how thulium impurities impact photodarkening effect in yb 3+ -doped fibre laser?
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How thulium impurities impact photodarkening effect
in Yb3+-doped fibre laser?
Peretti Romain1, Jurdyc Anne-Marie1, Jacquier Bernard1, Gonnet Cédric 2, Pastouret Alain 2, Burov Ekaterina 2, Cavani Olivier 2
Ytterbium fibre laser: status 1
Ytterbium-doped MCVD silica fibres:
• Jena (Ger)• Nlight (Leikki), Can/Fin• GSI/ JK lasers (UK)
• fiber provider: Draka…
CW opération and modulated:Single mode fibre, up to 500WMultimode fibre up to 50KW
Optical Conversion Efficiency, OPC Up to 75%Total efficiency : 25%
Power limitation due to Stimulated Raman Scattering (SRS)
• Fiber-laser sales: more than 240 M$ (USD) in 2007
• Expected to grow on average by 26% per year until 2011
Ytterbium fibre laser, status 2Recent route to reach very high power :
Large Mode Area fibre (LMA), using microstructured fibre
Theoretical profileMEB images (from XLIM)
But still power limitation due to material
Drawback and questions
[from Manek-Honninger et al. , 2007]
• Premature ageing of the lasers: power laser threshold increase with output power
• Photon Induced Absorption (PIA) in the near UV and visible range
• Photodarkening
Times in min.
10015
70
Photodarkening rate with excitation wavelength
1064 nm
633 nm
[Manek-Honninger et al. , 2007]).
What causes photodarkening? An open question
→ Attributed to defect centers such as color centers in the silica net :
• oxygen vacancies (Yoo & al 2007)
• existence of divalent ytterbium (Guzman Chávez et al. 2007, Engholm et al. , 2007, Koponen et al. 2008)
→ physical mechanism is not clear yet: need of a near UV energy interaction (supported by UV excitation experiments) to create defect centers. An intermediate step is necessary : proposition of Yb3+ pairs or agregates(Suzuki et al. 2009)
Experimental set-up
Characteristics of the Yb-doped fiberType:
Composition Weight % :
λc
(nm)
Dm
µm
Dm2
µm2
Dc
µm
ALUYb
Yb 1,7
1025 7.6 57,4 5,4Al ~3
Ge <0.1
P ~1
Absorption
Photo-Induced Absorption
400 450 500 550 600 650 700 750 800 850 9000,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,026 24 22 20 18 16 14 12
Wavenumber (103 cm-1)
Nor
malized
P.I.A.
Wavelength (nm)
P = 500mWt = 300’
P.I.A. spectrum as a function of irradiation time
PIA time dependence changes with wavelength
Blue-green fluorescence visible by naked eye
from [Kir'yanov et al, 2007]
Yb-doped and Yb:Tm doped fibres
N° Type:Compositionweigth % :
λc
(nm)
Dm
µm
Dm2
µm2
Dc
µm
Fib. 1ALUYb
Yb: 1,7
1025 7.5 57 5,4Al: ~3
Ge: <0.1
P: ~1
Fib.2ALU
Yb-Tm
Yb: 1,7
1043 8,0 65 5,6Al: ~3
Tm 3.10-4
Ge: <0.1P ~1
purity materials 99.998% correspond to 340 ppbw
Upconverted emission spectra under 976 nm excitation
300 350 400 450 500 550 600 6500.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.235 30 25 20 15
Yb3+
cooperativeemission
1G4->3F
4
1G4->3H
6
1D2->3H
6(1I
6,3P
0)->3H
6
Norm
aliz
ed e
mis
sion
Wavelength (nm)
Energy (103cm-1)
fibre 1, fibre 2
Upconversion mechanims
P.I.A. time dependences for fiber 1 and fiber 2
0 250 500 750 1000 1250 15000
5
10
15
0 10 20 30 400
5
10
15
(P.I.
A.)
(m
-1)
Times (min)
Yb Yb-Tm
Experimental conditions:
• λexc = 976 nm•λPIA = 440 nm
Excitation density:10,8 W/mm2
Clearly Tm ions are involved in the photodarkening process
Discussion (1)
→ fluorescence detection of Tm ions in the ytterbium-doped fibre, as a residual impurity < 330 ppbw
→ by increasing Tm impurity (~300ppm) : photodarkening is increased as well as PIA time dependence is faster
Thulium ions are involved in the photodarkening process
The questions :
by what physical mechanism?
can we propose some ideas to improve the performances of high energy ytterbium fibre lasers?
