the researches and investigations of pulsed laser in nir eye-safe wavelength...
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NCTU Electrophysics
Solid-State Laser Physics Lab.
Han-Lung Chang
11
The Researches and Investigations of The Researches and Investigations of Pulsed Laser in NIR Eye-safe WavelengthPulsed Laser in NIR Eye-safe Wavelength
脈衝式近紅外人眼安全雷射研究及探討脈衝式近紅外人眼安全雷射研究及探討
張漢龍張漢龍
指導教授:陳永富指導教授:陳永富
Department of ElectrophysicsDepartment of ElectrophysicsNational Chiao Tung University , TAIWANNational Chiao Tung University , TAIWAN
NCTU Electrophysics
Solid-State Laser Physics Lab.
Han-Lung Chang
22
OutlineOutline
Introduction, Background, and MotivationIntroduction, Background, and Motivation Intracavity Optical Parametric Oscillator (OPO) Intracavity Optical Parametric Oscillator (OPO)
Pumped by Nd:doped LaserPumped by Nd:doped Laser
Self-Stimulated Raman Scattering (Self-SRS)Self-Stimulated Raman Scattering (Self-SRS)
Passively Q-switched Erbium/Ytterbium Fiber LaserPassively Q-switched Erbium/Ytterbium Fiber Laser
PCF Laser pumped OPOPCF Laser pumped OPO
Optically Pumped Semiconductor Laser (OPSL)Optically Pumped Semiconductor Laser (OPSL)
ConclusionConclusion :: Contribution and Future WorkContribution and Future Work
NCTU Electrophysics
Solid-State Laser Physics Lab.
Han-Lung Chang
100-280nm
315-400nm
280-315nm
400-700nm
VIS
3
Eye-safe wavelength
UV
NIR > 1400 nm
NIR < 1400nm
IR
NCTU Electrophysics
Solid-State Laser Physics Lab.
Han-Lung Chang
Background and Motivation
4
High pulse energyHigh rep rate
Wavelength tunable
NCTU Electrophysics
Solid-State Laser Physics Lab.
Han-Lung Chang
55
Conventional methods for generating NIR Eye-safe laser
Nonlinear conversion process Optical Parametric Oscillator
Optical Parametric Amplification
Stimulated Raman Scattering
Rare-earth-ion-doped materials Er3+, Tm3+, Ho3+
Semiconductor Laser InGaAsP, AlGaInAs, GaInAsSb
12
3
NCTU Electrophysics
Solid-State Laser Physics Lab.
Han-Lung Chang
66
OutlineOutline Introduction, Background, and MotivationIntroduction, Background, and Motivation
Intracavity Optical Parametric Oscillator (OPO) Pumped by Intracavity Optical Parametric Oscillator (OPO) Pumped by Nd:doped LaserNd:doped Laser
Self-Stimulated Raman Scattering (Self-SRS)Self-Stimulated Raman Scattering (Self-SRS)
Passively Q-switched Erbium/Ytterbium Fiber LaserPassively Q-switched Erbium/Ytterbium Fiber Laser
PCF Laser pumped OPOPCF Laser pumped OPO
Optically Pumped Semiconductor Laser (OPSL)Optically Pumped Semiconductor Laser (OPSL)
ConclusionConclusion :: Contribution and Future WorkContribution and Future Work
NCTU Electrophysics
Solid-State Laser Physics Lab.
Han-Lung Chang
7
Optical Parametric OscillatorOptical Parametric Oscillator
signal
Idler
pump
NLCGM
External cavity
Intra-cavity
OPO Cavity
• Higher threshold
• Lower cavity stability requirement
• Lower threshold
• Higher efficiency
• Dynamic pulse
pump signal
Idler
NLC
NCTU Electrophysics
Solid-State Laser Physics Lab.
Han-Lung Chang
8
NIR Eye-safe Laser with Intra-cavity OPONIR Eye-safe Laser with Intra-cavity OPO
•High pulse energy up to ~mJ
•High peak power
•0.x~ x10 Hz Rep rate
Application
Laser Range Finder
Requirement
NCTU Electrophysics
Solid-State Laser Physics Lab.
Han-Lung Chang
Quasi-cwDiode stacks
Lens duct
Nd:YAG
Outputcoupler
HR@1064 nm (R>99.8%)HR@1573 nm (R>99%)HT@808 nm (T>70%)
Cr:YAG KTP
HR@1064 nm (R>99.8%)PR@1573 nm
Quasi-cwDiode stacks
Lens duct
Nd:YAG
Outputcoupler
HR@1064 nm (R>99.8%)HR@1573 nm (R>99%)HT@808 nm (T>70%)
Cr:YAG KTP
HR@1064 nm (R>99.8%)PR@1573 nm
9
Passively Q-switched Intra-cavity OPOPassively Q-switched Intra-cavity OPO
3-bars
x-cut KTP:•Temp. insensitive•Large nonlinear coeff.•Non-walk-off•High damage threshold
1064 nm 1572 nm
KTP
ASAP simulation
OPO
High power QCW LD
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Solid-State Laser Physics Lab.
