Presented at the International Conference on Luminescence - Wroclaw, Poland (July 13 - 18, 2014) Publication Reference: Brian M. Walsh, Hyung R. Lee, Norman P. Barnes, "Mid Infrared lasers for remote sensing applications," J. Lumin., 169, 400-405 (2016).

1. National Aeronautics and
Space Administration
ICL 2014 – Wroclaw, Poland
Brian M. Walsh
Devin Pugh-Thomas
Hyung Lee
Norman P. Barnes (SSAI)
NASA Langley Research Center
Hampton, VA 23681 USA
Lanthanide-Doped Mid-Infrared Materials
Spectroscopy and Laser Prospects
International Conference on Luminescence
Wroclaw, Poland, July 13 – 18, 2014

2. National Aeronautics and
Space Administration
ICL 2014 – Wroclaw, Poland
Why Study Mid Infrared Ln3+Lasers?
• Innovation - Mid Infrared lasers utilizing Lanthanide
series ions (Ln3+) have not been thoroughly studied.
• Decadal Survey – Mid Infrared lasers needed for DIAL
systems simply are not available at present.
• Enabling – Invent specialized lasers that industry is
unwilling to invest in or universities not likely to pursue.
• Atmosphere – Some constituents in atmospheric chemistry
only available for study at Mid IR wavelengths.

3. National Aeronautics and
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ICL 2014 – Wroclaw, Poland
MIR Molecular Absorption
Wavelength (µm)
Because of the molecular
absorption and the eye
safety requirements, the
optimum spectral range is
in the 2 to 10 µm region.
3 – 5 µm : Atmospheric sensing
7– 10 µm : Defense & Security
NIR MIR NIR MIR
• Lockheed Martin
Space Act Agreement - Interest in
Mid Infrared Lasers for 3 – 5 µm
& 9 – 12 µm applications (??)

4. National Aeronautics and
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ICL 2014 – Wroclaw, Poland
Atmospheric Molecular Absorption
Thermal IR (Mid IR to Far IR) Fingerprint Region

5. National Aeronautics and
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ICL 2014 – Wroclaw, Poland
Trace gasses of interest - GACM
Methane Carbon Monoxide Ozone
Nitrogen Dioxide Sulphur Dioxide Formaldehyde
GACM – Global Atmospheric Composition Mission

6. National Aeronautics and
Space Administration
ICL 2014 – Wroclaw, Poland
Methane Carbon Monoxide Ozone
Nitrogen Dioxide Sulphur Dioxide Formaldehyde
GACM – Global Atmospheric Composition Mission
Mid Infrared Wavelengths - GACM
3.15 – 3.57 µm
7.50 – 8.30 µm
2.31 – 2.41 µm
4.50 – 4.87 µm
4.70 – 4.79 µm
9.37 – 9.90 µm
3.40 – 3.84 µm
4.45 – 4.70 µm
7.50 – 8.10 µm
7.13 – 7.75 µm 3.20 – 3.40 µm

7. National Aeronautics and
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ICL 2014 – Wroclaw, Poland
Options for Mid Infrared Lasers
Mid-Infrared Laser Applications in Spectroscopy
F.K. Tittel, D. Richter, A. Fried, Solid-State Mid-Infrared Laser Sources (Springer-Verlag 2003)
Reference:
① Semiconductor Lasers: Lead-Salt, Quantum Cascade and Antimonide are possibilities, but
require cryogenic cooling and have highly divergent beams.
② Solid State lasers: Cr2+ II-VI lasers are low gain materials, resulting in low power/energy.
③ Parametric frequency conversion such as OPO & DFG suffer from a variety of drawbacks:
phase matching, design complexity, alignment sensitivity, and laser induced damage (LID).
④ Laser pumped Ln3+ lasers:
High power or energy in a narrow
spectral bandwidth or diffraction
limited beam is often a reason to
select them over other technologies.
A wide variety of pulse widths and
pulse repetition frequencies (from
cw to 1GHz) can be achieved.

