FLUORIDE GLASSES – MATERIALS FOR BULK LASERS AND

FIBRE OPTICAL AMLIFIERS

Michał Żelechower, Silesian University of Technology, Katowice, Poland

1. What are fluoride glasses?

2. The role of rare earth elelments

3. Interaction of electromagnetic radiation with matter

a. Scattering, absorption, spontaneous and stimulated emission

b. Reconstruction of electron energy structure

c. Radiative and non-radiative transitions

4. Real structure of fluoride glasses

5. Applications – advantages and disadvantages (drawbacks)

What is it?

Fluoride glasses can be formed by total replacement of oxygen atoms in oxide glasses

by fluorine atoms

They are manufactured by melting of high purity single element fluorides mixture

HEISENBERG’S UNCERTAINTY PRINCIPLE

tE

E~2·10-19 eV t~1h

E~10 eV t~10-15s

FREE ATOM SOLID

EN

ER

GY

Energy diagram showing two

atoms encountering and resulting in a new

molecule

DIELECTRICS

VALENCE BAND

FORBIDDEN BAND(ENERGY GAP)

CONDUCTION BAND

EN

ER

GY

Eg > 2 eV

EMPTY

FULL

EF

DOPED DIELECTRICS

VALENCE BAND

CONDUCTION BAND (EMPTY)

DOPED IONS LEVELS USED IN LASER ACTION

FOR INSTANCE RARE EARTH ELEMENTS IN

GLASSES

http://www.gel.ulaval.ca/~copgel/conferences/edfa1/tsld001.htm

RARE EARTH IONS IN CRYSTALS AND GLASSES

RARE EARTH IONS IN CRYSTALS AND GLASSES

RARE EARTH IONS IN CRYSTALS AND GLASSES

RARE EARTH IONS IN CRYSTALS AND GLASSES

TABLE 1. CONVERSION FACTORS FOR ENERGY UNITS

Unit jouleelectron

volt cm–1

joule 1 6.24 × 1018 5.034 × 1022

electron

volt1.602 × 10–19 1 8065.73

cm–1 1.9864 × 10–23 1.24 × 10–4 1

][cmE

10000600nmλ

eVE

1240nmλ

1

[nm]λ

10000600][cmE

nmλ

1240eVE

1

EXAMPLE : CONVERSION OF ENERGY IN JOULES TO CM-1

Given: A HeNe laser photon has a wavelength of 632.8 nanometers

Find: (a) Photon energy in joules(b) Photon energy in cm–1

Solution:

(a) find energy of HeNe laser photon in joules.

Where h=6.625´ 10-34J · secc=3´ 108m/sec =632.8nm=632.8´ 10-9m

(b) Use Table 1 to convert 3.14´ 10-19 joules to cm-1. Locate "joule" in the first row in the left hand column. Follow this row over to the column headed "cm-1." At the intersection of the row and column, find the conversion factor 5.034´ 1022 cm-1/joule. Multiply this factor by 3.14´ 10-19 joules to change the energy from joules to cm-1.

The "joule" units cancel, and you get E=15,806.8cm-1

THE INTERACTION OF RADIATION WITH MATTER

Small no. of states-almost transparent

Large no. of states -strongly absorbed

Energy

X-rays

Ultraviolet

Visible

Infrared

Microwaves

Ionisation energy

Rotation

Vibration

Electronic level changes

Phototionisation

Scattering

ATOM MUST RETURN FROM EXCITED STATE TO GROUND STATE.

HOW?

SEVERAL WAYS TO RETURN TO GROUND STATE

QUANTUM YIELD OF LUMINESCENCE

SEVERAL WAYS TO RETURN TO GROUND STATE.

LIFETIMES

FLUORESCENCE VERSUS PHOSPHORESCENCE

Spin multiplicity

A state can be specified by its spin multiplicity (2S+1).

No. unpaired electrons S Multiplicity State

0 S = 0 2S + 1 = 1 singlet1 S = 1/2 2S + 1 = 2 doublet2 S = 1 2S + 1 = 3 triplet3 S = 3/2 2S + 1 = 4 quartet

S0 ground state singletS1, S2……excited state singletsT1, T2….…excited state triplets

SYMBOLS USED IN ATOMIC PHYSICS

PrPr

EuEu

HoHo

ErEr

TmTm

Wavelength [nm]