Han-Lung Chang
• Output coupler with 40% ~ 60% reflectivity is commonly used to optimize energy conversion efficiency.
• How to optimize peak power?• Loss vs. threshold
Appl. Phys. B 79, 823-825 (2004)
Appl. Opt. V45 N25, 6007-6015 (2006)
10
NCTU Electrophysics
Solid-State Laser Physics Lab.
Han-Lung Chang
11
Threshold of IOPOThreshold of IOPO
Photon density of threshold in a passively Q-switched laser …JJ Degan (1995)
ψf,max ~ 1.5 x 1017 cm-3,max 1
gm if i t
cav t
l nn n
l n
Photon density of threshold in a SRO
2
, 2
1.12 1( ) 33 ln ln 4
(1 )
cavf th s s
s p s
lR L
Gg c R
…Brosnan and Byer (1979)
ψf,th = 6 x 1015 cm-3
~ 6 x 1016 cm-3
f,max >> f,th
The threshold of an intracavity OPO is determined by the bleach of the saturable absorber.
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Solid-State Laser Physics Lab.
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12
Experimental ResultExperimental Result
There is an individual optimum value of pulse energy and peak power.
Lasing threshold is nearly constant for different output coupler
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13
Pulse profilePulse profile
Eopo=3.7 mJPeak power=0.5 MW
Eopo=4 mJPeak power=0.7MW
Eopo=3.3 mJPeak power=1.5MW
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14
Experimental ResultExperimental Result
Opt. Express 15, 4902-4908 (2007) Output energy : 10.8 mJ
Enlarge cross section to enable higher pump power 22 5.35.37.27.2 cmcm
※ OPO back conversion
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Solid-State Laser Physics Lab.
Han-Lung Chang
n rn
r 'x
'y
z
x
y
( )E r[1 1 1]
r
02 2 2
0 0sin (2 )sin ( )
2
rrdrd
2( ) ( ) 2 crr n r l dl
• Portion of electric field transfer into another orthogonal axis. Energy feedback
Depolarization
Thermally induced birefringence effect
Nd:YAG
15
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Han-Lung Chang
16
Theoretical analysis of Passively Q-switched Theoretical analysis of Passively Q-switched IOPOIOPO
, ,( )p x p y
dnc n
dt
, , , ,,
1+ 1 2 ln 1 2p y p x p y p y
cr p opo s y nlr r p r
dnl L l
dt t t R t
, , , 11 2 lnp x p x p y
cr pr r p
dnl L
dt t t R
, ,, , ,
1( ) lns y s ynl
opo p y s y s y sca r s
d lc L
dt l t R
Depolarization term OPO loss term
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1717
Pulse profilePulse profile
Rs=9% Rs=16% Rs=34% Rs=50%
20 ns/div 20 ns/div 10 ns/div 10 ns/div
• Good coincidence between theory and experimental result.
• Output coupler with higher reflectivity gives higher feedback of energy and results in more fluctuation in pulse dynamics.
• Optimized peak power still holds in lower reflectivity.
0.9 MW 0.68 MW 0.62 MW 0.56 MW
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Han-Lung Chang
Summary in IOPOSummary in IOPO Up to 10-mJ pulse energy eye-safe laser is achieved with IOPO.Up to 10-mJ pulse energy eye-safe laser is achieved with IOPO. The threshold of passively Q-switched IOPO is dominated by The threshold of passively Q-switched IOPO is dominated by
the bleach of saturable absorber.the bleach of saturable absorber. The birefringence effect induced from thermal effect in Nd:YAG The birefringence effect induced from thermal effect in Nd:YAG
gives rise to parasitic pulse in time domain.gives rise to parasitic pulse in time domain.
Y. P. Huang, H. L. Chang, et al. “Subnanosecond mJ eye-safe with an intracavity optical parametric oscillator in a shared resonator”Opt. Express 17, 1551-1556 (2009)
18
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Solid-State Laser Physics Lab.
Han-Lung Chang
1919
OutlineOutline Introduction, Background, and MotivationIntroduction, Background, and Motivation
Optical Parametric Oscillator (OPO)Optical Parametric Oscillator (OPO)
Self-Stimulated Raman Scattering Self-Stimulated Raman Scattering (SRS)(SRS)
Passively Q-switched Erbium/Ytterbium Fiber LaserPassively Q-switched Erbium/Ytterbium Fiber Laser
PCF Laser pumped OPOPCF Laser pumped OPO
Optically Pumped Semiconductor Laser (OPSL)Optically Pumped Semiconductor Laser (OPSL)
ConclusionConclusion :: Contribution and Future WorkContribution and Future Work
NCTU Electrophysics
Solid-State Laser Physics Lab.
