Presented at the Laser Physics Workshop - Barcelona, Spain (July 13 - 17, 2009) Publication Reference: B.M. Walsh, “Dual Walelength Lasers”, Laser Physics, 20, 622-634 (2010).

1. Dual Wavelength Lasers
Brian M. Walsh
Norman P. Barnes
NASA Langley Research Center
Hampton, VA 23681 USA
Laser Physics Workshop - Barcelona, Spain (July 13 - 17, 2009)
National Aeronautics and Laser Physics Workshop
Space Administration Barcelona, Spain (July 13-17, 2009)

2. Outline
• Dual wavelength concept
• I. Two Wavelength Oscillation (TWO)
- Er:Tm:Ho:YAG (2.0 and 2.9 µm)
• II. Synchronous Tunable Optical Pulses (STOP)
- Nd:YAG (1.0xx and 1.3xx µm)
• IIa. Non-linear optics
- SHG, sum frequency techniques
• III. Other dual-λ lasers
- Er:Nd:YAG (2.9 µm and 1 µm)
- Ho:Nd:YAG (3 µm and 1 µm)
• Summary
National Aeronautics and Laser Physics Workshop
Space Administration Barcelona, Spain (July 13-17, 2009)

3. Dual Wavelength Concept
• Dual wavelength lasing on separate dopant ions:
- Energy transfer dynamics between the ions
- Lifetimes of the upper laser manifolds
- Duration of the pump pulse
• Dual wavelength lasing on same dopant ion:
- System design (e.g., prisms, mirrors, resonator design)
- Laser transition cross section
• Advantages
- Can produce widely or closely separated wavelengths
- Sum frequency, difference frequency readily implemented
- One laser serves dual purpose (efficient & cost effective)
- Medicine, remote sensing, surveillance, machining
National Aeronautics and Laser Physics Workshop
Space Administration Barcelona, Spain (July 13-17, 2009)

4. I. Er:Tm:Ho dual-λ laser
National Aeronautics and Laser Physics Workshop
Space Administration Barcelona, Spain (July 13-17, 2009)

5. TWO Laser schematic
Laser
National Aeronautics and Laser Physics Workshop
Space Administration Barcelona, Spain (July 13-17, 2009)

6. Er:Tm Energy Transfer
1.)
2.)
3.)
4.)
5.)
R. Balda, et. al., Optics Express, 17, 8788 (2009)
National Aeronautics and Laser Physics Workshop
Space Administration Barcelona, Spain (July 13-17, 2009)

7. Er:Tm:Ho Energy Transfer
15000
Short pump pulse - 2.9 µm Er lasing
4I
Long pump pulse - 2.1 µm Ho lasing
9/2
Intermediate pump pulse - Er and Ho
1
4I
11/2
10000
(! = 100 µs)
2.9 µm
Energy (cm -1)
3H 5I
5 6
4I
13/2
(! = 9 ms) 3F
4 5I
5000 (! = 14 ms) 7
(! = 8 ms)
2 2
3 3 2.1 µm
4 4
4I 3H 5I
15/2
0 6 8
Er3 + YAG Tm3 + YAG Ho3 + YAG
National Aeronautics and Laser Physics Workshop
Space Administration Barcelona, Spain (July 13-17, 2009)

8. Pump Pulse Wavelength Tuning
Short, high intensity Long, low intensity
2.9 µm 2.1 µm
Time Time
Moderate length, mid-intensity
2.9 µm 2.1 µm
Time
National Aeronautics and Laser Physics Workshop
Space Administration Barcelona, Spain (July 13-17, 2009)

