high energy 2-micron laser developments - nasa · june 28, 2007 high energy 2-micron laser...
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June 28, 2007
High Energy 2-micron Laser Developments
Jirong Yua, Bo C. Trieua, Mulugeta Petrosb, Yingxin Baic, Paul J. Petzarc, Grady J. Kocha, Upendra N. Singha,
Michael J Kavayaa
aNASA Langley Research Center, MS 468, Hampton, VA 23681bScience and Technology Corporation, Hampton, VA 23666
cSAIC, Hampton, VA 23666
2007 Solid State Diode Laser Technology Review
https://ntrs.nasa.gov/search.jsp?R=20070031110 2018-06-20T00:47:20+00:00Z
June 28, 2007
Outline
• Overview 2-micron solid state lasers• Modeling and population inversion
measurement• Side pump oscillator• One Joule 2-µm Laser• Conclusion
June 28, 2007
Solid State 2-micron Lasers
– Tm Lasers (pump diodes 780-805nm)• YAG, YLF, YAlO3, YVO4
– Ho:Tm Lasers (pump diodes 780-805nm)• LuLF, YLF, GdLF, YAG, YVO4
– Tm pumped Ho lasers (pump diodes 780nm)• Tm solid state laser pumped Ho Laser• Tm fiber laser pumped Ho Laser
– Ho Lasers (pump diodes 1900nm)• YAG
– Tm Fiber Lasers
June 28, 2007
Energy transfers between HoEnergy transfers between Ho3+3+ and Tmand Tm3+ 3+ ions ions and Pumpand Pump--probe experimentprobe experiment
0
5
10
153F23F3
3H4
3H5
3H6
3F4
Tm3+
Ener
gy(1
03 cm-1)
SQSQ
5I 8
Ho3+
5I 7
5I 6
probe
pump
5S 2
Pump at 792nm ( 3H6 → 3H4 transition)
Energy transfers :- Self-quenching (PSQ)
two Tm3+ ions in the 3F4 manifold
- (3F4 ⇒ 5I7 ) energy transfer (P(Tm → Ho) )
- (5I7 ⇒ 3F4 ) energy transfer (P(Ho → Tm) )
- Ho , Tm upconversion (PUC )
Probe at 543nm (5I8 → 5S2 transition)Probe the 5I8 ground-state depletion
5I 4
5I 5
Laser
June 28, 2007
Evolution of the probe beam transmission and the corresponding population of the Ho 5I7 manifold
-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.60.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
Rela
tive
popu
latio
n of
Ho
5 I 7 man
ifold
Time (ms)
Probe beam transmission
0.0
0.1
0.2
0.3
0.4
0.5
Tran
smiss
ion
of th
e pr
obe
beam
(%)
Ho 5I7 relative population
Pump pulse
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.40.0
0.1
0.2
0.3
0.4
0.5
Output pulse
Rela
tive
popu
latio
n of
Ho
5 I 7 leve
l
Time (ms)
Normal Mode Without lasing
Pump pulse
Ho 5I7 population at lasing and without lasing condition
Probe beam transmission and the population of the Ho 5I7 manifold
June 28, 2007
Oscillator features
• Injection seeded• Cavity length >2m Ring• Output coupler Reflectivity ~70%• Diode pump lasers: 36 bars 100W/bar
conductive cooled • crystal doped material length 21mm• undoped LuLF length 15 mm• Laser crystal cooling : H2O• Tube size: 6mm OD 5mm ID AR
coated for 792nm• Laser rod ends wedged 0.5° along c-axis
AR coated for 2.053µm
June 28, 2007
Laser Oscillator Ring Cavity
O.C.
