Q-switched cavity dumped CO2 laser for material processing

• US 20020167974A1
• Filed: 04/04/2002
• Published: 11/14/2002
• Est. Priority Date: 04/04/2001
• Status: Active Grant

• Current Assignee: Coherent Inc (Coherent Corp.)
• Original Assignee: Coherent Inc (Coherent Corp.)
• Inventors: Kennedy, John T., Fontanella, Joel, Laughman, Lanny, Newman, Leon A., Henschke, Robert, Hart, Richard A., Demaria, Anthony J.
• Granted Patent: US 6,697,408 B2
• Time in Patent Office: Days
• US Class Current: 372/10
• CPC Class Codes: H01S 3/03 of gas laser discharge tubes
• CPC Class Codes: H01S 3/0315 Waveguide lasers
• CPC Class Codes: H01S 3/0813 Configuration of resonator
• CPC Class Codes: H01S 3/097 by gas discharge of a gas laser
• CPC Class Codes: H01S 3/09702 Details of the driver electronics and electric discharge circuits
• CPC Class Codes: H01S 3/1061 using a variable absorption device
• CPC Class Codes: H01S 3/1075 for optical deflection
• CPC Class Codes: H01S 3/1103 Cavity dumping
• CPC Class Codes: H01S 3/115 using intracavity electro-optic devices
• CPC Class Codes: H01S 3/2232 Carbon dioxide (CO2) or monoxide [CO]
• CPC Class Codes: H01S 3/2325 Multi-pass amplifiers, e.g. regenerative amplifiers
• CPC Class Codes: H01S 3/2366 comprising a gas as the active medium H01S3/10092, H01S3/2383 take precedence

Abstract

This disclosure discusses techniques for obtaining wavelength selected simultaneously super pulsed Q-switched and cavity dumped laser pulses utilizing high optical damage threshold electro-optic modulators, maintaining a zero DC voltage bias on the CdTe electro-optic modulator (EOM) so as to minimize polarization variations depending on the location of the laser beam propagating through the CdSe EOM crystal, as well as the addition of one or more laser amplifiers in a compact package and the use of simultaneous gain switched, Q-switched and cavity dumped operation of CO₂ lasers for generating shorter pulses and higher peak power for the hole drilling, engraving and perforation applications.

Claims

1. A Q-switched, cavity dumped CO₂ laser system for material processing, the system comprising:

a plurality of mirrors defining an optical cavity;

a gain medium positioned within the optical cavity for generating laser beam radiation;

a cavity loss modulator for switching loss within the cavity from a high loss state to a low loss state or a low loss state to a high loss state, generating thereby one or more laser pulses;

a pulsed signal generation system connected to the cavity loss modulator for delivering pulsed signals to the cavity loss modulator thereby controlling the state of optical loss within the optical cavity;

a control unit connected to the pulsed signal generation system for controlling the pulsed signal generation system;

a time delay circuit receptive of a portion of the laser beam and connected to the pulsed signal generation system for timing the relative occurrence of the pulsed signals delivered to the cavity loss modulator by the pulsed signal generation system and the maximum build up of radiation within the optical cavity; and

a laser beam output coupler receptive of the laser beam and operative to direct laser pulses out of the optical cavity when the optical cavity is in a high optical loss condition.

2. The laser system as set forth in claim 1 further comprising:

a polarization rotator receptive of the laser pulses directed out of the optical cavity and operative to rotate the state of polarization of the laser beam; and

an amplifier receptive of the laser pulses from the polarization rotator for amplifying the laser pulses.

3. The laser system as set forth in claim 2 further comprising a reflective device receptive of the laser pulses directed out of the optical cavity and operative to direct said laser pulses to the polarization rotator.

4. The laser system as set forth in claim 2 further comprising a heat exchanger positioned between the gain medium and the amplifier for conducting heat away from the gain medium and the amplifier.

5. The laser system as set forth in claim 1 wherein the time delay circuit comprises:

a detector receptive of the portion of the laser beam providing thereby an output signal indicative of the laser pulses;

a bias circuit providing as output a reference signal;

a comparator for comparing the output signal of the detector with the reference signal providing thereby an output signal indicative of the greater or lesser of the detector output signal or the reference signal; and

a first timing device receptive of the comparator output signal and operative to provide a command signal to the pulsed signal generation system for controlling the duration of the pulsed signals delivered to the cavity loss modulator.

