Impedance-matching transformers for RF driven CO
View Patent ↗In a CO 2 gas discharge laser energized by a radio frequency (RF) power source a transformer having selectively variable output impedance is used to match output impedance of the power source to the impedance of discharge electrodes of the laser. A similar transformer can be used to impose a selective variable phase-shift on the RF power from the source. The variable impedance transformer can also be used for impedance matching between amplifier stages in the power source.
1. A method of optimizing the performance of a gas laser, said gas laser being driven by RF power source and wherein the load associated with the laser is unknown, said method comprising the steps of:
providing an electrical connection between the power source and the laser, said connection including first and second transmission-line sections each thereof having first and second opposite ends, with the first end of the first section being connected to the source, the second end of the first section being connected to the first end of the second section via a node therebetween, and the second end of the second section being connected to the load, with each of the first and second transmission-line sections having an electrical length equal to or less than about one-twelfth of a wavelength at the source-frequency, said connection including an electrical component having an electrical characteristic connected to the node between the first and second transmission-line sections, with the electrical characteristic of the component being selectively variable; and
varying the electrical characteristic of the component while operating the laser to find the value for the component that optimizes the transfer of the power between the source and the laser.
2. The method of claim 1 , wherein the electrical component is a capacitor having a selectively variable capacitance.
3. The method of claim 2 , wherein the capacitor has first and second opposite plates with the first plate being connected to the node between the first and second transmission-line sections and the second plate being connected to ground.
4. The method of claim 2 , wherein the electrical connection has an output impedance and varying the capacitance of the capacitor varies the output-impedance of the electrical connection.
5. The method of claim 2 , wherein the impedance of the laser has a value between a maximum anticipated value and a minimum anticipated value and the capacitance of the capacitor is variable between a minimum value and a maximum value, wherein the characteristic impedance of the first transmission-line section is about equal to the maximum anticipated value of the laser impedance, the characteristic impedance of the second transmission-line section is about equal to the impedance of the power source, and wherein varying the capacitance of the capacitor between the minimum and maximum values thereof varies the output impedance of the circuit between the maximum and minimum values, respectively, thereof.
6. The method of claim 5 , wherein the impedance of the source is 50 Ohms, the maximum and minimum values of impedance of the laser are 25 Ohms and 12 Ohms respectively, the minimum and maximum capacitance values of the capacitor are about 1.5 picofarads and about 30 picofarads respectively.
7. The method of claim 1 , wherein the electrical component is a third transmission-line section having first and second opposite ends and a selectively variable electrical-length.
8. The method of claim 7 , wherein the first end of the third transmission-line section is connected to the node between the first and second transmission-line sections and the second end of the third transmission-line section is open.
9. The method of claim 7 , wherein the electrical length of the third transmission line section is less than about one-twelfth of a wavelength at the source frequency.
10. The method of claim 7 , wherein the electrical connection has an output impedance and varying the electrical-length of the third transmission line section varies the output impedance of the electrical connection.
11. The method of claim 1 , wherein the electrical component is an inductor having a selectively variable inductance.
12. The method of claim 11 , wherein the inductor has first and second opposite ends the first end being connected to the node between the first and second transmission line sections and the second end being connected to ground.
13. The method of claim 11 , wherein the electrical connection imposes a phase-shift on the RF power delivered by the source and varying the inductance of the inductor varies the phase-shift imposed by the electrical connection.