8. National Aeronautics and
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ICL 2014 – Wroclaw, Poland
Advantages of Ln3+ Solid State Lasers
• All solid state laser-pumped lasers
- Capable of high power or high energy.
- Reliable, low voltage, compact, robust and versatile.
- No phase matching required, pump and laser are temporally separate.
- Probability of laser induced damage can be mitigated
• Tunable options
- 2 to 10 micrometers (many transitions in Ln3+:hosts)
- Can exhibit narrow spectral bandwidth.
- Selection more reliable (only 1 wavelength is resonant).
• Reasonable efficiency
- Ln3+ series ions in low phonon hosts (limit nonradiative processes)
- Can store energy over relatively long time intervals (Q-switching)
- Good laser beam quality even with pump laser quality over 2xDL

9. National Aeronautics and
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Approach
• Quantum Mechanics
- Quantum Mechanics describes the physics of laser materials.
- Computer models predict new materials to meet objectives.
• Spectroscopy of materials
- Validates the physics of potential laser materials.
- Provides parameters for understanding the laser.
• Challenges
- Nonradiative transitions quench luminescence.
- Low phonon materials needed (fluorides, chlorides, bromides).
• Outlook
- Many Transitions possible (Dieke Diagram)
- MIR transitions not well studied (Data is needed)

10. National Aeronautics and
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Materials Modeling
• Cost effective design tool
– Uses Quantum Mechanical model
– Models physics from lattice structure
• Predicts new materials
– Tm:Ho:LuLF, LuAG (Winds, CO2)
– Nd:YGAG, YSAG (Water Vapor)
• Predicts essential parameters
– Energy levels (laser wavelengths)
– Lifetimes (pump storage efficiency)
– Energy transfer rates (laser efficiency)
{Dodecahedral}
(Tetrahedral)[Octahedral]
Oxygen
Rare Earth
Al, Ga, Fe
{A3+}3[B3+]2 (C3+)3O12

11. National Aeronautics and
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Nonradiative Processes (Phonons)
photons phonons
A. Shalav et al, Solar Energy Materials & Solar Cells 91 (2007) 829–842

12. National Aeronautics and
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Energy levels of Ln3+ ions (Dieke)
Doped Oxides for High-Temperature Luminescence and Lifetime Thermometry
M.D. Chambers, D.R. Clarke, Annual Review of Materials Research, Vol. 39: 325-359 (August 2009)
Reference:

13. National Aeronautics and
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ICL 2014 – Wroclaw, Poland
NIR Lanthanide Lasers
0
5000
10000
15000
20000
Nd Ho Er Tm Yb
4I9/2
4I11/2
4I13/2
4I15/2
4F3/2
1.32
1.06
0.94
5I8
5I7
5I6
5I5
5I4
5F5
5F4
5S2
4F5/2
4F7/2
4F9/2
2H11/2
4G5/2
4G7/2
4I15/2
4I13/2
4I11/2
4I9/2
4F9/2
4S3/2
4F7/2
4F5/2
3H6
3F4
3H5
3H4
3F2
3F3
3.0
2.1
1.9
1.47
1.63
2.3
2.94
1.03
1.73
1.23
0.86
Energy(cm-1)
diode laser
pump bands
Rare Earth: Y, Sc, (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu)
Lanthanides

14. National Aeronautics and
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4I9/2
MIR Lanthanide Lasers I
4I11/2
4I13/2
4I15/2
NdPr Sm Eu Dy
3H4
3H5
3H6
6F1/2+3/2+6H15/2
3F3
3F4
6H5/2
5F5/2
6H7/2
6H9/2
6H11/2
6H13/2 7F5
7F3
7F2
7F1
7F0
7F4
6H15/2
6H9/2+6F11/2
6H11/2
6H13/2
4.2 – 6.2
4.4 – 5.9
2.2 – 2.8
2.3 – 2.5
3.7 – 5.6
4.7 – 12.8
2.9 – 4.6
5.9 – 10.6
4.4 – 13.3
3.9 – 5.8
2.8 – 3.6
4.0 – 4.8
3F2
6.3 – 8.5
2.6 – 3.2
3.4 – 6.0

15. National Aeronautics and
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ICL 2014 – Wroclaw, Poland
MIR Lanthanide Lasers II
Tb Ho Er Tm
4I15/2
4I9/2
4I11/2
4I13/2
3H6
5I8
3H4
3H5
3F4
5I4
5I5
5I6
5I7
7F6
7F2
7F3
7F4
7F5
7F0,1
7.4 – 14.9
3.9 – 5.6
2.1 – 2.5
3.6 – 4.2
2.8 – 3.5
4.0 – 5.3
2.6 – 3.0
2.2 – 2.5
3.4 – 4.3