6. The laser system as set forth in claim 5 further comprising a signal amplifier receptive of the detector output signal providing thereby an amplified detector output signal to the comparator.

7. The laser system as set forth in claim 5 wherein the bias circuit comprises a DC voltage.

8. The laser system as set forth in claim 7 wherein the bias circuit further comprises:

a signal generator generating a ramp signal;

a summing device for summing the ramp signal and the DC voltage.

9. The laser system as set forth in claim 8 further comprising a second timing device receptive of a signal commanding the laser to emit a pulse and operative to provide as output:

a first signal to generate the ramp signal;

a second signal to energize the cavity loss modulator; and

a default signal directed to the first timing device to deenergize the cavity loss modulator in the event that the command signal from the first timing device is not generated when the output signal of the detector indicative of the laser pulses is greater than or equal to the reference signal.

10. The laser system as set forth in claim 1 further comprising a system for automatically terminating the generation of the laser beam including:

a first polarizing device receptive of the laser beam in a first state of polarization and operative to pass the laser beam in the first state of polarization;

a polarization rotator receptive of the laser beam from the first polarizing device in the first state of polarization and operative to change the polarization of the laser beam to a second state of polarization and further operative to direct the laser beam to a workpiece;

wherein the polarization rotator is receptive of the laser beam reflected from the work piece in the second state of polarization and operative thereby to change the state of polarization of the laser beam to a third state of polarization; and

wherein the first polarization device is receptive of the laser beam from the polarization rotator in the third state of polarization;

a detector receptive of the laser beam from the first polarizing device providing thereby an output signal indicative of the reflectance of the work piece; and

a comparator for comparing the output signal of the detector with a reference signal, providing thereby an output signal indicative of the greater or lesser of the detector output signal or the reference signal.

11. The laser system as set forth in claim 10 further comprising a bias circuit for setting the value of the reference signal.

12. The laser system as set forth in claim 10 further comprising a lens for focusing the laser beam from the polarization rotator in the first state of polarization to the work piece and receptive of the laser beam reflected from the work piece.

13. The laser system as set forth in claim 10 further comprising a signal amplifier receptive of the detector output signal and providing thereby an amplified detector output signal.

14. The laser system as set forth in claim 10 further comprising a logic circuit receptive of the comparator output signal and a command signal from the control unit to Q-switch the laser.

15. The laser system as set forth in claim 14 wherein the logic circuit comprises:

a signal inverter for inverting the comparator output signal; and

a logical AND gate receptive of the inverted comparator signal and the command pulse providing thereby an output stop signal to the pulsed signal generation system.

16. The laser system as set forth in claim 10 further comprising a second polarizing device receptive of the laser beam from the first polarizing device in the first state of polarization and operative to pass the laser beam in the first state of polarization and further receptive of the laser beam from the polarization rotator in the third state of polarization and further operative thereby to reflect polarization components of the laser beam in the third state of polarization to the detector;

wherein the second polarizing device is rotatable with respect to the first polarizing device to attenuate the laser beam.

17. The laser system as set forth in claim 1 wherein the pulsed signal generation system comprises:

a switching circuit receptive of pulsed signals from the pulse receiver operative thereby to charge or discharge the cavity loss modulator a pulse receiver providing commands to the switching circuit; and

a power supply for the pulse receiver and the switching circuit.

18. The laser system as set forth in claim 17 wherein the power supply comprises:

a power converter connected to the switching circuit and receptive of a constant voltage input signal providing thereby a high voltage output signal to the switching circuit;

a power supply controller for controlling the power converter and receptive of a low voltage set point signal;

a voltage divider connected to the power converter at the high voltage output signal and to the power controller at the divided voltage and operative thereby to minimize the difference between the high voltage output signal and the low voltage set point.

19. The laser system as set forth in claim 1 further comprising a phase grating receptive of the laser beam and operative to diffract a portion of the laser beam away from the laser beam at a prescribed optical diffraction order.

20. The laser system as set forth in claim 19 wherein the phase grating comprises an acousto-optic cell connected to a signal generator receptive of a pulsed signal from the control unit and operative to generate an acoustically variable phase grating in the acousto-optic cell.

