Developments in new high power fiber lasers and ultrafast lasers

Martin RichardsonTownes Laser Institute & College of Optics and Photonics,

University of Central Florida,mcr@creol.ucf.edu

www.townes.ucf.edu www.lpl.creol.ucf.edu

Institute of Applied Science, Friedrich Schiller University, Jena

June 1, 2011

Townes Laser Institute at UCF

New Florida Center of Excellence at the University of Central Florida

Lasers in Medicine, Advanced Manufacturing & Defense.Economic Development

High power fiber lasers

Dedicated May 4 2007 ~ 57,000 students2nd largest university in USA

COLLEGE of OPTICS & PHOTONICSCurrent Faculty 45Graduate students ~ 180Space ~ 105,000 sq ftBudget ~ $12M/yr

Collaboration Agreement with Fraunhofer Institute for Laser Technology Aachen – Industrial Laser Materials Processing

Axel SchulzgenProfessor(ex Univ. Arizona, Humbolt Univ.)Multi-structured optical fibersPhosphate fibers, Fiber lasers, NLO fibers

Ayman AbouraddyAssistant Professor(ex MIT, Boston Univ)Multifunctional fibers, CG, polymer and photon band-gap fibersBiomed fibers

Rodrigo Amezcua-CorreaResearch Assisant Professor(ex Southampton & Bath Universities)PCF fibers. Silica fibers

New professors in Optical Fibers

Outline

Advances in High Tm fiber lasersSpectral control and tuningPulsed laser operation in ns, ps and fs regimes

Towards multi-kW power levels with spectral beam combiningGMRF-line controlled lasersDense spectral packing within Tm linewidth (1850 – 2150 nm)

Atmospheric transmission tests over 1 kmSpectral tuning through water absorption lines

First LIBS detection of organic signatures with Tm fiber lasersAdvantages of Detection

Next generation of high power ultrafast lasersCEP and quasi single cycle

1900 1950 2000 2050 2100 21500.0

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Wavelength �nm�

Avail

able

Powe

rInc

ludi

ngAt

mos

phere

Thulium Gain Cutoff

Atmospheric Induced Cutoff

100 pm

200 nm

Thulium Fiber Lasers

Control of the spectral regimenarrow linewidth outputtunable emissionstable frequency control

Pulsed operation at 2 umQ-switched ns regimeps pulses with fs pulse mode-locking

kW powers through beam combininginitial demonstrationdense wavelength stacking

Applications of cw and pulsed Tm fiber lasersHigh power beam propagationSpectral sensing technologiesMedical applicationsHigh Harmonic Generation

V-parameter ~ λ-1

SRSthresh ~ λ-1

Pcrit (self-focusing) ~ λ-2

Thulium laser characteristics6

• Many Potential Pump BandsDifferent applications call for different bands

• 790 nm pumping highly efficientHigh diode powers available

• Cross Relaxation processQuantum defect 40% → CR allows >75% efficiencyMulti-polar interaction between adjacent thulium ions allows energy transfer between themSingle pump photon can generate two laser photons

• Optimum dopingHigh Tm doping levels neededUse of Al to minimize clustering in silica host which causes energy transfer up-conversion

3H6

3H4

3F4

3H5

0 eV

0.09 eV

0.69 eV

0.78 eV

1.03 eV

1.10 eV

1.56 eV

1.63 eV

1.8-2.1 μm

0.79 μm

Potential Pump Bands

LaserCross

RelaxationEnergy

Transfer Upconversion

MultiphononEmission

1.1-1.2 μm

1.5-1.9 μm

1.8-2.1 μm

Propagation near 2 μm offers inherent benefits of increased MPE and reduced aerosol absorption.

Blue: Atmospheric transmission between 0.8 and 2.2 μmGreen: aerosol absorption (α = 0.18 km−1 at λ = 1 μm)

Black: Relative laser Gain in Yb, Er–Yb and Tm short length silica fiber lasersRed: Maximum Permitted Energy for 100 ns pulse (log scale).