Han-Lung Chang
20
Raman ScatteringRaman Scattering
p
s
phv Shv
Rhv
1hv AShv
Rhv
• First discovered by C. V. Raman in 1928.
• Third-order nonlinear process. (Four-wave mixing)
• Inelastic collision• No consideration of phase-
matching
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21
Conventional crystals for stimulated Raman scattering
MaterialMaterial Raman Raman shift (cmshift (cm--
11))
Raman Raman linewidtlinewidth (cmh (cm-1-1))
Cross Cross section section (arb. (arb.
Units)Units)
Raman Raman gain gain
(cm/GW)(cm/GW)
DamagDamage e
threshothreshold ld
(GW/cm(GW/cm22))
Ba(NOBa(NO33))22 10471047 0.40.4 2121 1111 ~ 0.4~ 0.4
BaWOBaWO44 924924 1.61.6 5252 8.58.5 ~ 5~ 5
KGd(WOKGd(WO44
))22
768768
9019016.76.7
5.75.75959
54544.44.4
3.33.3~ 10~ 10
YVOYVO44 890890 2.62.6 9292 > 4.5> 4.5 ~ 1~ 1
GdVOGdVO44 882882 33 9292 > 4.5> 4.5 ~ 1~ 1A. A Kaminskii et. al. Opt. Com. (2001)
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22
Nd:YVONd:YVO44 used as a self-SRS crystal used as a self-SRS crystal
Nd:YVO4 can be used to serve as a gain medium and Raman medium simultaneously.
Self-stimulated Raman scattering crystal
• Heat generation resulting from quantum defect restricts the available output power
“Diode-pumped actively Q-switched c-cut Nd:YVO4 self-Raman laser, “Y. F. Chen, V 29. No. 11 Opt. Lett. 1251 (2004)
“Compact efficient all-solid-state eye-safe laser with self-frequency Raman conversion in a Nd:YVO4 crystal,” Y. F. Chen, V 29. No. 18 Opt Lett 2172-2174 (2004)
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Han-Lung Chang
23
Thermal effectThermal effect
2
2
Raman gain:
/
s p
p ss
s R
g I l
N d dg
c n v
R sT v g
The influence of thermal effect• Thermal lens • Mode matching• Cavity stability• Conversion efficiency• Beam quality
NCTU Electrophysics
Solid-State Laser Physics Lab.
Han-Lung Chang
24
Thermal effectThermal effect
24
W. Webber et. al. IEEE J. Quantum Electron 34 (1998)
Uniform doped Nd:YAG
Temp dist.
Stress dist.
Undoped YAG-bundled
15W 15W
24
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Solid-State Laser Physics Lab.
Han-Lung Chang
25
Thermal lens in fundamental cavityThermal lens in fundamental cavity
25
R=92%
Nd:YVO4 YVO4YVO4
8mm10mm2mm
0.3-% doped Nd:YVO4
• The thermal lens effect is reduced by 1.6 times
20W
• Thermal diffuser
• Raman gain medium
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Han-Lung Chang
Actively Q-switched intra-cavity Self-SRSActively Q-switched intra-cavity Self-SRS
Limited by critical power
• Lasing threshold decreased.
• Maximum power of 2.23 W was obtained.
• Conversion efficiency was enhanced from 8.9% to 13% with double-end crystal.
26
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27
20 kHz 40 kHz
Pulse energy : 86 uJ
Peak power : 22 kW
Pulse energy : 56 uJ
Peak power : 17 kW
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Solid-State Laser Physics Lab.
Han-Lung Chang
28
Summary in Self-SRSSummary in Self-SRS
A double-end diffusion bond Nd:YVOA double-end diffusion bond Nd:YVO44 crystal was crystal was firstly used to be a self-stimulated Raman scattering firstly used to be a self-stimulated Raman scattering crystal in eye-safe wavelength.crystal in eye-safe wavelength.
Thermal effect ↓ (1.6X)Thermal effect ↓ (1.6X) Critical pump power ↑Critical pump power ↑ Raman power ↑ Raman power ↑ Conversion efficiency↑ (9%Conversion efficiency↑ (9% 13%) 13%)
Y. T. Chang, K. W. Su, H. L. Chang, et al. “Compact efficient Q-switched eye-safe laser at 1525 nm with a double-end diffusion-bonded Nd:YVO4 crystal as a self-Raman medium”Opt. Express 17, 4330-4335 (2009)
NCTU Electrophysics
Solid-State Laser Physics Lab.
