GB2101801A

GB2101801A - Laser apparatus

Info

Publication number: GB2101801A
Application number: GB08121894A
Authority: GB
Inventors: Iain Edward Ross
Original assignee: Ferranti PLC
Current assignee: Ferranti International PLC
Priority date: 1981-07-16
Filing date: 1981-07-16
Publication date: 1983-01-19
Also published as: GB2101801B; FR2509917B1; FR2509917A1; JPS5818987A; DE3225611A1

Abstract

Laser apparatus includes a gas laser tube (10) with electrodes (13, 14) between which a glow discharge is produced to cause laser action by an element of piezo-electric material (15) to which mechanical stress is applied. A limiting resistor (16) or other current limiter prevents the formation of an arc in the discharge. A discharge initiated by the piezo-electric element (15) may be maintained by a subsidiary power supply (17). <IMAGE>

Description

SPECIFICATION Laser apparatus This invention relates to laser apparatus, and in particular to the excitation of gas lasers.

As is well-known, gas lasers include a vessel containing a suitable gaseous active medium and provided with electrodes between which a glow discharge may be produced in the gas. This glow discharge provides the necessary excitation to enable laser action to occur. Such action may take place continuously or in pulses. The power supply which energisesthe laser has itself to be supplied with power from mains or battery sources, and these present problems in field situations. In a static role there is no great problem, but the provision of a portable laser, say for surveying purposes, involves the carrying of both batteries and a suitable converter unit. The problem is complicated by the fact that a higher voltage is necessary to initiate the discharge than to sustain it.This means that the voltage requirements are larger than necessary to run the laser once the discharge has been struck.

It is an object of the invention to provide laser apparatus in which a discharge in a gas laser may be initiated without the need for mains or battery power supplies.

According to the present invention there is provided laser apparatus which includes a laser tube containing a gaseous active medium and having electrodes between which a glow discharge may be produced to cause laser action, means for generating a potential difference sufficient to initiate said discharge and comprising an element of piezoelectric material and means for applying a mechanical stress to the element, and limiting means operable to limit the current flowing in the discharge to a value which prevents the formation of an unstable discharge in the gas.

The invention will now be described with reference to the accompanying drawings: Figure 1 is a schematic circuit diagram of laser apparatus; and Figure 2 illustrates one form of power supply means.

Referring now to Figure 1, this shows a lasertube 10 containing a gaseous active medium and having a pair of reflectors 11 and 12 defining the optical cavity of the laser. A pair of electrodes 13 and 14 are provided across which a potential difference must be applied to initiate and maintain a glow discharge in the gas to allow laser action to take place. Further details of the laser itself will not be given, since gas lasers may take many forms, and are well-known.

The power supply means, shown schematically at 15, comprise a member of piezo-electric material and some means for applying to the material a mechanical stress. This produces a high-voltage potential difference across the member which may be applied across the electrodes 13 and 14 of the laser to initiate a glow discharge in the gas. A current limiting resistor 16 is provided to prevent the current in the discharge from rising to a value which would result in the formation of an unstable discharge in the gas.

The power supply means 15 is shown in more detail in Figure 2, though this represents only one form which the device might take. A block of piezo-electric ceramic 20 is supported by an insulator 21. Some form of hammer 22 is provided which is able to strike or squeeze the block 20 so as to apply a mechanical stress, which results in the generation of a potential difference across the block. Many forms of mechanical device are known for applying the necessary stress, and may cause single-shot or repeated pulse outputs.

A number of suitable piezo-electric materials are known. Examples are polycrystalline compounds such as lead zirconate titanate, potassium sodium niobate, and lead metaniobate.

The power requirements for the initiation of a glow discharge in a gas laser are obviously dependent on a number of different parameters. Power supply means of the type described above are capable of generating up to, say 20kV across a capacitance of the order of 40pf, representing an energy of approximately 1 OmJ. A CO2 waveguide laser requires in excess of 12kV at a few milli-Joules to initiate a discharge, whilst a small He-Ne laser requires 5 to 1 OkV.

In many instances sufficient power is available for a sufficient period of time from the piezo-electric device for a laser output to be generated. This obviates the need for any further form of power supply. Some devices produce a train of pulses, and hence a train of laser output pulses may be obtained.

However, if continuous operation of the laser is required, initiated by the piezo-electric device, then a subsidiary power-supply is required to maintaina the discharge. This is shown in broken outline at 17 in Figure 1.

The current limiting means need not be a resistor as shown in Figure 1, but be provided by the inductance of the cable connecting the power supply to the laser. However, limiting means in some form or other must be provided.

