JAERI-Conf 95-021

PB47
Study of Differential Pumping System for Beam-Pumped Laser
by TIT Heavy-Ion RFQ Linac
H. Tomizawa, T. Hattori, Y. Oguri, M. Okamura, M. Okada, K. Sasa, T. Katayose
Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology
Meguro-ku, Tokyo,Ja pan
Abstract
4 He+ beamfrom V. d. G. was used to3.1MeVpump He-Ar gas Laser with a differential
pumping system. In our experiments, Laser
action of the 1.27 ~m line could not have been
observed above the threshold of 33W beam power
input. One of the reasons is that the differential
pumping system does not have the orificesaligned. For the experiments of Beam-Pumped
Laser by using 0. 88MeV 4 He+ beam from TIT
Heavy-Ion RFQ Linac, I designed a differential
pumping system with the orifices which are able
to be aligned easily.
!.Introduction
Heavy ion beam-pumping is a method to produce
the population inversion of a medium throughprojectiling heavy ions into the medium.
Experiments to study lasers pumped by heavyion beams in Munich were initiated by P. Kienle
in 1979, and optical gain and laser effect werefirst observed in 1982-1983. A low thresholdpumping power of 33 W was found in rare gas
mixtures lasing in the near infrared inexperiments performed at the Munich Tandem
van de Graaff

accelerator (Ulrich et al. 1983). This work had
been stimulated by results of nuclear-pumped
laser experiments in the Soviet Union and theUnited States that had been published in the1970s, and most of the laser lines observed by ion
beam pumping appear also on the list of nuclearpumped lasers (Fitaire 1978). This immediately
indicated that ion beam-pumped lasers can beused as model systems for nuclear-pumped
lasers. A practical advantage of working withaccelerators is that there is access to the target
area, often also during operation of the laser.
Continuous or quasicontinuous operation allows
experimental parameters such as gas mixtures
and the alignment of the optical cavity to be
optimized rapidly.
Heavy-ion accelerators are widely used in atomic
physics, especially to study few-electron atoms
and inner-shell excitation process. The possibilityof obtaining well-focused beams of particles witha high energy loss -dE/dx in the target material
has stimulated the idea of using heavy-ion
accelerators as drivers for inertial confinement
fusion experiments. On the basis of similararguments we have started a program to explore
the possibility of short-wavelength lasers pumpedby heavy-ion beams.

Fig. 1 The Experimental setup for Heavy-ion
Pumped Laser by V.d.G.

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3.Experimental Result and Improvement

2.Experiment
In our research program, at first we makeexperiment for 1.27~m(Arl) laser action of He-Ar
gas mixture with 50~A, 3.1MeV 4 He+beam by
TIT Van de Graaff.Then we are going to makeexperiment for 1. 79~m laser action with 0.88MeV
4He + beam by TIT Heavy-Ion RFQ Linac.
The program of the experiments with V.d.G.
(Fig. I) is as follows;(!)Designing for the experiment setup(2)Detecting the spontaneous emission from HeAr gas target with spectroscope to examine thepopulation inversion(3)Testing infrared laser action(4)In the case of no laser action, improving thesystems
In this paper, I report the result of theexperiments and some improvements of thissetup.
Laser action is a phenomenon which has athreshold. Therefore, on the development of lasersystems, it is hard to make clear what is going onin the whole system. For the method to check thepossibility on the. laser action, I used plasma
spectroscopy to measure the population inversion.

Fig.2 Compact Differential Pumping
SystemA) bottom view

We could not observeHe-Ar, 1.27~m laser actionin our experimental setup.
The cause of unsuccessful result of the laser
action is probably as follows;(1) The laser resonator is not aligned, or the laser
gain is less than laser resonator loss.
(2) This experimental setup needs a differential
pumping system to keep the pressure difference
between the accelerator and the gas cell. It
consists of 4 stages which are pumped
independently. In this system fine alignments ofthe beam axis obtained by means of orifice-shaft
nuts shimming.Thus the orifices are not stable on
the wall between the stages. It makes hard toalign the optic axis. Moreover it is almost
impossible to develop the study with it, because
this system can not have any reproducibility.
For the improvement of such a system, I made acompact differential pumping system (Fig.2)
which is machined from one brass block. As theloss of beam power was great in the differential
pumping system, the distance along beam axis of
the new compact differential pumping system ismade five times shorter than that of the exdifferential pumping system. I prepared 4 kindsof diameters of the orifices. They are 1.6mm,2.0mm, 2.5mm, and 3.0mm. Every orifice isscrewed to be self-aligned, when they are screwed
directly into walls of the main body of compact
differential system.
References~@~fli'MUll!li! Sf~

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[1] R. J. De Young, W. E. Wells and G. H. Miley,and T. Verdeyen, ''Direct nuclear pumping of a
Ne-N2laser",Appl. Phys. Lett. 28. (1976) 519.
[2] A illrich, H. Bohn, P. Kienle and G. J .
.Perlow, "Heavy ion pumped He-Ar laser",Appl.
Phys. Lett. 42 (1983) 782.
[3] D. E. Murnick and A illrich, ''HEAVY ION
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[4] A illrich, J. W. Hammer and W. Biermayer,"Laser pumped by ion beams", Appl. Phys. 63(1988) 2206.
[5] A illrich, B.Busch, H. Eylers, W. Krotz, R.
Miller, R. Pfaffenberger, G. Ribitzuki, J. Wieser
and D. E. Murnick, ''Lasers pumped by heavy ion beams", Laser and Particle Beams 8 (1990).
659.

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