Electrical transmission or interconnection systems – Wave form or wave shape determinative or pulse-producing... – With capacitor
Reexamination Certificate
1999-11-10
2001-02-13
Riley, Shawn (Department: 2838)
Electrical transmission or interconnection systems
Wave form or wave shape determinative or pulse-producing...
With capacitor
C372S038080, C307S107000
Reexamination Certificate
active
06188144
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power supply unit for a pulse laser using a magnetic switch (saturable reactor) used for pulse discharging a laser, and more particularly to an improvement for lowering the peaking capacity of the pulse laser without lowering the energy per pulse of the laser pulse.
2. Description of the Related Art
As a pulse power supply unit for a high-power pulse laser and an accelerator, those using a magnetic pulse compression circuit are often used for the improvement of the durability of a main switch such as a thyratron and GTO these years.
FIG. 20
shows an equivalent circuit of a general capacity shift type of magnetic pulse compression device used for the pulse power supply of a pulse laser, and
FIG. 21
shows an example of waveforms of the voltage and the current at respective points of the circuit shown in FIG.
20
.
The discharge circuit of
FIG. 20
is a two-step magnetic pulse compression circuit utilizing a saturation phenomenon of three magnetic switches AL
0
to AL
2
which consist of saturable reactors.
In
FIG. 20
, the electric charge is charged from high-voltage power supply HV to capacitor C
0
through magnetic switch AL
0
and coil L
1
.
Then, when pulse oscillation synchronizing signal (trigger signal) TR which turns on in synchronization with the repetition frequency of the pulse laser oscillation is input, main switch SW is turned on at this point (time t
0
in FIG.
10
). When the main switch SW is turned on, potential VSW of the main switch SW drops suddenly to zero, and then when time product (integration value of time of voltage VC
0
) S
0
of voltage difference VC
0
-VSW between the capacitor C
0
and the main switch SW which are both end voltages of the magnetic switch AL
0
reaches a limit value decided depending on a set characteristic of the magnetic switch AL
0
, the magnetic switch AL
0
is saturated at this time t
1
, and current pulse i
0
flows through a loop of the capacitor C
0
, the magnetic switch AL
0
, the main switch SW and capacitor C
1
.
Time &dgr;
0
elapsed between the start of flowing the current pulse i
0
and its termination to become zero (time t
2
), namely, electric charge transfer time &dgr;
0
elapsed to complete the transfer of the electric charge from the capacitor C
0
to the capacitor C
1
, is determined by respective capacities of a post-inductance of the magnetic switch AL
0
, the capacitor C
0
and the capacitor C
1
, provided that a loss by the main switch SW and the like is disregarded.
When time product S
1
of voltage VC
1
of the capacitor C
1
reaches a limit value which is determined by a determined characteristic of the magnetic switch AL
1
, the magnetic switch AL
1
saturates at this time t
3
to have a low inductance. Thus, current pulse i
1
flows through a loop of the capacitor C
1
, capacitor C
2
and the magnetic switch AL
1
. This current pulse i
1
becomes zero at time t
4
after a lapse of predetermined transfer time &dgr;
1
which is determined by the capacities of the capacitors C
1
and C
2
and the post-saturation inductance of the magnetic switch AL
1
.
And, when time product S
2
of voltage VC
2
of the capacitor C
2
reaches a limit value which is determined by a determined characteristic of the magnetic switch AL
2
, the magnetic switch AL
2
is saturated at this time t
5
, and current pulse i
2
flows through a loop of the capacitor C
2
, peaking capacitor CP and the magnetic switch AL
2
.
Then, voltage VCp of the peaking capacitor Cp rises with the progress of charging, and when this voltage VCp reaches a predetermined main discharge initiation voltage, a dielectric breakdown of the laser gas is caused between main electrodes
10
at this time t
6
to start the main discharge. The laser medium is excited by this main discharge, and the laser light is generated in several nsec.
Then, the voltage of the peaking capacitor Cp drops rapidly by the main discharge and returns to the state before starting to charge after a lapse of predetermined time.
This electric discharge operation is repeated by the switching operation of the main switch SW which is synchronized with the trigger signal TR, and the pulse laser oscillation is performed at a fixed repetition frequency (pulse oscillation frequency).
In this case, since it is determined that the inductances of the charge transfer circuits in respective stages comprising the magnetic switch and the capacitor become small toward the final stage, the pulse compression operation is performed so that the peak value of current pulses i
0
to i
2
rises sequentially and the current-carrying width becomes small sequentially. As a result, an intense electric discharge is obtained between the main electrodes
6
in a short time.
When the pulse compression rate is excessively raised by the aforesaid magnetic pulse compression, there is obtained a pulse laser light having a short pulse width and high peak output. But, this pulse laser light having a short pulse width and high peak output causes various problems such as follows:
durability of optical parts installed in the laser resonator is degraded;
a round trip frequency (shuttling frequency of the laser light in the resonator) is decreased; and
an incidence frequency to a narrow-banding optical element decreases as the round trip frequency is decreased, and a narrow-banding efficiency drops.
Accordingly, the pulse laser light that its pulse width is not too short and its peak output is not too large is often demanded recently. Because the pulse width becomes long even if the peaking capacity of the pulse laser light is lowered, the energy per pulse of the laser pulse does not become small as compared with the pulse laser light having a short pulse width and a high peak output.
However, the aforesaid conventional technology is designed to transfer all the charges as current pulse i
2
from the capacitor C
2
to the peaking capacitor Cp at a time. Therefore, the luminescence intensity and the luminescence time of the pulse laser light are determined univocally depending on the electric charge transfer time and the peak value of the current pulse i
2
only, and their fine adjustment is hardly made. The aforesaid conventional technology had a limitation in its circuit in increasing the pulse width of the laser pulse because the electric charge transferred from the capacitor C
2
to the peaking capacitor Cp is mostly consumed by the electric discharge, and the electric charge is not transferred to the peaking capacitor Cp after the laser luminescence is started.
The present invention was completed in view of the aforesaid circumstances, and it is an object of the invention to provide a power supply unit for a pulse laser, which has a simple structure but can provide a pulse laser light that its pulse width is not too short and its peak output is not too large.
SUMMARY OF THE INVENTION
The invention relates to a power supply unit for a pulse laser comprising discharge electrodes for a pulse laser disposed in a laser medium, a peaking capacitor connected in parallel to the discharge electrodes and a series circuit of saturable reactors and transferring capacitors connected in parallel to the peaking capacitor, which transfers electric charges charged in the transferring capacitors to the peaking capacitor by utilizing a magnetic saturation phenomenon of the saturable reactors to cause a pulse discharge between the discharge electrodes and excites the laser medium so to produce the pulse laser, wherein the series circuit of the saturable reactors and the transferring capacitors is connected in a plurality of numbers in parallel to the peaking capacitor, the plurality of saturable reactors are magnetically coupled, and post-saturation inductances of the plurality of saturable reactors are made different.
In the present invention, the series circuit of the saturable reactors and the transferring capacitors included in an electric charge transfer circuit in a final stage in a magnetic pulse compression circuit is connected in a plurality
Komatsu Ltd
Riley Shawn
Varndell & Varndell PLLC
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