U.S. patent application number 11/338478 was filed with the patent office on 2008-04-10 for cr4+doped mixed alloy laser materials and lasers and methods using the materials.
This patent application is currently assigned to Research Foundation of the City University. Invention is credited to Robert R. Alfano, Alexey Bykov, Vladimir Petricevic.
Application Number | 20080083905 11/338478 |
Document ID | / |
Family ID | 36741024 |
Filed Date | 2008-04-10 |
United States Patent
Application |
20080083905 |
Kind Code |
A1 |
Alfano; Robert R. ; et
al. |
April 10, 2008 |
CR4+DOPED MIXED ALLOY LASER MATERIALS AND LASERS AND METHODS USING
THE MATERIALS
Abstract
A laser medium includes a single crystal of
Cr.sup.4+:Mg.sub.2-xM.sub.xSi.sub.1-yA.sub.yO.sub.4, where, where M
is a bivalent ion having an ionic radius larger than Mg.sup.2+, and
A is a tetravalent ion having an ionic radius larger than
Si.sup.4+. In addition, either a) 0.ltoreq.x<2 and 0<y<1
or b) 0<x<2 and y is 0 or 1 with the proviso that if M is
Ca.sup.2+ and x=1 then y is not 0. The laser medium can be used in
a laser device, such as a tunable near infrared (NIR) laser.
Inventors: |
Alfano; Robert R.; (Bronx,
NY) ; Petricevic; Vladimir; (New York, NY) ;
Bykov; Alexey; (Bronx, NY) |
Correspondence
Address: |
DARBY & DARBY P.C.
P.O. BOX 770, Church Street Station
New York
NY
10008-0770
US
|
Assignee: |
Research Foundation of the City
University
New York
NY
|
Family ID: |
36741024 |
Appl. No.: |
11/338478 |
Filed: |
January 24, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60646546 |
Jan 25, 2005 |
|
|
|
Current U.S.
Class: |
252/301.4R ;
372/41; 372/70 |
Current CPC
Class: |
H01S 3/063 20130101;
H01S 3/0405 20130101; C30B 19/02 20130101; C30B 29/34 20130101;
H01S 3/1658 20130101; H01S 3/1655 20130101; H01S 3/0627 20130101;
H01S 3/1623 20130101; H01S 3/1675 20130101; H01S 3/0604 20130101;
H01S 3/09415 20130101 |
Class at
Publication: |
252/301.4R ;
372/41; 372/70 |
International
Class: |
H01S 3/16 20060101
H01S003/16; H01S 3/091 20060101 H01S003/091; C09K 11/77 20060101
C09K011/77 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] This invention was made with government support under Grant
No. NCC-1-03009 awarded by NASA and Grant No. W911NF0410023 from
the U.S. Department of Defense. The government may have certain
rights in this invention.
Claims
1. A laser medium, comprising: a single crystal of
Cr.sup.4+:Mg.sub.2-xM.sub.xSi.sub.1-yA.sub.yO.sub.4, wherein M is a
bivalent ion having an ionic radius larger than Mg.sup.2+, A is a
tetravalent ion having an ionic radius larger than Si.sup.4+; and
either a) 0.ltoreq.x<2 and 0<y<l; or b) 0<x<2 and y
is 0 or 1 with the proviso that if M is Ca.sup.2+ and x=1 then y is
not 0.
2. The laser medium of claim 1, wherein A is selected from
Ge.sup.4+, Ti.sup.4+, and Zr.sup.4+.
3. The laser medium of claim 2, wherein M is selected from
Ca.sup.2+, Sr.sup.2+, and Ba.sup.2+.
4. The laser medium of claim 2, wherein
0.1.ltoreq.y.ltoreq.0.9.
5. The laser medium of claim 1, wherein
0.1.ltoreq.x.ltoreq.1.9.
6. The laser medium of claim 1, wherein the laser medium is
disposed on a substrate comprising Mg.sub.2SiO.sub.4.
7. The laser medium of claim 1, wherein A is Ge.sup.4+ and x is
0.
8. The laser medium of claim 1, wherein a concentration of
Cr.sup.4+ is at least 1 at. %.