Han-Lung Chang
2929
OutlineOutline Introduction, Background, and MotivationIntroduction, Background, and Motivation
Optical Parametric Oscillator (OPO)Optical Parametric Oscillator (OPO)
Self-Stimulated Raman Scattering (Self-SRS)Self-Stimulated Raman Scattering (Self-SRS)
Passively Q-switched Erbium/Ytterbium Fiber LaserPassively Q-switched Erbium/Ytterbium Fiber Laser
PCF Laser pumped OPOPCF Laser pumped OPO
Optically Pumped Semiconductor Laser (OPSL)Optically Pumped Semiconductor Laser (OPSL)
ConclusionConclusion :: Contribution and Future WorkContribution and Future Work
NCTU Electrophysics
Solid-State Laser Physics Lab.
Han-Lung Chang
Double-Clad Fiber
Double clad fiber
• Low NA ~ 0.07 (Single mode )
• Large mode area
• High pump absorption : 3dB/m
Single-mode core (doped)
Outer cladding (polymer)Inner cladding (silica)
2 aV NA
core
1st clad
30
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Han-Lung Chang
Er/Yb codoped material
• Broad Yb Absorption relaxes pump wavelength constraints• 100X increase in ‘practical’ pump absorption
2F5/2
2F7/2Yb3+ Er3+
4FI11/2
4FI9/2
4FI13/2
Energy transfer
Pump 976 nm
Lasing 1540 nm
31
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Solid-State Laser Physics Lab.
Han-Lung Chang
32
Passively Q-switched Er/Yb Fiber Passively Q-switched Er/Yb Fiber LaserLaser
20W
HT@976 nmHR@1530~1600 nm
Laser output
Fiber-coupled LD @976 nm
Er/Yb doped double-clad fiber; clad/core: Dia. 300/25 μm NA : >0.46 /<0.07
cavity
R~4%
HR @ 1530~1600 nm
SA
7m
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Han-Lung Chang
33
• Conventional saturable absorber at 1.5 um CoCo2+2+:MgAl:MgAl33OO44, Cr, Cr22++:ZnSe, Co:ZnSe, Co2+2+:ZnS, Co:ZnS, Co2+2+:ZnSe:ZnSe
SA
• Semiconductor saturable absorber at 1.5 um Quantum wells:Quantum wells: InGaAsP InGaAsP, AlGaInAs, AlGaInAs
GaInN/GaN
200 400 1000600 1200800
1550
1400 1600
1300
AlGaAs/GaAs
InGaAsP/InP
GaInNAs/GaAs
GaAsSb/GaAs
InGaAs/GaAs
AlGaInP/GaAs
AlGaInAs/InP
Optical Disks, Displays Transmission systems
LAN’s, Interconnects
GaInN/GaN
200 400 1000600 1200800
1550
1400 1600
1300
AlGaAs/GaAs
InGaAsP/InP
GaInNAs/GaAs
GaAsSb/GaAs
InGaAs/GaAs
AlGaInP/GaAs
AlGaInAs/InP
Optical Disks, Displays Transmission systems
LAN’s, Interconnects
InGaAsP/InP
AlGaInAs/InP • AlGaInAs SA was firstly proposed in eye-safe fiber laser
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Semiconductor saturable absorber at 1.5 μmSemiconductor saturable absorber at 1.5 μm
AlGaInAs vs. InGaAsP
• Higher conduction band-offset better confinement
• Higher modulation depth
• Larger absorption cross section
34
InGaAsP v.s. AlGaInAs
c
v
E 0.4 =
E 0.6
ΔEC
ΔEV
InGaAsP
Eg,barrier
ΔEC
ΔEV
AlGaInAs
c
v
E 0.72 =
E 0.28
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Semiconductor saturable absorber
2
2×30 groups
InPSubstrate
1 0 1 2 3 4 5 6 7 8 9 100.5
1
1.5
2
2.52.5
0.5
1 sin x( ) 2
101 x
1 0 1 2 3 4 5 6 7 8 9 100.5
1
1.5
2
2.52.5
0.5
1 sin x( ) 2
101 x1 0 1 2 3 4 5 6 7 8 9 10
0.5
1
1.5
2
2.52.5
0.5
1 sin x( ) 2
101 x
1 0 1 2 3 4 5 6 7 8 9 100.5
1
1.5
2
2.52.5
0.5
1 sin x( ) 2
101 x
1E-3 0.01 0.1 1 1020
30
40
50
60
70
80
90
100
Tr
ansm
issi
on (
%)
Incident energy density (mJ/cm2)
ΔR~50%
• Periodic structure with half wavelength of lasing mode Damage avoided.
