Abstract:
A power efficient continuous wave gas ion laser system, associated laser tube and method are described. The system uses a fixed electrical input power and a power factor corrected power supply producing an output voltage and an output current from the fixed input electrical power. A gas ion laser tube is configured for use in the system having a particular cavity length which is established as a distance between a first mirror and a second mirror for operation using the output voltage and the output current. The system may be configured to provide a light output power improvement of approximately thirty percent over prior laser systems. In one feature, a laser tube is configured for providing the improved light output power in a conventional laser head configuration such that the laser tube may directly replace laser tubes in prior installations. Existing and new laser installations may benefit.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to continuous wave gas ion lasers and more particularly to a power efficient continuous wave gas ion laser system and associated laser tube. The invention is particularly well suited for improving gas ion laser performance in the instance of a fixed level of available electrical input power. An associated method is also disclosed. 
     Continuous discharge gas ion lasers are relatively inefficient with regard to the use of electrical input power. It should be appreciated that, for this reason, the maximum light output power of such lasers has traditionally been limited, at least in part, by available electrical input power. For example, a typical 120 Volt AC electrical outlet in the United States is rated to provide approximately 17 amps on a continuous basis. As will be seen below, several considerations must be kept in mind when implementing a laser under such an input power constraint. 
     One factor which relates directly to input power limitations resides in the fact that the input current that is required to maintain a fixed light output from a gas ion laser tube increases in a known way as the tube ages. Hence, the lifetime of the tube is reached when the current drawn by the tube, via a typical laser power supply, meets or exceeds the level of current which is available from the source. In the example of a typical US 120 Volt AC outlet, for a nominal voltage of 106 VAC at a current of 17.3 amps (slightly above the recommended current limit), the end of life power consumption value of a laser tube is therefore just over 1,830 watts. 
     Based on a particular constraining value of input electrical power, it should be appreciated that the light output of a particular laser tube may be increased by driving the tube at higher current levels. However, the increase in output power, in this instance, is achieved by sacrificing a significant portion of the lifetime of the tube, as compared with driving the tube at a lower rated current level. In other words, by driving the tube at a current level which is higher than its rated level the end of life power consumption value will be reached in a proportionately shortened period of time. 
     The present invention discloses a system, laser tube and associated method which provide a highly advantageous improvement in output power in view of a particular constraining value of input electrical power or, alternatively, a highly advantageous improvement in laser tube lifetime. 
     SUMMARY OF THE INVENTION 
     As will be described in more detail hereinafter, a power efficient continuous wave gas ion laser system and associated laser tube are disclosed. An associated method is also disclosed. The system is configured for use with a fixed electrical input power and includes a power factor corrected power supply which produces an output voltage and an output current using the fixed input electrical power such that the output voltage and the output current are substantially in phase. A gas ion laser tube is configured for use in the system having a particular cavity length which is established as a distance between a first mirror and a second mirror for operation using the output voltage and the output current. The tube includes a bore arrangement positioned between the first and second mirrors and defining a laser bore having an active gain length in the range of approximately 25 percent to 35 percent of the cavity length. 
     In one aspect of the invention, the system may be configured to provide a light output power improvement of approximately thirty percent over prior art laser systems. 
     In accordance with one feature of the present invention, a laser tube is configured for providing the aforementioned improved light output power in a conventional laser head configuration such that the laser tube may directly replace laser tubes in prior art installations. In this manner, existing as well as new laser installations may benefit from the advantages of the present invention. 
     In accordance with another feature of the present invention, the improved laser tube of the present invention provides an operational lifetime which is equivalent to that of prior art laser tubes while still providing an output power which is significantly greater than the output power capability of prior art laser tubes operating using an identical fixed wattage source of input power. Alternatively, the improved output laser tube of the present invention may be operated in a manner which provides a light output level equivalent to that of a prior art laser tube operating at full light output capacity from an identical fixed wattage source of input power while, at the same time, providing an improved operational lifetime. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention may be understood by reference to the following detailed description taken in conjunction with the drawings briefly described below. 