9. A laser comprising: a laser medium comprising a single crystal
of Cr.sup.4+:Mg.sub.2-xM.sub.xSi.sub.1-yA.sub.yO.sub.4, wherein M
is a bivalent ion having an ionic radius larger than Mg.sup.2+, A
is a tetravalent ion having an ionic radius larger than Si.sup.4+;
and either a) 0.ltoreq.x<2 and 0<y<1; or b) 0<x<2
and y is 0 or 1 with the proviso that if M is Ca.sup.2+ and x=1
then y is not 0.
10. The laser of claim 9, wherein the laser is a near infrared
laser.
11. The laser of claim 9, wherein the laser medium is a thin disk
or thin wedge.
12. The laser of claim 9, further comprising a heat sink attached
to a surface of the laser medium.
13. The laser of claim 9, further comprising a pump light source
configured and arranged to provide pumping light to the laser
medium.
14. The laser of claim 9, further comprising a tuning element to
tune a frequency of light emitted by the laser medium.
15. The laser of claim 9, wherein the laser is continuous-wave
mode-locked.
16. A method of making a laser medium, the method comprising:
forming a solution comprising at least one substituent for forming
the laser medium disposed in a solvent, wherein the at least one
substituent is a metal oxide; and forming at least one crystal of
Cr.sup.4+:Mg.sub.2-xM.sub.xSi.sub.1-yA.sub.yO.sub.4 from the
solution, wherein M is a bivalent ion having an ionic radius larger
than Mg.sup.2+, A is a tetravalent ion having an ionic radius
larger than Si.sup.4+; and either a) 0.ltoreq.x<2 and
0<y<1; or b) 0<x<2 and y is 0 or 1 with the proviso
that if M is Ca.sup.2+ and x=1 then y is not 0.
17. The method of claim 16, wherein forming at least one crystal
comprises forming a layer of
Cr.sup.4+:Mg.sub.2-xM.sub.xSi.sub.1-yA.sub.yO.sub.4 on a substrate
by liquid phase epitaxy.
18. The method of claim 17, wherein providing a substrate comprises
providing a Mg.sub.2SiO.sub.4 substrate.
19. The method of claim 16, wherein forming at least one crystal of
Cr.sup.4+:Mg.sub.2-xM.sub.xSi.sub.1-yA.sub.yO.sub.4, comprises
forming at least one crystal of
Cr.sup.4+:Mg.sub.2-xM.sub.xSi.sub.1-yA.sub.yO.sub.4, wherein A is
selected from Ge.sup.4+, Ti.sup.4+, and Zr.sup.4+.
20. The method of claim 16, wherein forming at least one crystal of
Cr.sup.4+:Mg.sub.2-xM.sub.xSi.sub.1-yA.sub.yO.sub.4, comprises
forming at least one crystal of
Cr.sup.4+:Mg.sub.2-xM.sub.xSi.sub.1-yA.sub.yO.sub.4 wherein M is
selected from Ca.sup.2+, Sr.sup.2+, and Ba.sup.2+.
21. The method of claim 16, wherein forming at least one crystal of
Cr.sup.4+:Mg.sub.2-xM.sub.xSi.sub.1-yA.sub.yO.sub.4, comprises
forming at least one crystal of
Cr.sup.4+:Mg.sub.2-xM.sub.xSi.sub.1-yA.sub.yO.sub.4, wherein
0.1.ltoreq.y.ltoreq.0.9.
22. The method of claim 16, wherein forming at least one crystal of
Cr.sup.4+:Mg.sub.2-xM.sub.xSi.sub.1-yA.sub.yO.sub.4, comprises
forming at least one crystal of
Cr.sup.4+:Mg.sub.2-xM.sub.xSi.sub.1-yA.sub.yO.sub.4, wherein
0.1.ltoreq.x.ltoreq.1.9.
Description
RELATED APPLICATIONS
[0001] This patent application claims the benefit of U.S.
Provisional Patent Application Ser. No. 60/646,546, filed Jan. 25,
2005, incorporated herein by reference.