9. Er Lifetime Quenching
1.0
Er 4!11/2 Manifold Lifetime
"2.9 µm upper laser level"
0.8 4I11/2
Normalized Intensity
Sample Lifetime
0.6
30%, 50%,60% Er YAG 90 µsec
10% Er 1% Ho 80 µsec
0.4 10% Er 4% Tm 50 µsec
10% Er 4% Tm 0.5% Ho 40 µsec
0.2 10% Er 5% Tm 1.0% Ho 35 µsec
0.0
0 50 100 150 200 250 300
Time (µs)
National Aeronautics and Laser Physics Workshop
Space Administration Barcelona, Spain (July 13-17, 2009)

10. Er:Tm:Ho pulse switched lasing
1.2
Er 2.9 µm, 100 µs pump pulse, 0.90R OC
Ho 2.1 µm, 1 ms pump pulse, 0.95R OC
1.0
Cr(1)Er(35)Tm(0.7)Ho(0.35) YAG
6x122 mm laser rod
0.80
Laser Energy (J)
0.60
0.40
0.20
0.0
0 50 100 150 200
Electrical energy (J)
National Aeronautics and Laser Physics Workshop
Space Administration Barcelona, Spain (July 13-17, 2009)

11. Er:Tm:Ho Simultaneous lasing
1 ms 100 µs
350 350
2.1 micron (0.95R) 2.1 micron (0.95R)
2.9 micron (0.85R) 2.9 micron (0.85R)
300 300
250 250
Laser Energy (mJ)
Laser Energy (mJ)
200 200
150 150
100 100
50 50
0 0
50 100 150 200 10 20 30 40 50 60 70 80 90
Electrical energy (J) Electrical energy (J)
National Aeronautics and Laser Physics Workshop
Space Administration Barcelona, Spain (July 13-17, 2009)

12. II. Nd:YAG dual-λ laser
National Aeronautics and Laser Physics Workshop
Space Administration Barcelona, Spain (July 13-17, 2009)

13. STOP laser schematic
Output Nd:YAG diode Q-Switch
Synchronous Mirror Pumped Head
laser pulses
Quartz
Prisms
1.0xx µm
HR mirror
1.3xx µm
HR mirror
National Aeronautics and Laser Physics Workshop
Space Administration Barcelona, Spain (July 13-17, 2009)

14. Dispersive Tuning in Nd:YAG
-20
L( m) e(10 cm2) (cm-1) EETH(J) s
1.0520 9.62 5.7 4.93 0.0123
1.0614 20.62 4.8 2.60 0.0184
4F → 4I11/2
3/2
1.0641 27.74 6.0 1.99 0.0193
Parameters 1.0737 15.15 5.2 3.62 0.0139
1.0779 6.26 9.9 7.63 0.0095
1.1120 3.97 12.1 10.28 0.0113
1.1160 3.95 14.4 11.48 0.0104
1.1225 3.97 11.4 11.26 0.0112
-20
L( m) e(10 cm2) (cm-1) EETH(J) s
1.3187 8.92 4.5 6.64 0.0127
4F →
3/2
4I
13/2 1.3336 4.03 3.7 11.82 0.0104
Parameters 1.3381 9.57 5.0 6.53 0.0131
1.3564 7.35 6.6 8.42 0.0107
National Aeronautics and Laser Physics Workshop
Space Administration Barcelona, Spain (July 13-17, 2009)

15. Synchronous Pulses
12000
4F R2 11506
3/2 R1 11421
• Synchronous pulses require equal
11000
pulse evolution time intervals
- Different emission cross sections
5000
X7 4494
- Resonator lengths adjustable
X6 4432
5X ?
4I
13/2 X4
X3
4050
4035
- Output losses adjustable (output coupling)
4000 X2 3932
X1 3925
1 , c % c ( /
" . ln ( R M R L ) + 2# el$ ' * ( E EP + E LTH ) 1
! c - 2lc & 2lc )
3000
Y6
Y5
2515
0
2462
4I
11/2 Y4 2146
Y3 2111
Y2
2000 Y1
2029
2003
1000
Z5 852
4I
9/2
Z4 312
Z3 199
Z2 133
0 Z1 0
-1 0 1 2 3 4
Nd3+:YAG
Time (µs)
National Aeronautics and Laser Physics Workshop
Space Administration Barcelona, Spain (July 13-17, 2009)

