Tm-doped disordered molybdate crystals for ultrafast mode-locked lasers

Abstract

5 at% Tm-doped NaGd(MoO4)2 laser crystal operated in CW conditions provided up to 641 mW of output power at lambda ~ 1910 nm with a slope efficiency of 50.8% and a pump power laser threshold of 166 mW. 10 at% Tm-doped Li3Ba2Lu3(MoO4)8 laser operated in quasi-CW conditions provided up to 510 mW of output power at lambda ~ 1950 nm with a slope efficiency of 71.4% and a pump power laser threshold of 125 mW. Both crystals were grown by the Top Seeded Solution Growth method at about two hundreds degrees below their melting points. The structural disorder of these crystals confers inhomogenous broadening to the Tm3+ electronic transitions. Slightly broader laser tuning range and laser emission bandwidths are observed in the Li3Ba2Lu3(MoO4)8 crystal despite of the lower expected degree of crystalline disorder. The crystals are promising for the development of mode locked ultrafast (fs) lasers with emission close to lambda = 2 mum.

Full text

Tm-doped disordered molybdate crystals for ultrafast mode-locked
lasers
M. D. Serrano*, X. Han, M. Rico, C. Cascales and C. Zaldo†
Instituto de Ciencia de Materiales de Madrid. Consejo Superior de Investigaciones Científicas.
c/ Sor Juana Inés de la Cruz 3. 28049 Madrid. Spain.
ABSTRACT
5 at% Tm-doped NaGd(MoO4)2 laser crystal operated in CW conditions provided up to 641 mW of output power at λ≈
1910 nm with a slope efficiency of 50.8% and a pump power laser threshold of 166 mW. 10 at% Tm-doped
Li3Ba2Lu3(MoO4)8 laser operated in quasi-CW conditions provided up to 510 mW of output power at λ≈ 1950 nm with a
slope efficiency of 71.4% and a pump power laser threshold of 125 mW. Both crystals were grown by the Top Seeded
Solution Growth method at about two hundreds degrees below their melting points. The structural disorder of these
crystals confers inhomogenous broadening to the Tm3+ electronic transitions. Slightly broader laser tuning range and
laser emission bandwidths are observed in the Li3Ba2Lu3(MoO4)8 crystal despite of the lower expected degree of
crystalline disorder. The crystals are promising for the development of mode locked ultrafast (fs) lasers with emission
close to λ= 2 μm.
Keywords: Crystalline-laser, Tm-laser, ultrafast-laser, disordered-crystals, crystal growth.
1. INTRODUCTION
The production of mode-locked femtosecond (fs) laser pulses requires of optical gain media with sufficient spectral
bandwidth. First fs laser demonstrations were made at in the 1970-1980 decade by using dyes dissolved in alcohols.
This culminated in 27 fs laser pulses with a Rhodamine 6G dye. 1 With different dyes the fluorescence can be tuned all
along the visible and in the near infrared spectral regions with full width at half maximum (FWHM) for each single dye
about 20-50 nm. Dye toxicity and optical bleaching effects limit the wide spread use of dye lasers. The development of
Ti-sapphire (Ti:Al2O3, Ti-sa) laser by Moulton in 1986 2 introduced the nowadays workhorse crystal for fs laser
applications. This laser can be tuned from λ= 650 nm to wavelengths slightly larger than λ=1000 nm, and it is based on
the electronic transitions of d electrons of Ti3+ (3d1 electronic configuration). The strong interaction of d electrons with
the crystal vibrating environment is the origin of the large emission bandwidth, Δλ> 100 nm. This is in fact also found
for other transition metal ions of interest for solid state lasers, such as Cr2+, etc.
