Coherent light generators – Particular resonant cavity – Specified output coupling device
Patent
1998-12-21
2000-10-24
Scott, Jr., Leon
Coherent light generators
Particular resonant cavity
Specified output coupling device
372 19, 372 57, 372 98, 372100, 372 5, 372102, 372 20, H01S 308
Patent
active
061378216
ABSTRACT:
A durable etalon based laser output coupler. The output coupler is especially useful for ultraviolet lasers such as an ArF excimer laser or an F.sub.2 laser. The principal elements of the etalon based output coupler are two prisms aligned so that a first surface of one of the two prisms is parallel to a first surface of the other prism. The first of the two prisms have a second surface forming an angle with a beam from a laser cavity equal to or approximately equal to Brewster's angle. The second of the two prisms has a second surface forming an angle with the coupler exit beam equal to or approximately equal to Brewster's angle. Preferably, the prisms are comprised of CaF.sub.2 and surrounded by nitrogen at about one atmosphere. Assuming the laser beam is at a wavelength of 193 nm (for ArF excimer laser), Brewster's angle is about 57 degrees and each of the first and second surfaces define an apex angle of about 34 degrees. In a preferred embodiment, the device is used as an output coupler for line narrowed ArF excimer laser having a diffraction grating based line narrowing module. The etalon based output coupler is adjusted to preferentially reflect light at or near the spectral maximum produced by the grating. Substantial improvement in line narrowing results from the amplification in the laser resonance chamber of light at or near the grating spectral maximum which is preferentially reflected by the etalon based output coupler. Several preferred methods are disclosed for tuning the etalon based output coupler to match the wavelength selected by the grating based line narrowing module.
REFERENCES:
patent: 5898725 (1999-04-01), Fomenkov et al.
patent: 5901163 (1999-05-01), Ershov
Cymer Inc.
Jr. Leon Scott
Ross John R.
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