GB2143075A

GB2143075A - Lasers

Info

Publication number: GB2143075A
Application number: GB08411515A
Authority: GB
Inventors: Donald Bowes; Peter N Allen; William Blake; Michael W Sasnett; Richard J Saunders; Donald Bennett
Original assignee: Coherent Inc
Current assignee: Coherent Inc
Priority date: 1983-05-06
Filing date: 1984-05-04
Publication date: 1985-01-30
Also published as: GB8625643D0; GB2181869B; GB2181869A; GB8625642D0; FR2545661A1; GB8625640D0; GB2181885A; GB8411515D0; GB2143075B; DE3416525A1; GB2181863A

Abstract

A gas laser 10 has a support tube 40 supporting and maintaining the alignment of the optical resonator structure 24, the tube containing active medium and being in communication with the discharge tube 26 in which lasing occurs. An active temperature controller maintains the lasing medium in the tube (40) at a substantially constant temperature above ambient by means of a temperature sensor 20 and a servo 22. An active pressure controller uses a pressure sensor 30, an electronic processor, and a motor-driven needle valve 14 to maintain the pressure of the lasing medium in the laser 10 within the desired operating pressure range. The laser 10 can be switched in operation from a continuous mode to a pulsing mode by using switches to create an asymmetrical flux pattern in the transformer of a power supply system. An active power control system maintains the power output of the laser at the desired level through an active feedback loop in which the output beam is used to generate a voltage signal for control of discharge current. Because the optical resonator structure 24 is lightweight, it can be mounted on a movable mechanical assembly (155) for delivery of the beam to a desired location. The assembly includes linked relatively movable members with reflecting mirrors in the joints for transmitting the beam. The laser may form part of a distributive lasing system comprising a centralized pump 36 delivering the lasing medium to a plurality of remotely located optical resonator structures 24, each of which may have a separate heat exchanger 18. <IMAGE>

Description

SPECIFICATION Lasers The invention relates to lasers, to improvements therein, and to components thereof. It has particular application to lasers using a gaseous lasing medium, for example CO2 lasers.

A laser has many components and, because it is a precision instrument, many of these components must be of high precision. One such component is the optical resonator structure. The optical resonator structure has a cavity in which the active lasing medium is excited to produce the beam of coherent radiation. At one end of the optical resonator cavity is a first highly polished mirror, which is nearly one hundred percent(100%) reflective. A second highly polished mirror is at the other end, which is less reflective than the first mirror and permits some of the radiation to be transmitted therethrough. Coherent radiation generated within the optical resonator cavity is reflected from the first mirror to the second mirror until sufficient amount of energy of coherent radiation is generated and is transmitted through the second mirror.

Because the optical resonator structure must be aligned such that photons of radiation reflected from one mirror is incident on the other mirror,the structure must be extremely precisely aligned. Any misalignment can cause the laserto produce a reducedoutputoreventofailtogeneratea beam of laser radiation. The optical resonator structure must be precisely aligned, even when it is subjected to variation in alignment and position duetovariations in the ambient temperature. In addition, heat generated within the optical resonator cavity caused by the excitation of the lasing medium can cause the optical resonator structure to become misaligned or mispositioned.

It is known to use a stablizing fluid, such aswateror oil, which is heated to a fixed temperature and passed into the optical resonator structure to maintain the structure at a fixed temperature. This, however, requires the use of a fluid which is different from the lasing medium, thereby necessitating another set of plumbing fixtures and the like. In addition,the temperature of the stablizing medium is generally maintained by a simple thermostatic heater.

Another component of a laser is the power-supply.

The power supply generally comprises a plurality of lines (usuallythree) connected to a three-phase power source. These plurality of lines are connected to a set of primary coils (also usuallythree),which are wound about a transformer. A plurality of secondary coils (alsousuallythree) arealsowoundaboutthetransformer. The transformer increases the voltage of the secondary coil from the primary coils. In the prior art, to control the mode of operation of the laser from continuous to pulsing, usually a control device, such as a vacuum tube, is used.Since a vacuum tube runs on DC voltage, and since the powersupplied to the primary coils is AC in nature, the vacuum tube is placed in the circuit afterthe secondary coils. Sincethe secondary coils receive an increased voltage from the transformer (usually on the order of tens of thousands of volts), the vacuum tube must be suitable for such high voltage application. Necessarily, these tubes are expensive.

In September of 1982 atthelnternational Machine Tool Show in Chicago, Illinois, a system was disclosed wherein a fixed laser generated a fixed beam of coherent radiation. A robot having an articulated arm moved a work piece in and out of the beam of coherent radiation to effectuate various cutting and scribing actions onto the work piece as a result of the relative movement of the fixed beam of coherent radiation and the movable work piece. In the medical area, a laser generating a beam of coherent radiation has been delivered to a desired location by passing the beam of coherent radiation through an articulated arm wherein the movement of the articulated arm moves the beam.

In a principal aspect, the present invention provides a laser in which means are included for maintaining the lasing medium at a substantially constanttemperature. Atypical laser of the invention comprises a discharge tube and a supporttube for enclosing a fluid lasing medium, such mediuminthesupporttube being in communication with the discharge tube, and means for exciting such medium in the discharge tube; an optical resonator structure aligned with said discharge tube, and the lasing medium in the support tube is maintained at a constanttemperature, preferably above ambienttemperature. The discharge tube is normally positioned within the optical resonator structure, and usually positioned parallel to the support tube. A plurality of lasers may be combined in a single lasing system.

The optical resonator structure normally comprises a first mirror positioned at one end ofthe supporttube and a second mirror positioned at the other end thereof, and may be mounted on the support tube.

Lasers according to the invention can include an exhausttube for receiving lasing medium from the discharge tube, the discharge tube being adapted to receive lasing medium from the support tube. The discharge tube will normally receive lasing medium from the supporttube proximate the ends thereof for transportation axially therethrough away from the ends for passage to the exhaust tube.