     FIG. 1 is a diagrammatic elevational view of a continuous wave gas ion laser system manufactured in accordance with the present invention. 
     FIG. 2 is a diagrammatic cross-sectional view of a highly advantageous laser tube manufactured in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Attention is immediately directed to FIG. 1, which diagrammatically illustrates a continuous wave gas ion laser system manufactured in accordance with the present invention and generally indicated by the reference numeral  10 . System  10  includes a switch mode power supply  12  which is supplied power from a standard AC power outlet  13 . For example, in the U.S., the supplied power may comprise 120 volt AC, 60 Hz. As is the case with any standard outlet, the electrical power which is available from the outlet is limited by protection devices such as, for example, a fuse or a circuit breaker (neither of which is shown). In the present example, a limit of 20 amps is common with a maximum recommended continuous current draw of approximately 17 amps. Thus, any device operating from such an outlet is limited by a constraining value of available electrical input power which will be referred to hereinafter as P lim . Power supply  12  provides power to a gas ion laser tube  14 , which is manufactured in accordance with the teachings herein, through a power cable  16 . As will be seen hereinafter, system  10  is configured in a highly advantageous way which provides performance capabilities which have not been seen heretofore in view of the limitations imposed by P lim . 
     Turning to FIG. 2 in conjunction with FIG. 1, specific details of the construction of gas ion laser tube  14  are illustrated. The latter includes a cathode housing  18  and an anode housing  20 . First and second laser mirrors  22  and  24  are positioned within anode housing  20  and cathode housing  18 , respectively. A laser bore arrangement  26  defines a bore  28 . Bore arrangement  26  is constructed from suitable materials such as, for example, beryllium oxide. Bore  28  includes a length L and a diameter D. Laser bore arrangement  26  also defines a gas return channel  29  in a manner which is known in the art. As noted above, power is supplied to tube  14  by cable  16  which includes a positive lead (not shown) connected with anode arrangement  20  and a negative lead (not shown) connected with cathode arrangement  18 . During steady state operation, a discharge is created within bore  28  that results in the production of light of one or more predetermined wavelengths which lase between mirrors  22  and  24  in a resonant cavity. 
     Having described the components which make up laser system  10  in a general way, basic considerations which govern the operation of the laser with respect to electrical power consumption will now be described. To that end, power supplied from AC outlet  13  to the laser system is defined as:              P   =         V   DIS     ·     I   DC           E   PS     ·     PF   PS                 (   1   )                                
     where P is the AC input power, V DIS  is the discharge voltage of the laser tube, I DC  is the DC tube current supplied by power supply  12  to the tube, E PS  is the thermal electrical efficiency of the power supply and PF PS  is the power factor of the power supply. In the prior art, switch mode power supplies are used which provide an E PS  of approximately 0.9 (90%) and a PF PS  of approximately 0.72 (72%). Assuming a conventional laser tube having an end of life current draw of 11.9 amps (I DC ) and a discharge voltage of 100 VDC (V DIS ), P is calculated as 1,836 watts which is approximately 17.3 amps (AC) at a nominal AC outlet voltage of 106 VAC. Thus, the light output power of the laser is constrained, as described above, to approximately 75-80 mW at 12 AMPs by the limited AC input electrical power. In contrast, the present invention advantageously recognizes a manner in which the performance of the system may be improved significantly with regard to either increasing output power or maintaining an equivalent output power while significantly lengthening the lifetime of a laser tube configured in accordance with the teachings herein. Moreover, with specific regard to the laser tube, these improvements may be advantageously provided in a conventional package outline, as will be described. It should be appreciated that a standard package outline allows for retrofit of many existing systems to the upgraded laser system manufactured in accordance with the present invention. Specific details regarding these advantages will be described immediately hereinafter. 