Despite of the very good physical and laser properties of Ti:Al2O3 crystals, their requirement of blue/green optical
pumping prevents efficient direct pumping with semiconductor diode lasers presently developed, what limits the energy
scaling of these lasers. This limitation along with the demand for applications for λ>1 μm have promoted a strong
investigation on other lasant ions which can be pumped directly with diode lasers. In particular Yb3+,3 Nd3+,4 Tm3+,5 and
Ho3+,4 are widely considered for the development of diode laser pumped solid state lasers at λ= 1.05 μm, λ= 1.06 μm,
λ= 1.8-2.0 μm, and λ= 2.06 μm, respectively.
Trivalent lanthanides with 4fn intraconfigurational electronic transitions typically exhibit absorption and emission bands
much narrower than those observed for transition metal ions with 3dn electronic configuration. This is due to the Crystal
Field shielding of 4f electrons by outer, although less energetic, 5s2 5p6 electrons. These optical bandwidths of the 4f-4f
absorption and emission transitions of trivalent lanthanides have typicallyΔλ≈ 1 nm, and they are not generally suited for
fs pulsed lasers. However, the magnitude of this shielding decreases as the 4f orbital is filled, and Tm3+ (4f12 electronic
configuration) and Yb3+ (4f13 electronic configuration) show significant band broadening in comparison to the rest of
* dolores.serrano@icmm.csic.es, phone (34)913349000; fax (34)913725623
† cezaldo@icmm.csic.es, phone (34)913349057; fax (34)913725623
Laser Technology for Defense and Security VII, edited by Mark Dubinskii, Stephen G. Post,
Proc. of SPIE Vol. 8039, 803904 · © 2011 SPIE · CCC code: 0277-786X/11/$18 · doi: 10.1117/12.886650
Proc. of SPIE Vol. 8039 803904-1
Downloaded from SPIE Digital Library on 14 Jul 2011 to 161.111.20.21. Terms of Use: http://spiedl.org/terms

trivalent lanthanides. In fact, a lot of work has been done in the past ten years on diode laser pumped (at λ≈ 980 nm)
ultrafast Yb3+ laser oscillators and amplifiers. 6
Because of the inherently large bandwidth of Tm3+ optical transitions this ion is also well suited for mode-locked solid
state lasers at λ= 1.8-2.0 μm and can be pumped with AlGaAs diode lasers at λ≈ 800 nm, but until very recently little
progress has been obtained in the achievement of fs laser pulses. The main limitation was the lack of fast enough
passive saturable absorbers. Recently, single walled carbon nanotubes have been used to produce 10 ps pulses with a
Tm-doped KLu(WO4)2 crystal, 7 but entering in the fs range with Tm3+ single doped crystals is still challenging.
Another use of Tm3+ is as sensitizer of Ho3+, since the later ion has emission at λ≈ 2.06 μm, but it can not be directly
excited with current diode lasers. As mentioned above, the Ho3+ emission in most single crystals is quite narrow and
should not support very short laser pulses, nevertheless, with a new design of semiconductor saturable absorber mirror
(SESAM), based on InGaAsSb quantum wells on a GaSb/AlAsSb Bragg reflector, and by using a Tm,Ho codoped
KY(WO4)2 crystal laser pulses as short as 570 fs have been demonstrated at λ= 2.055 μm. 8
Even more recently, a
significant reduction of the pulse duration down to 191 fs has been obtained by using a Tm:Ho co-doped NaY(WO4)2
disordered crystal in the same experimental setup. 9
This shows the relevance of lattice disorder for fs mode-locked
lasers.
We consider disordered crystals those having one or more crystallographic sites shared by two or more constituent ions
of the host crystal. In such crystals Tm3+ and other lanthanides undergo a spatially variable Crystal Field inducing
inhomogeneus broadening of their optical transitions. In this respect, disordered crystals resemble the spectroscopic
features of Tm-doped glasses but they provide better thermal conductivity (κ). Table 1 shows a non exhaustive list of
crystals with this characteristic along with some physical properties relevant for the laser applications.
