Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B41/00—Circuit arrangements or apparatus for igniting or operating discharge lamps
  • H05B41/14—Circuit arrangements
  • H05B41/30—Circuit arrangements in which the lamp is fed by pulses, e.g. flash lamp
  • H05B41/34—Circuit arrangements in which the lamp is fed by pulses, e.g. flash lamp to provide a sequence of flashes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/09—Processes or apparatus for excitation, e.g. pumping
  • H01S3/097—Processes or apparatus for excitation, e.g. pumping by gas discharge of a gas laser

Definitions

• Lasing action in a system is obtained by subjecting a gas-filled vessel or channel to an electric discharge - the electrons provided by the discharge collide with active gas molecules thereby exciting them to higher energy levels, from which they descent to lower energy levels and emit excess energy in the form of photons, or light quanta.
• the population density of particles in the higher energy level must exceed that in the lower energy level to achieve optical gain. This population inversion is the opposite of the natural state.
• a discharge normally, has a very thin diameter because -the heat transfer rates in different parts of the discharge are not uniform, and result in lower press ⁇ ure and density at the inside of the plasma column, thus constricting the column.
• the first listed patent to Hill reveals a high power C02 pulse laser wherein the required pulse voltage is in the order of 200 KV to 1 MV.
• the inven ⁇ tion to be later described herein provides a circuit for use with a high power C02 pulse laser and distinguish ⁇ es from the above identified patent by providing a low level ionization sustaining voltage to the laser elec ⁇ trodes and to superimpose short-time voltage pulse onto the low level ionization voltage.
• the pulse volt ⁇ age required to develop similar pulsed plasma current is much smaller than the above listed voltage range. This reduction in magnitude of voltage yields circuit param- eters which can easily be used in an industrial environ- ment.
• the uniformly distributed ionization provided by the co-pending patent application identified above provides a more uniform-pulsed plasma current distribu ⁇ tion and is stable over a longer pulse period. This results in greater achievable pulsed output power with a superior optical mode quality over that which could be achieved using the first listed patent.
• the second listed patent to Hill relates to a method of ballasting a gaseous discharge-tube system wherein a plurality of tubes are excited from a single power source.
• the third listed patent teaches the use of aerodynamic forces to control the spatial distribution of charge in a laser system to obtain a uniform plasma.
• the fourth listed patent also shows the use of aerodynamic forces to obtain uniform plasma in a laser system.
• the single figure shows a schematic circuit for the control of a laser system including a mode selector, whereby the laser operator can selectively operate the laser in the continuous mode* or the pulse mode or any combination.
• a second power supply is connected in para ⁇ llel with a first power supply to superimpose a series of shor -time pulses on a relatively low level DC laser voltage which results in a short-time repetitive peak power laser output pulse many times greater than the normal continuous power output.
• the first power supply is infinitely variable so that pulse power may be super- imposed upon continuous power.
• reference character 10 indicates a first power supply for multi- electrode laser 12, as shown schematically.
• a plurality of laser anodes 14 are connected through ballast resis ⁇ tors 16, current regulator 18, and pulse blocking diode 20 to the positive terminal of variable voltage power supply 10.
• A- plurality of cathodes 22 are connected through ballast resistors 24 to the negative terminal of power supply.
• the positive terminal of auxiliary power supply 26 is connected to the negative terminal of power supply 10 and to ground. The purpose of power supply 26 is to insure that the cathodes 22 float negative with respect to ground to avoid backstreaming. This completes the first power supply.
• a second power supply is connected in parallel with the above described first power supply and com ⁇ prises a pulse forming network shown generally as refer ⁇ ence character 28 connected to the primary of step-up transformer 30.
• the pulse forming circuit comprises a plurality of parallel connected capacitors 32 and series connected inductance coils 34 connected between thyra- tron switch 36 and resonant charging system 38.
• the secondary of transformer 30 is connected at one end through blocking diodes 40 to the laser anodes 14 and at its other end through blocking diodes 42 to the laser cathodes 22 to complete the circuit.
• a laser operation mode selector shown generally as referenced character 50, is connected mechanically or electrically to control the infinitely variable voltage first power supply 10 which is symbolically represented by the arrow appearing thereon.
• the selector is electrically connected through trigger transformer 60 to the grid of thyratron 36 for a purpose that will later be explained.
• the mode selector is actuated by the laser operator to reduce the voltage output of first power supply 10 to a low level sufficient to maintain ionization in the laser at about the voltage glow state, and a voltage pulse is applied to the grid of thyratron 36 through transformer 60.
• the oper ⁇ ating characteristics of the thyratron tube was found useful to control the high energy short-time duration pulse needed. Gas-filled tubes generate their charge carriers from ionizing electron-molecule collisions which produce an electrically neutral plasma with electrons and posi ⁇ tive ions moving in opposite directions.
• Conduction may be held off by a control grid in the absence of current flow, but once switched on, the ions form a space charge around the grid which tries to go negative so that its controlling electric field is cancelled. This results in an out of control arc.
• the gas filled tubes provide on-switching capability of almost unlimited currents, but must be externally turned off until recombination dissipates the plasma. Only then may the control grid hold-off function be re-established.
• Statistical ioniza ⁇ tion processes can also be important when jitter require ⁇ ments are severe, or when trigger-to-breakdown times must be 0.5 nanosecond or less.
• the system can be gated by superim ⁇ posing a short-time voltage pulse through the thyratron tube circuit onto the low level voltage thus increasing the current and the output power many times for the duration of the pulse.
• the duration of the high current state is not long enough to develop instabilities in the discharge. For example, ? ⁇ _ 5 KW maximum continuous wave laser operated in this manner yields from zero to 5 KW average power; however, the peak power is many times greater than the above-mentioned continuous power.
• the pulse width can be about 30 microseconds at 1000 pulses per second (1000 PPS) yielding a peak power of perhaps 300 times the continuous power level.
• Adroit design of circuit parameters permits a pulse repetition rate as a function of pulse forming circuit charging time and thyratron grid pulse-application rate.

Landscapes

• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Optics & Photonics (AREA)
• Lasers (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=25257029

Family Applications (1)

Country Status (6)

Families Citing this family (1)

Citations (4)

• 1987
  • 1987-02-13 GB GB8722166A patent/GB2194672B/en not_active Expired
  • 1987-02-13 DE DE19873790086 patent/DE3790086T1/de not_active Withdrawn
  • 1987-02-13 JP JP62501551A patent/JPS63502471A/ja active Pending
  • 1987-02-13 WO PCT/US1987/000301 patent/WO1987005161A1/en active Application Filing
  • 1987-02-16 CA CA000529788A patent/CA1273403A/en not_active Expired
  • 1987-02-18 FR FR8702113A patent/FR2594605B1/fr not_active Expired

Patent Citations (4)

Also Published As

Similar Documents

Legal Events