Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 47 (2014)

Offline experiment of high-resolution resonance ionization spectroscopy
on Titanium using injection-locked Ti:Sapphire laser system
T. Takamatsu,*1 H. Tomita,*1,*2 T. Takatsuka,*1,*2 Y. Adachi,*1,*2 Y. Furuta,*1
K. Wendt,*3 V. Sonnenschein,*4 T. Noto,*1,*2 T. Iguchi,*1 T. Sonoda*2 and M. Wada*2
Resonant ionization is useful for precise optical
spectroscopy of radioactive isotopes of many elements toinvestigate the structures of unstable nuclei. We havedeveloped a high-resolution resonance ionization
spectroscopy (HR-RIS) combined with a supersonic gas jetsystem 1,2）in the PArasitic Laser Ion Source (PALIS) system
at RIKEN and a narrow bandwidth tunable pulsed laser
system, i.e., an injection-locked Ti:Sapphire laser system 3,4).
An offline experiment was performed using thisinjection-locked Ti:Sapphire laser system.
The experimental setup for HR-RIS on Ti are shown in
Fig.1. Titanium atomic vapor was evaporated by resistive
heating of a Ti filament in a vacuum chamber called areference cell. For optical resonance excitation andionization from the ground state or a thermally populated
low-lying excited state using the Ti:Sapphire laser, anionization scheme shown in Fig.2 (a) was used. The
titanium atomic vapor was irradiated using the second
harmonics of the injection-locked Ti: Sapphire laser tuned
to the first step transition. The second harmonics of astandard Ti: Sapphire laser was additionally used for
efficient ionization via autoionization states. Here, anexternal cavity diode laser (ECDL) was used as a master
laser of the injection-locked Ti:Sapphire laser. We achieveda line width of 20 MHz and a 0.4 mJ/pulse at the maximum

output of the injection-locked Ti:Sapphire laser operated ata repetition rate of 1 kHz. Titanium ions produced byresonance ionization were accelerated with an electric fieldand detected by a multi channel plate (MCP) after
traversing the field free region. The number of pulses from
MCP was obtained from a counter with a timing gate in thetime-of-flight of Ti ions.
We investigated the Rydberg and autoionization states byscanning of the second step laser from 554800 cm-1 to55600 cm-1 for a higher count rate. We identified a strong
and broad autoionization state around 55400 cm-1 as shownin Fig.2 (a). The optical spectrum of stable Titanium
obtained by the frequency scan of ECDL, i.e., the scanningof the first step laser is shown in Fig.2 (b). The line-width in
the spectrum was estimated to be approximately 210 MHz,and five peaks corresponding to the 46,47,48,49,50Ti isotopes
were clearly resolved in the spectrum. Further, their ratios
were in good agreement with the natural abundances of Tiisotopes (46Ti-8.0% 47Ti-7.3% 48Ti-73.8% 49Ti-5.5%50Ti-5.4%). The isotope shift of the optical transition of 46Ti
and 50Ti to 48Ti were evaluated to be approximately 1.7 GHz
and 1.6 GHz, respectively. Presently, the particularly
narrow hyperfine splitting of 47Ti and 49Ti is not resolved
because of the remaining Doppler broadening of theexperimental geometry. In the near future, the resolution
will be improved by applying the supersonic gas-jet system.

(a)Fig.2 (a) Ionization
scheme on Ti(b)(b) Optical spectrum of Ti isotopes.

Fig.1 Experimental setup for HR-RIS on Ti*1

Department of Quantum Engineering, Nagoya University*2

RIKEN Nishina Center*3

Institute of Physics, Johannes Gutenberg-University Mainz*4

Department of Physics, University of Jyväskylä

References
1) T. Sonoda et al., Hyperfine Interact 216, 103, (2013).
2) T. Sonoda, et al., Nucl. Instrum. Meth. B 295, 1, (2013).
3) T. Takatsuka, et al., Nucl. Instrum. Meth. B 317, 586, (2013).
4) T. Kessler, H. Tomita et al., Laser Physics 18, 842, (2008).

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