35
• High modulation depth results in high pulse energy
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Han-Lung Chang
36
Laser Performance of Er/Yb Fiber Laser
Q-switching efficiency > 85 % Pulse energy ~ 105 μJ
[1] “Passively Q-switched 0.1-mJ fiber laser system at 1.53 um,” R. Pasbotta, et. al. Opt. Lett V24. 388 (1999)
Higher pulse energy than InGaAsP[1]Higher efficiency than bulk SA
200 ns/div
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37
Summary in EYDFLSummary in EYDFL
• An AlGaInAs/InP semiconductor absorber was An AlGaInAs/InP semiconductor absorber was firstlyfirstly used in used in eye-safe laser region.eye-safe laser region.
• No active cooling. No active cooling. • High pulse energy up to 100-μJ.High pulse energy up to 100-μJ.• Good beam quality was obtained with Good beam quality was obtained with MM22 < 1.5< 1.5
J. Y. Huang, S.C. Huang, H. L. Chang, et. al “Passive Q-switching of Er-Yb fiber laser with semiconductor saturable absorber” Opt. Express, V16, 3002-3007 (2008)
NCTU Electrophysics
Solid-State Laser Physics Lab.
Han-Lung Chang
3838
OutlineOutline Introduction, Background, and MotivationIntroduction, Background, and Motivation
Intracavity Optical Parametric Oscillator (OPO) Intracavity Optical Parametric Oscillator (OPO) Pumped by Nd:doped LaserPumped by Nd:doped Laser
Self-Stimulated Raman Scattering (Self-SRS)Self-Stimulated Raman Scattering (Self-SRS)
Passively Q-switched Erbium/Ytterbium Fiber LaserPassively Q-switched Erbium/Ytterbium Fiber Laser
Widely tunable eye-safe laser by a PCF laser and OPOWidely tunable eye-safe laser by a PCF laser and OPO
Optically Pumped Semiconductor Laser (OPSL)Optically Pumped Semiconductor Laser (OPSL)
ConclusionConclusion :: Contribution and Future WorkContribution and Future Work
NCTU Electrophysics
Solid-State Laser Physics Lab.
Han-Lung Chang
Pump Source of External-Pump Source of External-cavity OPOcavity OPO
AlGaInAs/InP
1 0 1 2 3 4 5 6 7 8 9 100.5
1
1.5
2
2.52.5
0.5
1 sin x( ) 2
101 x
1 0 1 2 3 4 5 6 7 8 9 100.5
1
1.5
2
2.52.5
0.5
1 sin x( ) 2
101 x
70/200
• Single mode
• Extreme large mode area
• Polarization maintain
• High pump absorption: 30 dB/m
Yb doped Photonic Crystal Fiber
• Periodic structure with half wavelength of lasing mode
• High modulation depth
• High absorption cross section
2 aV NA
39
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40
External cavity OPO – pump sourceExternal cavity OPO – pump source
40
Yb-doped PCF Passively Q-switched Laser
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41
Performance of PCF LaserPerformance of PCF Laser
41
(a) (b)20 ns/div 20 ns/div(a) (b)(a) (b)20 ns/div 20 ns/div6 8 10 12 140
1
2
3
4
5
Launched Pump Power (W)
Ou
tpu
t A
vera
ged
Po
wer
(W
)
300
400
500
600
700
800
Ou
tpu
t Pu
lse En
ergy (J)
1026 1028 1030 1032 10340.0
0.2
0.4
0.6
0.8
1.0
1.2
In
ten
sity
(a.u
.)
Wavelength(nm)
6 8 10 12 140
1
2
3
4
5
Launched Pump Power (W)
Ou
tpu
t A
vera
ged
Po
wer
(W
)
300
400
500
600
700
800
Ou
tpu
t Pu
lse En
ergy (J)
1026 1028 1030 1032 10340.0
0.2
0.4
0.6
0.8
1.0
1.2
In
ten
sity
(a.u
.)
