Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 49 (2016)

An injection-locked Titanium:Sapphire laser for high-resolution in-jet
resonance ionization spectroscopy at PALIS
M. Reponen,∗1 T. Sonoda,∗1 M. Wada,∗2 D. Matsui,∗3 V. Sonnenschein,∗3 T. Takamatsu,∗3 and H. Tomita∗3Fig. 1. Injection-locked laser in operationFig. 2. Wavelength vs. time-of-ﬂight spectra for stable Zr.

The PArasitic Laser Ion-Source (PALIS)1) of the
SLOWRI -facility2) at RIKEN Nishina Center is a gascell -based device intended for producing pure, lowenergy beams of exotic nuclei. The device primarilyoperates by ﬁrst stopping and neutralizing the discarded fraction of the isotopes produced in projectile fragmentation and in-ﬂight ﬁssion reactions, followed by selective re-ionization by lasers and subsequent mass separation.
The present PALIS laser system consists ofbroadband, high-power dye lasers and of a Titanium:Sapphire laser operating at a 10 kHz repetition
rate. The combination of dye and solid-state lasers
coupled with harmonic generation capability provides
high-pulse power and a broad wavelength coverage
from the near-infrared to deep UV regions thus enabling access to a wide selection of ionization schemes.
The wide ≥1.5 GHz bandwidth of these lasers is optimal for eﬃcient in-gas-cell resonance ionization where
the atomic transitions are broadened owing to the highbuﬀer gas pressure (up to 1000 mbar).
The broad overall linewidth in the case of the in-gascell resonance laser ionization masks the small perturbations the nucleus exerts on the atomic energy levels. The inability to resolve features such as hyperﬁnestructure and isotope shift limits the applicability ofin-gas-cell resonance ionization spectroscopy (RIS).
However, upon exiting the gas cell, the buﬀer gas expands to a supersonic jet where the temperature andpressure, and thus the primary line broadening mechanisms, are greatly suppressed3) . In order to take advantage of this environment and to provide a high∗1∗2∗3

RIKEN Nishina Center
Institute for Particle and Nuclear Studies (IPNS), High Energy Accelerator Res Org. (KEK)
Department of Quantum Engineering, University of Nagoya- 190 -resolution RIS capability for the PALIS -facility, aprogram to develop a narrowband Titanium:Sapphirelaser has been initiated. The ring cavity based slave
resonator is an evolution of the design from the University of Mainz4) and from the University of Jyväskylä5) .
The laser produces a narrowband output by utilizing
the so-called injection-locking that enables bandwidth
down to ∼20 MHz, while preserving the high pulse
power required to eﬃciently drive atomic transitions.
The laser, presented in Fig. 1, has been designedand constructed in collaboration with the Universityof Nagoya, where it has also been commissioned via
resonance ionization of zirconium using a transition at
388.65 nm combined with an non-resonant ionization
step (see Fig. 2). Initial results indicate a total resolution of ≤500 MHz, suﬃcient to partially resolve thehyperﬁne structure in 91 Zr and isotope shift δν 90,A .
The near future plan is to study the laser properties
in detail in order to determine the fundamental bandwidth and stability, and to expand the laser wavelength
range to 732 nm and 980 nm regions in order to gain
access to elements such as copper and silver. Following this, the initial oﬀ-line in-jet RIS of stable copper
isotopes will be performed at PALIS in order to verify
the lasers feasibility for nuclear laser spectroscopy.
References
1) T. Sonoda et.al AIP Conf. Proc. 1104, 132 (2009).
2) M. Wada et al. , Hyp. Int. 199, 269 (2011).
3) R. Ferrer et al. Nucl. Instrum. Methods. Phys. Res. B
291, 29 (2011).
4) T. Kessler et al., Las. Phys. 18, 842 (2008).
5) V. Sonnenschein: PhD Thesis, JYFL Res. Report No.
1/2015.