     Still referring to FIGS. 1 and 2, the present invention recognizes that laser performance can be improved by optimization of the variables of Equation 1 in a manner which has not been seen heretofore. Accordingly, switched mode power supply  12  is a power factor corrected power supply having an E PS  of approximately 0.85 (85%) and a PF PS  of approximately 0.99 (99%). One highly advantageous power supply which provides these operational values is disclosed in co-pending U.S. patent application Ser. No. 09/089,568, filed Jun. 6, 1998, entitled UNIVERSAL LASER POWER CONTROLLER IN A GAS ION LASER SYSTEM AND METHOD which is incorporated herein in its entirety by this reference. FIG. 3 of the subject U.S. application illustrates the various functional sections which may make up power supply pending  12 . 
     It can be seen from equation 1 that when the values for E PS =0.85 and PF PS =0.99 are used in place of the typical prior art values, a significant advantage is realized to the extent that the amount of AC power drawn by the system can be decreased by approximately 30% for an equivalent amount of light output power. Or, stated in a slightly different way, the improved efficiency conserves 30% of the available AC input power. While conservation of 30% of the AC input power is significant, the present invention recognizes that this conserved power may be applied to a laser tube, resulting in higher light output. To that end, power supply  12  accomplishes application of the conserved power to the laser tube by an internal voltage boost of approximately 30%, thereby permitting the voltage supplied to tube  14  to be raised from the conventional value of 100 VDC to approximately 130 VDC. Based on the available voltage increase and the highly advantageous way in which tube  14  is designed, system  10  achieves significant advantages over prior art lasers operating under the identical input electrical power constraints, as will be seen hereinafter. 
     Referring to FIG. 2, as mentioned, laser tube  14  includes a package outline having predetermined dimensions which are common among various manufacturers. The overall package outline is referred to by those of skill in the art as a “head size”. While it is true that a conventional gas ion laser tube could be “re-scaled” in a way which permits the tube to operate from power supply  12 , it is recognized herein that such re-scaling is of limited utility since the resulting head size would be incompatible with current products. That is, such a tube could be used in new designs, but would be useless in replacing worn out tubes in existing systems. In short, an existing system could not benefit from the advantages disclosed herein in view of an incompatible head size. For these reasons, gas ion laser tube  14  of the present invention includes a conventional head size which incorporates increased gain so as to compensate for the capability of power supply  12  to increase drive voltage from 100 VDC to 130 VDC. Specifically, length L of bore  28  is increased relative to cavity length C of the tube such that the ratio of L to C is within the range of approximately 25% to 35%. In the instance of a 130 VDC anode to cathode voltage, an L to C ratio of approximately 30% is preferred. This represents a percentage increase of approximately 30% in the length of the laser bore, as compared with a standard prior art laser tube. It should be appreciated that in a conventional tube the L to C ratio is approximately 22%. In this manner, the current density in bore  28  remains approximately the same as in a conventional tube. However, the gain region is significantly longer. Because light output is proportional to the length of the gain region, an increase in light output power of approximately 30% results for the same current density. Since tube lifetime is directly dependent on current density, tube  14  of the present invention advantageously provides a 30% increase in output light power accompanied by the further advantage of sustaining the expected lifetime of the tube. 
     Still referring to FIG. 2, the manner in which the gain length of tube  14  is extended without an associated increase in cavity length (i.e., no change in head size) will now be described. More specifically, bore arrangement  26  differs from prior art bore arrangements in two important features. In a first feature, anode end  30  of bore  28  does not include a taper. In the prior art, capillaries were designed having a taper at the anode end for purposes of preventing bore erosion. In fact, Applicant is not aware of any prior art bore which is not tapered at both ends. Remarkably, it has been discovered that the anode end taper is not needed. That is, the anode end of the bore is not subject to erosion in the manner of the cathode end of the bore. Thus, bore arrangement  26  of the present invention includes a cathode end taper  31 , but no taper is provided on the anode end of the bore. It should be noted that an active gain length Z, forming part of overall length L, does not include length T of cathode end taper  31  since a taper formed at either end of the bore does not contribute to the active length of the bore. Only the region of the bore having diameter D contributes as gain region due to the high current density confined within reduced diameter D. Thus, by eliminating the anode end taper in the laser bore, the present invention effectively lengthens the active gain length of the laser bore by a length T without the need to lengthen C, the tube&#39;s cavity length. In a typical laser tube, T is equal to approximately 0.40″. In accordance with this feature alone, the bore length may be increased to at least 26 percent of cavity length C. 