16. STOP light laser performance
0.60 35
1.052 QS
Inverse of pulse evolution interval (µs-1)
1.052
1.319 30 1.319 QS
0.50 Both QS
25
0.40
Laser Energy (mJ)
20
0.30
15
0.20
10
0.10
5
0.0 0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 0.6 0.8 1.0 1.2 1.4 1.6
Electrical energy (J) Electrical Energy (J)
National Aeronautics and Laser Physics Workshop
Space Administration Barcelona, Spain (July 13-17, 2009)

17. IIa. Non-linear optics
National Aeronautics and Laser Physics Workshop
Space Administration Barcelona, Spain (July 13-17, 2009)

18. Non-linear Conversion
VIS UV Synchronous
Synchronous Tunable
laser pulses
BBO waveplate BBO Optical
Crystal 1/2 wave Crystal
at 0.59 µm Pulses
SHG sum frequency SHG
~ 0.660 mm ~ 0.585 mm ~ 0.526 mm
Red Orange Green
National Aeronautics and Laser Physics Workshop
Space Administration Barcelona, Spain (July 13-17, 2009)

19. One dual laser - 172 wavelengths
A
3F
3/2 → 4I13/2
3F
3/2 → 4I11/2 B
1.00 1.05 1.10 1.15 1.20 1.25 1.30 1.35 1.40
Wavelength ( µm)
4A 2(A+B) 3A A+2B 2A A+B
4B B+2A 3B 2B
0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70
Wavelength ( µm)
National Aeronautics and Laser Physics Workshop
Space Administration Barcelona, Spain (July 13-17, 2009)

20. III. Other dual-λ lasers
National Aeronautics and Laser Physics Workshop
Space Administration Barcelona, Spain (July 13-17, 2009)

21. Nd:Er:YAG
4F 4I
3/2 9/2
12000 (! = 240 µs)
3
4I
11/2
10000 (! = 100 µs)
1 1.06 µm
2 2.9 µm
8000
Energy (cm -1)
4I
4I 13/2
15/2
(! = 9 ms)
6000
4I
13/2
4000
1 2
4I
11/2
2000
4I 4I
9/2 15/2
0
Nd:YAG Er:YAG
National Aeronautics and Laser Physics Workshop
Space Administration Barcelona, Spain (July 13-17, 2009)

22. Nd:Ho:YAG
12000
4F 5I
3/2 5
(! = 240 µs) (! = 1 µs)
10000 1 2
5I
1 6
1.06 µm (! = 50 µs)
8000
3.0 µm
Energy (cm -1)
4I
6000 15/2
5I
7
(! = 8 ms)
4I
4000 13/2
4I
2000 11/2
4I 5I
9/2 8
0
Nd:YAG Ho:YAG
National Aeronautics and Laser Physics Workshop
Space Administration Barcelona, Spain (July 13-17, 2009)

23. Summary
• Dual-λ lasers discussed and demonstrated
- Er:Tm:Ho:YAG (TWO laser)
- Nd:YAG (STOP laser)
• Physics & engineering criteria
- energy transfer, lifetime, transition cross section
- Optics, resonator design, pumping schemes
• Non-linear techniques
- SHG and sum frequency techniques
- Multitude of harmonic wavelengths realized
• Future work
- What new potential dual- λ lasers exist?
- Driven by application needs, multiple solutions
National Aeronautics and Laser Physics Workshop
Space Administration Barcelona, Spain (July 13-17, 2009)

24. NASA Langley Brian M. Walsh
Research Center Laser Remote Sensing Branch
National Aeronautics and Laser Physics Workshop
Email: brian.m.walsh@nasa.gov
Space Administration Barcelona, Spain (July 13-17, 2009)
Phone: 757 864-7112