In some embodiments of the invention the laser may include a plurality of discharge tubes, each parallel to the support member. Preferablythe discharge tubes will be positioned axially spaced from one another by substantially 900. In all embodiments it is preferred that the support tube is positioned substantially near the centre of the optical resonator structure.

The drawing(s) originally filed was (were) informal and the print here reproduced is taken from a later filed formal copy.

This print takes account of replacement documents submitted after the date of filing to enable the application to comply with the formal requirements of the Patents Rules 1982.

The temperature of the lasing medium in lasers according to the invention is normally controlled by the provision of a heat exchanger in the path of lasing medium in the laser; and means for passing a cooling fluid thereto. Operation of the heat exchanger can be controlled bya mechanism comprising a sensor for sensing the lasing medium temperature and for producing a first signal in response thereto; electronic signal processing means for receiving said first signal and a reference signal, representative of a reference temperature, andforgenerating a drive signal in response thereto; and solenoid means for controlling theflowfo cooling fluid to the heat exchanger in response to said drum signal.A preferred signal processing means includes means for generating a second signal varying repetitively overtime; means forsummingsaidfirstandsecondsignalsto produce a third signal; and meansforcomparingsaidthird signal to said reference signal to produce said drive signal.

To our knowledge, there has never been a laser using a temperature stablizing lasing medium whose temperature is actively controlled. By active control, it is meantthatthetemperature is sensed, is compared to a fixed reference, and in response to the compari son,thetemperatureofthefluid is changed. In preferred embodiments of the invention herein, all of this is done in a closed loop feedback control configuration.

The invention also provides apparatusfordelivering a beam of coherent radiation to a desired location, which apparatus comprises a mechanical assembly having a plurality of coupled structural members, wherein each structural member is linked for relative movement with an adjacent structural memberto form a plurality of joints; reflecting means positioned in one of the joints, whereby relative movement of the structural members forming said joint moves the reflecting means. A laser as defined above is mounted in one of said structural members for generating said beam, and aligned to impinge a said beam on the reflecting means, whereby movement of the assembly moves the laser and delivers a beam reflected from the reflecting means to a said desired location.

To our knowledge, in the prior artthere has not been any industrial system to deliver a beam of coherent radiation to a desired location by a mechanical assemblywhich comprises a pluralityofcoupled structural members in one of which a laser is located as described herein. The movement ofthe assembly moves the laser and the beam to deliverthe beam to the desired location. Finally, to our knowledge, there is nopriorartrelatingtoadistributive lasing system wherein a centralized pump and powersupplydeliv- ers the electrical power and the active gas lasing medium to a plurality of remotely located optical resonatorstructuresto activate the lasing action.

In the above apparatus according to the invention the reflecting means can provide a ninety degree phase shift to said beam to produce a circularly polarized beam from an incident linearly polarized beam. In an alternative, the reflecting means may provide zero degree phase shift from a beam reflected therefrom to a beam incident thereon. In any event, the apparatus can include focusing means in the assembly for focusing said beam onto said location.

The focusing means may be detachable, and provision can also be made for removing the focusing means and replacing it with a different focusing means.

It will be appreciated that the apparatus described above offers substantial advantages over prior radiation beam directing mechanisms, independantofthe meansforcontrollingthe lasing medium temperature, although some control is preferably accommodated.

The heat exchanger and sensing mechanisms described above may therefore be incorporated.

In another aspect, the present invention provides a system for controlling the power output of a laser having a regulatable power supply, which system comprises a power detector for generating a power signal in response to the output radiant energy of the laser; a switch for setting the desired power level of the laser; means for generating a level signal in response to the setting of the switch; and means for comparing said power signal to said level signal and for generating a control signal in response thereto; and meansforsupplying said control signal to the power supply for controlling the power output of the laser.

In yet another aspect, the invention provides a pressure regulating system for controlling the pressure of a gas lasing medium in a gas laser, which system comprises pressure sensing means for gener atingafirstsignal proportional to the pressure ofthe gas; means for processing said first signal and for generating a drive signal in response thereto; motor means operable in response to said drive signal to rotate a shaft; and flowtube means having a needle valve in the path of the gas, which tube means are coupled to the shaft to move the needle valve in response to the rotation thereof, thereby controlling the pressure of gas passing therethrough.

To our knowledge, there is in the prior art no system to control the power output of a laser in response to the desired level of power output Further, there is no prior laser system having an active pressure control loop to control the pressure of the gas lasing medium.

The invention will now be described by way of example and with reference to the accompanying drawings. It will be understood that various components and features of lasers described herein may be incorporated independantly in apparatus and devices of the invention; i.e. not necessarily in the combinations specifically referred to. In the drawings: Figure 1 is a schematic overall view of an improved laser, incorporating the present invention; Figure 2a is an enlarged view of the optical resonator structure of Figure 1; Figure 2b is a cross-sectional viewtaken along the line b-b of Figure 2a; Figure 3 is a circuit diagram of an active temperature controller; Figure 4(a-c) are various waveforms representing the signals atvarious locations of the circuit shown in Figure 3; Figure 5 is a schematic circuit diagram of the power supply used in the laserof Figure 1;; Figure 6 is a schematic circuit diagram of a type of switch suitablefor use in the powersupplyshown in Figure 5, Figure 7 is a side view of the mechanical coupling of a motor and a needle valve used in a pressure regulatorforthe laser of Figure 1; Figure 8 is a schematic circuit diagram of the active pressure controllerfor controlling the pressure of the gas in the laser shown in Figure 1; Figure9(a-c) are timing diagramsforvarious componentsofthecircuitshown in Figure8; Figure 10 is a schematic circuit diagram of a power control system used in the laser in Figure 1; Figure 11 is a perspective view of a laser beam delivery apparatus;; Figure 12 is a perspective view of another laser beam delivery apparatus; Figure 13 is a perspective view of yet another laser beam delivery apparatus; Figure 14 is a side view of still yet another laser beam delivery apparatus; Figure 15 is a block diagram of an apparatus for interchanging a component of the laser beam delivery apparatus; and Figure 16a-b are schematic block diagrams of laser distributive systems having a plurality of optical resonator structures and a centralized pump and power supply.

