Croissance et caractérisation de cristaux de saphir dopés Ti pour

lasers de puissanceThierry Duffar

Gourav Sen, Carmen Stelian

José Baruchel, Thu Nhi Tran Caliste

Nicolas Barthalay

RSA Le Rubis SARSA, a French company, is one of the world largest producer of synthetic sapphire, ruby and spinels.

TITANSAPHIR Project Growth of Titanium‐doped Sapphire single crystals for power laser applications.

Find growth process improvementsCharacterization of the defects inside the crystals

TITANSAPHIR Project

Industrial partners Research Labs

Crystal Growth

Growth Furnace Laser

Optics

Defect Characterisation

& Growth process

OpticalCharacterisation

2

3

Melting point: 2050 ºCMohs hardness: 9

Natural sapphire

Artificial grown sapphire

Sapphire:Al2O3

Industrial furnace

Fig. 3 Schematic representation of the Kyropoulos method

Pull Seed

Crucible

Crystal

Melt

Bottom

heater

Thermal

insulation

Side heater

Weight

Kyropoulos growth technique advantages

• Possibility to grow crystals with large diameter ( 30 cm).

• Growth inside melt and without contact with crucible.

• Low dislocation density.

Sapphire disks High power Lasers

Kyropoulos Crystal Growth

4

Crystal Morphology

20 cm5

Global modeling of thermal and velocity field(COMSOL)

Crucible diameter 30 cm

Plate formation at crystal head

h15.0t it

6

Temporal concave shape of the crystal

Marangoni No Marangoni

Effect of the Marangoni convection

Plate formation at crystal head

7

Fig. 3 Schematic representation of the Kyropoulos method

Pull Seed

Crucible

Crystal

Melt

Bottom

heater

Thermal

insulation

Side heater

Weight

Growth control system

0 10000 20000 30000Gro

wth

:Pu

llin

g(g

m/m

m)

Gro

wth

rat

e(g

m/h

r)

Mass of ingot(gm)

Ideal Growth Parameter

Growthrate(Ideal)growth:pulling(ideal)

Control Program

Feedback

Input Power control

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0.00100.00200.00300.00400.00500.00600.00700.00800.00900.00

0.00

50.00

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200.00

250.00

300.00

350.00

0 5000 10000 15000 20000 25000

Gro

wth

:Pu

llin

g(gm

/mm

)

Gro

wth

rat

e(g

m/h

r)

Mass of ingot(gm)

Growthrate(Ideal)

rate

growth:pulling(ideal)

0.00100.00200.00300.00400.00500.00600.00700.00800.00

0.00

50.00

100.00

150.00

200.00

250.00

0 1000 2000 3000 4000

Gro

wth

:Pu

llin

g(gm

/mm

)

Gro

wth

Rat

e(g

m/h

r)

Mass of Ingot(gm)

Non-uniform shape of crystal

9

10/20

0.00

200.00

400.00

600.00

800.00

1000.00

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1400.00

1600.00

0.00

50.00

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250.00

300.00

0 5000 10000 15000 20000 25000

Gro

wth

:Pu

llin

g(gm

/mm

)

Gro

wth

Rat

e(g

m/h

r)

Mass of ingot(gm)

Growth rate(Ideal)

rate

growth:pulling(ideal)

growth:pulling

0.00

500.00

1000.00

1500.00

2000.00

0.00

50.00

100.00

150.00

200.00

250.00

300.00

0 1000 2000 3000 4000

Gro

wth

:Pu

llin

g(gm

/mm

)

Gro

wth

Rat

e(g

m/h

r)

Mass of ingot(gm)

(initial)

Plate formation in crystal

10

11/20

0.00

100.00

200.00

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140.00

0 5000 1000015000200002500030000

Gro

wth

:Pu

llin

g(gm

/mm

)

Gro

wth

rat

e(g

m/h

r)

Mass of ingot(gm)

Growth rate(Ideal)

Growth rate

growth:pulling(ideal)

growth:pulling

0.00

200.00

400.00

600.00

800.00

0.00

20.00

40.00

60.00

80.00

0 1000 2000 3000 4000

Gro

wth

:Pu

llin

g(gm

/mm

)

