RF excited waveguide laser

Details RF excited waveguide laser RF excited waveguide laser

1998-03-13

2001-02-20

Arroyo, Teresa M. (Department: 2881)

Coherent light generators

Particular pumping means

Electrical

C372S064000, C372S107000

Reexamination Certificate

active

06192061

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to RF excited waveguide lasers and in particular to improvements to RF excited waveguide laser components.
2. Prior Art
In general, RF excited waveguide lasers having a distributed inductance are known. Referring to prior art
FIG. 1
, a conventional RF laser disclosed in U.S. Pat. No. 4,787,090 ('090) is shown. The '090 patent discloses a distributed inductance RF excited waveguide arrangement which is inserted into a metal housing structure which serves as both the vacuum housing and the structure to support resonator mirrors. The '090 patent teaches clamping the inserted assembly within this housing structure by deforming one surface of the structure with an external clamping plate. It has been found in practice that this clamping approach has a number of problems which adversely effect the laser's integrity and performance. For example, the clamping force is difficult to control which has resulted in clamping forces that are so large that fracture of the internal ceramic waveguide structure has occurred. In addition, this clamping arrangement requires that one surface of the vacuum housing be very thin so that it can be deformed by the clamping plate. This results in a reduction of the stiffness of the housing thereby compromising the optical alignment stability of the laser.
Referring to prior art
FIGS. 2 and 3
, a conventional folded waveguide which uses a common electrode to excite a gas discharge within a Z-fold optical waveguide structure so that a gas discharge is obtained in all the channels, is shown. The waveguide comprises a ceramic substrate
4
with waveguide channels
6
formed therein. Metal electrodes
8
are placed on either side of the ceramic substrate
4
. RF energy applied to this configuration results in a plasma discharge within the waveguide. It has been discovered that the plasma formed in the intersection regions
12
of the waveguide channels is characterized by a substantially higher current flow compared to the normal waveguide region resulting in a relatively hotter and more intense plasma in this region. This non-uniform gas discharge condition results in a decrease in laser conversion efficiency and in some cases sputtering of the electrode in this region.
Turning to prior art
FIG. 4
, a conventional waveguide Z-fold resonator configuration which incorporates a U-bore waveguide slab is shown. The phrase “Z-fold” refers to the arrangement of the waveguide channels
6
in a Z pattern (i.e., the three waveguide channels, each passing across the waveguide). Reflecting mirrors
11
are positioned adjacent to channels
6
. The output laser beam is emitted through a transmitting mirror
13
.
Referring to prior art
FIG. 5
, an end view of waveguide channels used in conventional waveguides is shown. As is shown, conventional waveguide channels have circular, square and U-shaped cross sections. Each of the channels has an aspect ratio (ratio of height to width) of approximately one-to-one.
Mirrors
11
and
13
(
FIG. 4
) positioned at the end of each waveguide channel are mounted on optical mounts that must satisfy a number of simultaneous requirements. First, the angular alignment of the mirror must be accomplished without compromising the vacuum integrity of the gas envelope, and second, the alignment should be stable over a wide range of environmental conditions. Additionally, in higher power lasers, the mount should remove excess heat from the mirror's optic substrate to minimize potential damage and surface figure distortions which, if left uncorrected, will lead to a loss of performance and reduced reliability. Fastening the resonator optic to the mount while maintaining angular stability and maintaining a low thermal resistance without distorting the surface figure is also critical, yet difficult to achieve. Finally, to be commercially useful, the cost must be low enough to make economic sense for the application and market being addressed.
Referring to prior art
FIG. 6
, a cross-sectional view of a conventional gas laser resonator transmitting mirror mount which utilizes a metal post
14
having a transmitting mirror
16
, is shown. A flexure arrangement
17
about the flexing point effects an angular movement through the vacuum envelope. The mirror mount is bolted onto a laser housing (not shown) by mounting bolts
19
as is well known. A hermetic seal with the mirror and the laser housing is obtained by “o” rings
21
and
23
, respectively. Angular movement of the mount is accomplished through the use of fine threaded adjustment screws
18
located outside the vacuum envelope. The screws in turn apply an angular force to post
14
which is usually monolithic with and hermetically sealed to the laser housing (not shown), as described above. In many applications, four adjusting screws
18
induce orthogonal angular movement but are not as stable as a three point mounting system. The transmitting mirror is held in compression against “o” ring
21
by a press-on cap
20
.
The conventional method used to attach mirror
16
to post
14
has disadvantages. Transmitting mirror
16
(and high reflecting mirrors, not shown) is typically attached using press on cap
20
which applies an axial force to the mirror. For cooling purposes, firm intimate contact of the back side of the high reflection mirrors is required and shown in FIG.
7
. The placement of press-on cap
20
creates forces in the axial direction of mirror
16
(as shown by the arrows F). This force often results in a deformation in a region
22
of the optic, thus ruining the mirror's surface figure. One approach to circumvent this problem is to mount the mirror against a classic three point contact on the end of the post. This approach, however, compromises the thermal aspects of the design.
SUMMARY OF THE INVENTION
The above-discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by the RF excited laser of the present invention. A clamping device is provided which reduces stress on ceramic components and also is less expensive than existing clamping devices. The electrode coverage of the waveguide intersection region is reduced or eliminated so as to reduce plasma build-up in this region. Ceramic covers are used over a portion of the channel intersection region in order to improve efficiency and mode quality. Increased power is achieved by adding a fourth channel to a conventional waveguide to form a “bow tie” (or “figure eight”) shaped ring resonator. Fourth, fifth or more channels can be added to a conventional waveguide to form a W(or M) or combination WI (or NV or MI) or a larger number of Zig-Zag configuration waveguide. To accommodate these additional channels added to the standard Z shape waveguide structure, additional laser folding high reflecting folding mirrors are provided for propagating the laser beam through the channels of the folded waveguide. An improved optical component mount uses radial compressive forces to hold the optical component to a post. This prevents the face of the optical component from being distorted. Mirror mounts are also configured to allow more mirrors to be mounted at each end of the laser. A waveguide channel having a U-shaped cross section and an aspect ratio greater than one-to-one improves laser output power performance without adding more complexity to a laser waveguide design. A beam redirection device allows the laser head to serve as a mounting surface for other optical components. For rectangular shaped laser beams emitted by a waveguide having an aspect ratio greater than one-to-one a cylindrical lens is placed at the point where the dimensions of the x, y axis of the laser beam are the same coupled with a two lens telescope maintains a circular beam and provide an ability to change the beam diameter. An alternative approach is the use of anamorphic beam expander prisms to change the laser beam diameter and recollimate the laser beam in a compact and rugged package. Relief holes or s

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