PULSED LASER SYSTEM HAVING IMPROVED ENERGY CONTROL WITH IMPROVED POWER SUPPLY LASER EMISSION ENERGY SENSOR AND ADJUSTABLE REPETITION RATE CONTROL FEATURES

• US 3,806,829 A
• Filed: 04/13/1971
• Issued: 04/23/1974
• Est. Priority Date: 04/13/1971
• Status: Expired due to Term

• Current Assignee: Glenville GAGE Company Incorporated
• Original Assignee: David K. Duston, Jeffrey B. Duncan
• Inventors: Duston, David K., Duncan, Jeffrey B.
• Primary Examiner(s): Wibert, Ronald L.
• Assistant Examiner(s): Webster, R. J.
• Application Number:
  US05/133,536
• Time in Patent Office: 1,106 Days
• Field of Search: 331/94.5 219/121L,121LM,121EB 315/242 90/58R
• US Class Current: 372/38.01
• CPC Class Codes: B23K 26/0622 by shaping pulses
• CPC Class Codes: H01S 3/0407 Liquid cooling, e.g. by water
• CPC Class Codes: H01S 3/0912 Electronics or drivers for the pump source, i.e. details of drivers or circuitry specific for laser pumping laser diode drivers H01S5/042
• CPC Class Codes: H01S 3/092 of flash lamp H01S3/0937 takes precedence ; flash lamps per se H01J61/80; circuit arrangements for operating flash lamps in general H05B41/30
• CPC Class Codes: H01S 3/1312 by controlling the optical pumping

Abstract

A pulsed, optically pumped laser, employing flashlamps excited via a pulse forming network from an array of storage capacitors and arranged so that the stored charge in these capacitors determines the laser beam emission intensity, is disclosed. The laser output beam intensity is sampled during each laser pulse by a photodiode for deriving a sensed actual laser beam energy signal. This signal is compared with a desired output energy intensity signal, the latter being pre-programmable into the system, or capable of being set manually. The flashlamp input is adjusted accordingly as a result of the comparison, to obtain laser output beam intensity uniformity on a pulse-to-pulse basis. The flashlamp trigger rate is variable. Also disclosed are an automatic workpiece positioning support, a heat sink and laser output beam diverter, and a protective tape for a laser beam focussing lens.

Claims

1. A pulsed laser system and control including in combination pumped laser means for producing a relatively high intensity laser beam of coherent light of high average energy which is variable over a predetermined range, pumping and resonator means coupled to the laser means for inducing emission of the laser beam at an energy level proportional to the energy level of the output emission from the pumping and resonator means, variable charge capacitor storage circuit means coupled to and supplying Electric energy to said pumping and resonator means at a charge elvel that determines the energy level of the stimulated output laser beam, electric power supply means energized from a conventional source of an electric power and coupled to and supplying electric energy to said variable charge capacitor storage circuit means, charging level control circuit means coupled to said electric power supply means for controlling the energy level to which the variable charge capacitor storage circuit means is charged, said electric power supply means comprising a voltage step-up transformer and high voltage rectifier circuit means, a low voltage monocyclic constant current charging networks for supplying said variable charge capacitor storage circuit means through said voltage step-up transformer and high voltage rectifier circuit means, said charging level control circuit means comprising fast responding SCR crowbar short circuiting means coupled across the output from said low voltage monocyclic constant current charging network for short circuiting the output from the network to thereby discontinue in a fast responding manner the charging of the variable charge capacitor storage circuit means from the monocyclic constant current charging network, capacitor storage circuit energy level sensing means coupled to the variable charge capacitor storage circuit means for sensing the energy level to which the variable charge capacitor storage circuit means is charged, computation circuit means coupled to the energy level sensing means for converting the sensed measure of energy into an electric signal representative of the total actual energy stored in the variable charge capacitor storage circuit means measured in terms of joules of energy, feedback control circuit means for controlling the operation of said SCR crowbar short circuiting means and responsive to the output from said computation circuit means for automatically discontinuing charging of said variable charge capacitor storage circuit means at a desired storage energy level, means disposed in the optical path of the laser beam for partially diverting a fractional portion of the beam, photosensitive means responsive to the diverted fractional portion of the laser beam for deriving sensed actual laser beam energy feedback signal, and comparison circuit means responsive to the output from said photosensitive means and to a preprogrammed value of energy level for controlling the operation of the computation circuit means for appropriately compensating the stored energy level in the variable charge capacitor storage circuit means intermediate each pulse operation of the laser system in accordance with the value of the sensed actual laser beam energy feedback signal whereby losses incurred in the high power pulsed laser system are compensated by adjusting the stored energy level of the capacitor storage circuit means to a value sufficient to make up for such losses following each pulsed operation of the laser system.