Gro

wth

rat

e(g

m/h

r)

Mass of ingot(gm)

(initial)

Good crystal morphology

11

Fig. 3 Schematic representation of the Kyropoulos method

Pull Seed

Crucible

Crystal

Melt

Bottom

heater

Thermal

insulation

Side heater

Weight

Automatic crystal radius control

Growth control

hmelt

Levelsensor

Feedback

12

53.1cm8.2/cm28.4 55.1cm9.2/cm5.4

Numerical modeling Experimental visualization

of the growth interface

Numerical Modelling

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Numerical modellingTi distribution

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Flow

100 mm

Radial distribution of titanium

Large curvatures of the crystal-melt

interface

Radial compositionalnon-homogeneity

Variations in the intensity of the emitted

laser beam

15

Crucible diameter 15 cmSlices of 10 cm in diameter Measurements of the absorption coefficient

C. Stelian, G. Alombert-Goget, G. Sen, N. Barthalay, K. Lebbou, T. Duffar, Analysis of titanium distribution in sapphire crystalsgrown by the Kyropoulos method, article in preparation

Radial distribution of titanium

16

23⁰

26⁰

≈ 25⁰

25⁰

65⁰

Seed axis

A-axisA-axis

Solid-liquid crystal interface realised fromprevious pulling. (Interface angle: approx 25⁰)

Prepare seeds from existing crystals with an axis offset of 65⁰ with A-axis

New approach to preparation of seeds

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A-axisA-axis

A-axis

A-axis

A-axis

Seed axis

A-axis

Crystal grown with the offset seed axis will lead to crystals having the A-plane parallel to the solid-liquid growthinterface. Thus A-Plane alligned discs can be cut out of various sizes parallel to the interface shape.

New approach to cutting Discs

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Sapphire crystal & sample

• 6 kg in weight• Diameter – 10 cm• Height – 16 cm• Duration of growth – 6 days

A-a

xis

C-a

xis

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X-ray diffraction imaging (x-ray topography)

• Bragg diffraction

• Image defects in the crystal lattice via the deformation around them diffracted intensity/direction altered contrast• White beam (polychromatic)• Section topography

Polychromatic (“white”) X-ray beam

SampleBeamstop

Detector

Diffraction images

(Beam sizes not to scale)

Beamline: BM – 05

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Projection & Section topography

V

2D detector

(Photographic plate)

Crystal2D detector

(Photographic plate)

Crystal

Projection Section (slit configuration)

Reveals the features within the depth of the sampleGood lateral spatial resolution, but poor depth resolution

Polychromatic

parallel beam

Polychromatic parallel

beam passing through

thin slits

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Diffraction spots

C-axis

Rectangular sample

A-axis

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Dislocation density(Quantitative estimation)

a1 and a2 – dislocations,

b – scratch marks,

c – precipitate

a1

a2

c

b1mm 0

5000

10000

15000

20000

25000

30000

35000

40000

0 20 40

Dis

loca

tio

n d

ensi

tyD

islo

cati

on

s/cm

^2

Distance from centre (mm)

Total no.ofdislocations

completedislocations

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16

17

18

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Numerical modeling (COMSOL)

0

500

1000

1500

2000

2500

0 1 2 3Te

mp

erat

ure

gra

die

nt

(K.c

m-1

)Radial Distance From Centre (cm

Temperature gradient vs Radial location

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Conclusions

• Growth of 20cm diameter Al2O3:Ti crystals by

Kyropoulos technique

• Top plate problem solved

• Full shape control under progress

• Radial Ti segregation solution

• Dislocations are the main type of defects,. 103-104 cm-2

• good quality which is suitable for optical applications

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Current Segregation profileWe have a concentric profile of segregation owing to the conical interface shape. The concentric profile isvery detrimental for the optical properties.

Improved Segregation profileThough we will still have segregation the gradient will bemuch reduced. Also we get rid of the concentric gradient profile and hence the centre is not distorted.

Change in Ti segregation pattern

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Diffraction spots(Circular Sample)

C-axis

A-axis

Circular sample

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