J-P. Cariou, B. Augere, M. Valla, C. R. Physique 7 (2006) 213–223

Atmospheric transmission

Spectral control of the large Tm bandwidth

Volume Bragg Gratings (VBG)Glebov Group @ CREOLhigh efficiency >95%tunable (100 pm)

Guided-Mode Resonant Filter (GMRF)Eric Johnson Group @ UNCCfixed wavelength by designlinewidth (50 pm)

Fiber Bragg Grating (FBG)Nufern Incall-fiber, monolithic fabricationlinewidth ~2.5nm

PS-GDF-20/400 fiberHR @ 2.05µm

Si filter

200W793nm

PS-GDF-20/400 fiberHR @ 2.05µm

Si filter

200W793nm

2044 2046 2048 2050 2052 2054 2056

Am

plitu

de (A

U)

Wavelength (nm)

Slope efficiency ~55%~110W output power at 2050nm (FWHM ~2.5nm) from a grating based laser cavityE-O efficiency = 17% at 110W with 793 nm barsVeff= 2.61 @ 2.05µm for 25/400 fiber

1905 1906 1907 1908 1909 19100.0

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Lase

r spe

ctru

m (A

U)

Ho:

YAG

abso

rptio

nA

tmos

pher

ic tr

ansm

ittan

ce

Wavelength (nm)

Laser AtmosphericHo:YAG

1905 1906 1907 1908 1909 19100.0

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1.0

Lase

r spe

ctru

m (A

U)

Ho:

YAG

abso

rptio

nA

tmos

pher

ic tr

ansm

ittan

ce

Wavelength (nm)

Laser AtmosphericHo:YAG

400 600 800 1000 1200

Equation: y² = A + Bx + Cx²

x yA 54.35216 56.77923B -0.13454609 -0.13972182C 8.34772E-05 8.616E-05R² 0.99853 0.9984

Displacement (mm)

x y

70W output at 1908nm

Monolithic FBG based Fiber Laser

B. SampsonNufern

300 W Stable, Tunable MOPA

t~5 m PM 

10/130 TDF

LD1

Grating L1 L3

PM 10/130 UDF 0.16NA

PM 10/130 UDF 0.16NA

AC

FC

Cladding Mode Stripper

~6 m 25/400 TDF

LD2

LD2L2

L5 L2

M1M2

25/400 UDF 0.08NA

25/400 UDF 0.08 NA

L4AC

FC

M3

M3

HWP

QWP

HWP

QWP

LD1

2+1:1 PM Pump 

CombinerOptical Isolator

T. S. McComb et al.,Appl. Opt, 49, 32, 6236-6242, ( 2010)

0

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e (%

)

Wavelength (nm)

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250

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Power (W

)

Wavelength (nm)

y = 0.6467x ‐ 7.9751

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150

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250

0.0 50.0 100.0 150.0 200.0 250.0 300.0 350.0 400.0

Power (W

)

Launched Power (W)

Power Amplifier Performance

• 8 W seed power• Up to 220 W power• Example slope at 1.967 μm (65%)• >1 hr Stability• Tuning from 1.927 μm – 2.097 μm • FWHM <200 pm (MO limited)• M2 <1.2

Slope ~65%

> 170 nm

2050.5 2051.0 2051.5 2052.0 2052.5 2053.0 2053.50.0

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1.0

Nor

mal

ized

Ref

lect

ivity

(a.u

.)

Wavelength (nm)

~5 m 25/400 TDF

LD1

LD1L2

L3 L2

M1M2

25/400 UDF 0.09NA

25/400 UDF 0.09 NA

L1FC

ACVBG or HR

VBG Front Surface

Uncoated5 mm

5 mm

6 mm

Grating tilted 0.6°in two axes

VBG Reflectivity

VBG Schematic

Volume Bragg Grating High Power Oscillator

0 50 100 150 200 250 300 3500

50

100

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200

HR Power VBG Power

Out

put P

ower

(W)

Launched Pump Power (W)

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0

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HR Spectral Power

Wavelength (nm)

VBG Spectral Power

Spec

tral P

ower

(a.u

.)

• 159 W VBG Stabilized Power at 2053 nm• 54% Slope (~5% less than for HR due to no AR coating on VBG)• Stable spectrum < 1nm 10dB width (linewidth limited by VBG)• M2<1.2 in all cases, independent of feedback• >1 hr stable operation time. Power limited by onset of parasitic lasing

VBG Slope ~54%

HR Slope ~60%

VBG Stabilized High Power Oscillator

Tuning of VBG Laser

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Maximum Power

Max

imum

Pow

er (W

)

Wavelength (nm)

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0.6

Slope Efficiency (%)