2. A pulsed laser system and control according to claim 1 wherein said feedback control circuit means is comprised by comparison circuit means supplied from the output of said computation circuit means and energy level selector programming means for supplying to the comparison circuit means an input command desired energy level value to which the variable charge capacitor storage circuit means is to be charged, the command value of energy level being supplied to the comparison circuit means in conjunction with the output from said computation circuit means for comparison in said comparison circuit means and for deriving an output feedback control signal upon the sensed energy level of the variable charge capacitor storage circuit means equaling the command value of energy for use in controlling operation of said charging level control circuit means.

3. A pulsed laser system and control according to claim 2 further including trigger circuit means for controlling operation of said pumping means and for initiatinG operation of said pumping means, trigger inhibit circuit means for controlling operation of said trigger circuit means, and means coupling said trigger inhibit circuit means to the output from said comparison circuit means for inhibiting triggering of said pumping means until the energy level obtained by the charging circuit means achieves the programmed value set by the energy level selector programming means.

4. A pulsed laser system and control according to claim 1 further including trigger circuit means for controlling operation of said pumping and resonator means and for initiating operation of said pumping and resonator means, trigger inhibit circuit means for controlling operation of said trigger circuit means, and means coupling said trigger inhibit circuit means to the compensated output from said comparison circuit means for inhibiting triggering of said puming and resonator means until the energy level obtained by the capacitor storage circuit means achieves the compensated value of charge level, and programmable variable trigger repetition rate control means coupled to and controlling said trigger inhibit circuit means for controlling the repetition rate of the pulsed laser emissions produced by the system.

5. A pulsed laser system and control according to claim 4 further including a laser beam heat sink, laser beam diverting means rotatable into the path of the laser beam for diverting the laser beam from its normal optical path and projecting it into the laser beam heat sink, beam diverter control means for controlling movement of said laser beam diverter means, and beam diverter inhibit and enabling signal generating means coupled to and controlling at least in part said trigger inhibit circuit means for inhibiting operation of said trigger circuit means during intervals while said lasser diverter means is being moved into or out of the laser beam optical path and for enabling said trigger inhibit circuit means upon the beam diverter assuming a commanded desired position relative to the laser beam optical path.

6. A pulsed laser system and control according to claim 5 wherein said high power pumped laser device includes an optical lens arrangement for focusing the laser beam into a highly focused intense laser light beam and further includes protective tape means moveable to a position intermediate the optical lens arrangement and a work piece for protecting the lens arrangement from back scattered particles, spray and the like, means for automatically moving a clean piece of protective tape into effective position intermediate the optical lens and the workpiece following each pulsed output of the laser beam, protective tape position monitoring means, and protective tape inhibit and enabling signal generating means coupled to and controlling at least in part said trigger inhibit circuit means for inhibiting operation of said trigger circuit means during movement of the protective tape and following a laser beam discharge therethrough, and for enabling said trigger inhibit circuit means only after a new portion of the protective tape has been moved into protective position intermediate the optical lens and the workpiece and is conditioned for a new pulsed laser beam output.

7. A high pulsed laser system and control according to claim 6 further including automatic workpiece position control means for supporting a workpiece relative to the optical axis of the laser beam and for automatically positioning the work piece relative to the laser beam in response to preprogrammed position command signals, automatis position control inhibit and enabling circuit means coupled to and controlling at least in part said trigger inhibit circuit means for inhibiting operation of the trigger circuit means during intervals of movement of the automatic position control and for enabling the trigger inhibit circuit means upon the automatic position control and for enabling the trigger inhibit circuit means upon the automatic position control having automatically positioned thE workpiece in the next commanded position for treatment with the laser beam.