21. The laser system as set forth in claim 20 further comprising a signal delay device receptive of the pulsed signal from the control unit providing a delayed signal to the pulsed signal generation system for synchronizing the acoustically variable phase grating and the laser pulses.

22. The laser system as set forth in claim 17 wherein the switching circuit comprises:

a first switch connected to the power supply and to the cavity loss modulator receptive of a first pulsed signal from the pulse receiver and operative thereby to charge the cavity loss modulator when the first switch is in the closed position;

a second switch connected across the cavity loss modulator and receptive of a second pulsed signal from the pulse clipping circuit and operative thereby to discharge the cavity loss modulator when the second switch is in the closed position.

23. The laser system as set forth in claim 22 further including an impedance connected to the first and second switch and the cavity loss modulator.

24. The laser system as set forth in claim 23 further comprising an amplifier-control circuit for amplifying and controlling the first and second pulsed signals to the first and second switch.

25. The laser system as set forth in claim 22 wherein the first and second switch comprise a metal oxide semiconductor field effect transistor connected to a transformer.

26. The laser system as set forth in claim 25 further comprising an impedance connected across the first and second switches.

27. The laser system as set forth in claim 1 wherein the mirrors are substantially one hundred percent reflecting mirrors.

28. The laser system as set forth in claim 27 farther comprising:

a first polarizing device positioned within the optical cavity and receptive of the laser beam for polarizing the laser beam; and

a polarization rotator positioned within the optical cavity and receptive of the laser beam for changing the polarization of the laser beam.

29. The laser system as set forth in claim 28 wherein the polarization rotator is operative to change the polarization of the laser beam from a first state of polarization to a second state of polarization and from the second state of polarization to a third state of polarization.

30. The laser system as set forth in claim 29 wherein the polarization rotator is operative to change the polarization of the laser beam from a first state of polarization to a second state of polarization and from the second state of polarization to a third state of polarization when no pulsed signals are delivered to the cavity loss modulator by the pulsed signal generation system.

31. The laser system as set forth in claim 29 wherein the polarization rotator is operative to change the polarization of the laser beam from the third state of polarization to the second state of polarization when a non-zero pulsed signal is delivered to the cavity loss modulator by the pulsed signal generation system.

32. The laser system as set forth in claim 28 wherein the first polarizing device is a thin film polarizer operative to allow passage of the laser beam therethrough in a first direction within the optical cavity when in the first state of polarization and to reflect the laser beam in a second direction within the optical cavity when in the third state of polarization when the optical cavity is in a high optical loss condition and further operative to allow passage of the laser beam therethrough in the first and second direction within the optical cavity when the optical cavity is in a low optical loss condition.

33. The laser system as set forth in claim 28 wherein the polarization rotator is a quarter wave plate.

34. The laser system as set forth in claim 28 wherein the polarization rotator is a reflective phase retarder.

35. The laser system as set forth in claim 1 wherein the cavity loss modulator comprises:

an optical crystal having an entrance surface receptive of the laser beam and an opposing laser beam exit surface;

a first optical window having an optical entrance surface receptive of the laser beam and an opposing laser beam exit surface, the exit surface of the first optical window being in physical contact with the entrance surface of the optical crystal thereby defining a first optical interface; and

an optical reflector in physical contact with the laser beam exit surface of the active optical crystal thereby defining a second optical interface, the optical reflector receptive of the laser beam from the optical crystal and operative to redirect the laser beam into the active optical crystal.

36. The laser system as set forth in claim 35 wherein the optical reflector comprises a prism.

37. The laser system as set forth in claim 35 wherein the optical reflector comprises a second optical window having an optical entrance surface receptive of the laser beam and an opposing reflective surface, the entrance surface of the second optical window being in physical contact with the exit surface of the active optical crystal thereby defining a second optical interface.

38. The laser system as set forth in claim 37 wherein the reflective surface comprises a reflecting thin film coating.

39. The laser system as set forth in claim 1 wherein the optical cavity includes a multiple pass optical assembly for directing the laser beam through the cavity loss modulator multiple times.

40. The laser system as set forth in claim 39 wherein the multiple pass optical assembly comprises:

a first reflective device positioned within the optical cavity and receptive of the laser beam from the cavity loss modulator and operative to redirect the laser beam into the cavity loss modulator; and

a second reflective device positioned within the optical cavity and receptive of the laser beam from the cavity loss modulator and an optical cavity mirror and operative to redirect the laser beam into the cavity loss modulator.