Referring to Figure 1, there is shown an overall view of an improved laser 10. Although the discussions set forth hereinafterwill relate to a CO2 type of laser, it should be apparentthatthe invention is not so limited.

In particular, the invention can be used in any type of laser having a fluid lasing medium.

The gas laser 10 comprises a gas inlet 12for introducing the gas lasing medium into the laser 10. In a CO2type laser, the gas is a mixture of CO2, N2 and He, althoughtheactivelasing mediumistheCO2gas.The gas is introduced into the inlet 12 and passes through a motor-driven needle valve 14 for controlling the flow of the gas passing through the needle valve 14. This will be explained in greater detail hereinafter. The gas is then combined with recycled gas from the recirculated pipe 16 and is introduced into a first heat exchanger 18. A cooling fluid, such as water, is also introduced intothefirst heat exchanger 18to cool the temperature of the gas. From the first heat exchanger 18, the gas is passed across a temperature sensor 20, which supplies a signal to a temperature control processor 22 which will also be explained hereinafter.

From thetemperature sensor 20, the gas is introduced into the optical resonator structure 24.

Within the optical resonator structure 24, the gas is passed into a discharge tube 26. Within the gas discharge tube 26 the lasing action ofthe gas is produced, generating a beam 28 of coherent radiation.

From the discharge tube 26, the gas is then supplied to an exhausttube 27. The gas is then passed through a pressure sensor 30 which, with the pressure controller 32. controls the pressure ofthe gas within the laser 10.

After passing through the pressure sensor30, the gas passes through a second heat exchanger 34. The gas is then pumped by a pump 36 and is recycled along with the new gas from the gas inlet 12. The pump 36 is a positive displacement "Roots" type pump. A small vacuum pump 35 ofthe rotating vane type maintains the gas mixture at about 60 torr, by continually drawing off a small amount ofgasthrough an orifice 37.

Optical Resonator Structure Referring to Figure 2a, there is shown the optical resonator structure 24 in greaterdetail.The optical resonator structure 24 comprises a supporttube 40, into which the gas lasing medium is first introduced.

The gas flow is indicated generally bythe arrow. The supporttube 40 aligns and supports the optical resonator structure 24 with a first mirror 42 positioned on a first end bracket 41 at one end ofthe supporttube 40 and a second mirror 44 positioned on a second end bracket 43 atthe other end of the supporttube 40. The supporttube 40 is attached to each end bracket 41 and 43, and is positioned substantially parallel to the discharge tube 26. Gas from the supporttube40 is passed to the discharge tube 26 substantially nearthe ends of the supporttube 40 and ofthe discharge tube 26 in a radial direction from the supporttube 40to the discharge tube 26. Once the gas is introduced into the discharge tube 26, they then flow axially awayfrom the ends ofthe discharge tube 26.Away from the ends of the discharge tube 26, the gas from the discharge tube 26 is passed to the exhaust tube 28.

As shown in Figure 2b, there are two discharge tubes 26 in communication with the supporttube 40 and the exhaust tube 27. Any number of discharge tubes 26 can be placed parallel to the support tube 40 and in communication therewith. However, preferably, the discharge tubes 26 are positioned axially spaced from one another by approximately 90 degrees. Also preferably for structural support, the supporttube 40 should be positioned substantially nearthe center ofthe optical resonator structure 24to achieve the greatest stability and alignment.

In order to achieve the greatest stability and support for the optical resonator structure 24, gas within the supporttube 40 is maintained at a substantially constant temperature. Furthermore, preferably, the temperature of the gas within the supporttube 40 is maintained above the ambient temperature.

With the gas in the supporttube 40 maintained at a constanttemperature, the stability ofthe optical resonator structure 24 and the alignment ofthe first and second mirrors 42 and 44 and the folding mirrors 5 (only one is shown) are less likely to be affected by temperature variations in the ambient or in the structure 24 caused by the excitation ofthe gas in the discharge tube 26.

Within the dischargetube 26 are a plurality of anodes 62 and cathodes 64. The anodes 62 and cathodes 64 are preferably spaced approximately 16.5 inches apart. The discharge tube 26 is preferably 74 inches in length, thereby accommodating four (4) anode-cathode sections. The outer diameter of the discharge tube is preferably5-1/4"with an inner diameter of 4-1/2". The anodes 62 are positioned substantially nearthe ends ofthe discharge tube 26 and nearthe gas inletfrom the supporttube 40. The cathodes 64 are positioned away from the ends of the discharge tube 26 nearthe gas exhaust from the discharge tube 26to the exhausttube 27. In the event more than one discharge tube 26 is used, the folding mirrors 5 or deflecting mirrors are used to provide increased output power.

To provide overall physical stability, the optical resonatorstructure 24 is made outofrigid cast aluminum. As a result, the structure 24 is of light weight. The end brackets 41 and 43 are kinematically mounted on support member 39. The support member39 is generally parallel with the supporttube 40 and with the discharge tubes 26 and the exhausttube 27. The first end bracket 4# is rigidly fastened onto the support member 39. A mounting bolt 45 bolts the first end bracket 41 to the structural member 39. The bolt 45 is fastened such that it prevents any movement of the end bracket 41 in any direction. The second end bracket 43 has a slot 47 th erein.A slot 47 is located on each side of the second end bracket 43 (only one is shown in Fig. 2a). The slot47 is generally in the x direction (as shown in the direction diagram of Fig.