Wavelength(nm)
(a) (b)20 ns/div 20 ns/div(a) (b)(a) (b)20 ns/div 20 ns/div
• Central wavelength : 1029~1031 nm
• Optical-to-optical conversion efficiency ~ 37 %
• Rep rate: 1k ~ 6 kHz
• Maximum output peak power : 170 kW
Low power pumping
High power pumping
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External-cavity OPOExternal-cavity OPO
2plate
PBS
Focusinglens
f=75mm PPLN29.6μ m
HT 1030 nm
HR 1550 nm
HT 1030 nm
PR 1550 nm
OPO part
1030 nmpump
2plate
PBS
Focusinglens
f=75mm PPLN29.6μ m
HT 1030 nm
HR 1550 nm
HT 1030 nm
PR 1550 nm
OPO part
1030 nmpump
L=2.0 cm R=55%
PPLN : • High nonlinear coefficient : 15pm/V (5 x of KTP)• Large phase matching wavelength coefficient (~0.5 nm/℃)
42
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Han-Lung Chang
20ns/divpump
signal
pump
signal
20nsdiv
pump
signal
10nsdiv10nsdiv
(a) (b)
pump
signal
20nsdiv
pump
signal
10nsdiv10nsdiv
(a) (b)
43
Performance of external-cavity Performance of external-cavity OPOOPO
43
22 2 2
30
2 (0)2
s i p
s i eff pth tot
d IL L a
n n n c
Round trip loss
Conversion efficiency ~ 35%
Pth=0.12W
Maximum pulse energy : 138 uJ
Maximum peak power : 19 kW
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Han-Lung Chang
44
Wavelength vs. TemperatureWavelength vs. Temperature
44
Wavelength tuning range: 1513 to 1593 nm
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Han-Lung Chang
45
Summary in PCF pumped OPOSummary in PCF pumped OPO
A 750 uJ PCF fiber with AlGaInAs semiconductor saturable absorber was used to be a 1030-nm OPO pump source.
Wavelength tuning range up to 80 nm and pulse energy of 138 uJ in eye-safe region from 1513 to 1593 nm was obtained by a PPLN-OPO.
45
H. L. Chang, W. Z. Zhuang, W. C. Huang, et. al “Widely tunable eye-safe laser by a passively Q-switched Photonic crystal fiber laser and an external-cavity optical parametric oscillator” Laser Phys. Lett. To be published.
NCTU Electrophysics
Solid-State Laser Physics Lab.
Han-Lung Chang
4646
OutlineOutline Introduction, Background, and MotivationIntroduction, Background, and Motivation
Optical Parametric Oscillator (OPO)Optical Parametric Oscillator (OPO)
Self-Stimulated Raman Scattering (SRS)Self-Stimulated Raman Scattering (SRS)
Passively Q-switched Erbium/Ytterbium Fiber LaserPassively Q-switched Erbium/Ytterbium Fiber Laser
PCF Laser pumped OPOPCF Laser pumped OPO
Optically Pumped Semiconductor Laser Optically Pumped Semiconductor Laser (OPSL)(OPSL)
ConclusionConclusion :: Contribution and Future WorkContribution and Future Work
NCTU Electrophysics
Solid-State Laser Physics Lab.
Han-Lung Chang
Optically Pumped Semiconductor Laser
Advantages:
• Uniform distribution of pump power over large active region
• Excellent beam quality
• Wide wavelength range
Substrate Substrate
Bragg mirrors
Active layer
Bragg mirrors
Cap layer
Bragg mirrors
Active layer
Output coupler
Pumping photon
Fig 1 : Typical structure of electrical pumped VCSEL (left) and optical pumped VECSEL (right).
Substrate Substrate
Bragg mirrors
Active layer
Bragg mirrors
Cap layer
Bragg mirrors
Active layer
Output coupler
Pumping photon
Fig 1 : Typical structure of electrical pumped VCSEL (left) and optical pumped VECSEL (right).
Concerning issue
• Thermal management
• Heat sink/spreader
• Pumping style
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Barrier pumping and in-well pumping
QWBarrier Barrier
CB
VB
1.06
4μm
1.57μm
Barrier pumping
1.57μm
CB
VB
1.34
2μm
Barrier BarrierQW
In-well pumping
The quantum defect of in-well pumping is reduced from 32% to 14% compared with barrier-pumping
Optically Pumped Optically Pumped Semiconductor LaserSemiconductor Laser
Transmission spectrum
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Barrier-pumpingBarrier-pumping
Beam expander
Focusing lens
Reflection mirror
Q-switched Nd:GdVO4
1064–nm laser
λ
2
1.56μm output
30 groups AlGaInAs QWs
HR at 1.56μm (R>99.8%)HT at 1.06μm (R>80%)
PR at 1.56μm (R=95%)PR at 1. 06μm (R=60%)
Fluorescence spectrum
1 0 1 2 3 4 5 6 7 8 9 100.5
1
1.5
2
2.52.5
0.5
1 sin x( ) 2
101 x
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The laser performance
10°C 30kHz
• Output power saturates at 135 mW at a repetition rate of 30 kHz
• The performance of output power depends on the temperature
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In-well pumpingIn-well pumping
51
Beam expander
Focusing lens
Reflection mirror
Q-switched Nd:YVO4 1342–nm laser
λ
2
1.56μm output
30 groups AlGaInAs QWs
HR at 1.56μm (R>99.8%)HT at 1.34μm (R>80%)
PR at 1.56μm (R=90%)PR at 1. 34μm (R=60%)
1 0 1 2 3 4 5 6 7 8 9 100.5
1
1.5
2
2.52.5
0.5
1 sin x( ) 2
101 x
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In-well v.s. Barrier Pumping
0 200 400 600 800 1000 1200 1400 16000
30
60
90
120
150
180
Av
erag
e o
utp
ut
po
wer
at
15
55
nm
(m
W)
Absorbed pump power (mW)
in-well pumping barrier pumping
Comparison of single chip
• Higher conversion efficiency in in-well pumping
• Lower absorption
Double chips were used to increase absorption efficiency
52
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Laser performance – Double chips
10°C
Conversion efficiency ~ 30% @ 9°C Optimum rep rate : 40kHz ~ 60 kHz
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Laser performance
M2 <1.3
The maximum output peak power ~ 290 W at a pump peak power of 2.3 kW
Barrier-pumping
The maximum output peak power ~ 520 W at a pump peak power of 3.7 kW.