41. The laser system as set forth in claim 40 further comprising:

a first polarizing device positioned within the cavity for polarizing the laser beam; and

a second polarizing device positioned within the cavity for changing the polarization of the laser beam.

42. The laser system as set forth in claim 40 wherein the first reflective device is a reflecting thin film or a prism.

43. The laser system as set forth in claim 40 wherein the second reflective device is a mirror.

44. The laser system as set forth in claim 41 wherein the first polarizing device is a thin film polarizer.

45. The laser system as set forth in claim 41 wherein the second polarizing device is a reflective phase retarder.

48. The method as set forth in claim 47 wherein maintaining zero voltage across the electro-optic crystal during the high optical loss interval of the Q-switching cycle includes:

changing the first state of polarization to a second state of polarization; and

changing the second state of polarization to a third state of polarization.

49. The method as set forth in claim 47 wherein maintaining a prescribed non-zero voltage across the electro-optic crystal during the low optical loss interval of the Q-switching cycle includes:

changing the first state of polarization to a second state of polarization; and

changing the second state of polarization to a third state of polarization;

changing the third state of polarization to the second state of polarization; and

changing the second state of polarization to the first state of polarization.

50. The method as set forth in claim 48 wherein the first state of polarization is a linear state of polarization and the second state of polarization is a circular state of polarization and the third state of polarization is a linear state of polarization perpendicular to the first state of polarization.

51. The method as set forth in claim 49 wherein the first state of polarization is a linear state of polarization and the second state of polarization is a circular state of polarization and the third state of polarization is a linear state of polarization perpendicular to the first state of polarization.

52. The method as set forth in claim 48 including:

propagating the laser beam in the first state of polarization through a first polarizing device;

propagating the laser beam through the electro-optic crystal a first time;

propagating the laser beam through a second polarizing device;

reflecting the laser beam in the second state of polarization from a reflecting device;

propagating the laser beam through the second polarizing device a second time; and

propagating the laser beam in a third state of polarization through the electro-optic crystal a second time;

reflecting the laser beam in the third state of polarization from the first polarizing device.

53. The method as set forth in claim 49 including:

propagating the laser beam in the first state of polarization through a first polarizing device;

propagating the laser beam through the electro-optic crystal a first time;

propagating the laser beam in the second state of polarization through a polarization rotator;

reflecting the laser beam in the third state of polarization from a reflecting device;

propagating the laser beam through the polarization rotator a second time;

propagating the laser beam in the second state of polarization through the electro-optic crystal a second time; and

propagating the laser beam through the first polarizing device in the first state of polarization.

54. The method as set forth in claim 47 further comprising alternately switching the voltage across the electro-optic crystal from a zero voltage during the high optical loss interval of the Q-switching cycle to a non-zero voltage during the low optical loss interval of the Q-switching cycle.

62. The laser system as set forth in claim 17 further comprising means for manually controlling the power from the power supply to the switching circuit.

63. The laser system as set forth in claim 62 wherein means for controlling the power from the power supply to the switching circuit comprises a potentiometer.

64. The laser system as set forth in claim 1 further comprising:

a sealed laser head including a waveguide plate positioned within the optical cavity, the waveguide plate including a plurality of waveguide channels arranged in a zig-zag folded pattern for guiding the laser beam therealong between the plurality of mirrors;

a housing housing the plurality of mirrors, the gain medium, the cavity loss modulator, the pulsed signal generation system, the pulse clipping circuit, the sealed laser head and the laser beam output coupler;

a radio frequency power supply;

a first electrode in contact with the radio frequency power supply and with the waveguide plate;

a second, low particulate generating, electrode in contact with gain medium within the waveguide channels;

a heat exchanger in thermal contact with the second electrode for conducting heat away from the waveguide plate.

65. The laser system as set forth in claim 64 further comprising a shutter connected to the control unit operative to block passage of the laser beam.

66. The laser system as set forth in claim 64 further comprising a polarizing device 114 for polarizing the laser beam.

67. The laser system as set forth in claim 64 wherein the plurality of mirrors are wavelength selective mirrors comprising:

a plurality of feedback mirrors having high reflectance at lasing wavelengths and receptive of the laser beam providing thereby optical feedback to the laser cavity;

a plurality of high reflectance laser beam turning mirrors for directing the laser beam along the waveguide channels.