Slope Efficiency

• Rotation of VBG changes wavelength • 50 W VBG Tunable Power• 47-54% Slope• >100 nm tuning range (1947-2053nm) • Range limited by onset of parasitic

lasing due to VBG design and fiber length

~5 m 25/400 TDF

LD1

LD1L2

L3 L2

M1M2

25/400 UDF 0.09NA

25/400 UDF 0.09 NA

L1FC

ACVBG

M2

0 10 20 30 40 501750

1800

1850

1900

1950

2000

2050

Wav

elen

gth

(nm

)

VBG Angle (degrees)

Fiber Lasers based on Guided Mode Resonance Filters

Pump diode: 790nm 400 μm, 0.22 NA fiber, 30 W; 11 cm coiling diameter on heatsink

GMRF provided by collaboration with Eric Johnson (UNCC)

GMRF Spectral Reflectivity

1940 1960 1980 2000 2020 2040 20600.0

1.0x10-7

2.0x10-7

3.0x10-7

4.0x10-7

5.0x10-7

6.0x10-7

OS

A S

igna

l (A

.U.)

Wavlength (nm)

Transmission ~ 50 pm linewidth

Fiber Lasers based on Guided Mode Resonance Filters

-60

-40

-20

Wavelength (nm)

HR Mirror

1980 2000 2020 2040

GMRF

GMRF provided by collaboration with Eric Johnson (UNCC)

> 10 W with GMRF linewidth < 100 nm

R.A Sims, Opt. Lett, 36, 5, 737-739 (2011)

Dense wavelength packing of Tm fiber lasers

Dense stacking of narrow line (~100 pm) wavelength-specific lasers undereffective bandwidth of 200 nm

Beam Combiner utilizes high damage resistant Dielectric Edge Mirrors (DEMs)

Principle Elements

Dielectric Edge Mirrors (DEMs)

Beam CombinerStacked Oscillators

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er In

clud

ing

Atm

osph

ere

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Wavelength (nm)Pow

er In

clud

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Atm

osph

ere

R.A Sims, et al., Opt. Comm, 284, 7, 1988-1991 (2011)

Q-switched 2 um Tm fiber laser LIBS sensing

Tm fiber laser:Wavelength:1992 nmDuration: 200 nsEnergy: 100 uJRepetition rate:20

kHz

Focusing optics:0.3 NA asphereDiameter: 10umIrradiance: 600

MW/cm2

Spectrometer:Acton HRE EchelleRange: 200-900 nmResolution: 0.04 nm

Acquisition:Delay: 0nsDuration: 300 ns

Matthieu Baudelet et al., Optics Express 18 7905 (2010)

Co-pumped LMA (23/250 TDF) “all-fiber” amplifier ~0.5 W Average power; Amplified at full 46 MHz~11 nJ pulse energy; Limited by feedback to modelocked laser due to poor isolation

5 ps CNT Modelocked Laser

40 W 790 nm Pump2050 nm  

Isolator 9/125 to 23/250 MFA

Cladding Mode Stripper / Pump Dump

~2m 23/250 TDF

2+1:1 Pump Combiner

All-Fiber Picosecond Pulse Amplifier System

• Improvements in Process• Use Isolator for correct wavelength• Higher seed power/preamp for better saturation and energy extraction• More seed power -> higher efficiency• Pulse down counter -> more per pulse energy

• Goals• Reach microJoules level in conventional fiber• Reach 10’s W average power• Compare nonlinear thresholds to similar Yb lasers

1950 1960 1970 1980 1990 2000 2010

-70

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Sign

al (d

B)

Wavelength (nm)

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-75

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-65

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-50

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tche

d Pu

lse

Sign

al (d

B)

Sign

al (d

B)

Wavelength (nm)

-80

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32% Slope Efficiency

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-58

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Am

plifi

er S

igna

l (dB

)

Sig

nal (

dB)

Wavelength (nm)

-62-60-58-56-54-52-50-48-46-44-42-40-38

15 20 25 30 35 40 45 50 550

2

4

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10

Out

put E

nerg

y (n

J)

Out

put P

ower

(W)

Launched Pump Power(W)

0

20

40

60

80

100

120

140

Average Power 12.8 W182 nJ uncompressed pulses 60 nm Bandwidth

Sims et al ASSP 2011

Towards an all-fiber fs Tm laser

Beam image at ~300 m on 1 km range

Innovative Science & Technology Experimentation Facility (ISTEF)