Flat HR (PZT)
Curved HR
Q-Switch
Curved HR
Injection seeding
Laser Head
Scope
Elec. Servo
June 28, 2007
Cavity Mode Simulation (Ring Cavity with two curved high reflectors)
M1 M2 M3 M4M4
X-axis
Y-axis Laser head Q-switch
June 28, 2007
Laser Output Energy
2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4
40
60
80
100
120
140
160
Sing
le Q
-Sw
itch
Puls
e En
ergy
(mJ)
Diode Pump Energy (J)
% (70% output coupler 8oC rod temperature) % (66% output coupler 8oC rod temperature)
2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2
25
50
75
100
125
150
Sing
le Q
-Sw
itch
Puls
e En
ergy
(mJ)
Diode Pump Energy (J)
70% output coupler 6oC rod temperature 70% output coupler 8oC rod temperature 70% output coupler 12oC rod temperature
June 28, 2007
Laser beam profile
0 20 40 60 80 1000.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6M2x: 1.142M2y: 1.060wx: 0.685wy: 0.655Dx: 2.511Dy: 2.400
Beam
Dia
met
er (m
m)
Distance from lens (cm)2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6
100
150
200
250
300
350
400
450
500
550
Q s
witc
hing
pul
se le
ngth
(nS)
Pump pulse energy of diode (J)
Pulse width
June 28, 2007
Seeding verification
2.4MHz
June 28, 2007
MOPA Experimental Diagram
O.C.Curved HR
PZT controlled Flat HR Flat HR
Q-Switch
Diode-pumped LuLiF4
Diode-pmped LuLiF4 Amp1
Diode-pmped LuLiF4 Amp2
Curved HR
Curved HR
Energy Meter
λ/2 Wave plate
λ/2 Wave plate
HR Prism
HR Prism
45° HR
45° HR
45° HR
45° HR
CWSeederLaser
FaradayIsolator
PZT Controller
June 28, 2007
Amplifier features
• Pump energy 7.2Joules12x6 bar arrays with 100w/bar• Diode laser conductive cooled ‘A’Pkg• Laser crystal Ho:Tm:LuLF 0.5% Ho 6%Tm• Doped Crystal length 41mm• Ends diffusion bonded 15 mm undoped LuLF crystals• Laser crystal cooling H2O • Flow tube size 7mm OD 6mm ID AR coated• Rod ends AR coated for 2.053µm flat• Path configuration double pass
June 28, 2007
Absorbed pump power distribution
4.0 mm Diameter Enclosure:
50.8 Absorbed Watts or 70.6%
3.5 mm Diameter Enclosure:
44.5 Absorbed Watts or 61.8%
3.0 mm Diameter Enclosure:
35.1 Absorbed Watts or 48.8%
2.5 mm Diameter Enclosure:
28.6 Absorbed Watts or 39.7%
2.0 mm Diameter Enclosure:
20.7 Absorbed Watts or 28.8%
5.0 mm Diameter Enclosure:
66.0 Absorbed Watts or 91.7%
4.5 mm Diameter Enclosure:
59.2 Absorbed Watts or 82.2%
June 28, 2007
Single and Double Pass Amplification
4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.01.0
1.5
2.0
2.5
3.0
3.5
4.0
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Out
put/I
nput
Pump pulse energy of diode (J)
Double-pass amplificationSingle-pass amplification
The probe pulse: 180nS, 133mJ Rod length: 4.25cmRod temperature: 8oCDiode temperature:15oC
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.00.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
Pul
se e
nerg
y (J
)
Position in the laser crystal (cm)
Single pass amplificationFirst pass amplificationSecond pass amplification
Probe energy (133 mJ)
June 28, 2007
Amplifier Performances
0.1
0.2
0.3
0.4
0.5
0.6
6 7 8 9 10 11 12
Am
plifi
er O
ne O
utpu
t Ene
rgy
(J)
Pump Energy (J)
Probe 150 mJ
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
8 10 12 14 16 18 20Sy
stem
Out
put E
nerg
y (J
)
System Pump Energy (J)
Probe 511 mJ
June 28, 2007
Objective
• Develop a technology that enables the production of a high-energy and a high- efficiency 2 mm LIDAR transmitter capable of measuring global wind from various platforms.
• Enhance the understanding atmospheric phenomena and improve weather prediction accuracy.
• Reduce risks associated with Doppler Lidar transmitter.
• Identify lifetime sensitive components and initiate early testing.
