Laser apparatus
In a first embodiment, the invention makes use of a Neodymium doped YAG (Nd:YAG) gain medium placed in an optical resonant cavity formed by two mirrors. Power extraction is maximized for a specific laser cavity. In particular the concave curvature on the rod ends contributes a negative lensing component to modify the strength of the thermal lens. In a second embodiment the present invention uses an amplifier rod medium with curved ends to act as lensing elements to collect emission from the laser gain medium and/or oscillator described in the first embodiment of the invention. The combination of thermal lens and curved rod ends produces a lensing effect which allows light to be directly coupled from a laser. In addition, variation of the input pump power allows for control of the thermal lens formed within the amplifier rod.
1. A laser amplifier including a solid state laser gain medium, the solid state laser gain medium having first and second ends along a laser optical axis in which each end is profiled concave to provide a level of thermal lens compensation at a desired operating pump power such that the beam has a beam quality factor M 2 maximized at the desired operating pump power, wherein the solid state laser gain medium is configured to operate in a laser oscillator cavity that is optically symmetrical and includes flat cavity end reflectors, said laser amplifier further comprising:
a laser cavity; and
an amplifying module external to the laser cavity, said amplifying module sharing a common axis of emission with said laser cavity and comprising an amplifier gain medium having first and second ends along said axis of emission;
whereby at least one of said first or second ends of said amplifying module is profiled to produce a lensing effect so as to directly couple light from said laser cavity into said amplifying module.
2. A laser amplifier as defined in claim 1 , wherein the solid state laser gain medium is configured to operate in a laser oscillator cavity arranged to incorporate a Q-switch or further gain modules.
3. A laser amplifier as defined in claim 1 , in which the solid state laser gain medium is formed of Nd:YAG.
4. A laser oscillator cavity including a solid state laser gain medium as defined in claim 1 .
5. A laser oscillator cavity as defined in claim 4 , further comprising:
a Q-switch having first and second acousto-optic cells in respective first and second non-parallel polarization orientations, wherein at least one of said first and second acousto-optic cells has a reflective end forming a cavity end reflector.
6. A laser oscillator cavity as defined in claim 4 , further comprising:
a frequency converter; and
a frequency selective reflector between the solid state laser gain medium and the frequency converter.
7. A laser including a solid state laser gain medium as defined in claim 1 .
8. A laser as defined in claim 7 , further comprising:
a side-pumping diode element.
9. A laser ablation device comprising a laser as defined in claim 7 .
10. A laser amplifier as defined in claim 1 , wherein one or both of said first or second ends of said amplifying module are profiled to form an amplifier lens having a predetermined focal length in order to maximize the beam quality factor M 2 of the laser cavity at a desired pump power, and wherein the amplifier lens is one of a refractive lens, a diffractive lens, or a GRIN lens.
11. A laser amplifier as defined in claim 10 , wherein said at least one end of said solid state laser gain medium is profiled to form a first lens having a focal length that is substantially equal to the focal length of said amplifier lens.
12. A laser amplifier as defined in claim 1 , whereby said laser gain medium lens and said amplifier gain medium lens are concavely profiled.
13. A laser amplifier as defined in claim 1 , wherein said laser gain medium and said amplifying gain medium are pumped simultaneously, and wherein said laser gain medium pump and said amplifying pump have equal power.
14. A laser amplifier as defined in claim 1 , in which an input surface to the amplifying module is tilted.
15. A laser amplifier having:
a laser cavity; and
an amplifying module external to the laser cavity, said amplifying module sharing a common axis of emission with said laser cavity and comprising a laser gain medium having first and second ends along said axis of emission;
whereby at least one of said first or second ends is profiled so as to directly couple light from said laser cavity into said amplifying module;
wherein said laser gain medium and said amplifying medium are pumped simultaneously;
wherein in said module for an amplifier medium comprising a rod of diameter D R , length L R , refractive index n L , refractive index of air n air , and thermal focal length f th arranged to receive an input beam from a laser having waist distance d 0 from the input rod end, the rod is profiled with a radius of curvature R given approximately by
R
=
d
0
(
4
f
th
-
L
R
)
(
n
L
-
n
air
)
n
L
(
4
f
th
-
L
R
-
2
d
0
)
.
16. A method of designing a laser amplifier having a profile as defined in claim 15 .
17. A laser assembly comprising a gain medium as defined in claim 1 and an amplifier as defined in claim 1 coupled therewith.
18. A module as defined in claim 13 , in which, for an amplifier medium comprising a rod of diameter D R , length L R , refractive index n L , refractive index of air n air , and thermal focal length f th arranged to receive an input beam from a laser gain medium having waist distance d 0 from the input rod end, the rod is profiled with a radius of curvature R given approximately by
R
=
d
0
(
4
f
th
-
L
R
)
(
n
L
-
n
air
)
n
L
(
4
f
th
-
L
R
-
2
d
0
)
.