NCTU Electrophysics Solid-State Laser Physics Lab. Han-Lung Chang 11 The Researches and Investigations of Pulsed Laser in NIR Eye-safe Wavelength 脈衝式近紅外人眼安全雷射研究及探討

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

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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

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100-280nm

315-400nm

280-315nm

400-700nm

VIS

3

Eye-safe wavelength

UV

NIR > 1400 nm

NIR < 1400nm

IR

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Background and Motivation

4

High pulse energyHigh rep rate

Wavelength tunable

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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

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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






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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

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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

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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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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)

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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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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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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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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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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

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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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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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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)

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1919


Optical Parametric Oscillator (OPO)Optical Parametric Oscillator (OPO)

Self-Stimulated Raman Scattering Self-Stimulated Raman Scattering (SRS)(SRS)





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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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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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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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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

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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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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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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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20 kHz 40 kHz

Pulse energy : 86 uJ

Peak power : 22 kW

Pulse energy : 56 uJ

Peak power : 17 kW

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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)

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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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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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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



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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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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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)

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3838


Intracavity Optical Parametric Oscillator (OPO) Intracavity Optical Parametric Oscillator (OPO) Pumped by Nd:doped LaserPumped by Nd:doped Laser



Widely tunable eye-safe laser by a PCF laser and OPOWidely tunable eye-safe laser by a PCF laser and OPO



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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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External cavity OPO – pump sourceExternal cavity OPO – pump source

40

Yb-doped PCF Passively Q-switched Laser

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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/℃)

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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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Wavelength vs. TemperatureWavelength vs. Temperature

44

Wavelength tuning range: 1513 to 1593 nm

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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.

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4646



Self-Stimulated Raman Scattering (SRS)Self-Stimulated Raman Scattering (SRS)



Optically Pumped Semiconductor Laser Optically Pumped Semiconductor Laser (OPSL)(OPSL)


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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



GaInN/GaN

200 400 1000600 1200800

1550

1400 1600

1300

AlGaAs/GaAs

InGaAsP/InP

GaInNAs/GaAs

GaAsSb/GaAs

InGaAs/GaAs

AlGaInP/GaAs

AlGaInAs/InP



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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NCTU Electrophysics Solid-State Laser Physics Lab. Han-Lung Chang 11 The Researches and Investigations of Pulsed Laser in NIR Eye-safe Wavelength 脈衝式近紅外人眼安全雷射研究及探討