Table 1. Single crystals with structural disorder used for generation of ultrafast laser pulses and some relevant thermal properties.
Melting point, mp (ºC). Thermal conductivity, κ (W m-1 K-1). Specific heat, Cv (J mol-1 K-1). Thermal expansion coefficient, α
(10-6 ºC-1). * , compounds with incongruent melting.
Crystal formula Site, disorder mp
κ
C
v α
Ca4TO(BO3)3 Ca/T=Y, Gd
≈
1480
CaT4(SiO4)3O Ca/T= Y, La Y - La
2050-2170
1.7-1.9 Y - La
a, 7.1-8.9
c, 5.1-6.6
SrY4(SiO4)3O 4f, 0.75Sr/0.25Y
6h, Y
//c, 2.85
⊥c, 1.5
NaT(WO4)2 T=Y, Gd, Lu*
2b, ≈0.5Na/0.5T
2d, ≈0.5Na/0.5T
Y - Gd
1210-1260
Y - Gd
a, 1.06-1.09
c, 1.17-1.24
Y, 232
Gd, 236
Y - Gd - Lu
a, 8.4 - 6.7 - 8.2
c, 18.5-16.3- 17.3
CaGdAlO4 Ca/Ga
≈
1700 a, 6.3
c, 6.9
a, 10.1
c, 16.2
Ca3(Nb,Ga)2-xGa3O12 <1500 3.43
NaGd(MoO4)2 Na/Gd
≈
1180 303
Li3Ba2T3(MoO4)8 Li/T=Gd, Lu
8f, 0.2Li/0.8Gd
Gd
983
Gd
205
Gd
a, 16.2
b, 17.3
c, 21.5
Tetragonal double tungstate disordered crystal family, NaT(WO4)2, has rather low congruent melting point and
therefore it is attractive for laser applications because platinum crucibles and normal atmospheric conditions can be used
during the crystal growth, leading to the reduction of the crystal cost. In the recent years a systematic characterization of
the laser properties of these crystals doped with Yb or Tm has been reported. 10,11 The isostructural double molybdates
are less studied, but they offer several advantages over tungstates, namely lower melting points and higher lanthanide
optical cross sections.
Proc. of SPIE Vol. 8039 803904-2
Downloaded from SPIE Digital Library on 14 Jul 2011 to 161.111.20.21. Terms of Use: http://spiedl.org/terms

In this work we present the spectroscopic characterization and continuous wave (CW) laser operation of two disorder
crystals related with the total or partial substitution of the divalent (Ca2+) cation of the CaMoO4 crystal. In the first case,
Ca2+ is completely substituted by a pair of monovalent and trivalent cations leading to the double molybdate
NaGd(MoO4)2 formula. In the second considered case, a mixture of 25 % of remaining divalent cations (Ba2+), and 75%
of monovalent Li+ and trivalent Lu3+ cations are coexisting, leading to the Li3Ba2Lu3(MoO4)8 formula. Crystals of both
compounds could be grown at temperatures much lower than other disordered crystals of Table 1 and they show efficient
laser operation.
2. EXPERIMENTAL
The Top Seeded Solution Growth (TSSG) method was used to obtain Tm-doped NaGd(MoO4)2 and Li3Ba2Lu3(MoO4)8
single crystals. The crystals were grown in open air using platinum crucibles and resistive furnaces with Kantal heating
elements. For Tm-doped NaGd(MoO4)2 the used flux was a Na2MoO4/Na2Mo2O7 mixture. The Tm doping level was 5
at%, the saturation temperature was found at 930 ºC, i.e. 250ºC lower than the melting temperature, and the crystal
growth proceeded during melt cooling at a rate of 0.06 ºC/h.
Li3Ba2Lu3-xTmx(MoO4)8 crystals were grown in Li2MoO4 flux with a 5:1 flux to solute molar ratio. The saturation
temperature was found at 799 °C. To grow the crystal the melt was cooled at a rate of 0.05 °C/h for an interval of 19 ºC.
