Developments in new high power fiber lasers and ultrafast lasers Martin Richardson Townes Laser Institute & College of Optics and Photonics, University of Central Florida, [email protected]www.townes.ucf.edu www.lpl.creol.ucf.edu Institute of Applied Science, Friedrich Schiller University, Jena June 1, 2011
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Developments in new high power fiber lasers and ultrafast lasers · 2020-04-11 · Developments in new high power fiber lasers and ultrafast lasers Martin Richardson Townes Laser
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Developments in new high power fiber lasers and ultrafast lasers
Martin RichardsonTownes Laser Institute & College of Optics and Photonics,
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
0.2
0.4
0.6
0.8
1.0
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
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
0.2
0.4
0.6
0.8
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
1905 1906 1907 1908 1909 19100.0
0.2
0.4
0.6
0.8
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)
• 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
• 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
1940 1960 1980 2000 2020 2040 20600
10
20
30
40
50
60
Maximum Power
Max
imum
Pow
er (W
)
Wavelength (nm)
0.0
0.1
0.2
0.3
0.4
0.5
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
1900 1950 2000 2050 2100 21500.0
0.2
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0.6
0.8
1.0
Wavelength (nm)Pow
er In
clud
ing
Atm
osph
ere
1900 1950 2000 2050 2100 21500.0
0.2
0.4
0.6
0.8
1.0
Wavelength (nm)Pow
er In
clud
ing
Atm
osph
ere
R.A Sims, et al., Opt. Comm, 284, 7, 1988-1991 (2011)
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
-60
-50
-40
-30
Sign
al (d
B)
Wavelength (nm)
1900 1950 2000 2050 2100 2150-80
-75
-70
-65
-60
-55
-50
Stre
tche
d Pu
lse
Sign
al (d
B)
Sign
al (d
B)
Wavelength (nm)
-80
-75
-70
-65
-60
-55
-50
-45
32% Slope Efficiency
1900 2000 2100-62
-60
-58
-56
-54
-52
-50
-48
-46
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
6
8
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
• 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