Coherent light generators – Particular component circuitry – Optical pumping
Patent
1998-09-14
2000-08-01
Arroyo, Teresa M.
Coherent light generators
Particular component circuitry
Optical pumping
H01S 300
Patent
active
060977477
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a gas discharge excitation laser device, and more particularly, to a gas discharge excitation laser device having an improved a response to a switching-off command of a beam output.
BACKGROUND ART
Generally, in laser devices to obtain a laser output by gas discharge excitation, there is a relationship such that a larger amount of electric power input for the gas discharge provides a higher laser output and a smaller input provides a lower laser output. However, the relationship between the amount of power input and the laser output is not in direct proportion and is affected by the temperature of laser gas. This relationship is illustrated in FIG. 2 with a horizontal axis indicating an amount of power input for gas discharge in terms of discharge current (A: ampere) and the vertical axis indicating a laser output (W: watt).
As indicated by the solid line in the graph of FIG. 2, while the laser gas is cold, no laser oscillation takes place within a range H1 of discharge current from "0" to a threshold indicated by point P, and once the discharge current exceeds the threshold indicated by the point P, the laser output increases linearly with the discharge current. On the other hand, while the laser gas is hot, the threshold for laser oscillation drops to a level indicated by point Q, as shown by the broken line in the graph of FIG. 2. The expression "cold" used here means a state of "ordinary temperature or thereabouts" and is typified by a temperature range of 280 to 320 K (7 to 47.degree. C.). Also, the term "hot" means a state of "sufficiently higher temperature than ordinary temperature" and is typified by a temperature range of 400 to 500 K (127 to 227.degree. C.).
The characteristic in the vicinity of the point Q to P (range H2) is in actuality considerably unstable and it is not certain whether laser oscillation actually takes place at an arbitrary point (e.g., point S1) within the range H2. In general, in a case where a laser output command is switched from ON to OFF and thus the discharge current value drops from a high value (e.g., point S2) to a lower value point within the range H2), the laser oscillation shows a tendency to continue, as described later.
As the discharge current becomes much larger than the threshold indicated by the point Q, the discharge current/laser output characteristic gradually becomes closer to that (solid line) as observed while the laser gas is cold. Symbol W1 in the graph represents a laser output while the laser gas is hot in supplying a discharge current equivalent to the threshold while the laser gas is cold, and W1>0.
In actually using a gas discharge laser, such control is performed as to switch between an OFF state in which a small discharge current called base current is supplied and an ON state in which a current to obtain a laser output required for machining or the like is supplied. In pulse operation mode, the two states are periodically and repeatedly alternated.
To smoothly carry out such control operation, it is necessary to set the base current to an appropriate value. If the base current value is set to a small value close to "0" as indicated by symbol R in FIG. 2, it is expedient for the laser output to be surely switched to the OFF state, but lowering of the gas temperature is unavoidable, making it difficult to maintain the gas discharge state. Once the gas discharge state is lost, special control is required again to restore gas discharge.
Specifically, it is necessary to apply a voltage much higher than that required to maintain the gas discharge state for inducing the gas discharge, and to control transition to the gas discharge-maintained state. It is apparently disadvantageous to perform such complicated and time-consuming control operation each time the laser is switched on and off.
Usually, therefore, the base current value is set to a value close to the point P (represented by the point S1). While a command to turn the laser output to the OFF state is output from a control section after
REFERENCES:
patent: 5530937 (1996-06-01), Sugiyama
Enokizono Hitoshi
Iehisa Nobuaki
Arroyo Teresa M.
Fanuc Ltd.
Wise Robert E.
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