Characterization of Transparent Lanthanides Doped Y3 Al5 O12 And
Y2 O3 Ceramics, And Their Laser Oscillation

Jianren LuSupervisor: Ken-ichi Ueda

Polycrystalline ceramic laser materials are an aggregate of crystalline grains,
each randomly oriented with respect to neighboring grains. Ceramic materials
are widely used in many fields, especially transparent polycrystalline ceramics canbe used as laser materials, windows in furnaces, lenses in high temperature microscopes, lamp envelopes, etc. In this dissertation, fabrication process of highly
transparent ceramic laser materials is summarized. Optical properties of rareearth ions doped Y3 Al5 O12 (YAG) and Y2 O3 laser ceramic materials were investigated. Highly efficient and high power laser oscillations were demonstrated.
Since 1999, we, Yanagitani and Yagi group in Konoshima Chemical, Co., Ltd.
and Ueda group in University of Electro-communications, began to develop highly
transparent neodymium doped YAG ceramics using vacuum sintering method, where
the raw materials were prepared by nanocrystalline technology. Compared withYAG single crystal, transparent ceramic laser materials have the following advantages, namely: (1) Ease of fabrication; (2) Less expensive; (3) Fabrication of large
size and high concentration; (4) Multi-layer and multi-functional ceramic structure; (5) Mass production, etc. Optical properties of Nd:YAG ceramics, such asabsorption, emission and fluorescence lifetime, were found to be similar to theseof Nd:YAG single crystal. The thermal conductivity of Nd:YAG ceramics was measured, which is also found to be very similar to that of Nd:YAG single crystal.
In 2000, we succeeded in demonstrating highly efficient laser oscillation onNd:YAG ceramics. By sing 1 W LD end-pumping scheme, CW output power of499 mW at 1064 nm was obtained with a slop efficiency of more than 60%. Its
laser efficiency is comparable to that of Nd:YAG single crystal lasers, which means
1the light scattering loss inside ceramics should be the same level with that of single crystal. Highly neodymium doped Nd:YAG ceramic lasers were also developed.
For 2% neodymium doped YAG ceramic, output power of 465 mW at 1064 nm wasobtained with a slope efficiency of 58%. Fig. 1 shows the laser output versus pump
power for 1%, 2% Nd:YAG ceramics and 0.9% Nd:YAG single crystal at 1064 nm.
Output power of 221 mW at 1064 nm was obtained in 4% microchip Nd:YAG ce-Output power (mW)

700
1% ceramic
2% ceramic
0.9% single crystal

600
500
400300200
10000200

400600

800

1000

Pump power (mW)
Fig. 1: CW laser output versus pump power of 1%, 2% Nd:YAG ceramic lasers and0.9% Nd:YAG single crystal laser
ramic with a slope efficiency of 40%. High power laser oscillation was demonstrated
for the first time. Using virtual point source (VPS) pumping system, output powerof 31 W at 1064 nm was obtained under 290 W pumping in 2000, output powerof 72 W and 88 W at 1064 nm were reported later. The thermally induced birefringence in Nd:YAG ceramics was also investigated. This year, cooperating withToshiba Cooperation, high power Nd:YAG ceramic laser with output power of 1.46
kW was demonstrated. The optical-to-optical efficiency reached up to 42%. Cr4+
doped YAG ceramics were also fabricated and passive Q-switch laser operation wasdemonstrated for the first time. Passively Q-switched output of 45 mW at 1064 nm
was obtained under 1 W LD pumping. Using the typical end pumping scheme,
laser oscillation was also generated at 1.32 µm and 1.34 µm. For 1 W end pump2

ing, Output power of 202 mW with a slope efficiency of 35% was obtained; Using
VPS pumping system, output power of 36 W was obtained at 1319 nm.
Cubic Y2 O3 crystal has been investigated for a long time as a laser host material
for lanthanide ions due to its favorable properties,such as its refractory nature,stability, ruggedness, and optical clarity over a broad spectral region, in particular,
thermal conductivity of Y2 O3 is about two times larger than that of YAG, while
their thermal expansion coefficients are very similar. Further more, the stimulated
emission cross section of Nd:Y2 O3 happened to be in the range that is required
for laser fusion driver. This makes Nd:Y2 O3 a potential candidate for being usedin laser fusion system. However, it is extremely difficult to grow large-size highquality Y2 O3 single crystal by conventional growth methods because of its very highmelting temperature (≈2430◦ C) of Y2 O3 and structural phase transition at 2280◦ C.
What’s more, the laser oscillation results of rare earth ions doped Y2 O3 were notsatisfying either. Recently, Nd:Y2 O3 ceramics were developed as well by using thenanocrystalline technology and vacuum sintering method. Compared with single
180
Intensity (arb. units)

Output power (mW)

160
140
120
10080

Optical spectrumof laser oscillation

1074

601076
1078
Wavelength (nm)

1080

40
2000200

400600
Pump power (mW)

800

Fig. 2: Input-output curve of 1.5% Nd:Y2 O3 ceramic laser generated at two wavelength of 4 F3/2 → 4 I11/2
crystal growth methods, it is easier to fabricate large size Y2 O3 ceramics becauseof the lower sintering temperature - about 700◦ C lower than melting temperatureof Y2 O3 . Some optical properties of Nd:Y2 O3 ceramics were investigated and for3

the first time, CW room-temperature laser oscillation at two wavelengths (1074.6nm and 1078.6 nm) of 4 F3/2 → 4 I11/2 channel was obtained with a slope efficiency of32%. Fig. 2 shows the laser output versus pump power for 1.5% uncoated Nd:Y2 O3
ceramic element.
In Table 1, we list the development progress of ceramic lasers from 1960s.
Based on the recent great progress of ceramic laser materials, the prospect ofceramic laser materials in the near future was also presented. The possible multifunctional structure laser ceramics was shown; The mass production scheme ofceramic laser chips was given; The possibilities of rare earth doped Y2 O3 for being
used in laser fusion system, femto-second lasers and high power industrial lasers
were discussed.

4YearAuthorFabrication method

Achievement

remarks

CaF2 ceramic laser, the1966

E. Carnall

Hot-pressing

first laser demonstration

Ref. 1on ceramic laser materialThe
1972

R. C. Anderson

1995

A. IkesueJ.

20002001

Lu,

cold-pressed

NDY ceramic laser

Solid-The first laser oscillationstate

was reported on Nd:YAG

reaction

ceramics

Ref. 2

Ref. 3K.

Ueda,H.

Yagi,T.

Yanagitani,
Y. Hirano, Y.
Akiyama, A.
A.

Cold-pressing

firstNanotechnology 499 mW → 31 W → 72 W
Ref. 4-+Vacuum→ 88 W → 128 W → 1460

Sintering

W Nd:YAG ceramic lasers

10

Kamin-skii

J.

2001

Lu,

K.

Ueda,H.

Yagi,T.

Yanagitani,A. A. Kamin-Nanotechnology
The first laser demonstra+Vacuum
tion on Nd:Y2 O3 ceramic

Sinteringskii

Table 1: Development progress of ceramic lasers

5Ref. 11

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