In-well pumping
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Summary in OPSL (1/2)
S. C. Huang, H. L. Chang, et. al “AlGaInAs/InP eye-safe laser pumped by a Q-switched Nd:GdVO4 laser” Appl. Phys. B, 94, 483-487 (2009)
• A periodic AlGaInAs QW/barrier structure was firstly developed to be a gain medium in a high-peak -power nanosecond laser at 1.57μm .
• With barrier pumping, a maximum average output power of 135 mW was obtained under 1.25 W pump power. The maximum peak power was up to 290 W at a peak pump power of 2.3 kW.
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• Barrier-pumping scheme and in-well pumping were compared in the performance of thermal improvement.
• The optical-to-optical conversion efficiency of in-well pumping scheme was up to 30%. The maximum output peak power was up to 0.52 kW under 3.7 kW pump peak power
Summary in OPSL (2/2)
H. L. Chang, S. C. Huang, et. al “Efficient high-peak-power AlGaInAs eye-safe wavelength disk laser with optical in-well pumping” Opt. Express. V17, 1409-11414 (2009)
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Conclusion: Contribution (1/2)Conclusion: Contribution (1/2)
We achieved eye-safe lasers by means of structures including OPO, self-SRS, Er/Yb fiber laser, PCF laser and OPSL.
Theoretical analyses of lasing threshold and dynamic pulse behavior in the passively Q-switched intracavtiy OPO were proposed and investigated.
A double-end diffusion bond self-SRS crystal were used to diminish the thermal effect.
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Conclusion: Contribution (2/2)Conclusion: Contribution (2/2)
A semiconductor saturable absorber, AlGaInAs, was used in a passively Q-switched Er/Yb laser to obtain a high pulse energy laser.
An 80-nm tuning range eye-safe laser was achieved by an AlGaInAs passively Q-switched PCF laser and an external-cavity OPO.
An optically pumped disk laser with AlGaInAs/InP quantum well/barrier structure as gain medium was demonstrated. In-well pump scheme was proposed to reduce the thermal effect.
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976nm LDCW 45W
~2.5cm
Beam combiner
1030~1080nm ARHR@1550nm
HR@1030~1080nm
Grating
Tunable eye-safe laser with narrow linewidth
PPLN
1550 ~ 1700 nm
pump
signal
Conclusion: Future workConclusion: Future work
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Thanks for you attention
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APPENDIXAPPENDIX
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Rep Rate and Peak Power vs. Range
1 2 3 4 50
20
40
60
80
100
120
Max rep rate Peak power
Range (km)
Max
rep
rat
e (k
Hz)
0
200
400
600
800
1000P
eak power (W
)
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Co2+:MgAl2O4 Specifications:High absorption cross section of 3.5 x 10-19 cm2
Wavelength range, 1200-1600 nm , in particular, for eye-safe 1.54 μm Er:glass laser Damage threshold, 10 J/cm2 Initial transmittance, 30-99 % The ratio of initial (small signal) to saturated absorption is higher than 10.which results in high contrast of Q-switch
V3+:YAG Specifications: High ground state absorption (GSA) cross section of 7x10-18 cm2 near 1.3μ m .Wavelength range, 1000-1450 nm , in particular, for 1.3 m Nd-lasers Damage threshold : 7-10 J/cm2 Initial transmittance : 50-99 % The ratio of initial (small signal) to saturated absorption is higher than 10 Excellent optical, mechanical, and thermal properties.