Wavenumber [cm-1]A

bso

rban

ce

3H6

3F2

3F3

3F4

1G4

7F6

5D0

5D1

5D2

5D3

5L6

5I7

5I6

5F5

5S2 , 5F

4

5F2

5F3

3K8

5G6

5G5

5G4

3K7

30000 20000

1D2

3P0

3P1,1I

6

3P2

4I13/24I

11/24I

9/2

4F9/2

4S3/2

2H11/2

4F7/2

4F5/2

4F3/2

2G9/2

4G11/2

4G9/2

2K15/2

300 400 500 600 700 800

3F4

3H5

3H4

3F2 , 3F

3

1G4

1D2

1000 2000

10000 5000

REE ABSORPTION SPECTRA IN FLUORIDE GLASSES

REE ABSORPTION SPECTRA IN FLUORIDE GLASSES

EACH ABSORPTION LINE CORRESPONDS TO THE RESPECTIVE ELECTRON TRANSITION BETWEEN

TWO ENERGY LEVELS (GROUND STATE AND EXCITED STATE)

WE ARE ABLE TO RECONSTRUCT THE ELECTRON ENERGY STRUCTURE ON THE BASE OF

ABSORPTION SPECTRA

PrPr EuEu HoHo ErEr TmTm

RECONSTRUCTED ELECTRON ENERGY LEVELS IN FLUOROINDATE GLASSES

Ene

rgy

[cm

-1]

0

5000

10000

15000

20000

25000

30000

4I15/2

3H4

1D2

1G4

3F23F3

3H4

3H5

3F4

3H6

2K15/24G9/2

4G11/2

2G9/2

4F3/2

4F5/2

4F7/2

2H11/2

4S3/2

4F9/2

4I9/2

4I11/2

4I13/2

3K7

5G4

5G5

5G6

3K85F

25F3

5S2

5F4

5F5

5I5

5I6

5I7

5I8

5D4

5G45G25L

6

5D3

5D2

5D1

5D0

3F0

3F63H

6

3F2

3F3

3F4

1G4

1D2

3P0

3P1

1I6

3P2

SPONTANEOUS EMISSION

E3

E2

E1

Pij = Pji

P23 > P13 >> P12

INVERSION

N2 >> N1

2 >> 3

THREE-LEVEL LASER (TRANSITION PROBABILITIES AND LIFETIMES)

STIMULATED EMISSION

Stimulated EmissionStimulated emission is the exact analogue of absorption. An excited species interacts with the oscillating electric field and gives up its energy to the incident radiation.

Emission of Radiation

Stimulated emission is an essential part of laser action.

U

L

h

L

hU

2h

LIFETIMES OF EXCITED STATES

FOUR-LEVEL LASER (Cr3+ doped ruby)

E3

E2

E1

E = h· = E2 – E1

THREE-LEVEL LASER (quantum amplifier)

OPTICAL PUMPING

10-8 s

10-3 s

Time-schedule of laser action

To amplify number of photons going through the atoms we need more atoms in upper energy level than in lower.

Amplification or loss is just Nupper-Nlower.

Nupper > Nlower, more out than in

Nupper < Nlower, fewer out than in

PRINCIPLE OF LASER ACTION

PRINCIPLE OF LASER ACTIONNUMBER OF PHOTONS ~ 2N (N – ACTIVE ELEMENT CONTENT)

LASER RESONANCE SYSTEM

First commercial fluoride glass – about 1990

FLUOROZIRCONATE GLASS

ZrF4-BaF2-LaF3-AlF3-NaF

Acronym - ZBLAN

FLUOROINDATE GLASS

InF3-ZnF2-BaF2-SrF2-GaF3-NaF

Acronym - IZBSGN

1974 - Marcel & Michel Poulain and Jacques Lucas discovered first fluoride glass

(Univ. Rennes, France)

HISTORY

Accidentally !!!

ADVANTAGES

1. Low phonon energy

2. Low absorption in IR range

3. Wide transmission band

4. High refraction index

Comparison of various glasses properties to those of silica glasses

A PIECE OF PHYSICS

Phonons in a lattice Acoustic branch-wide frequency band

Optical branch - almost constant frequency

THIS FREQUENCY IS MUCH LOWER IN FLUORIDE GLASSES THAN IN SILICA GLASSES

IR light absorbtion in fluoride glasses is much lower than in silica glasses

VIBRATIONS OF DIATOMIC CHAIN – OPTICAL PHONONS

Equation of motion (Newton’s second principle)

Disperssion relations

0 3000 6000 9000 12000 15000

DŁUGOŚĆ FALI [nm]Wavelength

TRANSMISSION BAND

FLUOROZIRCONATE GLASSES

SILICAGLASSES

FLUOROINDATE GLASSES

Wavelength [m]

Wavenumber [cm-1]

Tra

nsm

issi

on[%

]

TRANSMISSION BAND – FLUOROINDATE GLASS

0

100

4000 3000 2000 1000

6 12 18243

800 600 400

14

12 16 20 24

PrPr EuEu HoHo ErEr TmTm

ELECTRON ENERGY LEVELS

Ene

rgy

[cm

-1]

0

5000

10000

15000

20000

25000

30000

4I15/2

3H4

1D2

1G4

3F23F3

3H4

3H5

3F4

3H6

2K15/24G9/2

4G11/2

2G9/2

4F3/2

4F5/2

4F7/2

2H11/2

4S3/2

4F9/2

4I9/2

4I11/2

4I13/2

3K7

5G4

5G5

5G6

3K85F

25F3

5S2

5F4

5F5

5I5

5I6

5I7

5I8

5D4

5G45G25L

6

5D3

5D2

5D1

5D0

3F0

3F63H

6

3F2

3F3

3F4

1G4

1D2

3P0

3P1

1I6

3P2

Wavenumber [cm-1]

Wavelength [nm]

Lu

min

esce

nce

inte

nsi

ty [

a.u

.]