BACKGROUND
[0003] The development of tunable solid state lasers based on the
Cr.sup.4+-ion started in 1988 with forsterite, Cr:Mg.sub.2SiO.sub.4
[V. Petricevic, S. K. Gayen and R. R. Alfano, Appl. Phys. Letters
53 (1988) 2590]. It was extended to other crystalline media, such
as Cr.sup.4+-doped Y.sub.3Al.sub.5O.sub.12 [A. P. Shkadarevich, in:
OSA Proceedings on Tunable Solid State Lasers, Ed. M. L. Shand and
H. P. Jenssen (Optical Society of America, Washington, D.C., 1989),
Vol. 5, pp. 60-65], Y.sub.2SiO.sub.5 [J. Koetke, S. Kuck, K.
Petermann, G. Huber, G. Gerullo, M. Danailov, V. Magni, L. F. Qian,
and O. Svelto, Opt. Commun. 101 (1993) 195], and
Y.sub.3Sc.sub.xAl.sub.5-xO.sub.12 [S. Kuck, K. Peterman, U.
Pohlmann, U. Schonhoff, and G. Huber, Appl. Phys. B58, (1994) 153].
These materials also typically include the chromium dopant within
the crystalline structure in other valence states. These other
valence states can act as a trap and reduce the total concentration
of Cr.sup.4+ lasing ions. Increasing Cr.sup.4+ lasing ion
concentration in the laser materials can improve efficiency of
laser devices.
[0004] Different approaches have been used to increase Cr.sup.4+
concentration in crystals. For example, specific crystal growth
conditions have been created using different total amounts of
chromium oxide in the initial charge, different oxygen content in
the growth atmosphere, and/or different after-growth heat
treatments. Possible mechanisms for chromium ion incorporation in a
crystal structure, with appropriate charge compensation, have also
been discussed. (W. Chen and G. Boulon. Growth mechanism of
Cr:forsterite laser crystal with high Cr concentration, Optical
Materials, 24 (2003) 163-168; R. Feldman, Y. Shimony and Z.
Burshtein. Dynamics of chromium ion valence transformations in
Cr,Ca:YAG crystals used as laser gain and passive Q-switching media
Optical Materials, Volume 24, Issues 1-2, October-November 2003,
Pages 333-344; J. L. Mass, J. M. Burlitch, S. A. Markgraf, M.
Higuchi, R. Dieckmann, D. B. Barber and C. R. Pollock, Oxygen
activity dependence of the chromium (IV) population in
chromium-doped forsterite crystals grown by the floating zone
technique, Journal of Crystal Growth, Volume 165, Issue 3, 1 Aug.
1996, Pages 250-25).
BRIEF SUMMARY
[0005] One embodiment is a laser medium, comprising a single
crystal of Cr.sup.4+:Mg.sub.2-xM.sub.xSi.sub.1-yA.sub.yO.sub.4,
where M is a tetravalent ion having an ionic radius larger than
Mg.sup.2+, and A is a divalent ion having an ionic radius larger
than Si.sup.4+. In addition, either a) 0.ltoreq.x<2 and
0<y<1 or b) 0<x<2 and y is 0 or 1 with the proviso that
if M is Ca.sup.2+ and x=1 then y is not 0.
[0006] Another embodiment is a laser, such as a tunable near
infrared laser, that contains the laser medium.
[0007] Yet another embodiment is a method of making a laser medium.
The method includes forming a solution comprising at least one
substituent for forming the laser medium disposed in a solvent,
wherein the at least one substituent is a metal oxide. At least one
crystal of Cr.sup.4+:Mg.sub.2-xM.sub.xSi.sub.1-yA.sub.yO.sub.4 is
formed from the solution, where M is a tetravalent ion having an
ionic radius larger than Mg.sup.2+, and A is a divalent ion having
an ionic radius larger than Si.sup.4+. In addition, either a)
0.ltoreq.x<2 and 0<y<1 or b) 0<x<2 and y is 0 or 1
with the proviso that if M is Ca.sup.2+ and x=1 then y is not 0. In
one embodiment, the method includes providing a substrate; and
forming a layer of
Cr.sup.4+:Mg.sub.2-xM.sub.xSi.sub.1-yA.sub.yO.sub.4 on the
substrate by liquid phase epitaxy
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Non-limiting and non-exhaustive embodiments of the present
invention are described with reference to the following drawings.