2a). A mounting bolt 49 on the structural member 39 is passed through the slot 47. The bolts 49 passing through the slot47 permitthe second end bracket 43 to move in the x and directions. The bolts 49 prevent thesecondend bracket43from moving in then direction. Substantially nearthe center of the second end bracket 43 is a hole 53 through which an alignment pin 51 passes (as shown in the cut-away section of Fig. The alignment pin 51, through the slot 53, prevents the second end bracket 43 from moving intheydirection.Theoveralleffectofthe bolts 49 and the alignment pin 51 isto permitthe second end bracket 43 to move only in the x direction.

Thus, when there is thermal expansion ofthe optical resonator structure 24, due to increase in temperature, the supporttube 40 movesthefirst and second end bracket 41 and 43 relative to one another only in the x direction. The movement of the first and second mirrors 42 and 44 in the x direction,which is generally parallel to the axial direction of the discharge tube 26, maintains the alignment ofthe mirrorsforthe photons to reflectfrom one mirrortothe other.

Temperature Controller To maintain the temperature ofthe gas within the supporttube 40, a temperature controller is provided.

The temperature controller comprises a temperature sensor 20, an electronic processor 22, and a solenoid 50 for controlling the flow ofthe water into the first heat exchanger 18 to cool the gas.

Referring to Figure 3, there is shown a schematic circuit diagram ofthe temperature control processor 22. The temperature sensor 20 measures the temperature ofthe gas and produces afirstsignal in response thereto.The temperature sensor 20 is an industry component designated as LM334. A portion of the temperature processor 22 comprises a circuit known as a "dither" 52. The dither 52 produces a saw-tooth waveform which varies approximately every30 seconds. This is shown in Figure 4a. The saw-tooth signal from the dither 52 and thefirst signal from the temperature sensor 20, which is a DC signal, are combined at a summing junction 54. The summing junction 54 simply adds thetwo signals together. An example ofthe waveform atthejunction 54 is illustrated in Figure 46.The combined signal from the summing junction 54 is supplied to an operational amplifier 56, which merely isolates the signal from the rest of the system.

From the operational amplifier 56, the summed signal is supplied to a comparator 58. The comparator 58 is an industry part LM723. It has an internal reference voltage and an outside potentiometer can be attached to the internal voltage reference to adjust it. The outside potentiometer can adjust the internal voltage to a level which is representative of a reference temperature. The comparator 58 compares the summed signal to the reference signal to produce a drive signal. The comparator 58 compares the two signals by subtracting the reference signal from the summed signal. An example ofthe waveform from the comparator 58 is shown in Figure 4c. The drive signal is then supplied to the solenoid 50 through an optical SCR switch 62. The optical SCR switch is a component D2402 made by I. R. Crydom.

The drive signal from the comparator 58 which is supplied to the solenoid 50 is a DC signal with a saw-tooth signal superimposed thereon. The sawtooth signal turns on the solenoid approximately every 30 seconds. The length ofthe "on" period is determined bythe DC level. Thus, if the drive signal from the compa rator 58 were small,the solenoid 50 would nevertheless be turned on every 30 seconds for a momentary period oftime. An example ofthis is shown in Figure 4c. By having the solenoid 50 activate at a fixed rate but for a variable period of time, the temperature bandwidth is decreased.

In the priorart, a thermostat normallyvaries between two temperature values: a first temperature and a second temperature. When thetemperature of the medium reaches a first temperature, the thermostat will open to cool it. When the temperature of the medium reaches a second temperature, the thermo- stat will close to preventfurther cooling. The switch between the two temperature values is of constant amplitude. Onlythe amount oftime during which the switching operation is performed is varied.

In contrast, in the temperature control processor 22, the solenoid 50 is forced to switch at a constant rate, but at a variable pulse width, thereby decreasing the temperature amplitude. This reduces the variation between the firsttemperature and the second temperature; i.e., the temperature atwhich the gas medium should be cooled and the temperature atwhich the cooling process should be stopped. Thus, a more accurate temperature controller is achieved.

In the preferred embodiment, the temperature of the gas is maintained at a level above the ambient.

This avoids fluctuation oftemperature of the gas caused byvariation in temperature ofthe cooling fluid.

Power Supply System Referring to Figure 2a, there is shown the gas discharge tube 26. Positioned within the gas discharge tube are a plurality of anodes 62 and a plurality of cathodes 64. For a CO2 laser, to cause the lasing of the gas medium within the gas discharge tube 26, a high voltage DC source (typically on the orderoftensof thousands of volts) must be supplied to the anodes 62 and cathodes 64.

Referringto Figure5,there is shown a schematic circuit diagram of a power supply system 68 for supplying high voltage DC power to the electrodes 62 and 64 in the dischargetube 26. The power supply system comprises a first, a second and a third lead (,i(#, ssB, acl respectively). The first lead ssA is connected to a first saturable reactor 70. The second lead ssB is connected to a second saturable reactor 72. The third lead Be is connected to a third saturable reactor 74.

The leads ssA, ssB, and ssc are connected to a plurality of primary coils 76,78 and 80 of a transformerT1. Three secondary coils 82,84 and 86 are also connected to the transformerT. The output of the secondary coils 82, 84 and 86 are connected through a diode bridge comprising a plurality of diodes to form the DC power supply. This is the high voltage which is supplied to the electrodes 62 and 64 within the discharge tube 26.

Theforegoing described prior art power supply system 68, when connected to a three-phase power source (e.g. 480voltsA.C.) and the system 68 is in operation, will cause the gas laser 10 to operate in a continuous mode, i.e., the beam 28 of coherent radiation produced from the discharge tube 26 is generated continuously.

We have found that, by simply adding a switch, for example 90a, which connects between any ofthe two leads, for example, ## and ac, or a switch, for example 90b, in one ofthe leads, forexample, ac, from the primary coils to the power source, will cause a change in the flux pattern in thetransformerT1. More particularly,the change in the flux pattern results in an asymmetrical flux flow in the transformerT1. The result of an asymmetrical flux pattern in the transformerT1 is that when the power supply system 68 is connected to the electrodes 62 and 64 in the discharge tube 26, the laser 10 will operate in a pulsing mode.In the eventthe leads #B#Al ,ll'cwere connected to a 60Hzthree-phase powersource, and either switch 90a is introduced shorting the leads ,i(# and ,~c, or switch 90b is added opening the lead ,~c, a pulsing rate of 120 HZ is observed.