LUMINESCENCE (IZBSGN) HoHo

9000 10000 11000 12000 13000 14000 15000

5F

5-

5I

8

5S

2-

5I

7

5I

4-

5I

8

5I

5-

5I

8

5F

5-

5I

75S

2-

5I

6

5I

6-

5I

8

1200 1100 1000 900 800 700

0.5 % mol.

6 % mol.

0.5 % mol.

E [cm-1]E [cm-1]

6 % mol.EMISSIONEMISSION

E [cm-1] 0.5 % mol

EMISSION (IZBSGN)EMISSION (IZBSGN)

HoHo

Wavenumber [cm-1]

Wavelength [nm]

Lu

min

esce

nce

inte

nsi

ty [

a.u

.]

LUMINESCENCE (IZBSGN) PrPr

14000 15000 16000 17000 18000 19000

3P1

|3F

3

3P0

|3F

2

3P1

|3F

4

1D2

|3H

5

3P0

|3H

6

3P1

|3H

6

1D2

|3H

4

3P0

|3H

5

3P1

|3H

5

720 680 640 600 560 520

EMISSIONEMISSION

E [cm-1]

EMISSION (IZBSGN)EMISSION (IZBSGN)

PrPr

Wavenumber [cm-1]

Wavelength [nm]

Lu

min

esce

nce

inte

nsi

ty [

a.u

.]

LUMINESCENCE (IZBSGN)ErEr

14400 15000 15600

4S

3/2-

4I

15/2

4S

3/2-

4I

13/2

4F

9/2-

4I

15/2

11600 12000

4I

11/2-

4I

15/2

9600 10000 10400

690 660 630

1050 1000 950

870 840

18000 18600 19200

560 540 520

EMISSIONEMISSION

E [cm-1]ErEr

EMISSION (IZBSGN)EMISSION (IZBSGN)

Wavenumber [cm-1] Wavenumber [cm-1]

Lu

min

esce

nce

inte

nsi

ty [

a.u

.]

Inte

nsyw

ność

lum

ines

cenc

ji [

j.wzg

l.]

LUMINESCENCE (IZBSGN)

TmTm Tm + TbTm + Tb

EMISSIONEMISSION

12000 14000 16000 18000 20000 22000 24000

wzb.

= 470nm (1G

4)

wzb.

= 355nm (1D

2)

0.5% Tm

0.5% Tm

1G

4-

3F

4

1G

4-

3H

5

wzb.

= 470nm (1G

4)

wzb.

= 355nm (1D

2)

1% Tm + 3% Tb

1% Tm + 3% Tb

(Tb)

(Tm)1G

4-

3H

5

(Tb)5D

4-

7F

5

5D

4

|7F

4

5D

4

| 7F

3

1G

4-

3F

4 (Tm)

1D

2-

3F

2

1D

2-

3F

3 1D

2-

3H

4

1D

2-

3H

5

1D

2-

3F

4

1D

2-

3F

4 (Tm)

(Tb)5D

4-

7F

5

12000 14000 16000 18000 20000 22000

EMISSION (IZBSGN)EMISSION (IZBSGN)

TmTmE [cm-1]

E [cm-1]

EMISSION (IZBSGN)EMISSION (IZBSGN)

Tm - TbTm - Tb

useless

Czas życia [ms] Aktywator Poziom Stężenie [%mol] Zmierzony m Obliczony rad

Wydajność kwant.

=m/rad [%]

0.5 0.012 36.4 3P0 2 0.012

0.033 36.4

0.05 0.400 92.6

Pr 1D2

2 0.005

0.432

1.2

Eu 5D0 2 0.370 6.320 5.9

1 0.140 31.7 Ho 5S2

6 0.078

0.442

17.6

2 0.183 34.8 4S3/2 8 0.028

0.526 5.3

2 0.299 40.3 4F9/2 8 0.261

0.741 35.2

2 6.680 99.6

Er

4I11/2 8 3.550

6.710 52.9

0.1 0.048 66.7 0.5 0.048 66.7

1D2

5 0.005

0.072

6.9 0.1 0.634 77.8 0.5 0.313 38.4

1G4

5 0.004

0.815

0.5 0.1 1.287 99.0 0.5 1.000 76.9

3H4

5 0.020

1.300

1.5 0.1 4.400 55.0

Tm

3F4 5 0.700

8.000 8.8

Lifetime [ms] Dopant Level Concentr. [%mol] Experimental m Computed rad

Quantumefficiency

= m / rad [%]

