Review of Tm and Ho Materials;

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Presented at the Laser Physics Workshop - Trondheim, Norway (June 30 - July 4, 2008)

Publication Reference: B.M. Walsh, “A Review of Tm and Ho Materials; Spectroscopy and Lasers,” Laser Physics, 19, 855-866 (2009).

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Review of Tm and Ho Materials;

  1. 1. Review of Tm and Ho Materials; Spectroscopy and Lasers Brian M. Walsh Norman P. Barnes NASA Langley Research Center Hampton, VA 23681 USA Laser Physics Workshop - Trondheim, Norway (June 30 - July 4, 2008) National Aeronautics and Laser Physics Workshop Space Administration Trondheim, Norway (June/July 2008)
  2. 2. Prelude “Lanthanum has only one oxidation state, the +3 state. With few exceptions, this tells the whole boring story about the other 14 lanthanides.” G.C. Pimentel & R.D. Sprately, quot;Understanding Chemistryquot;, Holden-Day, 1971, p. 862 So much for ‘Understanding Chemistry’… Let’s do some physics! National Aeronautics and Laser Physics Workshop Space Administration Trondheim, Norway (June/July 2008)
  3. 3. NASA - Laser Material Research Activity Input Results Quantum X-ray data and Energy levels, transition Mechanics refractive index probabilities, ET parameters Materials meeting requirements Small spectroscopic Cross sections, lifetimes, Spectroscopy Samples - inexpensive energy levels, ET parameters Best Materials Only Laser quality samples Laser demonstration, Laser research (rods, discs, fibers modeling National Aeronautics and Laser Physics Workshop Space Administration Trondheim, Norway (June/July 2008)
  4. 4. Remote Sensing Applications 4X DIAL: CO2 Backscatter Lidar: Aerosols/Clouds 2 Micrometer laser Coherent Winds: Lower Troposphere & clouds 3X Noncoherent Winds: Mid/Upper Atmosphere 1 Micrometer 2X Altimetry: laser Surface Mapping Oceanography 2X OPO DIAL: Ozone Backscatter Lidar: Aerosols/Clouds National Aeronautics and Laser Physics Workshop Space Administration Trondheim, Norway (June/July 2008)
  5. 5. Quasi-4-Level Lasers It looks like a three level laser, but behaves more nearly like a 4-level laser! E3 E4 relaxation relaxation E2 E3 3-level example: Cr:Al2O3 - Ruby 2E → 4A (0.69 µm) 2 pump laser pump laser 4-level example: Nd:Y3Al5O12 - YAG 3/2 → I9/2 (1.064 µm) 4F 4 E2 relaxation E1 E1 Quasi-4-level Examples: (a) Three level laser (b) Four level laser g0 = ! e $quot; Nu # ( quot; # 1) C A Ns & % ' (small signal gain) Nd: 4I3/2 → 4I9/2 (~ 0.94 µm) Yb: 2F5/2 → 2F7/2 (~ 1.0 µm) fl γ = 2 for true 3-level-laser ! = 1+ Er: 4I13/2 → 4I15/2 (~ 1.5 µm) fu γ = 1 for true 4-level-laser Tm: 3F4 → 3H6 (~1.9 µm) Criteria: γ < 1.5; Laser is quasi-4-level Ho: 5I7 → 5I8 (~ 2.0 µm) γ >1.5; Laser is quasi-3-level National Aeronautics and Laser Physics Workshop Space Administration Trondheim, Norway (June/July 2008)
  6. 6. Dipole-dipole Energy transfer Dexter averages over dipole orientation, integrates over distances PSA = CDA/R6 Real situation: orientation and distance set by crystal lattice z N.P. Barnes, et al., IEEE JQE, 32, 92 (1996) z ra y R rs y x x rs • ra - 3 (ra• R )( rs• R )/ R2 National Aeronautics and Laser Physics Workshop Space Administration Trondheim, Norway (June/July 2008)
