Dielectric barrier discharge lamp light source

Details Dielectric barrier discharge lamp light source Dielectric barrier discharge lamp light source

2000-06-05

2002-04-09

Vu, David (Department: 2821)

Electric lamp and discharge devices: systems

Periodic switch in the supply circuit

Impedance or current regulator in the supply circuit

C315S276000, C315SDIG007

Reexamination Certificate

active

06369519

ABSTRACT:

FIELD OF TECHNOLOGY
This invention concerns light source equipment that includes what is called a dielectric-barrier discharge lamp, which is a type of discharge lamp used, for example, as a source of ultraviolet radiation for photochemical reactions, in which eximer molecules are formed by dielectric-barrier discharge, and which uses light emitted from the excimer molecules.
DESCRIPTION OF THE RELATED ART
Technical literature explaining the technology involved in the dielectric-barrier discharge lamps with which this invention is concerned can be found in, for example, JPO kokai patent report H2-7353. This document describes an emitter that produces light by causing the formation of eximer molecules by means of a dielectric barrier discharge in a discharge chamber filled with a discharge gas that forms eximer molecules, and using the light radiated by those eximer molecules (a dielectric barrier discharge is also known as ozonizer discharge or silent discharge; see Denki Gakkai, “Discharge Handbook,” revised edition, 7th printing, June 1989, p. 263).
Dielectric-barrier discharge lamps have a discharge plasma space and one or two dielectrics sandwiched between electrodes. FIG.
19
(
a
) shows a dielectric-barrier discharge lamp
1
with two dielectrics
5
,
6
. In FIG.
19
(
a
), by the way, the lamp seal
7
also serves as two dielectrics
5
,
6
.
When lighting up the dielectric-barrier discharge lamp
1
, a high-frequency, alternating current of, for example 10 to 200 kHz and 2 to 10 kV is imposed on the electrodes
3
,
4
.
However, because of the dielectrics
5
,
6
between the discharge plasma space
2
and the electrodes
3
,
4
, current does not flow directly from the electrodes
3
,
4
to the discharge plasma space
2
; the current flows by means of the action of the dielectrics
5
,
6
as a condenser. In other words, a charge equal in size and opposite in sign to that on electrodes
3
,
4
is induced on the discharge plasma space side of the dielectrics
5
,
6
because of polarization of the dielectric. The discharge occurs between the dielectrics
5
,
6
that face across the discharge plasma space
2
.
Little current flows along the discharge plasma space
2
side of the dielectrics
5
,
6
; when discharge occurs, the charge induced on the discharge plasma space
2
side of the dielectrics
5
,
6
is neutralized by the charge moved by the discharge, and the electrical field within the discharge plasma space
2
is reduced. For that reason, the current stops even if the voltage continues to be impressed on the electrodes
3
,
4
. But when the voltage impressed on the electrodes
3
,
4
rises again, the discharge current continues.
When the discharge ceases after having occurred, there is no further discharge until the polarity of the voltage impressed on the electrodes
3
,
4
has reversed.
In the case of a dielectric-barrier discharge lamp in which xenon gas, for example, is sealed, the xenon gas is dissociated into ions and electrons by the discharge, and becomes xenon plasma. When the xenon plasma is excited to a specified energy level, eximer molecules are formed within the plasma. Xenon eximers divide after a certain lifespan, but the energy released at that time is emitted as a photon of vacuum ultraviolet wavelength. To make a dielectric-barrier discharge lamp work efficiently as a vacuum ultraviolet light source, it is necessary to form the eximer molecules efficiently.
The greatest obstacle to efficient formation of eximer molecules during discharge is the excitation of the discharge plasma to energy levels that do not contribute to the formation of eximer molecules.
The movement of discharge plasma electrons immediately after discharge begins is collective, and the energy is high but the temperature is low. In this state, the discharge plasma has a high probability of transition to the resonant state required for formation of eximer molecules. If the discharge time is prolonged, however, the movement of the plasma electrons gradually becomes thermal. That is, it reaches a state of thermal equilibrium known as a Maxwell-Boltzmann distribution; the plasma temperature rises, and there is an increased probability of transition to a state of higher excitation where eximer molecules cannot form.
Moreover, sometimes when eximer molecules have been formed, a subsequent discharge will break down the eximer molecules before their lifespan elapses and they divide naturally by emitting the desired photon. In fact, in the case of xenon eximers, a period of about 1 &mgr;s is required between the beginning of discharge and emission of a vacuum ultraviolet photon, and a subsequent discharge or redischarge during that period reduces the efficiency of eximer light emission.
In other words, once discharge had commenced, it is most important to reduce as much as possible the energy of subsequent discharges.
Even in the event that the discharge time is short, if the energy injected during the discharge period is too great, there is similarly an increased probability of transition to a state of high excitation. Plasma that has transitioned to a state of high excitation moderates itself by emission of infrared radiation, which just raises the temperature of the lamp and does not contribute to eximer light emission.
That is, the discharge must be driven so as to suppress the excitation of discharge plasma to energy levels that do not contribute to the formation of eximer molecules. That point is one that cannot be satisfied by conventional dielectric-barrier discharge lamp light source equipment.
JPO kokai patent report H1-243363 is a proposal to achieve eximer light emission with high efficiency by means of all pulse discharges, including dielectric-barrier discharges. This follows the condition stated above that once a discharge has begun, the energy of the subsequent discharge is reduced as much as possible. However, what is described in this proposal is which parameters to control to increase the efficiency of eximer light emission; there is no specific mention of the effective conditions for those parameter values. Particularly in the case of dielectric-barrier discharges, there is little freedom for control of the voltage that has to be impressed and the current that has to be injected into the discharge plasma space through the dielectric, and it is extremely difficult to discover the optimum conditions.
There are proposals to improve the efficiency of dielectric-barrier discharge lamps, such as JPO patent report H8-508363 (U.S. Pat. No. 5,604,410). However, these reports say nothing about specific items that are truly effective in achieving control of the excitation of discharge plasma to energy levels that do not contribute to formation of eximer molecules, so as to form eximer molecules efficiently. There are descriptions of the results of experiments on variation of brightness relative to variation of impressed voltage, in connection with frequency and duty cycle, with regard to short pulse arrays and short waveforms, as well as explanations of improvement of efficiency relative to conventional sinewave drive.
Actual power supplies, however, include high-voltage transformers, and are unable to impress ideal short pulse arrays and short waveforms; because of interaction of the output impedance of the power supply and the impedance of the lamp, the waveform lacks precision, and partial resonance causes a sinewave voltage to be impressed.
In the event of discrepancies from ideal short waveforms in such actual power supplies, unless it is clear what degree of discrepancy is allowed, it is not possible to design or manufacture practical light source equipment economically.
This invention was made in consideration of the situation described above; its purpose is provide dielectric-barrier discharge lamp light source equipment that can produce eximer molecules efficiently and operate efficiently as a vacuum ultraviolet light source.
SUMMARY OF THE INVENTION
In order to form eximer molecules efficiently, which is the task of the invention of this application, the excitation of

Affiliated with

Also associated with

Rating

Dielectric barrier discharge lamp light source does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Dielectric barrier discharge lamp light source, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dielectric barrier discharge lamp light source will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2848489