IOP PUBLISHING JOURNAL OF PHYSICS D: APPLIED PHYSICS
J. Phys. D: Appl. Phys. 40 (2007) 6571–6582 doi:10.1088/0022-3727/40/21/017
Pressure scaling of an electro-discharge
singlet oxygen generator (ED SOG)
O V Braginsky, A S Kovalev, D V Lopaev, O V Proshina, T V Rakhimova,
A T Rakhimov and A N Vasilieva
Skobeltsyn Institute of Nuclear Physics, Moscow State University, 119992, Russia
Received 22 June 2007, in final form 28 August 2007
Published 19 October 2007
Online at stacks.iop.org/JPhysD/40/6571
Abstract
This work is devoted to the study of the possibility of obtaining the highest O
2
(a
1
g
)
yield in ED SOG at the high absolute O
2
(a
1
g
) concentration needed for developing a
powerful oxygen–iodine laser pumped by electric discharge. A singlet oxygen was
produced in a transversal rf discharge in the pressure range 10–30 Torr of pure oxygen
in the small-diameter (7 mm) quartz tube with HgO coating of the inner walls for
removing atomic oxygen to eliminate fast O
2
(a
1
g
) quenching. It is shown that pd
scaling (p—pressure, d —tube diameter) of the rf discharge actually allows an increase
of the absolute O
2
(a
1
g
) density. The increase in the rf frequency from 13.56 to
81 MHz results in the essential increase of the O
2
(a
1
g
) yield (beyond 15% at such a
high oxygen pressure as 15 Torr), but the subsequent transfer to the higher rf frequency
of 160 MHz only slightly influences the maximally obtained O
2
(a
1
g
) yield. The
effect of the NO admixture on the O
2
(a
1
g
) production has been also studied. The rate
constant of O
2
(a
1
g
) quenching by NO k
NO
q
= (8.5 ± 1.5) × 10
−17
cm
3
s
−1
was
directly measured. The NO admixture (up to 20%) resulted in the noticeable increase
in the O
2
(a
1
g
) yield mainly at low energy inputs. But this gain in the O
2
(a
1
g
)
concentration drops with increasing energy input. Nevertheless it is shown that by
combining the O
2
+ NO mixture with the HgO coating of the discharge tube walls one
can provide the O
2
(a
1
g
) yield on the level of ∼21% at 10 Torr, ∼17% at 20 Torr and
∼13% at 30 Torr of O
2
with the efficiency of ∼4–6%. The analysis of the NO
admixture influence on the discharge structure and O
2
(a
1
g
) production has been
carried out by using the 2D model. It was found that at the low energy input the NO
admixture acts as an easily ionized species that enlarges the region occupied by plasma.
Thus, in the O
2
+ NO discharge the normal current density is lower than in the pure
oxygen discharge. As a result a higher energetic efficiency of O
2
(a
1
g
) production is
also observed in the case of the O
2
+ NO mixture and the low energy input. In order to
provide the optimal conditions for O
2
(a
1
g
) production (with regard to the yield and
efficiency) in the continuous wave transversal VHF discharge at such high oxygen
pressures as of 10–30 Torr it is necessary to find out the range of energy inputs where
the VHF discharge operates in the regime of normal current density on the boundary
with the abnormal regime and to remove atomic oxygen produced in the discharge by
some volume or surface processes.
1. Introduction
After that as the possibility of a continuous wave
oxygen–iodine laser (OIL) using the electro-discharge singlet
oxygen generator (ED SOG) was really demonstrated [1],
the next important step in the way of a real technological
application of this achievement is the increase in both
efficiency and power of ED SOG. It is obvious that it can
be achieved only by increasing the O
2
(a
1
g
) density by
supporting simultaneously both high yield and high production
efficiency of O
2
(a
1
g
). Therefore at present a lot of research is
devoted to ED SOG scaling on oxygen pressure by conserving
the high energy efficiency of the O
2
(a
1
g
) production in the
discharge. As known [2–7], the low reduced electric fields
0022-3727/07/216571+12$30.00 © 2007 IOP Publishing Ltd Printed in the UK 6571