Ken'ichi Nakagawa

A study of inner-valence Auger transitions in Ne+ induced by the resonant Auger decay of photoexcited Ne 1s-1np states

High-resolution electron spectrometry is used to investigate inner-valence Auger transitions in Ne+. The following series of transitions have been observed: Ne+ 2s12p5(1,3P)np → Ne2+ 2s22p4 3P, 1D and Ne+ 2s02p6(1S)np→ Ne2+ 2s12p5 1,3P. In addition, we have observed a new series of valence inter-multiplet Auger transitions Ne+ 2s12p5(1P)np → Ne2+ 2s12p5 3P. The initial states of these transitions were populated by the resonant Auger decay of photoexcited Ne 1s−1np resonances. Thus, the investigated transitions constitute the second step in an Auger cascade process. The photon energy was chosen to effectively populate Rydberg states of Ne+ with n = 4–10. The energy positions, quantum defects, relative intensity and angular distribution parameters of the Ne+ Auger electron emission have been determined. Experimental results are compared with multi-configuration Dirac–Fock calculations carried out as a part of this study.

Developments of highly frequency and intensity stabilized lasers for space gravitational wave detector decigo/pre-decigo

Gravitational wave (GW), predicted by A. Einstein in his general theory of relativity, is temporal variation of spatial distortion caused from the change of enormous mass such as inspiral and merger of neutron star binaries, black hole binaries, explosion of supernovae, and inflation in early universe.

Highly frequency-stabilized laser for space gravitational wave detector DECIGO/DPF

Direct detections of gravitational wave (GW) by using a long-baseline laser interferometer have been tried in many countries. In Japan, a space-GW detector named DECIGO (Deci-hertz interferometer Gravitational wave detector), and its milestone mission DPF (DECIGO pathfinder) has been promoted. We have developed a spaceborne highly frequency-stabilized light source for DECIGO and DPF with high mechanical stability, long-term stable operation, high-efficiency and compactness. The frequency of an Yb doped fiber DFB laser at 1030 nm was locked to the saturated absorption signal of the iodine molecule (I2) at 515 nm. We have developed the breadboard model 1 (BBM1) of the I2 stabilized Yb:fiber laser, which was installed on a 550x300x20-mm aluminum plate. The frequency noise of the laser was suppressed down to 0.4 Hz/Hz1/2 at 1 Hz which was evaluated from the frequency error signal. In the present paper, we will report the details and performance of the BBM1 of the light source for DECIGO and DPF.