8. A pulsed laser system and control according to claim 7 further including manual-repetitive fire control circuit means coupled to and controlling at least in part said trigger inhibit circuit means for enabling said trigger circuit means for automatic operation by said programmable variable trigger repetition rate control means under automatic repetitive fire operating conditions and for inhbiting said trigger inhibit circuit means for operation only by a manually generated trigger signal developed through said manual-repetitive fire control circuit means manually by an operator of the equipment, and time delay signal generating means coupled to and controlled by the output from said computation circuit means and coupled to controlling operation of SCR crowbar short circuiting means for maintaining said SCR crowbar short circuiting means conducting for a predetermined time interval following initiation of conduction thereof to allow adequate recovery time for components of the pumping means following each operation thereof.

9. A pulsed laser system and control according to claim 3 further including resettable variable repetition rate trigger pulse generating circuit means for generating repetitive trigger pulses for supply to said trigger circuit means through said trigger inhibit circuit means, repetition rate selector programming means coupled to and controlling operation of said variable repetition rate trigger pulse generating means for setting the repetition rate of the trigger signal pulses derived by said variable repetition rate pulse generating means, and means for coupling the output from said variable repetition rate trigger pulse generating means said trigger inhibit circuit means for assuring a minimum desired interval of time between each operation of the trigger circuit means. 10. A pulsed laser system and control according to claim 9 further including reset feedback circuit means responsive to the production of a trigger enabling signal from said trigger inhibit circuit and discharge of the capacitor storage circuit means for resetting the variable repetition rate trigger pulse signal generating circuit means to zero to initiate the production of the next sucessive repetitive trigger signal pulse, said reset feedback circuit means including a reset period timing pulse generator circuit means responsive to the output from said trigger inhibit circuit means for producing a reset period timing signal pulse of predetermined time duration, reset period inhibit circuit means responsive to the output from said reset timing pulse signal generator, the output from said capacitor storage energy level sensing circuit means and to the comparison circuit means for producting a reset period initiating output signal pulse and means for supplying said reset initiating output signal pulse to said trigger signal generating means in response to the production of an output enabling trigger signal and a drop in the energy level of the capacitor storage circuit means.

11. A pulsed laser system and control according to claim 10 further including a laser beam heat sink, laser beam diverting means rotatable into the path of the laser beam for diverting the laser beam from its normal optical path into the laser beam heat sink, beam diverter control means for controlling movement inhibit signal generating means coupled to and controlling at least in part said trigger inhibit circuit means for inhibiting operation of said trigger circuit means during intervals while said laser diverter means is being moved into or out of the laser beam optical path and for enabling said trigger inhibit circuit means upon the beam diverter assuming a commanded desired position relative to the laser beam optical path.

12. A high pulsed laser system and control according to claim 11 wherein said high power pumped laser device includes an optical lens arrangement for focusing the laser beam into a highly focUsed intense laser light beam and further includes protective tape means moveable to a position intermediate the optical lens arrangement and a work piece for protecting the lens arrangement from back scattered particles, spray and the like, means for automatically moving a clean piece of protective tape into effective positions intermediate the optical lens and the workpiece following each pulsed output of the laser beam protective tape position monitoring means, and protective tape inhibit and enabling signal generating means coupled to and controlling at least part of said trigger inhibit circuit means for inhibiting operation of said trigger circuit means during movement of the protective tape and enabling said trigger inhibit circuit means only on the protective tape being properly moved and positioned for a new pulsed laser beam output.

13. A high power pulsed laser system and control according to claim 12 further including automatic workpiece position control means for supporting a work piece relative to the optical axis of the laser beam and for automatically positioning the work piece relative to the laser beam in response to preprogrammmed command position signals, automatic position control inhibit and enabling circuit means coupled to and controlling at least in part said trigger inhibit circuit means for inhibiting operation of the trigger circuit means during intervals of movement of the automatic position control and for enabling the trigger inhibit circuit means upon the automatic position control having automatically positioned the work piece in the next commanded position for treatment with the laser beam.