69. The laser system as set forth in claim 68 wherein the electro-optic crystal comprises an optically polished Cadmium Teluride crystal.

70. The laser system as set forth in claim 68 wherein the first and second optical windows comprise optically polished Zinc Selinide windows.

71. The laser system as set forth in claim 68 wherein the first and second optical windows include anti-reflection coatings on the outer surfaces thereof.

72. The laser system as set forth in claim 68 further comprising:

a housing having an interior volume enclosing the electro-optic crystal and the first and second conductive electrodes;

a retaining device positioned within the interior volume to retain the electro-optic crystal and the first and second conductive electrodes fixed within the interior volume;

a cushioning device enveloping the electro-optic crystal to absorb acoustic energy of the electro-optic crystal, the cushioning device positioned between the housing and the electro-optic crystal and between the first and second conductive electrodes and the electro-optic crystal.

73. The laser system as set forth in claim 72 wherein the cushioning device comprises an Indium strip.

74. The laser system as set forth in claim 72 wherein the retaining device comprises a dielectric material.

75. The laser system as set forth in claim 72 further comprising a plurality of spring loaded screws for adjusting the retention of the retaining device.

84. The laser system as set forth in claim 1 further comprising a system for automatically terminating the generation of the laser beam including:

a first polarizing device receptive of the laser beam in a first state of polarization and operative to pass the laser beam in the first state of polarization;

a second polarizing device receptive of the laser beam from the first polarizing device operative to pass the laser beam in the first state of polarization;

a polarization rotator receptive of the laser beam from the second polarizing device in the first state of polarization and operative to change the polarization of the laser beam to a second state of polarization and further operative to direct the laser beam to a workpiece;

wherein the polarization rotator is receptive of the laser beam reflected from the work piece in the second state of polarization and operative thereby to change the state of polarization of the laser beam to a third state of polarization; and

wherein the second polarizing device is receptive of the laser beam from the polarization rotator in the third state of polarization and operative thereby to direct the laser beam reflected from the workpiece away from the optical cavity;

a detector receptive of the laser beam from the second polarizing device providing thereby an output signal indicative of the reflectance of the work piece; and

a comparator for comparing the output signal of the detector with a reference signal, providing thereby an output signal indicative of the greater or lesser of the detector output signal or the reference signal.

85. The laser system as set forth in claim 84 further comprising a bias circuit for setting the value of the reference signal.

86. The laser system as set forth in claim 84 further comprising a lens for focusing the laser beam from the polarization rotator in the first state of polarization to the work piece and receptive of the laser beam reflected from the work piece.

87. The laser system as set forth in claim 84 further comprising a signal amplifier receptive of the detector output signal and providing thereby an amplified detector output signal.

88. The laser system as set forth in claim 84 further comprising a logic circuit receptive of the comparator output signal and a command signal from the control unit to Q-switch the laser.

89. The laser system as set forth in claim 88 wherein the logic circuit comprises:

a signal inverter for inverting the comparator output signal; and

a logical AND gate receptive of the inverted comparator signal and a command pulse providing thereby an output signal to the pulsed signal generation system.

90. The laser system as set forth in claim 84 further comprising a second polarizing device receptive of the laser beam from the first polarizing device in the first state of polarization and operative to pass the laser beam in the first state of polarization and further receptive of the laser beam from the polarization rotator in the third state of polarization and further operative thereby to direct the laser beam reflected from the workpiece away from the optical cavity.

93. The laser system as set forth in claim 8 wherein the ramp signal has a positive slope or a negative slope or is a decaying exponential.

94. The method as set forth in claim 48 including:

propagating the laser beam in the first state of polarization through a first polarizing device;

propagating the laser beam through the electro-optic crystal a first time;

reflecting the laser beam from a polarization rotator;

reflecting the laser beam in the second state of polarization from a reflecting device;

reflecting the laser beam from the polarization rotator a second time; and

propagating the laser beam in a third state of polarization through the electro-optic crystal a second time; and

reflecting the laser beam in the third state of polarization from the first polarizing device.