In the drawings, like reference numerals refer to like parts
throughout the various figures unless otherwise specified.
[0009] For a better understanding of the present invention,
reference will be made to the following Detailed Description, which
is to be read in association with the accompanying drawings,
wherein:
[0010] FIG. 1 is a fluorescence spectrum of a chromium-doped
Mg.sub.2GeO.sub.4 powder sample;
[0011] FIG. 2 presents fluorescence spectra for various
chromium-doped Mg.sub.2(Ge.sub.ySi.sub.1-y)O.sub.4 powders;
[0012] FIG. 3 presents fluorescence spectra for chromium-doped
Mg.sub.2GeO.sub.4 in crystals formed in a liquid phase epitaxy
solution (left) and on a Mg.sub.2SiO.sub.4 substrate (right);
[0013] FIG. 4A is a schematic illustration of a first embodiment of
a laser, according to the invention;
[0014] FIG. 4B is a schematic illustration of a second embodiment
of a laser, according to the invention;
[0015] FIG. 5 is a schematic illustration of a third embodiment of
a laser, according to the invention;
[0016] FIGS. 6A and 6B are schematic illustrations of two
embodiments of laser systems, according to the invention;
[0017] FIG. 7 is a schematic illustration of another embodiment of
a laser system, according to the invention; and
[0018] FIG. 8 is a schematic illustration of one embodiment of a
waveguide laser/amplifier, according to the invention.
DETAILED DESCRIPTION
[0019] New laser materials, including near infrared (NIR) laser
materials, can be based on alloys of forsterite
(Mg.sub.2SiO.sub.4). These materials can be used as chromium doped
laser materials (e.g., laser media) for lasers, such as tunable NIR
lasers. Increased Cr.sup.4+ concentrations can often be achieved by
certain isomorphic substitutions which provide enhanced Cr.sup.4+
incorporation conditions in the forsterite crystal structure.
Examples of a suitable laser medium (material) is the Cr-doped
mixed alloy single crystal composition,
Mg.sub.2-xM.sub.xSi.sub.1-yA.sub.yO.sub.4, which has an
olivine-type crystal structure. In this alloy, M=Ca, Sr, Ba or any
other bivalent ions with a larger ionic radius than Mg.sup.2+, and
A=Ge, Ti, Zr or any other tetravalent ions with a larger ionic
radius than Si.sup.4+.
[0020] For these materials, either a) 0.ltoreq.x<2 and
0<y<1 or b) 0<x<2 and y is 0 or 1 with the proviso that
if M is Ca.sup.2+ and x=1 then y is not 0. In some embodiments,
0<x<2 or 0.1.ltoreq.x.ltoreq.1.9 or 0.1.ltoreq.x.ltoreq.1. In
some embodiments, 0.1.ltoreq.y.ltoreq.0.9. In some embodiments,
0.1.ltoreq.x.ltoreq.1.9 and 0.1.ltoreq.y.ltoreq.0.9.
[0021] In some embodiments, the single crystal can have at least
0.05 wt. % Cr.sup.4+ and may have at least 0.1 wt. %, 0.5 wt. %, or
1 wt. % Cr.sup.4+ or more. In some embodiments, the single crystals
have 1 to 5 wt. % Cr.sup.4+.
[0022] In the past, the laser operation of chromium-doped
forsterite (Cr:Mg.sub.2SiO.sub.4) was attributed to the Cr.sup.4+
ion substituting for Si.sup.4+ in the tetrahedrally coordinated
sites of the forsterite structure. Unfortunately, there is also
typically Cr.sup.3+ substitution for Mg.sup.2+ in the octahedrally
coordinated sites. By controlling the crystal growth process
(oxidizing atmosphere, crystal growth direction, etc.) the
Cr.sup.4+/Cr.sup.3+ ratio may be increased, but the total amount
(e.g., concentration) of Cr.sup.4+ in forsterite typically stays at
a relatively low level (typically not exceeding 0.05 wt. %). The
presence of larger divalent ions, such as Ca.sup.2+, can promote
the formation of an optically active Cr.sup.4+ center.