0.5 0.012 36.4

LIFETIMES & QUANTUM YIELDS OF DOPED FLUOROINDATE GLASSES

DISADVANTAGES (DRAWBACKS)

1. Substrates are hygroscopic (built-in OH groups result in additional absorption band in IR range)

2. Difference of TX and Tg is low ( 100 0C)

3. Crystallization susceptibility is high

Tg – glass transformation temperature

TX – crystallization temperature (beginning)

TP - crystallization temperature (peak)

T = Tx – Tg

HRUBY PARAMETER

H = (TX – TG) / TG

SAAD PARAMETER :

S = [(TX – TG) (TP – TX)] / TG

PARAMETERS OF STABILITY

Szkło fluoroindowe domieszkowane Ln3+

Tg [0C] Tx [

0C] Tp [0C] T [0C] H S

A

K

T

Y

W

A

T

O

R

1 % mol PrF3 (*)

2 % mol EuF3 (**)

2 % mol EuF3 (*)

8 % mol EuF3 (*)

0.5 % mol HoF3 (*)

6 % mol HoF3 (*)

2 % mol ErF3 (***)

8 % mol ErF3 (***)

0.5 % mol TmF3 (*)

5 % mol TmF3 (*)

294

294

294

307

294

306

305

310

294

300

408

402

406

389

410

386

423

375

409

388

434

426

431

398

430

399

457.5

382

430

394

114

108

112

82

116

80

118

65

115

88

0.39

0.37

0.38

0.27

0.39

0.26

0.39

0.21

0.39

0.29

10.08

8.82

9.52

2.40

7.89

3.40

13.35

1.47

8.21

1.76

(*) IZBSGN (**) IZBS (***) IZBSGL

Various dopants in fluoride glass

108 112

116

118

115

CHARACTERISTIC TEMPERATURES OF FLUORINDATE GLASSES

GLOVE DRY PREPARATION BOX

GLOVE DRY MELTING BOX

Pr3+ doped fluoroindate glassPr3+ doped fluoroindate glass

REVERSE MONTE CARLO MODELLING (RMC)

RIETVELD MODELLING

STRUCTURE OF FLUORIDE GLASSES

VARIATION OF GIBBS FREE ENERGY DURING VITRIFICATION AND CRYSTALLIZATION

liquid

Overcooled liquid

glass

Single crystal

Stable glass

Range of structural order

STRUCTURE OF FLUOROZIRCONATE

GLASS (ZBLAN)

POULAIN & LUCAS

1974

PROJECTION OF THE RMC CUBIC BOX SHOWING THE 300 [MF6] POLYHEDRA NETWORK.

EXAMPLE OF RMC MODELLING (NaPbM2F9)

NaPbFe2F9

[MF6] octahedra are in blue; Na atoms in green and Pb atoms in red

Five [MF6] polyhedra linked by edges as found in the RMC model

NaPbM2F9

EXPERIMENTAL VERIFICATION BY NEUTRON DIFFRACTION OR

LOW ANGLE X-RAY SCATTERING

SiO2 - crystallineI coordination zone – 3 at

II coordination zone – 3 at

III coordination zone – 6 at

SiO2 - amorphousI coordination zone – 3 at

II coordination zone – 4 at

III coordination zone – 4 at

EXAMPLE

LEAST SQUARES FIT TO EXPERIMENTAL RESULTS (NEUTRON DIFFRACTION AND X-RAY

SCATTERING)

NaPbM2F9 : neutron data for M = Fe

neutron data for M = V

LEAST SQUARES FIT TO EXPERIMENTAL RESULTS (NEUTRON DIFFRACTION AND X-RAY

SCATTERING)NaPbM2F9 (M = Fe, V)

X-ray data for M = Fe

LEAST SQUARES FIT TO EXPERIMENTAL RESULTS (NEUTRON DIFFRACTION AND X-RAY

SCATTERING)NaPbM2F9 (M = Fe, V)

REFERENCES

http://www.studsvik.uu.se/Software/RMC/mcgr.htm

http://tigger.phy.bris.ac.uk/~liqwww/links.html

http://www.cristal.org/glasses/glassvir.html

http://www.cis.tugraz.at/ptc/specmag/struct/s.htm

http://www.materials.leeds.ac.uk/Groups/Photonics/photonic.htm

http://www.gel.ulaval.ca/~copgel/conferences/edfa1/sld001.htm

http://irfibers.rutgers.edu/ir_rev_intro.html

http://www.mete.metu.edu.tr/PEOPLE/FACULTY/aydinol/gfa/sld001.htm