14. A pulsed laser system and control according to claim 13 further including manual-repetitive fire control circuit means coupled to and controlling at least in part said trigger inhibit circuit means for enabling said trigger circuit means for automatic operation by said programmable variable trigger repetition rate control means under automatic to repetitive fire operating conditions and for inhibiting said trigger inhibit circuit means for operation only by a manually generated trigger signal developed through said manual-repetitive fire control circuit means manually by an operator of the equipment and time delay signal generating means coupled to and controlled by the output from said computation circuit means and coupled to and controlling operation of said SCR crowbar short circuiting means for maintaining said SCR crowbar short circuiting means conducting for a predetermined time interval following initiation of conduction thereof to allow adequate recover time for components of the pumping means following each operation thereof.

15. A pulsed laser system and control according to claim 14 wherein said laser beam heat sink is water cooled and the laser system further includes a coolant system for circulating cooling water through said laser beam heat sink and other ocmponents of the laser system including the laser cavity for temperature stabilizing purposes, coolant system monitoring means coupled to and minitoring operation of the coolant system for characteristics such as pressure of the coolant, temperature of the coolant, conductivity of the coolant, and the like, and coolant system protective means coupled to and controlled by said coolant system monitoring means for indicating the existence of a malfunction condition within the coolant system.

16. A pulsed laser system and control according to claim 1 wherein the photosensitive means responsive to a fractional portion of a laser beam for developing an output signal representative of the actual energy of the laser beam further includes summing circuit means responsive to the output signal from a photosensitive device and an input reference level signal representative of the desired energy level of the beam for deriving an output signal indicative of the magnitude and polarity of any difference, stepping motor means for driving a potentiometer that develops a semi-fixed feedback refeRence signal representative of the value of the laser beam energy and which is retained at a set value from one laser beam emission to the next, polarity sensitive circuit means responsive to the summing circuit means for enabling said stepping motor means to step the poteniometer up or down, and means for deriving a signal representative of the stepping action of the potentiometer for use in driving the magnitude of the error signal at the output of the summing amplifier means towards zero whereupon the stepping action of the stepping motor will be stopped, said means for deriving a signal representative of the stepping action of the potentiometer comprises bipolar staircase signal generator circuit means for generating either a positive polarity or negative polarity staircase waveform biasing signal with each step in the staircase waveform biasing signal corresponding to one stepping motion of the stepping motor means which in turn corresponds to an incremental adjustment to the potentiometer for deriving a semi-fixed feedback reference signal representative of the actual value of the laser beam energy, and means for applying the staircase biasing signal to a third summing input of said summing circuit means for driving the magnitude of the error output signal of the summing amplifier means towards zero.

17. A pulsed laser system and control according to claim 16 further including reset timing signal generating circuit means responsive to an input timing signal that anticipates the laser emission to be measured by a preset interval of time, said reset timing signal generating circuit means serving to amplify and develop a corresponding timing signal for application to the bipolar staircase biasing signal generator means to reset the bipolar staircase generating circuit means to zero in advance of a laser emission to be measured, photosensitive device switching circuit means connected intermediate the output of the photosensitive device and the summing input of the summing circuit means for connecting the output of the photosensitive device to the input of the summing circuit means only during intervals while a laser emission is anticipated, and delayed timing pulse signal generating circuit means comprising a part of said reset timing signal generating circuit means and triggered thereby for supplying an enabling switching signal of predetermined time duration to said photosensitive switching circuit means for closing the same during the predetermined time duration while a pulsed laser emission is anticipated and following reset of the staircase signal generating circuit means, and wherein said polarity sensitive circuit means is responsive only to error output signals from said summing circuit means in excess of predetermined limiting minimum voltage values above and below zero value, and the controller further includes threshold detector circuit means connected to the output from said summing circuit means and responsive only to output error voltages in excess of predetermined maximum limiting voltage values above and below zero for deriving a disabling switching signal, and disabling protective switching circuit means responsive to the output from said threshold detector circuit means for disabling said energy controller upon the sensed actual energy of the laser beam exceeding the threshold values established by said threshold detector circuit means.