[0023] Synthesis, crystal growth and successful laser operation of
another Cr.sup.4+-doped crystal, Ca.sub.2GeO.sub.4, also having the
olivine structure, has been studied. (V. Petricevic, A. B. Bykov,
J. M. Evans and R. R. Alfano Optics Letters 21 (1996), p. 1750)
This material demonstrated that the crystalline structure,
including the geometry of octahedral and tetrahedral sites, is a
prominent factor for Cr.sup.4+ incorporation (e.g., substitution)
in the crystal structure. The composition of the laser material
defines the parameters of the crystalline structure which
determines the fit of the Cr.sup.4+-ions in the tetrahedral sites.
The composition can provide the conditions for improving Cr.sup.4+
concentration in a laser crystal. Growth conditions such as
temperature and growth atmosphere seem to be secondary factors.
[0024] Spectroscopic studies of different alloys of Cr-doped
olivines related to forsterite show changes of fluorescence
properties demonstrating that the Cr.sup.4+/Cr.sup.3+ ratio depends
on composition of the material. For example, a number of powder
samples of Cr-doped Mg.sub.2GeO.sub.4 were synthesized by solid
state reaction. Synthesis was carried out at 1400.degree. C. for 20
hours in a muffle furnace in an air atmosphere. The initial powder
mixture contained stoichiometric amounts of MgO and GeO.sub.2 doped
with .about.1 wt % Cr.sub.2O.sub.3. The cooling rate was varied
from fast quenching (e.g., crucibles with the material were taken
out from the hot furnace) to slow cooling from 1400.degree. C. to
room temperature over a period ranging up to 48 hours. X-ray powder
diffraction analysis did not reveal any structural difference for
quenched and slow cooled samples. Only the olivine structure was
observed without any traces of a spinel structure.
[0025] Differential thermal analysis (DTA) experiments were also
conducted to detect any polymorphic transitions. The experiments
included very slow heating and cooling conditions around
800.degree. C. No thermal anomalies have been found for the
samples. As a result, no evidence of a spinel structure was
revealed by this DTA study.
[0026] Fluorescence measurements, illustrated in FIG. 1, have been
made for the samples. These measurements also confirmed the
presence of only the olivine structure of Cr-doped
Mg.sub.2GeO.sub.4. The spectrum consisted of two broad bands
attributed to emission from Cr.sup.3+ ions in octahedral occupation
(maximum at 925 nm) and from Cr.sup.4+ ions in tetrahedral
occupation (maximum at 1170 nm). The sharp line at 1360 nm is the
2.sup.nd order emission of the pump diode laser (680 nm)
[0027] In view of the results of the X-ray diffraction, DTA, and
fluorescence measurements on the powder samples, the olivine type
structure of Mg.sub.2GeO.sub.4 is very stable and only this type of
structure is formed during the synthesis procedure. Heating and
cooling procedures do not lead to spinel transformation as
demonstrated in the MgO--GeO.sub.2 diagram of the system. [C. R.
Robbins and E. M. Levin, Am. J. Sci., 257, 65 (1959).]
[0028] A number of Cr-doped alloy Mg.sub.2Ge.sub.1-ySi.sub.yO.sub.4
powder samples (where y varies from 0.1 to 0.9) were generated and
lattice parameters were measured using standard X-ray diffraction
technique together with fluorescence measurements. It was found
that the lattice parameters generally change linearly with
substitution (y=0 to y=1) from pure Mg.sub.2GeO.sub.4 to pure
Mg.sub.2SiO.sub.4. Fluorescence measurements revealed a very
interesting feature concerning Cr.sup.3+ and Cr.sup.4+ distribution
in these materials. As can be seen from FIG. 2, the emission of
Cr.sup.3+ is suppressed (Cr.sup.3+/Cr.sup.4+ ratio is decreased)
for the samples with a composition approaching a Si/Ge ratio equal
to 1. In addition, the wavelength of maximum Cr.sup.4+ emission
shifts to longer wavelength with increasing germanium content in
the samples. (The sharp line at 1360 nm is the 2.sup.nd order
emission of the pump diode laser (680 nm).)