The switch 90a or 90b can be an optical SCR switch, such as the D2402 from I. R. Crydom, as previously described. The schematic circuit for such a switch is shown in Figure 6.

Active Pressure Controller The active pressure controllerforthe laser 10 comprises a pressure sensor 30, a pressure control processer 32 and a motor driven valve 14. This is shown in Figure 8. The pressure ofthe gas in the laser 10 is crucial inorderto maintain the proper output of the gas discharge tube 26. Also, the vacuum pump 35 pumping through a small orifice 37, is continually draining the laser 10 of a small percentage of its gas loadt This leakrate is replenished through the motor drivenvalve 14.

The sensor 30 is a solid state, temperature compensated pressure transducer. The preferred embodiment of the pressure sensor is a 1 42PC1 5A, commer ciallyavailablefrom MicroswitchlHoneywell.The pressuretransducer30 generates afirstvoltagesignal which is proportional to the pressure ofthe gas. The output of the transducer 30 increases monotonically with the absolute pressure.

The first signal from the pressure sensor 30 is supplied to a first operational amplifier 92 (shown in the upper right hand portion of the first LM324). The first operational amplifier 92 is a DC comparator whose output is proportional to the error difference between pressure transducer output voltage (from the sensor30) and pressure reference level setpoint (from the first adjustable potentiometer 94). A summing junction 96follows the first operational amplifier 92.

Thefirstoperational amplifier92suppliesthesum mingjunction96withthesignalnecessaryto maintain DC pressure level during normal long term operation.

A second potentiometer 98 is directly connected to the gear train ofthe motor and gas flow valve 14. The second potentiometer 98 is driven by a DC level and the output ofthe second potentiometer provides a signal proportional to the valve opening. A second operational amplifier 100 is connected in parallel with the first operational amplifier 92 and translates the second potentiometer 98 output signal into a second signal proportional to rate of change of inlet gas flowrate. This provides a velocity feedback signal to the summing junction 96 that is necessary for stable operation.

Athird operational amplifier 93 provides as its output a voltage proportional to the position ofthe second potentiometer 98 and therefore of the gas flow control valve. Afourth operational amplifier 95 also provides a voltage proportional to position of the second potentiometer 98 and therefore ofthe gas flow control valve. These two operational amplifiers 93 and 95, when provided with proper high and low limit reference values will supply a signal to the summing junction 96 necessary to restrict the needle valve excursion and keepthevalvefromjamming onto the stop or from excessive flow rate during startup. The third operational amplifier 93 prevents excessiveflow rate while the fourth operational amplifier 95 prevents jamming.

Afifth operational amplifier 97 is a driverforthe outputtransistors (shown as 2N3439 and 2N541 6).

Thesetransistors are connected in a configuration commonly known as a totem-pole configuration. The motor 14 is connected to the center of the totem-pole in order to receive proper drive of either positive or negative polarity necessary to drive the valve clockwise or counter-clockwise, thereby closing or opening the valve in response to the voltage present at the summing junction 96.

The motor and valve 14 assembly comprises an ETI/Polaris Industrial Enterprise motor assembly, consisting of a DC motor, the second potentiometer 98 and a reduction gear. The motor 104 rotates the shaft 106. Attached to the shaft 106 is a reduction gear 108.

The reduction gear 108 is coupled to another gear 110 which is attachedtothe shaft 112 of a flowtube 114.

Theflowtube 114 has a needle valve therein (not shown) and in response to the rotation of the shaft 106 of the motor 104, the shaft 112 oftheflowtube is rotated which movesthe needle valve, thereby controlling the pressure ofthe gas passing through theflowtube 114. The preferred embodiment of the flowtube 114 is commercially available as B-1 25-60 manufactured by Porter Instrument Company.

In normal steady-state operation, the high limit and the low limit operational amplifiers 93 and 95 respectively provide no signal to the summing junction 96.

The summing junction 96therefore combines the pressure transducer feedback, the setpoint reference level, and the gas flowrate rate of change. This combined signal is compared against zero by the fifth operational amplifier 97. Any offset from zero, either positive or negative is supplied to the motor 104 as a DC drive level proportional to the offset from zero. The gas flowrate into the laser 10 is therefore actively controlled so as to maintain gas pressure developed in the laser 10 at a constant and selected level.

The four additional operational amplifiers shown on the schematic are used to trip three pressure level setpoints used for various startup signals and to provide stiffvoltage references to the pressure control processor. The voltage reference could be derived elsewhere. Therefore these four operational amplifiers are not required for proper operation of the pressure control processor.

Power Control System Referring to Figure 10, there is shown a schematic block circuit diagram of a power control system 120 used in the laser 10. A percentage of the intercavity power of the laser 10, a beam of coherent electromagnetic radiation, is detected by a power meter 122.

The power meter 122 generates a voltage signal which is proportional to the output radiant energy of the laser 10. This powersignal is supplied to a first operational amplifier 124 which serves merely to buffer the power signal from the rest of the system 120. The power signal is then passed to afirst comparator 126.