18. A pulsed laser system and control according to claim 17 wherein the photosensitive device comprises a photodiode and further including integrating circuit means responsive to the output from said photodiode for converting the photodiode current to a voltage value proportional to energy, said integrating circuit means including reset switching means responsive to the output from said reset timing circuit generator circuit means and operative synchronously with the resetting operation of the bipolar staircase signal generating means to reset the integrating circuit to zero prior to each measurement of the actual energy leVel of a laser beam emission, and output meter indicating means calibrated in joules of energy responsive to the output from said integrating circuit means for providing an operator of the equipment with a visible output indication of the actual measured energy level of the laser beam emission, and clock pulse signal generating means for deriving a synchronizing clock pulse signal and means for supplying said synchronizing clock pulse signal to said staircase signal generating circuit means and to said stepping motor means for synchronizing the operation thereof.

19. A pulsed laser system and control according to claim 18 wherein said laser emission sensing photodiode is connected in series circuit relationship with a battery source of direct current bias potential and an adjustable resistor for adjusting the dark current output from the photodiode, the series circuit thus comprised being coupled to the input of said integrating circuit means, and said integrating circuit means comprising a feedback amplifier including an integrating capacitor coupled between its output and input terminals for integrating the input current supplied from the photodiode over the interval of a pulsed laser emission and converting the sensed photodiode current into an output voltage proportional to energy based on an energy level reference, clamping circuit means coupled across said feedback capacitor for clamping the feedback voltage between predetermined limits, said reset switching means for resetting the integrating circuit means to zero in advance of each laser emission measurement comprising relay actuated switch contacts connected in parallel circuit relationship with said feedback capacitor and serving to discharge the feedback capacitor in advance of a laser beam emission measurement and said output indicating meter means comprising a milliameter connected to the output of said feedback amplifier integrating circuit means through an adjustable resitor employed for calibration purposes.

20. A pulsed laser and control according to claim 19 wherein the monocyclic constant current charging networks comprises a three phase monocyclic constant current charging network and the power supply further comprises a three phase relay actuated contactor for supplying the monocyclic network from a conventional three phase source of electric current, a three phase voltage step-up transformer coupled to the output of the three phase monocyclic constant current charging network having primary and secondary windings for stepping-up the voltage to a desired level, said fast responding SCR crow bar short circuiting means comprising bidirectional conducting crow bar SCR'"'"''"'"'s connected across each of the three phase primary windings for quickly short-circuiting the primaries, SCR driver circuit means coupled to and controlling conduction of all of said bidirectional conducting SCR'"'"''"'"'s simultaneously and responsive to the output from said comparison circuit means for discontinuing charging from the power supply, and three phase, full-wave rectifier circuit means coupled to the secondary winding of the three phase voltage step-up transformer for supplying electric energy to an energy storage means being supplied.

21. A pulsed laser and control according to claim 3 wherein the monocyclic constant current charging network comprises a three phase monocyclic constant current charging network and the power supply further comprises a three phase relay actuated contactor for supplying the monocyclic network from a conventional three phase source of electric current, a three phase voltage step-up transformer coupled to the output of the three phase monocyclic constant current charging network having primary and secondary windings for stepping-up the voltage to a desired level, said fast responding SCR crow bar short circuiting means comprising bidirectional conducting crow bar SCR'"'"''"'"'s connected across each of the three phase primary windings for quickly short-circuiting the primaries, SCR driver circuit mEans coupled to and controlling conduction of all of said bidirectional conducting SCR'"'"''"'"'s simultaneously and responsive to the output from said comparison circuit means for discontinuing charging from the power supply, and three phase, full-wave rectifier circuit means coupled to the secondary winding of the three phase voltage step-up transformer for supplying electric energy to an energy storage means being supplied.

