Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 50 (2017)

Experimental evaluation of laser-MW double resonance signal
intensity in OROCHI project
T. Egami,∗1,∗2 K. Imamura,∗1,∗3 A. Takamine,∗1 W. Kobayashi,∗1,∗2 T. Fujita,∗1,∗4 D. Tominaga,∗1,∗2M. Sanjo,∗1,∗2 Y. Nakamura,∗1,∗3 T. Wakui,∗1,∗5 T. Furukawa,∗1,∗6 H. Ueno,∗1 and Y. Matsuo∗1,∗2
We are developing a laser spectroscopy technique
named OROCHI to study the properties of lowproduction-yield nuclei. In the OROCHI experiment,
energetic ions are injected into superﬂuid helium andare neutralized during their stopping process. We irradiate the neutralized atoms with a circularly polarized laser light to produce spin polarization and measure the atomic Zeeman splitting by laser-radio frequency (RF) double resonance method and the hyperﬁne splitting by laser-microwave (MW) double resonance method. The measurements enable us to deduce nuclear spin and moment values. We succeededin observing the resonance signal by the double resonance methods in the online experiment using 84−87 Rb1,2)
However, theion beams of an order of 1044 ions/s.1)2)
However,resonance signal was smaller than that in the oﬄine
experiments, and diﬃculties were anticipated for theapplication of this method to lower-production yield
nuclides. One of the possible causes for small resonance signal intensity was attributed to an insuﬃcient
MW radiation power. So we performed an oﬄine test
using Rb vapor which was enclosed in pyrex glass cellwith He buﬀer gas (Rb cell) in order to ﬁnd the experimental conditions to maximize the MW resonancesignal intensity in our experimental setup.
We irradiated Rb atoms in the cell with a circularly
polarized laser light for spin polarization and a MW
radiation at a ﬁxed frequency. Laser intensity was 1.0
mW (with the diameter 2 mm, wavelength 795 nm).
In order to maintain spin polarization, a magnetic ﬁeld
was applied to the atoms in the direction coaxial withthe laser axis. We detected ﬂuorescence photons from
Rb atoms by using a photomultiplier tube. By sweeping magnetic ﬁeld strength, we obtained a MW resonance peak (yr ) and a maximum de-excitation peakwhich corresponds to the signal level of spin unpolarization (y max ).1) We deﬁned resonance intensity(I) as
I = (yr - y0 )/(ymax - y0 ), where y0 is the backgroundsignal level. We measured the dependence of the resonance intensity on antenna position and MW power.
Figure 1 shows the resonance intensity as a function of distance between the antenna and observation
region. MW power was 3.0(3) W. In the previous online experiment, MW of 2-3 W was applied and theantenna was placed about 4 cm away from the obser∗1∗2∗3∗4∗5∗6RIKEN Nishina Center
Department of advanced science, Hosei University
Department of Physics, Meiji University
Department of Physics, Osaka University
QST
Department of Physics, Tokyo Metropolitan UniversityFig. 1. Resonance intensity dependence on the antenna position. Horizontal axis indicates the distance between
the MW antenna and observation region.

vation region. From this result, we estimate that theresonance intensity can be increased by a factor of approximately 5 by bringing the antenna 1 cm away fromthe observation region.
We also measured the resonance intensity with different applied MW power (Fig. 2). The Rb cell wasplaced at the observation region in our cryostat usedfor online experiments. The antenna was set about 1
cm away from the observation region. De-excitation
light from Rb atoms was detected by the newly developed LIF detection system3) . When the MW power of
8 W was applied to the atoms, the resonance intensity
was increased by a factor of approximately 1.2 fromthat of 3 W.

Fig. 2. Resonance intensity dependence on the MW appliedpower

The two results above showed diﬀerent resonance intensities at the same condition of MW irradiation due
to diﬀerent optical pumping rates and slightly diﬀerent
antenna orientation. Nevertheless, taking into accountof the two factors, namely optimizing antenna position
and applied power, the MW resonance signal intensity
increment is estimated to be able to reach at least 6
times higher than that of the previous online experiment. In next online experiment, we will evaluate
the ampliﬁcation of the resonance intensity discussedabove.
References1) X. F. Yang et al.: Phys. Rev. A. 90, 052516(2014).
2) K. Imamura et al.: JPS Conf. Proc. 6, 030115(2015).
3) W. Kobayashi et al.: In this report.

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