A b-oriented seed of the same crystal was used to induce crystal nucleation. After growth finish the crystal was removed
from the melt and cooled to room temperature at a rate of 6 °C/h. The grown crystals have square cross section shape
with dimensions about 30×20 mm2.
Laser characterization was made with a plane-concave resonator formed by a mirror M1 designed for high transmission
at the pump wavelength (T>98%) and high reflectivity in 1800-2100 nm range and ended by output couplers (OC) with
-100 mm of radius and different transmissions (TOC) at λ≈ 2000 nm. To study the laser tunability a birrefringent (Lyot)
filter made of quartz was introduced in the optical cavity at Brewster angle.
Figure 1. 5 at% Tm-doped NaGd(MoO4)2 crystal used in laser experiments (top). Setup used for
laser demonstration (bottom). The laser crystal is pumped with a Ti-sapphire laser focused with a
70 mm of focal length lens through a plane mirror, M1. Output couplers, OC, with a radius of
curvature of 100 mm and different optical transmissions were used to extract the laser beam. For
tuning experiments a Lyot filter set at Brewster angle was introduced in the cavity. The sample
was glued with silver paint to a copper plate.
Proc. of SPIE Vol. 8039 803904-3
Downloaded from SPIE Digital Library on 14 Jul 2011 to 161.111.20.21. Terms of Use: http://spiedl.org/terms

3. RESULTS
3.1. NaGd(MoO4)2
It is expected that the tetragonal Tm-doped NaGd(MoO4)2 crystal has a Na and Gd distribution over the two possible 2d
and 2b crystal sites similar to that observed in other tetragonal double tungstates, i.e. close to 50 % for each ion.12 Tm
doped NaGd(MoO4)2 crystals can be grown by the Czochralski method but after growth they appear colored due to the
presence of a broad absorption band covering the whole visible and near infrared region. 13 Such coloration was avoided
in the crystals presently used by growing them at a temperature lower than in the Czochralski case and by using the flux
as reservoir for the Na and W evaporated from the melt. TSSG as-grown crystals were fully transparent and there was
not need of post-growth annealing.
Figure 2. Output power as a function of absorbed pump power in CW regime of a 2.496 mm thick 5 at% Tm-doped NaGd(MoO4)2
crystal grown by TSSG (filled symbols, ● and ■), excitation parallel to a-axis, λEXC= 794.5 nm. Hollow symbols (○ and □) represent
the data obtained in Ref. [12] for crystals grown by the Czochralski method and annealed in air.
Figure 3. Room temperature free running spectra of the laser emission of 5 at% Tm-doped NaGd(MoO4)2 (a) and 10 at% Tm-doped
Li3Ba2Lu3(MoO4)8 (b) crystals grown by TSSG for different output coupler transmissions. λEXC= 794.5 nm (a) and λEXC= 796.2 nm
(b). The figure shows in different colours superimposed spectra taken at different times. The dotted line for TOC= 2.4% indicate the
envelop of the laser emission spectrum used for the estimation of the FWHM of the laser emission.
Proc. of SPIE Vol. 8039 803904-4
Downloaded from SPIE Digital Library on 14 Jul 2011 to 161.111.20.21. Terms of Use: http://spiedl.org/terms

Figure 2 shows the room temperature input-output power characteristic of a 2.496 mm thick a-cut 5 at% Tm-doped
NaGd(MoO4)2 (with a Tm concentration [Tm]≈ 2.5×1020 cm-3) laser sample in comparison to previous results obtained in
Czochralski grown crystals. 13 The crystal was pumped at λ= 794.5 nm and the laser emission was at λ≈ 1910 nm At
the maximum incident pump power of 2.4 W the absorbed power under laser operation was about 1.4 W, i.e. the sample
absorption was only about 60%. The pump power laser threshold varied from 99 mW to 166 mW for TOC= 2.4 and 8%,
respectively. The output power (Pout) increased with the output coupler transmission. The Pout and slope efficiency versus
absorber power (η) reached 477.5 mW – 37.2% and 641 mW – 50.8% for TOC transmissions of 2.4 %, and 8 %,
respectively. These results are superior to those obtained with a similar cavity setup in Czochralski grown crystals
annealed to eliminate the coloration. It must be concluded that residual defects after the annealing act as killer centers of
the Tm3+ emission.