June 28, 2007
Compact Laser Design Goal
• Pulse energy: >250mJ• Repetition rate: 10Hz• Wavelength: 2.053 µm• Laser material: LuLF 0.5% Ho, 6%Tm• Pulse length: > 100ns• Line width: < 2.5 MHz• Heterodyne frequency offset: 105 MHz• Beam quality: <1.3 diffraction limit• Beam size: 6 mm at the amplifier
output
June 28, 2007
Environment Requirements
• Platform: ground-based (Airborne qualify-able)
• Operational Temperature 0°C -30°C• Operating Altitude Range Sea level to 30,000 ft• Vibration 2.0 g-rms• Coolant Temperature 5 °C and 15 °C • Coolant Flow
– Laser rod .5 GPM– Diode Laser 2 GPM– Bench 2 GPM
• Coolant Pressure 50 psi at 6 GPM
June 28, 2007
Mechanical Design Guidelines
• Laser enclosure compact, sealed, and dry air purged
• Optical benchpopulated on both sidestemperature controlled
• Optical mountshardened- space laser inherited Optical height 1 inch
June 28, 2007
Enclosure & Optical Bench
11.5”
6.5”
June 28, 2007
Optical Layout Side 1
26.5”
11.5
June 28, 2007
Optical Layout Side 2
June 28, 2007
3m Long Ring Resonator Design
• The rod is placed between two curved mirrors.
• Angles between the folding mirrors minimized.
• In the final configuration a 4m radius of curvature mirror is selected.
0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
0 500 1000 1500 2000 2500 3000
TEMoo Mode size for various curved mirrors
3m ROC4m ROC5m ROC3.5m ROC
mod
e ra
dius
(mm
)
distance from Output mirror (mm)
QS
ROD
June 28, 2007
10Hz Oscillator Performance
June 28, 2007
Seeding Verification
Seeded pulse has no mode-beating Unseeded pulse
June 28, 2007
Oscillator Line Width
2.4MHz
June 28, 2007
Amplifier Architecture Considerations
Osc.2
Osc.3
Option 3 selected - Minimum loss, No optical damage, and Optical distortion corrected
Osc.
Mirror at rod end
1
Half waveplate
FaradayIsolator
Half waveplate Amplifier
June 28, 2007
Amplifier rod size selection
907045Probe E (mJ)
2151901701581191084mm rod E. (mJ)
1801721341368296895mm rod E. (mJ)
432432432Probe dia. (mm)
Single pass gain for 4mm rod ~ 2.3 4mm rod with a 3mm probe performs better.
• 4 and 5 mm diameter rods were compared• Probe energy and size were varied
June 28, 2007
4.0 mm Diameter Laser Rod Absorption
4.0 mm Diameter Enclosure:
63.1 Absorbed Watts or 87.6%
3.5 mm Diameter Enclosure:
53.7 Absorbed Watts or 74.6%
3.0 mm Diameter Enclosure:
44.3 Absorbed Watts or 61.5%
2.5 mm Diameter Enclosure:
35.3 Absorbed Watts or 49.0%
2.0 mm Diameter Enclosure:
25.7 Absorbed Watts or 35.7%
June 28, 2007
Amplifier Thermal Lensing
• Amplifier thermal lensing is -1.1m in the x-axis and -1.8m in y-axis.
• To reduce this effect the c-axis of the amplifier rod is oriented orthogonal to the oscillator rod.
• Once the thermal lensing was measured, the parameter is used in an optical model and a cylindrical correction lens was chosen and implemented that circularized the beam.
June 28, 2007
Double pass amplifier performance
50
100
150
200
250
300
60 70 80 90 100 110 120 130
10Hz Amplifier Double-pass Performance
out
put(m
J)
current(A)
probe=95 mJ
Rod temperature=8°C
50
100
150
200
250
300
350
60 70 80 90 100 110 120 130
Double pass amplifier performance
double pass output @5°C
out
put (
mJ)
current(A)
probe=101mJ
Amplifier gain: double pass ~3
June 28, 2007
Conclusion
• A diode-laser-side-pumped 2 µm Ho:Tm:LuLF laser oscillator and two amplifiers (MOPA) have been developed
Master OscillatorMaster Oscillator MOPAMOPAOutput energy 142 mJ (SP) 1.2 J(SP)Optical efficiency 4.3 % 6.5 %