16. National Aeronautics and
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ICL 2014 – Wroclaw, Poland
MIR Laser Systems
Crystal Pump Laser Storage level Upper level Lower level Wavelength (µm) Upper gap (cm-1) Lower gap (cm-1)
Pr:LaF3 Ho:YAG 3H6
3H6
3H5 5.6 - 3.8 1789 1976
Pr:LaF3 Ho:YAG 3H6
3H5
3H4 6.0 - 3.4 1243 1678
Nd:LaF3 Er:YAG 4I15/2
4I15/2
4I13/2 6.2 - 4.2 1608 1695
Nd:LaF3 Cr:ZnSe 4I13/2
4I13/2
4I11/2 5.9 - 4.5 1695 1478
Sm:LaF3 Er:YAG 6H15/2
6H15/2
6H13/2 8.4 - 6.3 1186 1181
Sm:LaF3 Er:YAG 6H15/2
6H15/2
6H11/2 4.0 - 3.3 1186 1047
Sm:LaF3 Ho:YAG 6H11/2
6H11/2
6H9/2 9.6 - 6.3 1186 930
Eu:LaF3 Tm:gls 7F6
7F6
7F2 13.0 - 6.0 750 539
Eu:LaF3 Tm:gls 7F6
7F6
7F4 5.8 - 3.9 750 635
Eu:LaF3 Tm:gls 7F6
7F6
7F3 3.6 - 2.7 750 474
Tb:LaF3 Ho:YAG 7F3
7F3
7F4 13.0 - 6.0 1645 413
Tb:LaF3 Ho:YAG 7F3
7F3
7F4 3.9 - 5.6 1645 413
Dy:LaF3 Er:YLF 6H9/2
4I9/2
7F11/2 4.9 - 4.1 2024 2024
Ho:LaF3 Tm:gls 5I5
4I5
5I6 4.0 - 3.8 2369 3278
Ho:LaF3 Nd:YAG 5I6
5I6
5I7 2.8 - 3.4 3278 2697
Er:LaF3 Cr:alex 4I9/2
4I9/2
4I11/2 4.9 - 4.1 2024 3697
Er:LaF3 Er:YAG 4I9/2
4I9/2
4I13/2 3.0 - 2.6 2024 6230

17. National Aeronautics and
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ICL 2014 – Wroclaw, Poland
Mid-IR Spectroscopy Laboratory
A
B C
D
E
F
G
H
A Laser
B Sample Stage
C Collection Optics
D Spectrometer
E Detector
F Lock-in Amplifier
G Power Supply
H Computer

18. National Aeronautics and
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ICL 2014 – Wroclaw, Poland
Dysprosium:BaY2F8
6H13/2 Lifetimes
Johnson & Guggenheim:
1.3 ms (300K)
7.0 ms (77K)
Christensen & Jenssen:
1.28 ms (300K)
8.0 ms (77K)
This work:
1.38 ms (300K)
35 ms (Judd-Ofelt)

19. National Aeronautics and
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ICL 2014 – Wroclaw, Poland
Holmium:BaY2F8
5I6 Lifetimes
Johnson & Guggenheim:
5.0 ms (77K)
Christensen & Jenssen:
5.4 ms (300K)
This work:
5.78 ms (300K)
4.8 ms (Judd-Ofelt)

20. National Aeronautics and
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ICL 2014 – Wroclaw, Poland
Praseodymium: KPb2Br5 Emission
3H6 Lifetimes
This work:
15 ms (300K)
20 ms (Judd-Ofelt)
3H5 Lifetimes
This work:
37 ms (300K)
40 ms (Judd-Ofelt)

21. National Aeronautics and
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Praseodymium: KPb2Br5 Decay

22. National Aeronautics and
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Pr: LaF3 , KYF4 , BaY2F8 , YLiF4
Phonon Energy:
LaF3 (300 cm-1)
KYF4 (350 cm-1)
BaY2F8 (420 cm-1)
YLiF4 (560 cm-1)