95. The method as set forth in claim 49 including:

propagating the laser beam in the first state of polarization through a first polarizing device;

propagating the laser beam through the electro-optic crystal a first time;

reflecting the laser beam in the second state of polarization from a polarization rotator;

reflecting the laser beam in the third state of polarization from a reflecting device;

reflecting the laser beam from the polarization rotator a second time;

propagating the laser beam in the second state of polarization through the electro-optic crystal a second time; and

propagating the laser beam through the first polarizing device in the first state of polarization.

98. The laser system as set forth in claim 1 further comprising:

a sealed laser head;

a second plurality of mirrors within the sealed laser head for guiding the laser beam along a folded zig-zag optical path;

a housing for housing the plurality of mirrors, the gain medium, the cavity loss modulator, the pulsed signal generation system, the time delay circuit and the sealed laser head;

a radio frequency power supply;

first and second electrodes in contact with the radio frequency power supply energizing the gain medium; and

a heat exchanger for conducting heat away from the gain medium.

46. A method of maintaining constant phase retardation induced in a laser beam by an electro-optic crystal in a repetitively Q-switched, cavity dumped material processing CO₂ laser, the method comprising:

maintaining zero voltage across the electro-optic crystal during the high optical loss interval of the Q-switching cycle; and

maintaining a prescribed non-zero voltage across the electro-optic crystal during the low optical loss interval of the Q-switching cycle.

47. A method of cavity dumping a laser pulse out of an optical cavity in a material processing CO₂ laser having an electro-optically modulated crystal, the method comprising:

generating a laser beam in a first state of polarization;

maintaining zero voltage across the electro-optic crystal during a high optical loss interval of a Q-switching cycle; and

maintaining a prescribed non-zero voltage across the electro-optic crystal during a low optical loss interval of a Q-switching cycle.

55. A method of operating a Q-switched, cavity dumped CO₂ laser for material processing, the laser having a gain medium and a cavity loss modulator, the method comprising:

energizing the gain medium for a first prescribed time duration 602;

with a radio frequency pulse having a power equal to an integer multiple of a maximum average radio frequency power; and

energizing the cavity loss modulator for a second prescribed time duration 604 causing the laser cavity to switch from a high optical loss state to a low optical loss state generating thereby one or more laser pulses;

wherein energizing the cavity loss modulator occurs after a third time duration of one to two population decay times of the upper laser level of the gain medium measured from first energizing of the gain medium.

56. The method as set forth in claim 55 wherein energizing the gain medium for a first prescribed time duration comprises energizing the gain medium for a first prescribed duty cycle wherein the amount of power of the radio frequency pulse applied to the gain medium is approximately equal to the maximum average radio frequency power divided by the duty cycle.

57. The method as set forth in claim 55 wherein energizing the cavity loss modulator for a second prescribed time duration comprises alternately energizing and deenergizing the cavity loss modulator.

58. The method as set forth in claim 57 wherein alternately energizing and deenergizing the cavity loss modulator comprises alternately energizing and denergizing the cavity loss modulator during the first prescribed time duration.

59. The method as set forth in claim 55 further comprising varying the third time duration.

60. The method as set forth in claim 59 wherein alternately energizing and deenergizing the cavity loss modulator comprises increasing subsequent energizing amplitudes of the energization of the cavity loss modulator a prescribed number of times during the first prescribed time duration.

61. A method of controlling the amplitude of the output pulses of a repetitively Q-switched, cavity dumped CO₂ laser including a diffraction grating for material processing, the method comprising:

diffracting a portion of the laser output pulses into a diffraction side order; and

varying the amplitude of the diffraction grating.

68. The laser system as set forth in claim 61 wherein the cavity loss modulator comprises:

first and second optical windows having a prescribed refractive index and receptive of the laser beam;

an electro-optic crystal having a laser beam entrance surface and a laser beam exit surface;

wherein the electro-optic crystal possesses a refractive index substantially equivalent to the refractive index of the first and second optical windows;

wherein the electro-optic crystal is positioned between and in optical and thermal contact with the first and second optical windows at the laser beam entrance and exit surfaces creating thereby first and second optical interfaces;

a first conductive electrode connected to the electro-optic crystal and to electrical ground;

a second conductive electrode connected to the electro-optic crystal and to a voltage source creating thereby a voltage across the electro-optic crystal.