1. Laser apparatus which includes a lasertube containing a gaseous active medium and having electrodes between which a glow discharge may be produced to cause laser action, power supply means for generating a potential difference sufficient to initiate said discharge and comprising an element of piezo-electric material and means for applying a mechanical stress to the element, and limiting means operable to limit the current flowing in the discharge to a value which prevents the formation of an unstable discharge in the gas.

2. Apparatus as claimed in Claim 1 in which the power supply means is operable to cause the laser to emit at least one pulse of laser radiation.

3. Apparatus as claimed in either of Claims 1 or 2 in which the limiting means comprise a resistor.

4. Apparatus as claimed in any one of Claims 1 to 3 in which the piezo-electric material comprises a ceramic polycrystalline compound.

5. Apparatus as claimed in any one of Claims 1 to

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Laser apparatus This invention relates to laser apparatus, and in particular to the excitation of gas lasers. As is well-known, gas lasers include a vessel containing a suitable gaseous active medium and provided with electrodes between which a glow discharge may be produced in the gas. This glow discharge provides the necessary excitation to enable laser action to occur. Such action may take place continuously or in pulses. The power supply which energisesthe laser has itself to be supplied with power from mains or battery sources, and these present problems in field situations. In a static role there is no great problem, but the provision of a portable laser, say for surveying purposes, involves the carrying of both batteries and a suitable converter unit. The problem is complicated by the fact that a higher voltage is necessary to initiate the discharge than to sustain it.This means that the voltage requirements are larger than necessary to run the laser once the discharge has been struck. It is an object of the invention to provide laser apparatus in which a discharge in a gas laser may be initiated without the need for mains or battery power supplies. According to the present invention there is provided laser apparatus which includes a laser tube containing a gaseous active medium and having electrodes between which a glow discharge may be produced to cause laser action, means for generating a potential difference sufficient to initiate said discharge and comprising an element of piezoelectric material and means for applying a mechanical stress to the element, and limiting means operable to limit the current flowing in the discharge to a value which prevents the formation of an unstable discharge in the gas. The invention will now be described with reference to the accompanying drawings: Figure 1 is a schematic circuit diagram of laser apparatus; and Figure 2 illustrates one form of power supply means. Referring now to Figure 1, this shows a lasertube 10 containing a gaseous active medium and having a pair of reflectors 11 and 12 defining the optical cavity of the laser. A pair of electrodes 13 and 14 are provided across which a potential difference must be applied to initiate and maintain a glow discharge in the gas to allow laser action to take place. Further details of the laser itself will not be given, since gas lasers may take many forms, and are well-known. The power supply means, shown schematically at 15, comprise a member of piezo-electric material and some means for applying to the material a mechanical stress. This produces a high-voltage potential difference across the member which may be applied across the electrodes 13 and 14 of the laser to initiate a glow discharge in the gas. A current limiting resistor 16 is provided to prevent the current in the discharge from rising to a value which would result in the formation of an unstable discharge in the gas. The power supply means 15 is shown in more detail in Figure 2, though this represents only one form which the device might take. A block of piezo-electric ceramic 20 is supported by an insulator 21. Some form of hammer 22 is provided which is able to strike or squeeze the block 20 so as to apply a mechanical stress, which results in the generation of a potential difference across the block. Many forms of mechanical device are known for applying the necessary stress, and may cause single-shot or repeated pulse outputs. A number of suitable piezo-electric materials are known. Examples are polycrystalline compounds such as lead zirconate titanate, potassium sodium niobate, and lead metaniobate. The power requirements for the initiation of a glow discharge in a gas laser are obviously dependent on a number of different parameters. Power supply means of the type described above are capable of generating up to, say 20kV across a capacitance of the order of 40pf, representing an energy of approximately 1 OmJ. A CO2 waveguide laser requires in excess of 12kV at a few milli-Joules to initiate a discharge, whilst a small He-Ne laser requires 5 to 1 OkV. In many instances sufficient power is available for a sufficient period of time from the piezo-electric device for a laser output to be generated. This obviates the need for any further form of power supply. Some devices produce a train of pulses, and hence a train of laser output pulses may be obtained. However, if continuous operation of the laser is required, initiated by the piezo-electric device, then a subsidiary power-supply is required to maintaina the discharge. This is shown in broken outline at 17 in Figure 1. The current limiting means need not be a resistor as shown in Figure 1, but be provided by the inductance of the cable connecting the power supply to the laser. However, limiting means in some form or other must be provided. CLAIMS

5. Apparatus as claimed in any one of Claims 1 to 4which includes means for maintaining a discharge initiated by the power supply means so as to provide a continuous output from the laser.

6. Apparatus as claimed in any one of the preceding claims in which the laser active medium contains carbon dioxide.

7. Apparatus as claimed in any one of Claims 1 to 5 in which the laser active medium contains helium and neon.

8. Laser apparatus substantially as herein described with reference to the accompanying drawings.