Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 48 (2015)

Production of spin polarization of atoms insuperfluid helium using a pulsed Ti: sapphire laser
M. Hayasaka,＊1,＊2 T. Furukawa,＊3 H. Tomita,＊4 T. Takamatsu,＊4 K. Imamura,＊2,＊5 T. Fujita,＊6T. Kobayashi,＊7 H. Uematsu,＊1 H. Ueno,＊2 and Y. Matsuo＊8
We are developing a new laser spectroscopic technique“OROCHI” to determine nuclear spins and moments of RIatoms. In this technique, superfluid helium (He II) is used
as a material for trapping short-lived RI atoms. We utilize
optical pumping to produce atomic spin polarization, andlaser - radio frequency (RF) /microwave double resonancemethod to investigate Zeeman and hyperfine splittings ofthe RI atoms, respectively. In He II spin polarization can be
maintained for a long time (>2 s in the case of Cs),1) whichenables us to produce a high degree of spin polarization. As
for optical pumping, CW lasers are generally used toproduce spin polarization. High-repetition-rate pulsed lasers
can be superior in producing spin polarization owing to thelarge pumping rate. Using pulsed lasers, we expect toproduce spin polarization efficiently for various atomic
species that have not been spin-polarized yet. We herereport on the production of spin polarization and RF
resonance of Rb atoms in He II using a tunable pulsed Ti:
sapphire (Ti: Sa) laser operated at 1-3 kHz.
We have constructed a pulsed Ti: Sa laser with a z-shapedcavity2) originally developed at Mainz University (see Fig.
1). The Ti: Sa laser canlase in wide range of wavelengthfrom 670 to 1050 nm3) andUV output can be easily
obtained by second harmonic generation. The Ti: Sa crystal
is pumped by a second harmonic output of a Nd: YLF laser.
The laser cavity contains four mirrors for light ofwavelength ranging from 750 to 850 nm. The tunable rangeof wavelength using a birefringent filter is 749-790 nm.For
the Rb experiment, the laser is tuned to the excitation
wavelength of Rb atoms in He II (780 nm)4). At thiswavelength the achieved output power is >150 mW at 1kHz, and >200 mW at 2 and 3 kHz.

Fig. 1. Schematic diagram of the Ti: sapphire laser layout＊1

Department of Physics, Tokyo Gakugei University
RIKEN Nishina Center＊3
Department of Physics, Tokyo Metropolitan University＊4
Department of Quantum Engineering, Nagoya University＊5
Department of Physics, Meiji University＊6
Department of Physics, Osaka University＊7
RIKEN Center for Advanced Photonics＊8
Department of Advanced Sciences, Hosei University＊2

Fig. 2. RF resonance of 85Rb obtained by applying RF
frequency of 2.35 MHz. We can see the resonance peak at B
= 5.4(9) Gauss and peak of LIF intensity with no spinpolarization at B = 0 Gauss. The repetition rate of the pulsed
laser was 3 kHz and the output power was 7.5 mW.
Using this pulsed Ti: Sa laser, we conducted experiments
for Rb atoms in He II with optical pumping and laser-RF
double resonance method.
Figure. 2 shows laser induced fluorescence (LIF) signal
from Rb atom by the magnetic field swept from 0 to 7Gauss. At B = 0, the LIF intensity was larger than that withmagnetic field because spin polarization of atoms was notconserved. With increasing external magnetic field, the LIFintensity decreased due to the increase in spin polarization.
When the RF frequency is in resonance with Zeeman
splittings, the spin polarization was decreased and then LIF
intensity was increased. In Fig. 2, we can see the RF
resonance of the 85Rb Zeeman transitions in He II. These
results reveal that the produced spin polarization using
pulsed laser was sufficient to observe RF resonance clearly.
In the case of using pulsed lasers under 10 mW at 1 to 3
kHz repetition rate, we could produce comparable spinpolarization to the CW laser experiment 4) and observe RFresonance.
In the future, we plan to use the pulsed Ti: Sa laser for
optical pumping of atomic species that have not yet been
spin-polarized and develop a technique to produce spinpolarization of various atoms. The excitation wavelength ofIn atoms is 370 nm in He II5). We expect to produce spinpolarization of In atoms using a second harmonic
generation of the pulsed Ti: Sa laser.
References

1) T. Furukawa et al.:Phys. Rev. Lett. 96, 095301 (2006)
2) J. Yi et al.: Jpn. J. Appl. Phys. 42, 5066-5070 (2003)
3) K. Muramatsu.: Master Dissertation, Nagoya University (2011)4) T. Furukawa.: Doctor Dissertation, Osaka University (2007)
5) Y. Kato. Master Dissertation, Meiji University (2012)- 223 -

完全版2014_本文.indd 223

15/10/16 17:55