22. A pulsed laser system and control including in combination pumped laser means for producing a relatively high intensity laser beam of coherent light of high average energy which is variable over a predetermined range, pumping and resonator means coupled to the laser means for inducing emission of the laser beam at an energy level proportional to the energy level of the output emission from the pumping and resonator means, variable charge capacitor storage circuit means coupled to and supplying electric energy to said pumping and resonator means at a charge level that determines the energy level of the stimulated output laser beam, electric power supply means energized from a conventional source of an electric power and coupled to and supplying electric energy to said variable charge capacitor storage circuit means, charging level control circuit means coupled to said electric power supply mans for controlling the energy level to which the variable charge capacitor storage circuit means is charged, said electric power supply means comprising a voltage step-up transformer and high voltage rectifier circuit means, a low voltage monocyclic constant current charging network for supplying said variable charge capacitor storage circuit means through said voltage step-up transformer and high voltage rectifier circuit means, said charging level control circuit means comprising fast responding SCR crowbar short circuiting means coupled across the output from said low voltage monocyclic constant current charging network for short circuiting the output from the network to thereby discontinue in a fast responding manner the charging of the variable charge capacitor storage circuit means from the monocyclic constant current charging network, capacitor storage circuit energy level sensing means coupled to the variable charge capacitor storage circuit means for sensing the energy level to which the capacitor storage circuit means is charged, and feedback control circuit means coupled to and controlling the operation of said charging level control circuit means, said feedback control circuit means comprising comparison circuit means having the sensed energy level derived by said capacitor storage circuit energy level sensing means supplied thereto, laser beam sensing means for sensing the actual energy level of each laser beam emission and deriving a semi-fixed feedback reference signal proportional to the actual measured energy level of each laser beam emission, said semi-fixed feedback reference signal being retained at a set value from one laser beam emission to the next for use in controlling succeeding laser beam emissions, means for supplying the semi-fixed feedback reference signal from said laser bean sensing means to said comparison circuit means following each laser emission, and energy level selector programming means coupled to and supplying to said comparison circuit means a selected command value of laser beam energy for each emission of the laser beam, said comparison circuit means serving to compare the input commanded value for the laser beam emissions to the measured actual value of the laser beam energy level and to the sensed energy level to which the capacitor storage circuit means is charged, and deriving an output error signal for controlling the operation of the charging level control circuit means following each laser emission in a manner to maintain the actual measured energy level of the laser beam emissions at the command energy level value despite losses incurred in the system.

23. A pulsed laser system and control according to claim 22 wherein said laser beam sensing means comprises means disposed in the optical path of the laser beam for partially diverting a fractional portion of the laser beam, photosensitive means responsive to the diverted fractional portion of the laser beam for deriving a sensed actual laser beam energy feedback signal, and compensating circuit means responsive to the output from said photosensitive means and operative to modify the operation of the comparison circuit means in a direction and by a magnitude appropriate to modify the stored energy level in the variable charge capacitor storage circuit means so as to compensate for losses.

24. A pulsed laser system and control according to claim 23 wherein said compensating circuit means further includes a laser beam measured energy feedback reference signal deriving means for deriving a semi-fixed feedback reference signal representative of the value of the laser beam measured energy and which is retained at a set value from one laser beam emission to the next for use in compensating the output derived from said comparison circuit means, said laser beam measured energy feedback reference signal deriving means being coupled to and controlled by said photosensitive means.

25. A pulsed laser system and control according to claim 23 wherein said photosensitive means comprises a photodiode and said laser beam measured energy feedback reference signal deriving means comprises integrating circuit means coupled to said photodiode for converting the photodiode current to a voltage proportionate to the energy of the laser beam, summing amplifier means responsive to the output from the integrating circuit means and an input reference level signal representative of the desired energy level of the beam for deriving an output signal indicative of the magnitude and polarity of any difference, stepping motor means driving a potentiometer that develops the semi-fixed feedback reference signal representative of the value of the laser beam energy and which is retained at a set value from one laser beam emission to the next, polarity sensitive circuit means responsive to the summing circuit means for enabling said stepping motor means to step the potentiometer up or down, and means for deriving a signal representative of the stepping action of the potentiometer for use in driving the magnitude of the error signal at the output of the summing amplifier means towards zero whereupon the stepping action of the stepping motor will be stopped.