The tuning range of the emission obtained with the Lyot filter and TOC= 8% extends from λ= 1874 nm to λ= 1967 nm.
We also monitored the spectral distributions of the free running laser emission for different laser gains, see Figure 3a.
From these results we concluded that the average laser emission wavelength systematically decreases with increasing
cavity losses: 1948 nm (T=0.6%), 1936 nm (TOC= 1.1%), 1927 nm (TOC= 2.4%), 1923 nm (TOC= 4%) and 1910 nm
(TOC= 8%). Moreover, as a first approximation we can take these spectral distribution as a reference for the fs laser
potential of this crystal. The FWHM of the envelop of the superposition of the free running spectra is about 14 nm for
TOC= 2.4%. If this is considered as the spectral bandwidth during mode locked laser operation the crystal could support
sech2 pulses with duration below 300 fs.
3.2. Li3Ba2Lu3-xTmx(MoO4)8
The disordered Li3Ba2Lu3-xTmx(MoO4)8 crystal is monoclinic (space group C2/c). In this crystal the disorder arises from
the Li and Lu (and Tm) occupancy of a same 8f crystal site with occupancy factors about 0.2 and 0.8, respectively. 14
Although the crystal is monoclinic, β angle is 91.52º , i.e. the crystal structure is close to orthorhombic. While the b
crystal axis of the monoclinic system coincides with one of the principal optical axes, the two other optical axes are
rotated with regards to a and c crystal axes. Preliminary measurements made on this crystal show that for the 3H4
absorption at λ≈ 800 nm these optical axes are rotated ≈20º with regards to the crystallographic a and c axes. Figure 4a
shows one of the Li3Ba2Lu3-xTmx(MoO4)8 crystals grown.
Figure 4. Image of an as-grown Li3Ba2Lu3-xTmx(MoO4)8 crystal (a). Input-output power characteristics in quasi-cw regime of the 10
at% Tm-doped Li3Ba2Lu3(MoO4)8 laser for TOC= 4%. The symbols are the experimental results and the lines are fits for calculation of
the slope efficiency. a-cut sample pumped parallel to b crystal axis (b) and same sample pumped parallel to c crystal axis (c).
The largest absorption cross section of the 3H4 multiplet was found at λ= 797 nm for light polarized parallel to the
optical a´-axis (20º apart from the a crystal axis), σa´= 3.8×10-20 cm2. For other orientations the absorption cross section
decreases, for instance σb= 2.7×10-20 cm2 for light polarized parallel to the b crystal axis. However, the 3F4 Tm3+ gain
Proc. of SPIE Vol. 8039 803904-5
Downloaded from SPIE Digital Library on 14 Jul 2011 to 161.111.20.21. Terms of Use: http://spiedl.org/terms

cross section is optimized for light polarized parallel to the b crystal axis. For this reason in the laser studies we used a-
cut samples.
Laser tests were made with a 10 at% Tm doped a-cut Li3Ba2Lu3-xTmx(MoO4)8 crystal sample with thickness 2.04 mm.
