate a laser-based method of identifying pathogens based on aminopeptidase profiling. Suitability of the method was tested by evaluating the recognition accuracy for differentiation of four bacterial genera as well as four races within a single Species. Even though variations in profile replicates were relatively large, the kNN approach successfully differentiated these pathogens. Recognition accuracies of 100% and 92% were achieved for the differentiation of genera and races, respectively. Feature-selection algorithms were used which allowed the rejection of features which did not add useful information towards identification or improve recognition accuracy. Identification of races was facilitated by constructing a data set comprised of only races of one species, because feature selection and weighting were strongly affected by the easily differentiated genera. Methods used for feature selection and weighting were also evaluated.     

PHOTODYNAMIC TREATMENT OF HERPES SIMPLEX VIRUS INFECTION IN VITRO

Abstract— The effects of photodynamic action on in vitro herpes simplex virus infections of CV-1 monkey kidney fibroblasts or human skin fibroblasts were determined using proflavine sulfate and white fluorescent lamps. Photodynamic treatment of confluent cell monolayers prior to virus infection inactivated cell capacity, i.e. the capacity of the treated cells to support subsequent virus growth as measured by plaque formation. The capacity of human cells was more sensitive to inactivation than the capacity of monkey cells when 6 μM proflavine was used. Treated cell monolayers recovered the capacity to support virus plaque formation when virus infection was delayed four days after the treatment. Experiments in which the photodynamically treated monolayers were infected with UV-irradiated virus demonstrated that this treatment induced Weigle reactivation in both types of cells. This reactivation occurred for virus infection just after treatment or 4 days later. A Luria-Latarjet-type experiment was also performed in which cultures infected with unirradiated virus were photodynamically treated at different times after the start of infection. The results showed that for the first several hours of the virus infection the infected cultures were more sensitive to inactivation by photodynamic treatment than cell capacity. By the end of the eclipse period the infected cultures were less sensitive to inactivation than cell capacity. Results from extracellular inactivation of virus grown in monkey cells at 6 μM proflavine indicated that at physiological pH the virus has a sensitivity to photodynamic inactivation similar to that for inactivation of cell capacity. The combined data indicated that photodynamic treatment of the cell before or after virus infection could prevent virus growth. Thus, photodynamic inactivation of infected and uninfected cells may be as important as inactivation of virus particles when considering possible mechanisms in clinical photodynamic therapy for herpes simplex.     

Atmospheric pressure chemical ionization and atmospheric pressure photoionization for simultaneous mass spectrometric analysis of microbial respiratory ubiquinones and menaquinones

An atmospheric pressure photoionization (APPI) source and an atmospheric pressure chemical ionization (APCI) source were compared for the selective detection of microbial respiratory ubiquinone and menaquinone isoprenologues using tandem mass spectrometry. Ionization source- and compound mass-dependent parameters were optimized individually for both sources, using the available quinone standards. Detection levels for the two ion sources were determined with ubiquinone-6 (UQ6) and menaquinone-4 (MK4, vitamin K2) standards using flow injection analysis and selected reaction monitoring (SRM). With APPI the calculated lower limit of detection (LLOD) was 1.7 fmol microl(-1) for UQ6 and 2.2 fmol microl(-1) for MK4 at a signal-to-noise ratio of 3. These LLODs were at least three times lower than with APCI. The selectivity of detection afforded by SRM detection reduced complex mixture analysis to 3 min per sample by eliminating the need for chromatographic separations. The detection method was successfully applied to quinone quantification in a variety of environmental samples and cell cultures. Adequate amounts of respiratory quinones can be extracted and quantified from samples containing as low as 2 x 10(7) cells.     

HOST CELL REACTIVATION AND UV-ENHANCED REACTIVATION IN SYNCHRONIZED MAMMALIAN CELLS

Abstract— Does host cell reactivation (HCR) or UV-enhanced reactivation (UVER) of UV-irradiated Herpes simplex virus (UV-HSV) vary during the host mammalian cell cycle? The answer could be useful for interpreting UVER and/or the two-component nature of the UV-HSV survival curve. Procedures were developed for infection of mitotically-synchronized CV-1 monkey kidney cells. All virus survival curves determined at different cell cycle stages had two components with similar D₀'s and intercepts of the second components. Thus, no single stage of the host cell cycle was responsible for the second component of the virus survival curve. When the cells were UV-irradiated immediately prior to infection, enhanced survival of UV-HSV occurred for cell irradiation and virus infection initiated during late G₁/early S phase or late S/early G₂ phase but not during early G₁ phase. For infection delayed by 24 h after cell irradiation, UVER was found at all investigated times. These results indicate that: (1) HCR is similar at all stages of the host cell cycle; and (2) the “induction” of UVER is not as rapid for cell-irradiation in early G₁ phase. This latter observation may be one reason why normal, contact-inhibited cells do not express UVER as rapidly as faster growing, less contact-inhibited cells.     

11-W average power Ti:sapphire amplifier system using downchirped pulse amplification

We demonstrate a high-power laser system that employs a new scheme in which pulses with negative chirp are amplified and then recompressed by dispersion in a block of transparent material. This scheme has significant advantages for amplification of intermediate energy pulses at high average power, including insensitivity to small misalignments of the pulse compressor, elimination of compressor gratings and their thermal loading issues, low compressor energy and bandwidth throughput losses, and a simplified optical design. Using this scheme, we demonstrate what we believe is the highest-average-power single-stage Ti:sapphire amplifier system with 11-W compressed output.     

Doppler-free spectroscopy of mercury at 253.7 nm using a high-power, frequency-quadrupled, optically pumped external-cavity semiconductor laser

We have developed a stable, high-power, single-frequency optically pumped external-cavity semiconductor laser system and generate up to 125 mW of power at 253.7 nm using successive frequency doubling stages. We demonstrate precision scanning and control of the laser frequency in the UV to be used for cooling and trapping of mercury atoms. With active frequency stabilization, a linewidth of <60 kHz is measured in the IR. Doppler-free spectroscopy and stabilization to the 6(1)S(0)-6(3)P(1) mercury transition at 253.7 nm is demonstrated. To our knowledge, this is the first demonstration of Doppler-free spectroscopy in the deep UV based on a frequency-quadrupled, high-power (>1 W) optically pumped semiconductor laser system. The results demonstrate the utility of these devices for precision spectroscopy at deep-UV wavelengths.