A switch 128 has a plurality of settings which the operator can setto the desired power level forthe laser 10. A programmable read only memory 130 generates a digital signal in response to the address setting derived from the switch 128. The digital signal is then passed to a DC reference 132 which decodes the value from the PROM 130 and generates a level signal. The level signal from the DC reference 132 is then buffered by amplifier 134. A signal which is representative ofthetemperature ofthe ambient is also suppliedto the amplifier 134. The signal from the DC reference 132 is supplied to the "+" input of the amplifier 134, while the signal representative of temperature is supplied to the "-" input of the amplifier 134.The signal representativeoftempera- turn can be derived from anysource,such as a thermistor. The compensated signal is then passed to the first comparator 126. The first comparator 126 is an operational amplifier with the signal from the amplifier 134 being supplied to the "+" inputandwith the powersignal from the power meter 122 being supplied to the"-" of the input. The output ofthe first operational amplifier 126 is then used to control a reactor drive 136. The reactor drive 136 controls the first, second and third saturable control coils 70,72, and 74, respetively, as shown and discussed in Figure 5. By controlling the saturable control coils70,72 and 74, the high voltage supply system 68 is thereby controlled.The power level of the high voltage system 68, in turn, controls the degree of discharge current which occurs within the discharge tube 26.

It will be appreciated that, with the power control system 120, active control of the power ofthe output of laser 10 is achieved. Furthermore, direct power setting of the laser 10 with feedback control has also been accomplished.

Laser Beam DeliveryApparatus Referring to Fig. 1 there is shown a laser beam delivery apparatus 140. As previously described, the laser 10 comprises an optical resonatorstructure 24 which can be of extremely light weight. Thus, the optical resonator structure 24 can be mounted away from the pumps, heat exchangers, etc. In the laser beam delivery apparatus 140 shown in Fig. 11, the optical resonator structure 24 is shown as producing a beam of coherent radiation 28. A mechanical assembly 155 is also shown. The mechanical assembly 155 comprises a plurality of coupled structural members.

Afirststructural member 142 is linked to a second structural member 144which is linked to a third structural member 148, etc. At each of the linkage of the structural members is a joint, shown for example, as 146 or 150. Within each joint is a mirror. The structural members are preferably of hollow, cylindrical tubes. The beam 28 is aligned to pass substan tiallythrough the center of the cylindrical member, to impinge the mirror positioned in the joint. The relative movements ofthe structural members forming the joint moves the mirror. Thus, the beam 28 can be delivered to the desired location by moving the structural members relative to one another such that the beam 28 reflected from the mirror in the joint will then impinge on the desired location.

More specifically, in Fig. 11, the beam 28 is aligned to pass substantially nearthe center of the axis of the cylinder of the first structural member 142. The beam 28 is aligned to impinge the first mirror 146 and to reflect therefrom. Beam 28 reflected from the first mirror 146 is aligned to pass substantially through the center ofthe axis ofthe second cylindrical structural member 144 and is aligned to impinge a second mirror 150. Beam 28 is then reflected from the second mirror 150 and is aligned to pass through the center of the cylinder ofthethird structural member 148, and is aligned to impinge a third mirror 152. The beam reflecting from the third mirror 152 is aligned to pass through a telescopic member 154. Atthe end ofthe telescopic member 154 is a fourth mirror 156 from which the beam 28 is reflected.The beam 28 is then passed through a focusing lens 158 and is then focused onto the desired location 160.

The entire mechanical assembly 155 is mounted on aframe 162 with motor-driven belts 164 and 166, respectively. The motor-driven belts 164 and 166 propel the mechanical assembly 155 with the optical resonator structure 24 in eitherthexorthey directions. The movement of the mechanical assembly 155 in the x ory direction moves the beam 28 in the x andy directions. The telescopic member 154 delivers the beam 28 inthezdirection.

In the apparatus 140, shown in Fig. 11 ,the relative alignments ofthe mirrors 146,150, and 152 are set at the factory. The beam 28 is aligned to impinge the first, second and third mirrors 146,150 and 152, respectively, and to be delivered down the center of the telescopic member 154. In operation, only the entire assembly 155 is moved either in the x ory direction and the telescopic member 154 is moved inthez direction. In addition, the telescopic member 154 can be rotated aboutthe z axis, while the focusing lens 158 can be rotated abouttheyaxis.

Referring Fig. 12, there is shown another laser beam delivery apparatus 170. This laser delivery apparatus 170 is similar to the laser delivery apparatus 140. The appratus 170 comprises an optical resonator structure 24forgenerating a beam 28 of coherent radiation. The mechanical assembly 172 for delivering the beam of coherent radiation comprises a first structural mem ber 142, a second structural member 144, with a first joint 146 having a mirrortherein, and a second joint 150 having a mirrortherein, all similartothat described for the apparatus 140.The beam 28 from the resonator structure 24 is aligned to impinge the first mirror 146,to reflect therefrom and to impinge the second mirror ? 50 and to reflect therefrom to impinge a movable focusing head 174. The movable focusing head 174 comprises a third mirror 176 which is aligned to receive the beam 28to reflecttherefrom and to impinge a focusing lens 178.

The mechanical assembly 172 is mounted on a pair of guide rails 180 and 182 respectively. The optical resonator structure 24, mounted on the mechanical assembly 172 is movable in the Y direction. The movable focusing head 174 is adapted to move along a third rail 184 in the X direction. The focusing action of the beam 28 by the focusing lens 178 delivers the beam 28 in the Z direction.

Referring to Figure 13 there is shown yet another laser beam delivery apparatus 190. The laser beam delivery apparatus 190 comprises an optical resonator structure 24for generating a beam 28 of coherent radiation. A mechanical assembly 192 comprises a plurality of coupled structural members, some of which are shown as 142,144,148 and 154, all as previously described. Each structural member is linked for relative movement with another adjacent structural membertherebyforming a plurality of joints. At each joint, a mirror is positioned to receive the beam 28 and to reflectthe beam 28 onto the next joint. A plurality of such mirrors is shown as 146,150, 152 etc. The mechanical assembly 192 shown in figure 13 is capable of an innumerable degree of motion.The rotational degrees offreedom of each of those structural members is shown by the arrows. The movement of the mechanical assembly 192 moves the beam 28 and delivers a reflective beam, the beam 28 which has been reflected through the internal workings of the structural members, through a focusing lens 194tothe desired location 196.