The Tm density of this crystal is [Tm]= 2.95×1020 cm-3 , i.e. similar to that used for the NaGd(MoO4)2 crystal above. This
sample allowed the excitation along the b and c crystal axes. The Ti-sa pump laser was tuned at λEXC= 796.2 nm. As the
thermal conductivity of this crystal is yet unknown to avoid thermal effects or sample damage the pump laser beam was
chopped with a 50% duty cycle. The pump absorption of the samples at low pump power and under non-lasing
conditions was ≈80%. In both crystal orientations the maximum laser efficiency was obtained with TOC= 4%. The laser
pump threshold power was about 125 mW and in both orientations the laser provided ≈510 mW of laser output at λ≈
1950 nm with slope efficiency around 70 %. The emission of the crystal was always polarized parallel to the crystal b
axis.
The tuning range obtained for this laser extends from λ= 1853 nm to λ= 2009 nm. The FWHM of the multimode envelop
of the free running spectra was studied in a manner similar to that described above for the NaGd(MoO4)2 case, see Figure
3b. We obtained a FWHM of the free running laser emission spectra of about Δλ= 22 nm, which promise a Fourier limit
of sub 200 fs for the pulse duration during mode locked laser operation at λ≈ 1900 nm. Interestingly, both the Fourier
limit and the laser tuning range obtained for the Tm-doped Li3Ba2Lu3(MoO4)8 crystal are shorter than the equivalent
values estimated for Tm-doped NaGd(MoO4)2 despite that in the latter crystal the occupancy factors of the
crystallographic shared sites are closer to a random disorder. More work is required to fully understand this situation.
4. CONCLUSIONS
NaGd(MoO4)2 and Li3Ba2Lu3(MoO4)8 are single crystals with different degrees of structural disorder. In NaGd(MoO4)2
Na and Gd (or Tm) share two crystallographic sites, 2b and 2d, with occupancy factors close to 0.5/0.5 for both sites
while in Li3Ba2Lu3(MoO4)8, Li and Lu (or Tm) fill the same 8f crystal site with occupancy factors about 0.2 and 0.8,
respectively, i.e. NaGd(MoO4)2 appears to have a larger degree of disorder than Li3Ba2Lu3(MoO4)8 and consequently
larger inhomogenous spectral band broadening may be expected in the first crystal with tetragonal structure. Single
crystals of both compounds have been grown by the Top Seeded Solution Growth method at temperatures of several
hundreds degrees below their melting points. Na2MoO4/Na2Mo2O7 and Li2Mo2O7 fluxes were successfully used for the
growth purposes for each crystal composition, respectively.
5 at% Tm-doped NaGd(MoO4)2 laser was operated in CW conditions and provided up to 641 mW of output power with
a slope efficiency of 50.8% and a pump power laser threshold of 166 mW. These performances improve notably those
obtained for the same crystal grown by the Czochralski method. 10 at% Tm-doped Li3Ba2Lu3(MoO4)8 laser was
operated in quasi-CW conditions and provided up to 510 mW of output power λ≈ 1950 with a slope efficiency of 71.4%
and a pump power laser threshold of 125 mW. Slightly broader laser tuning range and laser emission bandwidths are
observed in the Li3Ba2Lu3(MoO4)8 crystal despite of its apparently lower degree of crystalline disorder.
Acknowledgements. This work has been supported by Spanish Government under project MAT2008-06729-C02-01.
5. REFERENCES
[1] Valdmains, J. A., Fork, R. L., Gordon, J. P., “Generation of optical pulses as short as 27 femtoseconds directly form
a laser balancing self-phase modulation, group-velocity dispersion, saturable absorption, and saturable gain” Opt. Lett.
10, 131-133 (1985)
[2] Moulton, P. F., “Spectroscopic and laser charactristics of Ti-Al2O3”, J. Opt. Soc. Am. B 3, 125-133 (1986).
[3] Hönninger, C., Paschotta, R., Graf., M., Morier-Genoud, F., Zhang, G., Moser, M., Biswal, S., Nees, J., Braun, A.,
Mourou, G. A., Johannsen, I., Giesen, A., Seeber, W. and Keller, U., “Ultrafast ytterbium-doped bulk lasers and laser
amplifiers” Appl. Phys. B 69, 3-17 (1999).