76. An electro-optic modulator comprising:

first and second optical windows having a prescribed refractive index and receptive of the laser beam;

an electro-optic crystal having a laser beam entrance surface and a laser beam exit surface;

wherein the electro-optic crystal possesses a refractive index substantially equivalent to the refractive index of the first and second optical windows;

wherein the electro-optic crystal is positioned between and in optical and thermal contact with the first and second optical windows at the laser beam entrance and exit surfaces creating thereby first and second optical interfaces;

a first conductive electrode connected to the electro-optic crystal and to electrical ground;

a second conductive electrode connected to the electro-optic crystal and to a voltage source creating thereby a voltage across the electro-optic crystal; and

an Indium cushioning device for absorbing energy of the electro-optic crystal.

77. The electro-optic modulator as set forth in claim 76 wherein the electro-optic crystal comprises an optically polished Cadmium Teluride crystal.

78. The electro-optic modulator as set forth in claim 76 wherein the first and second optical windows comprise optically polished Zinc Selinide windows.

79. The electro-optic modulator as set forth in claim 76 wherein the first and second optical windows include anti-reflection coatings on the outer surfaces thereof.

80. The electro-optic modulator as set forth in claim 76 further comprising:

a housing having an interior volume enclosing the electro-optic crystal and the first and second conductive electrodes; and

a retaining device positioned within the interior volume to retain the electro-optic crystal and the first and second conducting electrodes fixed within the interior volume;

wherein the cushioning device envelopes the electro-optic crystal to absorb acoustic energy of the electro-optic crystal, the cushioning device positioned between the housing and the electro-optic crystal and between the first and second conductive electrodes and the electro-optic crystal.

81. The electro-optic modulator as set forth in claim 80 wherein the cushioning device comprises a thin strip.

82. The electro-optic modulator as set forth in claim 80 wherein the retaining device comprises a dielectric material.

83. The electro-optic modulator as set forth in claim 80 further comprising a plurality of spring loaded screws for adjusting the retention of the retaining device.

91. A method of Q-switch-cavity dumping a laser pulse out of an optical cavity in a material processing CO₂ laser having an electro-optically modulated crystal, the method comprising:

during a high optical loss condition within the laser, energizing the electro-optic crystal within the laser until the electro-optic crystal is fully charged;

allowing radiation to build up within the laser for a cavity build up time;

during a low optical loss condition within the laser generating a laser pulse;

confining the built up radiation within the laser cavity; and

deenergizing the electro-optic crystalat the maximum build up of radiation within the laser cavity.

92. The method as set forth in claim 91 further comprising:

truncating the radiation confined within the laser cavity; and

dumping the radiation confined within the laser cavity out of the laser cavity.

96. A Q-switched cavity dumped CO₂ laser system for material processing, the system comprising:

a folded waveguide laser having a plurality of wavelength selective mirrors defining an optical cavity;

a gain medium positioned within the optical cavity for generating a laser beam;

a cavity loss modulator for switching loss within the cavity from a high loss state to a low loss state or a low loss state to a high loss state , generating thereby one or more laser pulses;

a pulsed signal generation system connected to the cavity loss modulator for delivering pulsed signals to the cavity loss modulator thereby controlling the state of optical loss within the optical cavity;

a control unit connected to the pulsed signal generation system for controlling the pulsed signal generation system; and

a time delay circuit receptive of a portion of the laser beam and connected to the pulsed signal generation system for truncating a part of the laser pulses.

97. The laser system as set forth in claim 96 wherein the wavelength selective mirrors are thin film coated mirrors comprising:

an output coupling mirror having high transmission at non-lasing wavelengths for coupling the laser beam out of the optical cavity;

a plurality of laser beam turning mirrors having high reflectivity at lasing wavelengths for directing the laser beam between the waveguide channels; and

a feedback mirror providing optical feedback to the laser cavity.

99. A CO₂ laser system for material processing, the system comprising:

a folded waveguide laser having a plurality of wavelength selective mirrors defining an optical cavity;

a gain medium positioned within the optical cavity for generating a laser beam;

a cavity loss modulator for switching loss within the cavity from a high loss state to a low loss state or a low loss state to a high loss state , generating thereby one or more laser pulses;

a pulsed signal generation system connected to the cavity loss modulator for delivering pulsed signals to the cavity loss modulator thereby controlling the state of optical loss within the optical cavity; and

a control unit connected to the pulsed signal generation system for controlling the pulsed signal generation system