Cr4+:YAG (Cr4+:Y3A15O12) Specifications:High absorption cross section of 4.3 x 10-18 cm2
Wavelength range : 900-1200 nm Damage threshold : >500 MW/cm2 Initial transmittance : 10-99 % Recovery time : 8.5μs
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Semiconductor saturable absorber (SESA)
AlGaInAs quantum well as a saturable absorber in diode-pumped solid state (DPSS)
laser with proper parameters for passively Q-switched (PQS) and mode-locked laser
For 1.06μm PQS , SESA would be designed
with large cross section , large modulation
depth and high damage threshold
Optically-pumped semiconductor laser (OPSL)
By use of AlGaInAs quantum well as a gain medium in OPSL
◆ Design for 1.1-1.6μm wavelength spectral range
◆ Power scaling :
Different wavelength spectral (red) with different semiconductor materials
For 0.9-1.2μm wavelength
Cr+4:YAG SESA
TA ~μs ~ ns-ps
σA 10-18-10-17cm2 ~10-14cm2
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Saturable absorber fluence intensitySaturable absorber fluence intensity
4+SESA Cr :YAG
SESA SESA
SESA
~ 100
1 1 181
13
sat
fiber
hF
A
A
FP filterCr4+:YAG
~ ωO
~ 13 ωO
FP filter SESAFsat,SESA Fsat,Cr
4+:YAG
Easier for cavity setupLower optical intensity on SA
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• Conventional saturable absorber at 1.5 um CoCo2+2+:MgAl:MgAl33OO44, Cr, Cr22++:ZnSe, Co:ZnSe, Co2+2+:ZnS, Co:ZnS, Co2+2+:ZnSe:ZnSe
SA
• Semiconductor saturable absorber at 1.5 um Quantum wells:Quantum wells: InGaAsP InGaAsP, AlGaInAs, AlGaInAs
GaInN/GaN
200 400 1000600 1200800
1550
1400 1600
1300
AlGaAs/GaAs
InGaAsP/InP
GaInNAs/GaAs
GaAsSb/GaAs
InGaAs/GaAs
AlGaInP/GaAs
AlGaInAs/InP
Optical Disks, Displays Transmission systems
LAN’s, Interconnects
GaInN/GaN
200 400 1000600 1200800
1550
1400 1600
1300
AlGaAs/GaAs
InGaAsP/InP
GaInNAs/GaAs
GaAsSb/GaAs
InGaAs/GaAs
AlGaInP/GaAs
AlGaInAs/InP
Optical Disks, Displays Transmission systems
LAN’s, Interconnects
InGaAsP/InP
AlGaInAs/InP
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Conventional saturable absorber at 1.5 um
SA Lifetime(μs)
σes/ σgs
(10-
19cm2)
Results Fiberparameters
Active medium
CoCo2+2+:MgAl:MgAl33OO
4 4 [1][1]
0.340.34 0/2.40/2.4 22μJ, 370 ns22μJ, 370 ns
60W@60kHz60W@60kHz12μm, NA=0.2212μm, NA=0.22 Er/YbEr/Yb
CrCr2+2+:ZnSe:ZnSe[1][1] 88 0.2/3.40.2/3.4 18μJ, 380 ns18μJ, 380 ns
45W@70kHz45W@70kHz12μm, NA=0.2212μm, NA=0.22 Er/YbEr/Yb
CoCo2+2+:ZnS:ZnS[2][2] 200200 1.1/101.1/10 60μJ, 3.5 ns60μJ, 3.5 ns
>10 kW@6kHz>10 kW@6kHz11 μm, NA~ 0.2111 μm, NA~ 0.21 Er/YbEr/Yb
CoCo2+2+:ZnSe:ZnSe[3][3] 290290 1.1/11.1.1/11.55
15 nJ, 43 mW, 15 nJ, 43 mW, 350 ns 350 ns @235kHz@235kHz
2.7 μm, NA~ 0.272.7 μm, NA~ 0.27 ErEr
[1] Philippov, V et al., In, XI International Conference on Lasers Optics (LO'2003), St Petersburg, Russia, 30 Jun - 4 Jul 2003 . [2] M. Laroche et al., Opt. Lett. 27, 1980-1982 (2002).[3] V. Filippm. et al., Opt. Lett 26, ,343-345 (2001).
SA
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The laser performance
30kHz
• The performance of output power depends on the temperature
• Output power saturates at 135 mW at a repetition rate of 30 kHz
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The transmittance of the gain
material exceeds 85% at the
excitation intensity higher than
3.0 MW/cm2.
Laser Performance
The maximum output peak power ~ 290 W at a pump peak power of 2.3 kW
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20ns/div
1342nm
1570nm
70
Time domain of in-well pumping
20ns/div
1064nm
1565nm
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“Narrow-linewidth widely tunable hybrid Q-switched double-clad fiber laser” Y. X. Fan et al. Opt. Lett. V28, No. 7 (2003)
• Tuning range: > 60 nm
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