  7. 7. Energy Transfer: Tm-Tm, Ho-Ho Tm-Tm Energy transfer Ho-Ho Energy transfer B.M. Walsh, N.P. Barnes, et al., N.P. Barnes, B.M. Walsh, et al., J. Non-Cryst. Sol., 352, 5344 (2006) J. Opt. Soc. Am. B, 20, 1212 (2003) National Aeronautics and Laser Physics Workshop Space Administration Trondheim, Norway (June/July 2008)
  8. 8. Energy Transfer: Tm-Ho 16000 3F 5F 3 5 3F 14000 2 5I 4 3H 4 4 12000 5I 5 5 P 41 P 22 !4 !5 Energy (cm-1 ) 10000 P 27 P 51 3H 5I 6 3 5 6 8000 P 38 P 61 !3 P 38 P 61 !6 6000 2 3F 4 5I 7 7 4000 P 28 P 71 P 41 P 22 P 27 P 51 !2 P 28 P 71 !7 2000 1 3H 5I 8 0 6 8 Tm3+ Ho3+ Tm-Ho Energy transfer B.M. Walsh, N.P. Barnes, et al., J. Appl Phys., 95, 3255 (2004) National Aeronautics and Laser Physics Workshop Space Administration Trondheim, Norway (June/July 2008)
  9. 9. Decay of Tm 3F4 and Ho 5I7 Excitation of Tm 3F4 manifold Short times: energy transfer Long times: thermalization 1.0 1.0 Ho:YAG decay Tm:YAG decay 0.8 0.8 Normalized intensity Normalized intensity 0.6 0.6 0.4 0.4 0.2 Ho:YAG decay 0.2 Tm:YAG decay 0.0 0.0 0.0 0.5 1.0 1.5 2.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 Time (ms) Time (ms) National Aeronautics and Laser Physics Workshop Space Administration Trondheim, Norway (June/July 2008)
  10. 10. Forward and Backward transfer P28/P71 = [Z7T Z1T/Z2T Z8T] exp[(E2ZL - E7ZL)/kT] E2 E7 E7ZL E2ZL P28 P71 P28 P71 E1 E8 Ho Tm National Aeronautics and Laser Physics Workshop Space Administration Trondheim, Norway (June/July 2008)
  11. 11. Laser Modeling • Useful tool - Predicting and diagnosing laser performance - Understanding the physics • Rate equation approach - Coupled set of complex equations - Laser simulation on the computer • Many parameters needed - Laser parameters - Spectroscopic parameters - Quantum Mechanical Model • Modeling of pulsed Tm:Ho lasers - Agrees reasonably well with experiment National Aeronautics and Laser Physics Workshop Space Administration Trondheim, Norway (June/July 2008)
  12. 12. Rate Equation Approach N g + N2 = N t (See O. Svelto, “Principles of Lasers”) dN 2 N = Wp N g ! BqN 2 ! 2 dt quot; N3 fast decay dq q = Va BqN 2 ! N2 dt quot;c Nt = total density of laser atoms (1/cm3) pump laser Ni = population density of states (1/cm3) τ = spontaneous lifetime of level 2 (s) N1 τc = lifetime of photons in the resonator (s) Va = laser-active volume (cm3) fast decay Ng Wp = pump rate from g to 3 (1/s) B = Stimulated emission coefficient (1/s) q = number of photons in cavity (no units) National Aeronautics and Laser Physics Workshop Space Administration Trondheim, Norway (June/July 2008)