• A fully equipped laser ranging facility on Cape Canaveral Air Force Station

• Full laser and telemetry support• 1 km (fully secure) range• 5 km and 10 km ranges• Many different receivers

1 km Atmospheric Propagation

t~5 m PM 

10/130 TDF

LD1

Grating L1 L3

PM 10/130 UDF 0.16NA

PM 10/130 UDF 0.16NA

AC

FC

Cladding Mode Stripper

~5 m 25/400 TDF

LD2

LD2L2

L5 L2

M1M2

25/400 UDF 0.08NA

25/400 UDF 0.08 NA

L4AC

AC

M3

M3

HWP

QWP

HWP

QWP

LD1

2+1:1 PM Pump 

CombinerOptical Isolator

GLP

• Beam diameter measurements along the 1 km range confirm nearly diffraction-limited beam divergence

• The centroid moved between 6.5 – 7.5 % of the full beam diameter corresponding to pointing variation of <45 μrad including beam distortion from atmospheric turbulence

A 50 mm lens is used to collimated the beam from the fiber facet along a 1 km laser range

Initial 2 m Tm fiber laser propagation tests

High power lasers in the Richardson Labs

TW Laser1995 -2010

MFL 2004–2010

MTFL2010 -

HERACLES2010-

PhaSTHEUS 2011-

100 fs 850 nmCPA Cr:LiSAF300 mJ 0.1 Hz1 J single shot 40 fs 800 nmCPA Ti:Sapphire40 mJ 10 Hz 2mJ 1 kHz40 fs 800 nmCPA Ti:Sapphire400 mJ 10 Hz

High intensity laser plasmasHard X-ray generation & imagiAir filamentation studies

LIBS sensing studiesFemtosecond spectroscopyAir filamentation studies

Air filamentation studiesLIBS sensing studiesStandoff spectroscopy

5 fs 800 nmOPCPA CEP Hybrid2 mJ 10 kHz

AttoscienceEUV generation & applicationsTHz studies

5 fs 800 nmOPCPA CEP Hybrid100 mJ 1 Hz

AttoscienceEUV generation & applicationsStand-off THz studiesAir filamentation studies

Energy scaling of few cycle systems

10 Hz 100 Hz 1 kHz 10 kHz 100 kHz 1 MHz +

1 J

10 J

100 J

1 mJ

10 mJ

100 mJAdachi et al., Opt. Expr 2008 Witte et al., Opt. Expr 2006

Mid‐IR systems

800 nm systemsHerrmann et al ASSP 2009

Krausz et al. CLEO, 2007

Tünnermann et al., Opt. Expr 2009

Chalus et al., Opt. Expr 2009

1 Hz

HERACLES

HERACLES: High Energy Repetition‐rate Adjustable Carrier Locked to Envelope System

PhaSTHEUS

Architecture of HERACLES

Stretcher/Compressor strategy

Technique implemented on HERACLES limits losses in compressor

..low loss compressor enables higher output energy at low cost

mJ, multi-kHz, TEM00 pump beam generation

Gain region

Amplified spectrum supporting a 7.3 fs transform‐limited pulse

Optical Parametric Amplifier

The high energy beam line

Summary

New laser technologies are breathing new concepts into ultra-fast laser technologies

Many new applications opening for ultra-short pulse lasers

After 50 years of lasersAfter 25 years of ultrafast

This field offers so much for the next generation of scientists and engineers

In addition to pressing to higher powers, we are pushing to towards shorter pulses, higher efficiencies, more compact and rugged systems.

Educational Programs in Laser Marterials Processing

NSF International REU Program in Optics, Lasers Photonics and Optical Materials

International summer internship program for undergraduates

1998 – present> 70 students2 year program

Clemson University, UCF,Bordeaux University Turin University,Adelaide University

NSF Materials World Network ProgramIn novel IR fibers

2007 – 2012Mobility program~ 20 students

ATLANTIS-MILMI University Central FloridaBordeaux UniversityClemson University,

Friedrich-Schiller Univ.

2008 – presentInternational MS degreeLasers and Materials Interaction Science~ 16 students

Co-tutelle doctoral degree Program in

Laser Materials Processing and Optical Materials

University Central FloridaClemson University

Bordeaux U.

2004 – presentJoint Ph.D

7 graduatesexpansion

Acknowledgements

Funding JTO-HEL OfficeARONAVAIR

Industrial Affiliates