GB2225668A - Circuit arrangements - Google Patents

Abstract

An arrangement for operating a laser 1, such as, for example, a strontium recombination laser, includes a magnetic switch 2 arranged in parallel with the laser 1. When a current pulse is applied to the laser 1, the inductance of the magnetic switch 2 is initially relatively high and the beginning of the current pulse passes through the laser 1. During the pulse, the inductance of the switch drops and the remainder of the pulse is then transmitted through the switch 2, bypassing the laser 1. This enables a pulse having a fast fall time to be applied to the laser 1 which is particularly advantageous for recombination type lasers. A load other than a laser may be included in the circuit. <IMAGE>

Description

CIRCUIT ARRANGEMENTS This invention relates to circuit arrangements and more particularly, but not exclusively, to arrangements for operating recombination lasers.

In many types of laser, a discharge is established within the laser so that a current pulse passes between the laser electrodes. This enables a population inversion to be obtained between lasing states, which is sufficient to cause laser radiation to be generated.

The present invention arose in an attempt to provide an improved circuit arrangement which is particularly suited to the operation of recombination lasers.

According to the invention there is provided a circuit arrangement comprising a load, a magnetic switch connected electrically in parallel with it and means for applying a current pulse to the load, the magnetic switch being arranged such that a first part of the pulse is transmitted through the load and a second part through the switch. By employing a magnetic switch in this way, it is possible to shape the tail end of the pulse which may be advantageous in many applications. The invention may be particularly advantageously used where the load is a laser and especially a laser of the recombination type.

The circuit arrangement may be such that the beginning of the pulse is transmitted through the laser and then the remainder of it is diverted to pass through the switch and bypass the laser. This may enable a faster pulse fall time to be achieved than would be posible where pulse shaping is imposed by other circuit elements alone.

A magnetic switch generally comprises ferromagnetic material about which is wound an electrical conductor.

When current is transmitted along the conductor, a magnetic field is produced which tends to align the magnetic domains within the ferromagnetic material until eventually they are all parallel, this condition being known as "saturation". Once this point has been reached, no further movement of the magnetic domains occurs until the magnetic field is removed, when the domains move out of alignment and the magnetic flux density is reduced to the level known as "remanence". When a magnetic field is applied by passing a current through the conductor, the inductance presented by the magnetic switch is relatively large as the domains move to become aligned with the field. Once saturation has been reached, the inductance of the switch falls.Thus, by including the magnetic switch in parallel with the load, the inductance of the switch is initially large and the beginning of the pulse is directed through the load. Once saturation is achieved, however, the remainder of the pulse is then transmitted through the switch rather than the load.

This enables the shape of the pulse which is transmitted through a laser, for example, to be controlled so that it has a fast fall time.

The invention is particularly applicable to arrangements in which the load is a laser, and more especially a recombination laser such as, for example, a strontium recombination laser. In a strontium laser, a current pulse is passed through the laser to produce a discharge. In the after-glow of the plasma, recombination of doubly ionised strontium occurs to produce excited, singly ionised strontium. A population inversion is established between two energy levels of the singly ionised strontium, and laser radiation is generated.

However', at this time, it is possible for the lower laser level to become populated as neutral strontium atoms collide with fast moving electrons associated with the tail of the current pulse. This mechanism tends to reduce the population inversion and impair operation of the laser. Thus, it is desirable to rapidly terminate the discharge current pulse, which is the source of the high energy electrons, and to allow the high pressure buffer gas to cool the electrons by collisions. By employing the invention, the current pulse can be arranged to have a short fall time, thus reducing the number of high energy electrons available and improving laser action.

The magnetic switch may include biassing means, which may be d.c. or pulsed, to enable the time of saturation of the magnetic switch to be controlled.

One way in which the invention may be performed is now described by way of example with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of an arrangement in accordance with the invention; Figures 2, 2a and 2b are explanatory diagrams relating to the operation of the arrangement of Figure 1; and Figure 3 is a schematic diagram of another arrangement in accordance with the invention.

With reference to Figure 1, a circuit arrangement includes a strontium recombination laser 1 which is connected in parallel with a magnetic switch 2 and a capacitor 3. Another capacitor 4 is connected to one of the laser electrodes and a thyratron 5 is included, being connected across the capacitors 3 and 4.

During operation of the arrangement, the thyratron 5 is initially in a non-conductive state and the capacitor 4 is charged. When charging is complete, the thyratron 5 is triggered into conduction and the charge stored by the capacitor 4 is transferred to the capacitor 3. A discharge is then produced within the laser 1 when the breakdown voltage across its electrodes is exceeded and current is transmitted through the laser. At this stage, the inductance of the magnetic switch 2 is high and substantially all of the current passes through the laser.

During transmission of the pulse, the ferromagnetic core of the magnetic switch 2 reaches saturation and its inductance drops. The remainder of the current pulse is therefore diverted through the switch 2 and bypasses the laser 1. This is illustrated by Figures 2, 2a and 2b.

Figure 2 illustrates the whole of the current pulse which is applied to the laser 1 and switch 2, and Figures 2a and 2b show the parts of the pulse passed by the laser 1 and magnetic switch 2 respectively. By including the switch 2, a very short fall time may be achieved, thus giving improved operation of the laser 1.

With reference to Figure 3, another circuit arrangement for operating a strontium recombination laser is similar to that illustrated in Figure 1, but includes means 6 for biassing the core of the magnetic switch so as to permit control of its time of saturation. The biassing may be pulsed or d.c.

Claims (7)

1. A A circuit arrangement comprising a load, a magnetic switch connected electrically in parallel with it and means for applying a current pulse to the load, the magnetic switch being arranged such that a first part of the pulse is transmitted through the load and a second part through the switch.
2. 2. A circuit arrangement as claimed in claim 1 wherein the load is a laser.
3. 3. A laser arrangement as claimed in claim 2 wherein the laser is a recombination laser.
4. 4. A laser arrangement as claimed in claim 3 wherein the laser is a strontium laser.
5. 5. A laser arrangement as claimed in any preceding claim and including a thyratron arranged to control the application of the current pulse to the load.
6. 6. A laser arrangement as claimed in any preceding claim and including biassing means arranged to control the time of saturation of the ferromagnetic core of the switch.
7. 7. A laser arrangement substantially as illustrated in and described with reference to Figure 1 or Figure 3 of the accompanying drawings.