Byung-Hoon Kim

Optimization of multi-cycle two-color laser fields for the generation of an isolated attosecond pulse

The effect of the mixing of pulsed two color fields on the generation of an isolated attosecond pulse has been systematically investigated. One main color is 800 nm and the other color (or secondary color) is varied from 1.2 to 2.4 microm. This work shows that the continuum length behaves in a similar way to the behavior of the difference in the square of the amplitude of the strongest and next strongest cycle. As the mixing ratio is increased, the optimal wavelength for the extended continuum shifts toward shorter wavelength side. There is a certain mixing ratio of intensities at which the continuum length bifurcates, i.e., the existence of two optimal wavelengths. As the mixing ratio is further increased, each branch bifurcates again into two sub-branches. This 2D map analysis of the mixing ratio and the wavelength of the secondary field easily allows one to select a proper wavelength and the mixing ratio for a given pulse duration of the primary field. The study shows that an isolated sub-100 attosecond pulse can be generated mixing an 11 fs full-width-half-maximum (FWHM), 800 laser pulse with an 1840 nm FWHM pulse. Furthermore the result reveals that a 33 fs FWHM, 800 nm pulse can produce an isolated pulse below 200 as, when properly mixed.

Pressure dependence of argon cluster size for different nozzle geometries

We experimentally study Rayleigh scattering from a cluster jet produced by high pressure argon gas expanding into vacuum through four different nozzles (a supersonic slit nozzle, a slit nozzle, a conical nozzle, and a sonic nozzle). The scattering signal intensity and the scattering image are recorded by photomultiplier tube and charge-coupled device camera, respectively. Based on the scattering image, the atom density in the gas flow is estimated. This allows for the comparison of the dependence of average cluster size on argon gas backing pressure between the nozzles. The experimental results show that the planar expansion developed from the supersonic slit and the slit nozzles exhibits the higher atom density than the axisymmetric expansion from the conical and the sonic nozzles. The slit nozzle is shown to have the highest pressure dependence of average cluster size. It is found that the supersonic slit nozzle is more favorable to the large clusters than the slit nozzle under the backing pressure of u...

Experimental investigation on argon cluster sizes for conical nozzles with different opening angles

Using Rayleigh scattering measurement, we experimentally studied the effect of the opening angle of conical nozzles on the average sizes of argon clusters produced by high-pressure argon gas (up to 50 bars) expanding into vacuum. Both the scattering signal intensity and the scattering image were synchronically recorded by a photomultiplier tube and a charge-coupled device camera. These measurements allow for the comparison of average cluster sizes among conical nozzles of different opening angles. The experimental results indicate that, as expected by Hagena’s scaling law, the argon cluster size is dependent on the opening angle. However, it is also found that (1) the cluster size exhibits a larger deviation from Hagena’s scaling law at high backing pressure for a nozzle of a smaller opening angle and (2) the smaller the opening angle of conical nozzle gets, the weaker the pressure dependence of cluster size becomes.

Congener-specific distribution of polychlorinated dibenzo-p-dioxins, dibenzofurans and biphenyls in animal feed.

Polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) were extracted by accelerated solvent extraction from animal feed samples and analysed by high-resolution gas chromatography/high-resolution mass spectrometry (HRGC/HRMS). In all of the feed samples analysed, the concentrations of PCDD/Fs and PCBs were below the existing tolerance limit of 5 pg I-TEQ g−1and 200 ng g−1 fat, respectively. The mean concentrations of the total PCDDs, total PCDFs and total PCBs were 1.73–11.50 pg g−1, 0.23–11.91 pg g−1 and 60.00–234.40 pg g−1 feed, respectively. Investigation of the correlations among the concentrations of PCDDs, PCDFs and PCBs showed that samples containing increased amounts of PCDFs also contained higher concentrations of PCDDs, with an average ratio of PCDF:PCDD of about 1.23:1 (r2 = 0.72, p < 0.05). The correlation between the concentrations of PCDD/Fs and PCBs was positive but not significant.

Sequencing of novel protein from Bacillus pumilus PH-01 using a high-resolution hybrid quadrupole-time-of-flight mass spectrometer

Abstract Protein identification can be accomplished with an enzymatic digestion of the protein followed by mass spectrometric analysis of the peptide mass fingerprint followed by database searching. However, if a protein is not in a database, sequence information must be obtained to characterize and identify it. This can be done either by classical Edman sequencing or/and by tandem mass spectrometry. To determine the sequence of an unknown protein from Bacillus pumilus PH-01, which adsorbs environmental pollutants such as polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs), both sequencing and de novo peptide sequencing by tandem MS/MS of the peptide fragments were performed. Edman sequencing of the reduced and alkylated protein revealed the majority of the sequence; however, all information on disulfide bonding was lost. Therefore, a tryptic digest of the native protein was performed to obtain both complete sequence information and the connectivity of the disulfide bonds. We performed the de novo sequencing using a hybrid quadrupole-time-of-flight mass spectrometer (Q-TOF MS) instrument. The high mass accuracy and sensitivity of the hybrid Q-TOF MS made low-level sequencing of this novel naturally isolated protein possible.

Using irregularly spaced current peaks to generate an isolated attosecond X-ray pulse in free-electron lasers

A method is proposed to generate an isolated attosecond X-ray free-electron laser pulse with the peak power beyond 1 TW.

For the extension of current attosecond pulses to multi-cycle driver regime and hard X-ray regime

For the wider application of attosecond pulses, new physical schemes are devised for the usage of a multi-cycle driver laser and for the extension of photon energy of attosecond pulse into keV range.