Referring to Figure 14there is shown yet another laser beam delivery apparatus 250. The apparatus 250 comprises an optical resonator structure 24 mounted on a mechanical assembly 232. The mechanical assembly 232 has a base 230. Afirst structural member 231 is rotatably mounted on the base 230.

The resonator structure 24 is rotatably mounted on the first structural member 231. The beam 28 (not shown) from the resonator structure 24 is passed through an elastic joint 236 and impinges a focusing head 238.

The head 238 is rotatable aboutthe point 236. A focusing lens 240 focuses the beam 28 and delivers it tothe desire location.

Each of the foregoing describe the laser beam delivery apparatus, 140, 170, 190 and 250 have been shown with only an optical resonator structure. Of course, as previously stated, the heat exchangers, the vacuum pump, and the power supply, all as previously described as being necessaryforthe operation of laser 10 must also be provided. Forthe laser beam delivery apparatus 140,170,190and 250, these other portions are not shown but are connected to the optical resonatorstructure24throughflexiblecou- pling, and electrical connectors.

Each ofthe mirrors positioned in the joint formed by two adjacent structural members of the mechanical assembly portion ofthe apparatus 140,170,190 ro 250, can be a reflective means, of the type as shown and described in U.S. Patent No.4,379,622, which in addition to reflecting coherent beam impinging thereon also imparts a certain degree of phase shift to that reflective beam. As shown and as described in U.S.

Patent No.4,336,439, a circularly polarized beam, formed by a linearly polarized beam which is subsequently passed through a ninety degree (90 ) phase shifter has beneficial cutting and scribing properties.

Therefore, the reflective mirror can be a reflective mirrorwhich imparts a phase shiftto the beam. The reflective mirror can impart ninety degrees (90 ), forty-five degrees (45 ) or even zero degree (0 ) phase shift.

Since each laser beam delivery apparatus 140, 170, 190 and 250, also comprises a focusing head which focuses the beam 28 onto the desired location, the focusing head, which comprises a focusing lens, determines the distance of focus from the head to the desired location. Referring to figure 15 there is shown an apparatus for changing the focusing head of the laser beam delivery apparatus. A laser beam delivery apparatus 140 is shown with a laserfocusing head 158. A plurality of interchangeablefocusing heads: 200,202,204 and 206 are positioned nearby. A second mechanical assembly 155 having an arm and a grasp 208 is shown.Mechanical assembly 155 with the grasp 208 is capable of removing the focusing head 158 from the laser beam delivery apparatus 140, and replacing it with a focusing head of choice from the rack of interchangeable focusing heads 201. Therefore, by permitting the interchangeability of the focusing head ofthe laser delivery apparatus 140, greaterflexibility is achieved.

Distributive Lasing System Referring to figure 16(a) there is shown a distributive lasing system 210. The distributive lasing system 210 is suitable for use in a factory where a plurality of optical resonator structures 24a, 24b, 24c etc. are in use in different locations of the factory. Each one of the optical resonator structures 24(a-d) can be mounted on a mechanical assembly of the type as previously described. In the distributive lasing system 210 shown in figure 16(a), a centralized gas pump 36 and heat exchanger 18 are shown. The lasing medium, the gas, is delivered from the central pump 36 through the heat exchanger 18to each one of the optical resonator structures 24(a-d), via pipes or hoses located throughout the factory. The gas is pumped from the centralized pump 36 and is heated by a centralized heat exchanger 18 and is passed on to a first optical resonator structure 24(a), a second optical resonator structure 24(b), a third optical resonator structure 24(c) etc. The gas is then recycled back to the pump 36.

A centralized power supply 212 supplies the necessary electrical power to create the discharge within the discharge tube of each of the optical resonator structures 24(a-d). A backup vacuum pump 36' is shown as a pump to be used in the event of failure of the primary pump 36.

Referring to figure 16(b) there is shown another distributive lasing system 220. Similarto the distributive lasing system 210 shown in figure 16(a), the distributive lasing system 220 shown in figure 16(b) comprises a centralized pump 36. The pump 36 provides the active lasing medium to each of the optical resonator structures 24(a-d). Again, the delivery is made through pipes, hoses and the like. The gas is supplied to each ofthe optical resonator structures 24(a-d) and the exhaust gas from the optical resonators structure is returned to the central pump 36.

However, unlike the system 210 shown in figure 16(a), a heat exchanger 18(a-d) is provided for heating the gas ofthe gas lasing medium to each of the optical resonator structures 24(a-d). In this example, if the centralized pump 36 were far away, a heat exchanger 18(a-d) should be placed close to the respective optical resonator structure 24(a-d) in orderto minimize the heat loss from the transmission of the gas from the heat exchanger to the optical resonator structure.

Similarto the system 210 shown in figure 16(a), a backup pump 36' is also shown. Of course, in addition, a centralized power supply 212 would also be provided.

The advantage of a distributive lasing system 210 or 220 is that neartheworksite all that is required would be the optical resonator structure 24. Since as previously described the optical resonator structure can be made lightweight and compact, the plumbing and the electrical supply necessary to maintain the lasing action within the optical resonatorstructure can all be centralized. This would result in elimination of duplication of vacuum pumps and power supplies. In addition, banks of vacuum pumps and of power supplies can be connected in tandem to be switched on in the event of failure of one ofthe components.

From the foregoing description, it can be seen that there are numerous advantages to a distributive lasing system as described.

Claims

1. A laser comprising: a discharge tube and a support tube for enclosing a fluid lasing medium, such medium in the supporttube being in communication with the dischargetube, and means for exciting such medium in the discharge tube; an optical resonator structure aligned with said discharge tube; and means for maintaining lasing medium inthesupporttubeata substantially constanttemperature.

2. A laser according to Claim 1, wherein the optical resonator structure comprises a first mirror positioned at one end ofthe supporttube and a second mirror positioned atthe other end thereof.