[0029] Laser materials can be formed by a variety of methods
including, but not limited to, liquid phase epitaxy. For oxide
materials, one example of the LPE process is the following: The
constituents of the solution are melted in a platinum crucible at
about 50-100.degree. C. above the saturation temperature. For
example, the solution can include a solvent and stoichiometric
quantities of the desired reactants, such as germanium oxide,
silicon oxide, magnesium oxide, and chromium oxide (or mixed oxides
such as Mg.sub.2SiO.sub.4 or Mg.sub.2GeO.sub.4) in the desired
stoichiometric amounts. Before growth, the melt is stirred to
provide complete dissolution of solute components. The substrate is
mounted horizontally on a platinum holder and preheated in the
furnace. The substrate has an alternate rotation of 50-100 rpm with
a change every 5-10 s. Before dipping, in order to limit the
temperature fluctuations, the substrate is to stay a few minutes
above the melt. During growth, the melt temperature is kept
constant. After the growth a rapid speed rotation (800 rpm) should
be used in order to eliminate the solvent droplets. Then the
substrate is pulled out of the furnace slowly in order to avoid
thermal stresses.
[0030] Two types of solvent, based on PbO and Bi.sub.2O.sub.3, were
tested. The test method was based on preparation of a number of
compositions in "Solvent (PbO or Bi.sub.2O.sub.3)--Solute
(Cr:Mg.sub.2GeO.sub.4)" systems with different concentrations of
solute and then undergoing a heating procedure until partial
melting occurred. It was found that PbO did not generally provide
good crystallization parameters, but Bi.sub.2O.sub.3 proved to be
very promising, because even compositions with Cr:Mg.sub.2GeO.sub.4
content less that 10 mol. % were characterized by crystallization
of Cr:Mg.sub.2GeO.sub.4. The presence of Cr:Mg.sub.2GeO.sub.4
micro-crystals in solidified samples was detected by measurement of
emission properties.
[0031] A starting composition for crystal growth of
Cr:Mg.sub.2GeO.sub.4 was the following: MgO--0.025 mol.,
GeO.sub.2--0.025 mol., Bi.sub.2O.sub.3--0.25 mol.,
Cr.sub.2O.sub.3--0.0075 mol. Crystallization temperature for this
composition was below 1050.degree. C. It was found that
Mg.sub.2SiO.sub.4 crystal placed in the melt did not exhibit any
traces of dissolution. Only oriented heteroepitaxial growth of
Cr:Mg.sub.2GeO.sub.4 was observed on the surface of
Mg.sub.2SiO.sub.4 crystal.
[0032] Spontaneous crystallization of Cr:Mg.sub.2GeO.sub.4 was also
observed in the high-temperature solution. Crystals up to 1 mm in
size were formed on the surface as a crust for a period of 20
hours. Emission properties of crystals and layers grown in
Bi.sub.2O.sub.3-based flux are shown in FIG. 3. Both crystals and
layers exhibit Cr.sup.3+ and Cr.sup.4+ emission.
[0033] As can be seen from FIGS. 1, 2, and 3 the fluorescence
spectra of powder, single crystals, and epitaxial layers of
Cr-doped Mg.sub.2GeO.sub.4 are similar, and all of them contain
both Cr.sup.3+ and Cr.sup.4+ emission bands. The results of
fluorescence measurements of Cr-doped mixed Mg.sub.2(Ge,Si)O.sub.4
compositions indicate that compositions containing mixtures of
germanium and silicon ions have spectra similar to that of
Mg.sub.2GeO.sub.4 and Mg.sub.2SiO.sub.4.
[0034] FIGS. 4A and 4B illustrate two different designs for using
the laser medium in a thin disk or slab laser system depending on
pumping geometry. In both concepts the dielectric mirror coatings
108, 110 on the disk itself define the resonator of the oscillator.
In the first configuration (FIG. 4A), the cooled face of the disc
102 is optically coated to act as a total reflector, the disk is
mounted on a heat sink 104 (e.g., a copper heat sink), and pumping
light 106 is directed to the front disk surface. In another
configuration (FIG. 4B), the cooled face of the disk 102 is
transparent to pumping radiation and highly reflecting for laser
emission, the laser disk is mounted on a transparent heat sink 104
(e.g., a sapphire heat sink) and axial back pumping light 106 is
directed through the transparent sapphire heat sink.