26. A pulsed laser system and control according to claim 25 wherein the means for deriving a signal representative of the stepping action of the potentiometer comprises bipolar staircase signal generator circuit means for generating either a positive polarity or negative polarity staircase waveform biasing signal with each step in the staircase waveform biasing signal corresponding to one stepping motion of the stepping motor means which in turn corresponds to an incremental adjustment to the potentiometer deriving a semi-fixed feedback reference signal representative of the actual value of the laser beam energy, means for applying the staircase biasing signal to a third summing input of said summing circuit means for driving the magnitude of the error output signal of the summing amplifier means towards zero, reset timing signal generating circuit means responsive to an input timing signal that anticipates the laser emission to be measured by a preset interval of time, said reset timing signal generating circuit means serving to amplify and develop a corresponding timing signal for application to the bipolar staircase biasing signal generator means to reset the bipolar staircase generating circuit means to zero in advance of a laser emission to be measured, photosensitive device switching circuit means connected intermediate the output of the photosensitive device and the summing input of the summing circuit means for connecting the output of the photosensitive device to the input of the summing circuit means onlY during intervals while a laser emission is anticipated, and delay timing pulse signal generating circuit means and triggered thereby for supplying an enabling switching signal of predetermined time duration to said photosensitive switching circuit means for closing the same during the predetermined time duration while a pulsed laser emission is anticipated and following reset of the staircase signal generating circuit means.

27. A pulsed laser system and control according to claim 26 wherein said polarity sensitive circuit means is responsive to the error output signal from said summing circuit means in excess of predetermined limiting minimum voltage values above and below zero value, and the controller further includes threshold detector circuit means connected to the output from said summing circuit means and responsive only to output error voltages in excess of predetermined maximum limiting voltage values above and below zero for deriving a disabling switching signal, and disabling protective switching circuit means responsive to the output from said threshold detector circuit means for disabling said energy controller upon the sensed actual energy of the laser beam exceeding the threshold values established by said threshold detector circuit means, and wherein the photosensitive device comprises a photodiode and further including integrating circuit means responsive to the output from said photodiode for converting the photodiode current to a voltage value proportional to energy, said integrating circuit means including reset switching means responsive to the output from said reset timing circuit generator circuit means and operative synchronously with the resetting operation of the bipolar staircase signal generating means to reset the integrating circuit to zero prior to each measurement of the actual energy level of a laser beam emission, and output meter indicating means calibrated in joules for providing an operator of the equipment with a visible output indication of the actual measured energy level of the laser beam emission.

28. A pulsed laser system and control according to claim 27 further including analog computation circuit means coupled intermediate the output from said integrating circuit means and the input to the summing circuit means for converting the output voltage proportional to actual measured energy derived from the output of said integrating circuit means and which is in essence an energy level reference signal to a voltage reference level signal by deriving the square root value of the energy level reference signal derived by said integrating circuit means, clock pulse signal generating means for deriving a synchronizing clock pulse signal and means for supplying said synchronizing clock pulse signal to said staircase signal generating circuit means and to said stepping motor means for synchronizing the operation thereof, said laser emission sensing photodiode is connected in series circuit relationship with a battery source of direct current bias potential and an adjustable resistor for adjusting the dark current output from the photodiode, the series circuit thus comprised being coupled to the input of said integrating circuit means, and said integrating circuit means comprising a feedback amplifier including an integrating capacitor coupled between its output and input terminals for integrating the input current supplied from the photodiode over the interval of a pulsed laser emission and converting the sensed photodiode current into an output voltage proportional to energy based on an energy level reference, clamping circuit means coupled across said feedback capacitor for clamping the feedback voltage between predetermined limits, said reset switching means for resetting the integrating circuit means to zero in advance of each laser emission measurement comprising relay actuated switch contacts connected in parallel circuit relationship with said feedback capacitor and serving to dishcarge the feedback capacitor in advance of a laser beam emission measurement and said output indicating means comprising a multiameter connected to the output of said feedback amplifier integrating circuit means through an adjustable resistor employed for calibration purposes, and separate reference level signal generating circuit means under the control of an operator of the equipment and/or susceptible to automatic program control for generating the desired input reference level signal representative of the desired energy level of the laser beam for supply to the summing circuit means.