Yoshiki Kondo

Spectral investigation of highly ionized bismuth plasmas produced by subnanosecond Nd:YAG laser pulses

The unresolved transition arrays (UTAs) emitted from laser produced bismuth (Bi) plasma sources show potential for single-shot live cell imaging. We have measured extreme ultraviolet spectra from bismuth laser produced plasmas in the 1-7 nm region using a lambda = 1064 nm Nd: YAG laser with a pulse duration of 150 ps. Comparison of spectra obtained under different laser power densities with calculations using the Hartree-Fock with configuration interaction Cowan suite of codes and the UTA formalism, as well as consideration of previous predictions of isoelectronic trends, are employed to identify lines and a number of new features in spectra from Bi XXIII to Bi XLVII. The results show that Delta n. =. 0, n = 4-4 emission from highly charged ions merges to form intense UTAs in the 4 nm region and Delta n - 1, n - 4-5 resonance transitions UTAs dominate the 1-3 nm region of the Bi spectrum.

Soft X-ray emission from molybdenum plasmas generated by dual laser pulses

We demonstrate efficient enhancement of soft X-ray (SXR) emission from molybdenum plasmas produced using dual pulse irradiation, in which 10-ns and 150-ps pre-pulses were followed by a 150-ps main pulse. The number of photons was observed to be 5.3 × 1016 photons/sr, which corresponded to a conversion efficiency of 1.5%/sr in λ = 2.34–4.38 nm region at a pulse separation time of 1 ns with the 150-ps pre-pulse. The conversion efficiency became 1.3 times as large as that produced by a single pulse. The results indicate the advantage of dual pulse irradiation using sub-ns pre-and main pulses to produce the bright plasmas required for applications such as laboratory based SXR microscopy.

Evaluation of a flat-field grazing incidence spectrometer for highly charged ion plasma emission in soft x-ray spectral region from 1 to 10 nm

A flat-field grazing incidence spectrometer operating on the spectral region from 1 to 10 nm was built for research on physics of high temperature and high energy density plasmas. It consists of a flat-field grating with 2400 lines/mm as a dispersing element and an x-ray charged coupled device (CCD) camera as the detector. The diffraction efficiency of the grating and the sensitivity of the CCD camera were directly measured by use of synchrotron radiation at the BL-11D beamline of the Photon Factory (PF). The influence of contamination to the spectrometer also was characterized. This result enables us to evaluate the absolute number of photons in a wide range wavelength between 1 and 10 nm within an acquisition. We obtained absolutely calibrated spectra from highly charged ion plasmas of Gd, from which a maximum energy conversion efficiency of 0.26% was observed at a Nd:YAG laser intensity of 3 × 1012 W/cm2.

Characteristics of the soft X-ray emission from laser-produced highly charged platinum plasmas

We characterized the spectral structure of the soft X-ray emission and determined the plasma parameters in laser-produced highly charged platinum plasmas. The spectral structure observed originated from Pt21+ to Pt34+ ions, emissions from which overlapped to produce a high output flux in the carbon-window soft X-ray spectral region. Using dual laser pulse irradiation, we observed the maximum output flux, which was 20% larger than that obtained under single-laser irradiation, and the evolution of a strongly absorbed spectral structure, which was attributed to the effects of both opacity and long-scale length of the expanding pre-plasma.

Development of Soft X-Ray Microscope in Water Window Using Laser-Produced Plasma Light Source

For the sake of observation of samples in solution, a contact-type soft X-ray microscope is under construction by the use of both an optical microscope for readout and a laser-produced plasma light source with a heavy metal target. Edge response is evaluated through a water layer.

Evaluation of a Flat-Field Grazing Incidence Spectrometer for Highly Charged Ion Plasma Emission in 1–10 nm

A flat-field grazing incident spectrometer was built to investigate highly charged ion (HCI) plasmas in the spectral region from 1 to 10 nm. The spectrometer consists of a flat-filed grating with 2400 lines/mm as a dispersing element and an X-ray charged-coupled device (CCD) camera as the detector. In order to produce accurate intensity calibrated spectra of the HCI plasmas, the diffraction efficiency of the grating and the sensitivity of the CCD camera were directly measured by using the reflectometer installed at the BL-11D of the Photon Factory (PF). We also studied the calibrated spectra of Gd HCI plasmas which were produced by an Nd:YAG laser.