[4] Kemp, A. J., Valentine, G. J., and Burns, D., “Progress towards high-power, high-brightness neodymium-based thin-
disk lasers” Progr. Quantum Eletr. 28, 305-344 (2004).
[5] Sorokin, E., Sorokina, I. T., and Wintner, E., “Diode-pumped ultra-short-pulse solid state lasers” Appl. Phys. B. 72,
3-14 (2001).
Proc. of SPIE Vol. 8039 803904-6
Downloaded from SPIE Digital Library on 14 Jul 2011 to 161.111.20.21. Terms of Use: http://spiedl.org/terms

[6] Südmeyer, T., Kränkel, C., Baer, C.R.E., Heckl, O. H. Saraceno, C. J., Golling. M., Peters, R., Petermann, K., Huber,
G., and Keller, U., “High-power ultrafast thin disk laser oscillators and their potential for sub-100-femtosecond pulse
generation” Appl. Phys. B 97, 281-295 (2009).
[7] Cho, W. B., Schmidt, A., Yim, J. H., Choi, S. Y., Lee, S., Rotermund, F., Griebner, U., Steinmeyer, G., Petrov, V.,
Mateos, X., Pujol, M. C., Carvajal, J. J., Aguiló, M., and Díaz, F., “Passive mode-locking of a Tm-doped bulk laser near
2 μm using a carbon nanotube saturable absorber” Opt. Express 17, 11007-11012 (2009).
[8] Lagatsky, A. A., Fusari, F., Calvez, S., Kurilchik, S. V., Kisel, V. E., Kuleshov, N. V., Dawson, M. D., Brown, C. T.
A., and Sibbett, W., “Femtosecond pulse operation of a Tm,Ho-codoped crystalline laser near 2 μm” Opt. Lett. 35, 172-
174 (2010).
[9] Lagatsky, A. A., Han, X., Serrano, M. D., Cascales, C., Zaldo, C., Calvez, S., Dawson, M. D., Gupta, J. A., Brown,
C. T. A., and Sibbett, W., “Femtosecond (191 fs) NaY(WO4)2 Tm,Ho-codoped laser at 2060 nm” Opt. Lett. 15, 3027-
3029 (2010).
[10] Zharikov, E. V., Zaldo, C., and Díaz, F., “Double tungstate and molybdate crystals for laser and non linear optical
applications” MRS Bull. 34, 271-276 (2009).
[11] Zaldo, C., Cascales, C., Serrano, M. D., and Han, X., “Recent advances in the development of scheelite-like- MT1-
xLnx(WO4)2 – lasers” Proc. SPIE 7686, 1-12 (2010).
[12] Cascales, C., Serrano, M. D., Esteban-Betegón, F., Zaldo, C. , Peters, R., Petermann, K., Huber, G., Ackermann,
L., Rytz, D., Dupré, C., Rico, M., Liu, J., Griebner, U. , Petrov, V., “Structural, spectroscopic, and tunable laser
properties of Yb3+-doped NaGd(WO4)2” Phys. Rev. B 74(17), 174114 (2006).
[13] Guo, W. J., Chen, Y. J., Lin, Y. F., Gong, X. H., Luo, Z. D., and Huang, Y. D., "Spectroscopic analysis and laser
performance of Tm3+:NaGd(MoO4)2 crystal." J. Phys. D-Appl. Phys. 41, 115409 (2008).
[14] García-Cortés, A., and Cascales, C., “Crystal growth and optical and spectroscopic characterization of ytterbium-
doped laser molybdates Yb-Li3Gd3Ba2(MoO4)8” Chem. Mater. 20, 3884-3891 (2008).
Proc. of SPIE Vol. 8039 803904-7
Downloaded from SPIE Digital Library on 14 Jul 2011 to 161.111.20.21. Terms of Use: http://spiedl.org/terms