Coherent light generators – Particular resonant cavity – Mirror support or alignment structure
Reexamination Certificate
1999-08-23
2003-05-20
Scott, Jr., Leon (Department: 2828)
Coherent light generators
Particular resonant cavity
Mirror support or alignment structure
C372S065000, C372S099000
Reexamination Certificate
active
06567456
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains generally to laser devices, and more particularly, to a novel dual-mirror mirror mount for polarizing light emitted from a laser without the use of an intra-cavity Brewster window.
BACKGROUND OF THE INVENTION
As increased applications of lasers are found due to the unique high-energy, high-precision properties of the output beam from such devices, the use of lasers throughout many areas of technology is becoming increasingly ubiquitous. As known by those skilled in the art, a laser is a very high frequency optical oscillator constructed from an amplifier and an appropriate amount of positive feedback. Lasers are used as critical components in a number of industries, including optical telecommunications, medical surgery, and manufacturing.
A typical gas laser comprises a plasma tubule discharge chamber enclosing a gaseous medium. An arc discharge is established through the gaseous medium, which serves to ionize the gas, thereby forming a plasma and elevating the electron energy states to the level required for lasing action. As the electrons recombine to lower energy states, light is emitted via spontaneous emission. Typically, a pair of optical resonator mirrors seal the two ends of the plasma tube so that light emitted by the plasma oscillates between the optical resonator mirrors and is amplified as it passes through the gaseous medium to achieve a lasing action in a manner known by those skilled in the art.
In a simple gaseous laser plasma discharge chamber with a cylindrical symmetry, the light output from the laser is randomly polarized. Each individual cavity mode has a linear polarization at any one time. However, the overall laser output is a time-varying mix of modes of different polarization. As a result, the output beam appears to be non-polarized when integrated over a fairly short period of time. Although the beam intensity is fairly constant, if the application involves polarization-dependent optics, then a polarizing intra-cavity Brewster window is employed which introduces sufficient loss in the plane of s-polarization (defined by the mode whose polarization vector for the electric field is perpendicular to the plane of incidence) so that only p-polarized output (defined by the mode whose polarization vector for the electric field is parallel to the plane of incidence) is produced. This occurs when the Brewster window is positioned at a Brewster's angle defined as:
2(
b
)=arctan(
n
)
where n is the index of refraction of the window material and the index of refraction on either side of the window is assumed to be exactly 1. The Brewster window acts as a partial polarizer that ensures partial reflectivity for S-polarization and nominally zero reflectivity for p-polarization. Thus, the Brewster window provides maximum transmission efficiency at a preferred orientation for the polarization within the laser. The use of Brewster angle window assemblies is a standard technique that has been in use for many years, and, prior to the present invention, was the standard polarization method in commercial use for gas lasers. Polarization in gaseous lasers is described in greater detail in “Lasers and Electro-Optics: Fundamentals and Engineering” by Christopher C. Davis, Cambridge University Press, 1996 (ISBN 0-521-30831-3), which is incorporated herein by reference for all that it teaches.
To facilitate a better understanding of the advantages conferred by the present invention, a brief description of a conventional helium-neon laser
10
will be first described in conjunction with FIG.
1
. As illustrated, laser
10
includes a coaxial gas discharge chamber
12
defining a first end
2
and a second end
4
at opposite ends of the coaxial axis. Discharge chamber
12
comprises a concentric capillary bore
18
located coaxially therein. Typically, a support web
20
provides support to ensure centralization and better rotational stability of the capillary bore
18
. A cylindrical cathode
16
is positioned coaxially within the first end
2
of the discharge chamber
12
.
A first mirror mount assembly
40
is hard sealed to the first end
2
. First mirror mount assembly
40
includes a steel mirror mount
42
brazed to end plate
38
. A mirror substrate
44
is coated with a mirror coating
46
and hard-sealed to a mirror cup formed in the mirror mount
42
using a pre-formed glass frit
48
. End plate
38
is sealed to the first end
2
of discharge chamber
12
via a glass-to-metal seal
34
.
A second mirror mount assembly
50
is hard sealed to the second end
4
of discharge chamber
12
. Second mirror mount assembly
50
includes a steel mirror mount
52
brazed to end plate
68
. A mirror substrate
54
is coated with a mirror coating
56
and hard-sealed to a mirror cup formed in the mirror mount
52
using a pre-formed glass frit
58
. In the illustrative embodiment, second mirror mount assembly
50
includes an optional polarizing Brewster window
66
. Brewster window is positioned within the internal chamber of the mirror mount
42
and arranged at a Brewster angle with respect to coaxial axis of the capillary bore
18
. End plate
68
is sealed to the second end
4
of discharge chamber
12
formed by the glass capillary bore
18
via a glass-to-metal seal
64
.
The electrical anode
14
of the laser in this embodiment is formed by the steel mirror mount
58
. Electrical contacts to the cathode
16
are provided by support bonding straps
36
bonded to the cathode
16
and to the end plate
38
. In an illustrative 2 mW design, the resonator defined by the two mirrors
46
and
56
and the capillary bore
18
is typically of a hemispherical design with the bore diameter being 1.5 mm, mirror
54
being a flat mirror, and mirror
44
being a 30 cm concave mirror. The 30 cm concave mirror
44
is the output coupler which has a convex output radius to collimate the exiting radiation. Typical reflectivity for the high reflector is 99.9+%, while the output coupler
44
has a nominal 1% transmission.
An arc discharge is established by applying a voltage from a power supply (not shown) across the anode
14
and cathode
16
. The arc discharge causes the gasses within the discharge chamber
12
to be ionized, forming a plasma thereby. As the ions decay to lower energy states, light radiation is emitted in a manner well-known to those skilled in the art, and amplified by the optical resonator formed by mirrors
44
,
54
and capillary bore
18
such that a lasing action occurs.
The current prior art configuration of a polarizing Brewster window mirror mount assembly as exemplified by mirror mount assembly
50
of the gas laser
10
shown in
FIG. 1
is problematic. Because the Brewster window
66
is configured to reside within the mirror mount, manufacture of the mirror mount
50
is difficult because of the need to clean both sides of the window
66
during manufacture, the need to precisely position the window
66
at the Brewster's angle in order to prevent loss in efficiency (i.e., reduced power output) of the laser from deviation from the Brewster's angle, and the care required to mount the window in order to avoid stressing the window.
Accordingly, a need exists for a new and improved technique for polarizing a laser beam without the use of an internal Brewster angle window integrated into the mirror mount.
SUMMARY OF THE INVENTION
The present invention is a novel method and apparatus for polarizing a laser beam without the use of a mirror mount with an internal integral Brewster window. In accordance with the method and apparatus of the invention, the present invention eliminates the Brewster window altogether and integrates two mirrors, one preferably at approximately 45° with respect to the other, along the exterior of the mirror mount structure. The mirror mount structure is open at one end and has a hollow cavity therein. A pair of mirrors are hard-sealed to the mirror mount structure. The first mirror is partially reflective and the second mirror is maximally reflective. The secon
Costa Jessica
Research Electro-Optics, Inc.
The Law Offices of Jessica Costa, PC
LandOfFree
Method and apparatus for achieving polarization in a laser... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for achieving polarization in a laser..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for achieving polarization in a laser... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3049016