  13. 13. Coupled Rate Eqns. - Tm:Ho Model dn1 n ( = !R p #1 ! exp(!quot; a !n1 ) % + 2 + 41 n 4 + n 2 n 8 p 28 ! n 7 n1p 71 ! n 4 n1p 41 + n 2 p 22 $ & '2 '4 2 dt +n 2 n 7 p 27 ! n 5 n1p 51 ! n 6 n1p 61 + n 3n 8 p 38 dn 2 n ( ( = ! 2 + 32 n 3 + 42 n 4 ! n 2 n 8 p 28 + n 7 n1p 71 + 2n 4 n1p 41 ! 2n 2 p 22 ! n 2 n 7 p 27 + n 5 n1p 51 dt '2 '3 '4 2 dn 3 n 3 ( 43 =! + n + n 6 n1p 61 ! n 3n 8 p 38 dt '3 '4 4 dn 4 n = R p #1 ! exp(!quot; a !n1 ) % ! 4 ! n 4 n1p 41 + n 2 p 22 $ & '4 2 dt dn 5 n = ! 5 + n 2 n 7 p 27 ! n 5 n1p 51 dt '5 dn 6 n ( = ! 6 + 56 n 5 ! n 6 n1p 61 + n 3n 8 p 38 dt '6 '5 dn 7 n ( ( = ! 7 + 67 n 6 + 57 n 5 + n 2 n 8 p 28 ! n 7 n1p 71 ! n 2 n 7 p 27 + n 5 n1p 51 ! quot; se (f7 n 7 ! f8 n 8 )) dt '7 '6 '5 dn 8 n = ! 7 ! n 2 n 8 p 28 + n 7 n1p 71 + quot; se (f7 n 7 ! f8 n 8 )) dt '7 d) ) n = ! + c ! quot; se (f7 n 7 ! f8 n 8 )) + c ! 7 B dt 'c Lopt Lopt ' 7 National Aeronautics and Laser Physics Workshop Space Administration Trondheim, Norway (June/July 2008)
  14. 14. Spectroscopic Parameters 0.40 1.2 Tm:YLF Ho:YLF level I.R. E (exp.) E (theo.) !E level I.R. E (exp.) E (theo.) !E Tm:LuLF Ho:LuLF (cm-1) (cm-1) (cm-1) (cm-1) (cm-1) (cm-1) 1.00 quot;3,4 0 quot;2 Cross Section (x10-20 cm2) Cross Section (x10-20 cm2) 1 0 0 14 5157.1 5157.5 0.4 0.30 2 quot;2 7.5 6.1 0.4 15 quot;3,4 5161.5 5161.1 0.4 3 quot;2 27.6 26.9 0.7 16 quot;1 5167.0 5167.4 0.4 0.80 4 quot;1 47.2 48.2 1.0 17 quot;2 5168.6 5169.5 0.9 5 quot;1 57.8 55.1 2.7 18 quot;3,4 5190.6 5189.4 0.6 0.20 0.60 quot;3,4 76.2 quot;1 6 77.8 1.6 19 5211.7 5210.1 1.6 7 quot;1 222.0 222.1 0.1 20 quot;3,4 5229.6 5233.4 3.8 8 quot;1 - 279.7 - 21 quot;2 5235.3 5239.1 3.8 0.40 9 quot;3,4 - 284.9 - 22 quot;2 5295.0 5295.2 0.2 0.10 10 quot;2 - 288.9 - 23 quot;3,4 5299.1 5297.3 1.2 0.20 11 quot;1 - 305.1 - 24 quot;1 5301.6 5298.2 2.4 12 quot;3,4 315.0 315.6 0.6 0.0 13 quot;2 332.0 333.7 1.7 0.0 740 750 760 770 780 790 800 810 820 830 840 1850 1900 1950 2000 2050 2100 2150 Wavelength (nm) Wavelength (nm) Pump absorption Laser emission Energy Levels (absorption cross section) (emission cross section) (Thermal population) 1.0 Ho:YLF Ho: 5I7 ! 5I8 decay Ho:YAG 0.80 Normalized Intensity 0.60 0.40 0.20 0.0 0 10 20 30 40 50 60 70 80 Time (ms) Judd-Ofelt Analysis Decay Dynamics (Radiative lifetime, branching ratios) (ET parameters, lifetimes) National Aeronautics and Laser Physics Workshop Space Administration Trondheim, Norway (June/July 2008)
  15. 15. Laser Parameters Laser crystal Pumped volume M1 M2 l Laser mode volume Active volume of the laser 1 L quot; quot; Va = 2 # # # 2 The volume of the laser mode that spatially overlaps E(x, y, z) dxdydz with the pumped volume in the laser medium E0 0 !quot; !quot; 1 c The cavity photon lifetime that accounts for the removal of = ln(R m R L ) ! c 2L opt photons due to mirror losses and internal losses. National Aeronautics and Laser Physics Workshop Space Administration Trondheim, Norway (June/July 2008)
  16. 16. Tm:Ho:YLF/LuLF Modeling 1.0 0.8 LuLF experiment LuLF model YLF experiment 0.7 YLF model 0.8 0.6 Laser energy (J) Laser energy (J) 0.5 0.6 0.4 0.4 0.3 0.2 0.2 0.1 0.0 0.0 2.5 3.5 4.5 5.5 6.5 7.5 2.5 3.5 4.5 5.5 6.5 7.5 Pump energy (J) Pump energy (J) Diode laser side-pumped experiment vs. model Parameter YLF experiment LuLF experiment % difference YLF model LuLF model % difference Threshold 3.22 J 2.74 J 14.9% 4.00 J 3.46 J 13.5 % Slope efficiency 0.2003 0.2216 9.6% 0.2002 0.2168 7.6% Walsh, Barnes, Petros, Yu, Singh, J. Appl. Phys. 95, 3255 (2004) National Aeronautics and Laser Physics Workshop Space Administration Trondheim, Norway (June/July 2008)