[0035] In a modified version (FIG. 5) of the first configuration,
the cooled face of the disk 102 (in this embodiment, a wedge slab)
is optically coated to act as a total reflector. The wedge slab can
be used as an active element to increase pump efficiency. The
reflective coatings 108, 110 are on different components of the
laser forming a resonator cavity 112. The disk 102 also includes an
antireflective coating 114 on the surface that receives the pumping
light 106.
[0036] A variety of lasers, including near infrared (NIR) lasers,
can be formed using these materials, including, for example, lasers
containing the arrangements schematically illustrated in FIGS. 4A,
4B, and 5. One example of a laser system that can be built as an
all solid state compact laser with a thin
Mg.sub.2-xM.sub.xSi.sub.1-yA.sub.yO.sub.4 disk is schematically
illustrated in FIG. 6A. At the heart of the laser is a
Mg.sub.2-xM.sub.xSi.sub.1-yA.sub.yO.sub.4 disk 302 disposed on a
transparent heat sink 304 (e.g., a sapphire heat sink.) The disk is
pumped with light from diode bars 306 (or any other suitable
pumping light source.) For example, a laser diode stack consisting
of a number bars can be used for pumping. Pumping light is
delivered to the laser head by a planar waveguide 308. The
radiation emitted by each bar was first collimated individually by
a cylindrical microlens 310. A planar waveguide is used to shape
the emitting beams of the laser diodes. Two cylindrical lenses 312
are used to focus the collimated diode laser beam into the planar
waveguide. Using imaging optics, for example, cylindrical and
spherical lenses, after the waveguide, a homogeneous pumping line
is obtained and coupled into the
Mg.sub.2-xM.sub.xSi.sub.1-yA.sub.yO.sub.4 disk crystal through the
transparent heat sink 304. The dielectric mirror coatings 314, 316
on the disk itself define the resonator of the oscillator. The
cooling face of the disk attached to the heat sink is coated for
high reflectivity at the laser wavelength and high transmission at
the pumping wavelength, while the other side is high reflection
coated for both wavelengths.
[0037] A second example is schematically illustrated in FIG. 6B,
where a similar pump assembly (with laser diode bars 306, optics
310, 312, and waveguide 308) is used to pump a
Mg.sub.2-xM.sub.xSi.sub.1-yA.sub.yO.sub.4 wedge 302 from its front
surface. Heat management in the gain medium (wedge) is central to
successful operation of this laser and is provided by a heat sink
304 (e.g., a copper heat sink.) The wedge 302 includes a high
reflective coating 314 on the back side near the heat sink 304 and
an antireflective coating 318 on the front side. A coupler 320 is
provided with a 95% reflective coating at the laser wavelength.
[0038] In another embodiment schematically illustrated in FIG. 7,
for pulsed operation, the near-IR light from the laser head (e.g.,
laser disk 402) can then be directed through a series of dispersive
mirrors 404a, 404b to a semiconductor saturable absorber mirror 406
that induces passive mode-locking. The laser light can pass through
a mirror 408 and a tuning element 410 to an output coupler 412.
[0039] An example of a waveguide laser device is schematically
illustrated in FIG. 8. A pump diode laser 502 provide pumping light
through a coupling optic 506 to a waveguide 504 made of the
Cr.sup.4+ material described above. As an example, the waveguide
has a coating 508 that is highly reflective at the laser frequency
and highly transmissive at the pumping frequency and a second
coating 510 that is 95% reflective at the laser frequency.
[0040] It will be recognized that these examples of lasers and
waveguide laser devices can include more or fewer components or can
be modified in accordance with known configurations of lasers and
other devices.
[0041] The above specification, examples and data provide a
description of the manufacture and use of the composition of the
invention. Since many embodiments of the invention can be made
without departing from the spirit and scope of the invention, the
invention also resides in the claims hereinafter appended. The
entire disclosure of each paper, patent, patent application, and
other reference cited herein is incorporated herein by reference
for all purposes.
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