Capacitive-discharge KrCl excilamps with short radiation pulsewidth
M. V. Erofeev, M. I. Lomaev, E
´
.A. Sosnin, V. F. Tarasenko, and D. V. Shitts
Institute of High-Current Electronics, Siberian Branch, Russian Academy of Sciences, Tomsk
Submitted February 12, 2001
Opticheski Zhurnal 68, 75–77 October 2001
This paper presents the results of studies of the amplitude–time characteristics of the radiation of
electrodeless pulsed KrCl excilamps ( 222 nm. The maximum pulse power density was
300 W/cm
2
. It is shown that the pulse power density of the radiation is determined by the voltage
on the excilamp, the discharge geometry, the value of the peaking capacitor, and the density
of the gaseous medium. © 2001 The Optical Society of America.
Interest in the creation of UV lamps excited by a pulse
discharge in inert gases, in halogens, and in mixtures of them
has increased in recent years.
1–9
However, the question of
creating excilamps with high pulse power kilowatts or
higher has been studied very little. A high-power electric-
discharge excilamp was described in Ref. 1. When the output
beam was 10 cm in diameter, pulse power densities of 2 kW/
cm
2
were obtained at 308 nm, 0.5 kW/cm
2
at 222 nm,
and 1 kW/cm
2
at 350 nm. The pulsewidth of the radiation
at half-height was about 60 ns.
In order to increase the radiance of the pulsed light
source, Ref. 3 used an L-shaped design of the bulb. In Ref. 4,
a so-called triggered longitudinal discharge was used to in-
crease the pulse power of the excilamps. When binary mix-
tures of Xe + HCl were used, the pulse power density with
a total pressure of the mixture here reached 3 kW/cm
2
. The
pulsewidth of the radiation was not very sensitive to the
pressure of the gas mixture and was in the range 0.7–0.9 s
for p 1 atm. It was pointed out that the pulse power
smoothly decreased by 1/3 of the initial level after the first
10
4
pulses. This undesirable effect can be avoided by using
electrodeless excilamps.
This paper continues the studies begun in Ref. 5. The
object of the work is to experimentally investigate the
amplitude–time characteristics of the radiation of pulsed
electrodeless KrCl excilamps having various geometries.
The capacitive-discharge electrodeless excilamps shown
in Fig. 1 were used in the experiments. Our choice was de-
termined by the low level of degradation of the working
mixtures and accordingly by the high service life of lamps of
this type.
6
The lamp envelopes were made from cylindrical
quartz tubes with a spectral transmission of more than 80%
in the 200–300-nm wavelength range. The cylindrical elec-
trodes were made from aluminum foil, close to the surface of
the quartz tubes shown in gray in Fig. 1. The characteristic
dimensions of the excilamps are shown in Table I. The wall
thickness of the quartz tubes equaled 1.5–2 mm. All the
lamps were filled with the binary mixture Kr + Cl
2
.
Two generators were used to excite the excilamps. The
first was a standard circuit with a multiple switch and a stor-
age condenser that could be charged to a voltage of 23kV,
while the second was a Fitch circuit, providing a twofold
gain of the voltage supplied from an external source up to
45 kV. The circuit included a bank of capacitors made up
of KVI capacitors with a capacitance C no greater than
12.5 nF, a charging resistor R, a TGI-1000.25 thyristor as a
switch, commercial peaker discharge gaps RU-26 or RU-
47, and a thyratron trigger unit. Choke D or peaker capaci-
tor ( C
pik
1500 pf could be mounted in parallel to the lamp.
Step-up transformer Tr , with a transformation factor of
about 3, was attached between the lamp and the main storage
capacitor C. As a result, voltage pulses with an amplitude of
up to 63 kV and 135 kV and a repetition rate of 1 Hz were
formed at the output for generators 1 and 2, respectively.
An FE
´
K-22SPU vacuum photodiode was used to record
the radiation pulses, and the signal from it was fed to a
TDS-220 two-beam storage oscilloscope. The spectral con-
tent of the radiation was monitored in real time by means of
SZS, BS, and ZhS calibrated light filters.
The percentage of radiation in the region 260 nm ex-
ceeded 90% in the optimum mixtures in all the KrCl excil-
amps that we studied, as is typical of this class of excilamps.
The experiments were carried out at pressures from 15 to
FIG. 1. Excilamps of types I a, H b, and L c. SG is the grounding
electrode, and HV is the high-voltage electrode. The arrows indicate the
radiation-output direction. The lightly stippled zones denote the typical
shape of the discharge.
TABLE I. Dimensions of excilamps.
Type of
lamp
Diameter of
outer tube, cm
Diameter of
inner tube, cm
Minimum length of
discharge gap, cm
Length of
electrode zone
of lamp, cm
I 5.5 4.3 8 30
H 5.5 2.2 8.5 23
L 4 ••• 3 28
HV/18
SG
785 785 J. Opt. Technol. 68 (10), October 2001 1070-9762/2001/100785-02$18.00 © 2001 The Optical Society of America