  17. 17. Recent Developments: Tm-pump Ho • Laser physics predicts high efficiency - No Tm:Ho up-conversion or energy sharing - Ho:Ho up-conversion minimal • Diode pumped Tm:YLF/Tm:fiber & direct diode pump - Overlaps with Ho:YAG/LuAG absorption • Ho:YAG and Ho:LuAG - Ho:YAG has higher absorption - Ho:LuAG has lower thermal population • Low quantum defect - implies low heat deposition - minimal thermal focusing National Aeronautics and Laser Physics Workshop Space Administration Trondheim, Norway (June/July 2008)
  18. 18. Tm-YLF Pump Ho:YAG Scheme Pump lines Tm:YLF pumped Ho:YAG laser Laser lines Output mirror 0.5m RC Diode Laser pumped Tm:YLF laser Diode Laser Dichroic HR@1.9µm Output Ho:YAG HR Tm:YLF RG-1000 Lens HT@0.79µm mirror laser rod 2.1µm disc filter f=100mm Lens f=125mm Aperture Dichroic HR@2.1µm HT@1.9µm HR@1.9µm 0.5m RC National Aeronautics and Laser Physics Workshop Space Administration Trondheim, Norway (June/July 2008)
  19. 19. Tm-YLF Pump Ho:YAG (Pulsed) 0.50 0.50 0.40 0.40 Slope efficiency Slope efficiency 0.30 0.30 0.20 0.20 0.10 0.10 0.0 0.0 0 4 8 12 16 20 24 28 32 36 0.00 0.05 0.10 0.15 0.20 0.25 0.30 Ho rod length (mm) -ln (R m) 0.50 5.0 Slope efficiency = 41% 0.40 4.0 Threshold = 3.28 mJ Ho laser energy (mJ) Slope efficiency 0.30 3.0 0.20 2.0 0.10 1.0 0.0 0.0 1.905 1.906 1.907 1.908 1.909 1.910 1.911 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 Pump wavelength (µm) Tm pump energy (mJ) National Aeronautics and Laser Physics Workshop Space Administration Trondheim, Norway (June/July 2008)
  20. 20. Tm-fiber Pump Ho:YAG Scheme 4 0.9 0.8 0.7 3 0.6 0.5 2 0.4 0.3 6.02 m 1 0.2 2.76 m 0.1 Grating 0.0 0 1.8 1.9 2.0 2.1 Wavelength in micrometers 600 g/mm grating Dichroic Tm:glass Laser diode !/2 Laser HR diode Ho:YAG National Aeronautics and Laser Physics Workshop Space Administration Trondheim, Norway (June/July 2008)
  21. 21. Tm-fiber Pump Ho:YAG (cw) Ho:YAG, 0.010 Ho, 8.0 mm 0.8 0.5 0.7 Ho:YAG (!s = 0.37, E th = 1.45 W) 0.6 0.4 0.5 0.3 0.4 0.3 0.2 0.2 0.1 0.1 0.0 0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Pump power in W Pump power in W Absorption in Ho:YAG Ho:YAG Laser Performance (absorption efficiency ≈ 0.35) National Aeronautics and Laser Physics Workshop Space Administration Trondheim, Norway (June/July 2008)
  22. 22. Summary • Quasi-4-level lasers - Look like 3-level, behave more like 4-level. - Based on physics • Energy transfer - Prolific in Tm and Ho materials - Distinction: classical vs. crystal • Modeling - Based on rate equations - Agrees reasonably well with experiment • Laser schemes - Tm:YLF pump Ho:YAG - Tm:fiber pump Ho:YAG National Aeronautics and Laser Physics Workshop Space Administration Trondheim, Norway (June/July 2008)
  23. 23. 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 Trondheim, Norway (June/July 2008) Phone: 757 864-7112

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