Tm3+ fluorescence spectrum and host absorption
300 350 400 450 500 550 600 650 7000,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,035 30 25 20 15
0
100
200
300
400
500
Norm
aliz
ed e
mis
sion
Wavelength(nm)
Gla
ss m
atr
ix a
bso
rptio
n (
m-1)
Energy (103cm-1)
Discussion (2)
→ Upconversion process can bring 4f electron in high energy states of Tm3+
different mechanisms: Up conversion energy transfer from two Yb3+ to Tm3+
followed by several possible mechanisms involving: Excited State Absorption, or multistep Yb to Tm energy transfer…
They all lead to high power dependences of the upconverted Tm fluorescence ( P2, P3 and P4)
This has been studied by several authors already, for instance in: G. Huber & al, Journal of Luminescence 72-74, 1 – 3 (1997)
→ Whatever the upconversion mechanism is, it brings population in the different upper excited states in resonance with lattice absorption due to either charge transfer band and to defect centers near the band gap
then we understand the observation of an increased UV and visible absorption:
Yb absorption + upconversion energy transfer to TM excited states → creation of traps
Agreement with other experimental observations from litterature
From material point of view:• Photodarkening is increasing with ytterbium contents ( Kitabayashi et al. 2006)• Photodarkening is decreasing with increasing : → alumina contents (Kitabayashi et al 2006) → phosphorus ((LEE et al, 2008)
• Photodarkening is decreasing with erbium doping (Morasse et al 2007)
• Photodarkening is decreasing with heat treatment under oxygen atmosphere (Yoo et al , 2007 but Yb2+ was already present)
From spectroscopic arguments:• PIA comparable for 980nm, visible and UV irradiation (Yoo et al, 2007 Morasse et al, 2007)• Correlation with UV absorption and photodarkening efficiency (Engholm et al 2008)• Recovering from photodarkening by specific UV radiation (Manek-Honninhger et al 2007) or infrared (Jetscke et al 2007)
Prospectives
→ decrease as much as possible thulium or other R.E impurities but experimental and cost limitations; nanostructuration of the materials to isolate Yb ions from other luminescent centers (see poster)
→ on the contrary, introduce impurity to quench the creation of defect centers: for instance : by doping with other ions to deplete population in Tm high energy states = under investigation (pattern)
→ reach limitations due to • intrinsic break down of the materials• physical process such as Stimulated Raman Scattering
Supports:
CNRS organisation
Draka company
Thank you for your attention
Power dependences of the upconverted fluorescences
10 100
0,01
0,1
110 100
Longueur d'onde (nm) 300 360 475 487 500 515
Lum
inesc
ence
nor
mal
isée
Puissance @976 nm (mW)
Intensitée lumineuse W.mm-2
Type de fibre
Composition [Yb] PD puissance Lambda PD Temps de PD
Blanchiment Interprétation défauts affiliation
LMA DC ?Yb2O3
:0,3 and 0:43 mol%
2-8W/6µm² 976 3H X Yb2+/Yb-O/color center Liekki
Fibres monomodes
phosphate1027 ions/ m3
12 % Yb2O3
0.552 J/cm² 10 ns 266nm 2 min
XNp photonics
stanford400 mW 976 nm 10000 min
Préforme aluminosilicate0,2% atomique O
déduitX X X X
Transfert de charge =>Yb2+=> centre colorés
ACREOFIBERLAB
préforme aluminosilicate 1% poids ~5mW/µm² 488nm 5h26 jours at 160 bar
et50°CYb-OODC
Southampton
4 µm core aluminosilicatecore abs. @ 976nm
1200dB/m500mW/(4µm)² 977 nm 5-240min 543nm Paires Yb2+-Yb3+ Mexique
Fibre Liekki
LMA DC « commercial » 45 W / (22µm)² 976 nm 5-100 min350nm 5 kHz 90µJ
5 minutesPaires Yb3+-Yb3+ EOLITE
LMA DC Aluminosilicate 103 dB/m@915 300mW/ (17µm)² 976 nm 25 min Chauffe OFS laboratories
Fibre multi 0.5 mol% P2O5 and 4 mol% Al2O3
0.6 mol% Yb2O3 (N = 2.65 1026 m-3)
1 à 13 W 915 nm 500 min 13 à 1W@ 915 nm
Jena
Préforme Si AlSi P
1,2% at. X X X X c.f. 2007 ACREOFIBERLAB
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