Coherent light generators – Particular beam control device – Having particular beam control circuit component
Patent
1989-06-29
1990-08-07
Davie, James W.
Coherent light generators
Particular beam control device
Having particular beam control circuit component
372 32, H01S 310
Patent
active
049473980
ABSTRACT:
Methods of controlling the wavelength and output power of a laser device with two intracavity etalons are disclosed, together with a wavelength monitor capable of detecting sidebands. A method is characterized by the usage of hot/cold parameter K which takes two values 0 and 1 indicating the cold and hot state of the device, respectively. The parameter K, which is reset to 0 at the start, is set to 1 when the laser beam is stabilized; it is reset to 0, whenever the lasing pause exceeds a predetermined time length. Preparatory starting steps are performed or omitted at the start, depending on the value of K. Another method is characterized by the adjustment of the intracavity etalons during the lasing pauses, in accordance with exponential functions with thermal time constants. The sideband detecting wavelength monitor comprises a single etalon whose free spectal region FSRm is selected with respect to that, FSR.sub.2, of the fine tuning intracavity etalon in such a manner that the interference fringes of the sidebands formed by the monitor etalon are distinct from each other and from those of the central wavelength .lambda..sub.0. Namely, when i is the integer which is associated with a sideband wavelength .lambda..sub.S via the equation: .lambda..sub.S =.lambda..sub.0 +i.times.FSR.sub.2, the free spectral regions FSR.sub.2 and FSRm are selected in such a manner that the apparent wavelength differences: R=i.multidot.FSR.sub.2 +j.multidot.FSRm between the central wavelength .lambda..sub.0 and the sideband wavelengths .lambda..sub.S, wherein j is an integer which minimizes the value of R for each i, are different from zero and from each other.
REFERENCES:
patent: 4081765 (1978-03-01), Berg et al.
patent: 4159453 (1979-06-01), Brandt et al.
Pol et al., "Excimer Laser-Based Lithography: A Deep Ultraviolet Wafer Stepper", 1986, vol. 633, pp. 6-16.
McKee, "Spectral-Narrowing Techniques for Excimer Laser Oscillators", Jun. 1984, vol. 63, pp. 214-219.
Nakatani Hajime
Wakata Hitoshi
Yasuda Ken'ichi
Davie James W.
Mitsubishi Denki & Kabushiki Kaisha
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