3. A laser according to Claim 1 or Claim 2 wherein the optical resonator structure is mounted on the supporttube.

4. A laser according to any preceding Claim wherein said substantially constanttemperature is above the ambient.

5. A laser according to any preceding Claim wherein the discharge tube is positioned parallel to the supporttube.

6. A laser according to any preceding Claim including an exhausttubeforreceiving lasing medium from the discharge tube, the discharge tube being adapted to receive lasing medium from the supporttube.

7. A laser according to Claim 6wherein the discharge tube is adapted to receive lasing medium from the supporttube proximatetheendsthereoffor transportation axiallytherethrough away from the ends for passage to the exhaust tube.

8. A laser according to any preceding Claim including a plurality of discharge tubes, each parallel to the support member, and positioned axially spaced from one another by substantially 900.

9. A laser according to any preceding Claim wherein the support tube is positioned substantially near the centre of the optical resonator structure.

10. Alaseraccordingto any preceding Claim including a heat exchanger in the path of lasing medium in the laser; and means for passing a cooling fluid thereto.

11. A laser according to Claim 10 wherein the meansfor maintaining the temperature of lasing medium in the supporttube comprises a sensorfor sensing the lasing medium temperature and for producingafirstsignal in response thereto; electronic signal processing means for receiving saidfirstsignal and a reference signal, representative of a reference temperature, and for generating a drive signal in response thereto; and solenoid means for controlling the flow of cooling fluid to the heat exchanger in response to said drum signal.

12. A laser according to Claim 11 wherein the electronic signal processing means includes means for generating a second signal varying repetitively overtime; means for summing said first and second signals to produce a third signal; and means for comparing said third signal to said reference signal to produce said drive signal.

13. A laser according to any preceding Claim including a gaseous lasing medium in the support and discharge tubes.

14. A laser substantially as described herein with reference to the accompanying drawings.

15. A lasing system comprising a plurality of lasers according to any preceding Claim.

16. Apparatusfordelivering a beam of coherent radiation to a desired location comprising a mechanical assembly having a plurality of coupled structural members, wherein each structural member is linked for relative movement with an adjacent structural membertoform a plurality of joints; reflecting means positioned in one of the joints, whereby relative movement of the structural members forming said joint moves the reflecting means; andalaseraccord- ing to any preceding Claim in one of said structural membersforgeneratingsaid beam, and aligned to impinge a said beam on the reflecting means, whereby movement of the assembly moves the laser and delivers a beam reflectedfrornthe reflecting means to a said desired location.

17. Apparatus for delivering a beam of coherent radiation to a desired location comprising a mechanical assembly having a plurality of coupled structural members, wherein each structural member is linked for relative movement with an adjacent structural member to form a plurality ofjoints; reflecting a mirror means positioned in one of the joints, whereby relative movement of the structural members forming said one joint moves the reflecting means; laser means in one of said structural members for generating said beam, and aligned to impinge a said beam on the reflecting means, whereby movement ofthe assembly moves the laser means and delivers a beam reflected from the reflecting means to a said desired located.

18. Apparatus according to Claim 17 including a heat exchanger coupled to the lasing means whereby a lasing medium therein is passed therethrough; and means for supplying a cooling fluid to the heat exchangerforcooling a said medium.

19. Apparatus according to Claim 18 including a sensorforsensing the temperature of a said lasing medium and for producing a first signal in response thereto; electronic signal processing means for receiving said first signal and for receiving a reference signal, representative of a reference temperature, and for generating a drive signal in response thereto; and solenoid means for controlling the flow of cooling fluid to the heat exchanger in response to said drive signal.

20. Apparatus according to Claim 19 wherein the electronic signal processing means includes means for generating a second signal varying repetitively overtime; means for summing said first and second signalsto produce a third signal; and meansfor comparing said third signal to said reference signal to produce said drive signal.

21. Apparatus according to any of Claims 16to 20 wherein the reflecting means provides a ninety degree phase shift to said beam to produce a circularly polarized beam from an incident linearly polarized beam.

22. Apparatus according to any of Claims 16 to 21 wherein the reflecting means provides zero degree phase shift from a beam reflected therefrom to a beam incident thereon.

23. Apparatus according to any of Claims 16to 22 including focusing means in the assemblyforfocusing said beam onto said location.

24. Apparatus according to Claim 23 wherein the focusing means is detachable.

25. Apparatus according to Claim 24 including means for removing the focusing means and replacing it with a differentfocusing means.

26. A pressure regulating system for controlling the pressure of a gas lasing medium in a gas laser, which system comprises pressure sensing means for generating afirstsignal proportionaltothe pressure of the gas; means for processing said first signal and for generating a drive signal in response thereto; motor means operable in response to said drive signal to rotate a shaft; and flow tube means having a needle valve in the path of the gas, which tube means are coupled to the shaft to move the needle valve in response to the rotation thereof, thereby controlling the pressure of gas passing therethrough.

27. A system according to Claim 26 wherein the sensing means is a temperature compensated, solid state piezo-resistive pressure transducer.

28. A system according to Claim 27 wherein the transducer generates a signal which monotonically increases with the gas pressure.

29. A system according to any of Claims 26 to 28 including means for generating a second signal which is proportional to the opening of the needle valve; the processing means being operative to process said first and second signals to generate said drive signal in response thereto.

30. A system for controlling the power output of a laser having a regulatable power supply, which system comprises a power detector for generating a power signal in response to the output radiant energy ofthe laser; a switch for setting the desired power level ofthe laser; meansforgenerating a level signal in responsetothesetting oftheswitch; and meansfor comparing said power signal to said level signal and for generating a control signal in response thereto; and means for supplying said control signal to the powersupplyforcontrolling the power output ofthe laser.

31. A system according to Claim 30 including meansforcomparing said level signal to a temperature signal representative of the ambient temperature.

32. A system according to Claim 31 wherein the comparing means is an operational amplifier, said level signal being supplied to the "+" input of the amplifier, and said temperature signal being supplied to the "-" inputthereof.

33. A system according to any of Claims 30 to 32 wherein the generating means is a PROM.