23. E3
E2
E1
pump laser
(a) 3-level
E4
E3
E2
E1
pump laser
(b) 4-level
E4
E3
E2
E1
pump laser
(c) Quasi 4-level
E4
E3
E2
E1
pump
laser
(d) Terminated 4-level
National Aeronautics and
Space Administration
ICL 2014 – Wroclaw, Poland
Types of Solid State Lasers
N1 = N2
Cr:Al2O3
N2 = 0
Nd:YAG
N2 > 0
Ho:YLF
E32 < E21
Dy:YLF

24. National Aeronautics and
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ICL 2014 – Wroclaw, Poland
Optical Schematic for Pr MIR Laser
• Simple configurations
– Diode Pumping (1.9 µm)
– EDFA Pumping (1.55 µm)
– Efficient resonator designs
• Selection of materials
– Fluorides: BaY2F8, LaF3, KYF4
– Chlorides: KPb2Cl5
– Bromides: KPb2Br5
• Laser pump parameters
– Pump power ~ 10 - 30W
– Pulse duration ~ 1 - 5 ms
– Pump wavelengths ~1.5 µm & 1.9 µm
Z-type resonator with diode laser pumping
Q-switch
HR M
Laser Crystal DichroicDichroic
Output M
Ring Resonator for EDFA pumping
1.55 µm
EDFA
Input
Mirror
Output
Mirror
HR Mirror

25. National Aeronautics and
Space Administration
National Aeronautics and
Space Administration
Laser Gain in Pr:LaF3
ICL 2014 – Wroclaw, Poland
• Calculation of gain in Pr:LaF3 based on MIR absorption
– Curve fit absorption coefficient versus wavelength using a series of Lorentzian line shape functions.
– Correlate the measured transmission with the results of the curve fit to identify participating levels.
– Calculate thermal occupation of upper and lower levels for each of the participating levels.
– Calculate energy density needed to achieve optical transparency for each pair of energy levels.
– Calculate gain coefficients for all pairs of levels and select the pair of levels for best performance.
– Use the best pair of energy levels and determine the wavelength and predicted performance.

26. National Aeronautics and
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• MIR applications
- Decadal survey (MIR lasers for DIAL not available)
- GACM (CH4, CO, O3, NO2, SO2, CH2O)
• Challenges
- Nonradiative decay processes influence laser transitions
- Low phonon materials needed (e.g., LaF3, BaY2F8, KPb2Br5)
• Spectroscopy of materials
- Spectroscopic properties of Dy:BaY2F8, Ho:BaY2F8, Pr-doped materials
- Consider pumping lasers that match spectroscopy (1 – 2 µm)
• Laser design
- Method for calculation of laser gain in Pr:LaF3
- Optical schematic of Pr MIR lasers designed
Summary

27. National Aeronautics and
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• Materials for MIR lasers
- Hosts: BaY2F8, KYF4, LaF3, KPb2Br5, KPb2Cl5
- Ions: Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm
- Apply QMM efforts to facilitate development
• Spectroscopic measurements
- Absorption for identification of pump wavelengths
- Emission for identification of laser wavelengths
- Temporal decay for determination of laser dynamics
• Laser engineering
- Consider pump laser sources (Ln3+ SSL, diode)
- Consider optics for laser resonator specific for MIR
- Construct resonator based on design for MIR lasers
Future Directions

28. National Aeronautics and
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Acknowledgements
• Dr. Uwe Hommerich (Hampton University, Hampton, VA)
- Provided Pr:KPb2Br5 sample
- Helpful discussions about low phonon mid infrared materials.
• Dr. Alessandra Toncelli (Universita di Pisa, Pisa, Italy)
- Provided Pr:KYF4 sample
• Dr. Akira Yoshikawa (C & A Corporation, Sendai, Japan)
- Vendor for Pr:LaF3 sample
• Dr. Arlete Cassanho, Dr. Hans Jensen (AC Materials, Tarpon Springs, FL)
- Vendor for Pr:BaY2F8 sample

29. National Aeronautics and
Space Administration
2011 LRSB Peer Review
Brian M. Walsh
Laser Remote Sensing Branch
Email: brian.m.walsh@nasa.gov
Phone: 757 864-7112
NASA Langley
Research Center