Coherent light generators – Particular active media – Gas
Reexamination Certificate
1999-07-08
2001-01-09
Scott, Jr., Leon (Department: 2881)
Coherent light generators
Particular active media
Gas
C372S092000, C372S098000, C372S100000, C372S020000, C372S103000
Reexamination Certificate
active
06173000
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to excimer lasers, and more particularly to an oscillator that provides for narrow/variable bandwidth selection and an amplifier that provides improved spectral brightness for a dual discharge tube excimer laser.
BACKGROUND OF THE INVENTION
Dual discharge tube excimer lasers are used in a variety of applications to include spectroscopy, combustion diagnostics, harmonic generation, stimulated Raman scattering, Brillouin scattering, laser fusion and remote sensing. A standard optical set-up for a dual discharge tube excimer laser is shown schematically in FIG.
1
and referenced generally by numeral
10
.
Excimer laser
10
has first and second discharge tubes
12
and
14
, respectively. Discharge tubes
12
and
14
are filled with gas mixtures such as argon fluoride, krypton fluoride, xenon chloride, xenon fluoride, etc., as is known in the art of excimer lasers. The oscillator portion of excimer laser
10
includes: discharge tube
12
; variable circular aperture elements
16
and
18
disposed at either end of discharge tube
12
; optical prisms
20
,
22
and
24
; an optical grating
26
; and an output coupler
30
.
As is known in the art, when discharge tube
12
is energized (i.e., its electrodes are energized), a gaseous lasing medium is generated in discharge tube
12
and transmitted therefrom as a laser beam. The laser beam passes through aperture element
18
and impinges on the front surface of each of prisms
20
/
22
/
24
at Brewster's angle before impinging on optical grating
26
. The cross-sectional shape of the lasing medium and resulting laser beam is defined by discharge tube
12
. The bandwidth of the laser beam is selected as the beam is transmitted back through prisms
20
/
22
/
24
and aperture element
18
before re-entering discharge tube
12
. The bandwidth-defined laser beam exits the opposite side of discharge tube
12
and passes through aperture element
16
before impinging upon output coupler
30
which is typically a partially reflective mirror. Output coupler
30
outputs a laser beam
32
which is turned 180° by mirrors
34
and
36
.
Laser beam
32
is amplified by a combination of a concave mirror
38
, discharge tube
14
and a window mirror
40
where mirrors
38
and
40
form an unstable resonator. Specifically, laser beam
32
first passes through a small hole (not shown) in concave mirror
38
and discharge tube
14
before impinging on window mirror
40
. Mirror
40
has a flat window portion
40
A with a meniscus lens
40
B at its center. Flat window portion
40
A is slightly reflective (e.g., 10%) at the wavelength(s) of interest while meniscus lens
40
B is highly reflective (e.g., 95%) at its center. As a result of this structure, the laser beam passes back through discharge tube
14
along a laser beam path
32
A. Laser beam path
32
A exits discharge tube
14
, reflects off concave mirror
38
, and is directed back through discharge tube
14
along a laser beam path
32
B which exits flat window portion
40
A of mirror
40
as the output laser beam. That is, three passes through discharge tube
14
are used to amplify the laser beam.
While the above-described excimer laser design performs satisfactorily, improvements in terms of decreased divergence, increased output energy, locking efficiency, range of tunability and spectral brightness are goals that are continually sought.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a dual discharge tube excimer laser having improved performance characteristics.
Another object of the present invention to provide a dual discharge tube excimer laser that can achieve decreased divergence, and increased output energy, locking efficiency, range of tunability and spectral brightness.
Still another object of the present invention to provide a dual discharge tube excimer laser that can easily be adjusted to operate over a range of bandwidths.
Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings.
In accordance with the present invention, an excimer laser is provided in which an oscillator having a first discharge tube generates a laser beam having a cross-sectional shape as initially defined by the first discharge tube. The oscillator including means for selecting a bandwidth of the laser beam and means for maintaining the cross-sectional shape of the laser beam within the oscillator and as the laser beam exits the oscillator. An amplifier receives the laser beam exiting the oscillator. The amplifier includes a second discharge tube. During amplification, the laser beam is passed once through the first discharge tube and then twice through the second discharge tube.
REFERENCES:
patent: 4644555 (1987-02-01), Amano
patent: 4897849 (1990-01-01), Hughes
patent: 5812308 (1998-09-01), Kafka et al.
Bergen Peter J. Van
Jr. Leon Scott
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