     In accordance with a second feature of the bore arrangement of the present invention, tube  14  provides another highly advantageous manner for increasing bore length L without the need to change the head size of the laser tube. Specifically, laser tube  14  differs from prior art laser tubes with regard to the way in which bore arrangement  26  is received by cathode can  18 . The bore arrangement includes a cathode end  32  which defines an inset step portion  34 . A Kovar sleeve  36  is brazed or attached in a suitable manner to a region  38  of the bore immediately adjacent to inset step portion  34 . The opposite end of the Kovar sleeve is, in turn, brazed or attached in a suitable manner to cathode can  18  in a region  40 . It should be appreciated that the configuration of the cathode end of the bore arrangement (with inset step portion  34 ) allows extension of bore length L into a region  42  of the laser&#39;s resonant cavity, which is defined by cathode can  18 , without interfering with the typical manner in which cathode can  18  is normally attached to bore arrangement  26 . In this regard, Applicant is unaware of any prior art arrangement which permits extension of any portion of the length of the bore into the cathode can. In contrast, this second feature, like the first feature described above, permits extension of the bore without resorting to a change in the head size of the laser tube. In the illustrated configuration of FIG. 2, the bore length has been extended into the cathode can by approximately 7 millimeters or approximately 30% of cavity length C. However, it is submitted that the bore length may be extended into the cathode can by as much as 9 millimeters. Thus, in accordance with this feature alone, the bore length may be increased to up to 34 percent of cavity length L. In this regard, it should be noted that a portion of the active gain length of the laser bore i.e., having diameter D, may actually extend into cathode can cavity  42 . It should be noted that the illustrated configuration for interconnecting cathode end  32  of bore  26  with cathode can  18  represents only one configuration out of a wide range of possible configurations and that all of these configurations are considered to be within the scope of the present invention provided only that a portion of the laser bore is positioned within that portion of the laser cavity defined by the cathode can. 
     It should be appreciated that the advantages provided by the present invention may be utilized in a manner which provides for a significant increase in tube lifetime, as opposed to higher light output. As described above, tube lifetime is directly proportional to the current density in the bore of the tube. Therefore, by reducing the current density in a particular tube, the lifetime of the tube will increase, but the light output power of the tube will decrease. Tube  14  of the present invention is highly advantageous for the reason that its increased gain length allows power supply  12  to drive the tube at a current level well below that of a conventional tube operating at full power while maintaining the same level of light output as a conventional tube operating at full rated capability from an identical input power source. Thus, under such reduced current density conditions, the lifetime of tube  14  of the present invention can be potentially extended up to 5,000 to 10,000 hours as compared to a conventional tube. Of course, this dramatic increase in tube lifetime is highly advantageous in reducing the frequency of tube replacement. Another advantage attends in reduced energy consumption. That is, for a particular level of light output as compared with a laser system of the prior art, electrical input power for the laser system of the present invention is reduced by the efficiency of power supply  12  in cooperation with the increased gain length of tube  14 . 
     Since the laser system, laser tube and associated method disclosed herein may be provided in a variety of different configurations and the method may be practiced in a variety of different ways, it should be understood that the present invention may be embodied in many other specific ways without departing from the spirit or scope of the invention. Therefore, the present examples and methods are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope of the appended claims.