Nonlinear Refraction Spectroscopy

Transcription

1 UNIVERSIDADE DE SÃO PAULO Instituto de Física de São Carlos Nonlinear Refraction Spectroscopy of Ion Doped Laser Materials Tomaz Catunda Instituto de Física de São Carlos, Universidade de São Paulo São Carlos, SP Brazil

2 Nonlinear refraction spectroscopy of Solid-State Laser Materials outiline Introduction Time resolved Z-scan technique results for Nd:YAG at 808nm n spectroscopy (Yb3+ glass, Cr 3+ and Nd 3+ doped crystals) Pump-probe n spectroscopy (Nd 3+ and Cr 3+ doped crystals) conclusions

3 Motivation alaser behavior, lens effect, instabilities, optical switching, transverse effects... aphase Conjugation Lasers by wave mixing (transient gratings) in gain media aspectroscopy of laser materials (ESA, energy transfer, polarizabilities ) aslow and fast light propagation Cr 3+ doped crystals (ruby and alexandrite), Er 3+ fibers amplifiers, semiconductors (coherent population oscillations R.W. Boyd group)

4 5d Nd 3+ Δn (α ex α g )N ex = ΔαN ex E~ 50000cm -1 f ~ 10 - (f 5d allowed transition ) main contribution to Δα Free ion f r 5d ~ x10-9 cm λ ex ex Δα ~ 10-5 cm 3 = 0.1A 3 σ g E ~10000cm -1 g f ~ 10-6 (f f ~forbidden transition ) Eichler (67), Riedel and Baldwin (67), Dianov (78), Powell and Payne; Antipov... interferometry, wave mixing, Z-scan, etc.

5 Z-scan Method n = n o + n I Sample Z Aperture Detector I r w ( r) = Io. e w0π ΔZ pv = 1.7 = 1.7 λ z 0 peak ΔT ~ 0. Δφ pv 0 Normalized Trans. valley ΔZ pv ΔT pv Δφ = 0 π ' ni 0 L λ

6 Z-SCAN METHOD OPEN APERTURE Detector T ΔT " niol N ex Δσ z

7 Time resolved Z-scan method peak valley Slow nonlinearity Δn ~ N ex ~N o (1-e -t/t ) t > 100μs t i t f middle Cavalcanti, Catunda and Zilio Jnp J. A.P. (1996)

8 Z-scan Method Time resolved Chopper Lens Sample iris Detector t i t f

9 Time resolved Z-scan method Slow nonlinearity Al O 3 :Cr 3+ τ = 3.8 ms T 1 T E Ar + laser λ = 515nm A Cavalcanti and Zilio A.P.L. (199)

10 Experimental set-up chopper M laser S Pd L Lens f~ 1cm sample aperture S M L D 1 D L signal Reference signal Closed aperture 50% n Open aperture 100% n

11 35000 Nd 3+ -energy level Energy ( cm -1 ) G 7/ + G 9/ nm 1 3 F 3/ I 15/ 808nm 1,06μm I 13/ I 11/ I 9/

12 Normalized Transmittance S 1 = 50% S = 100% Ratio = S 1 /S Theoretical fit (c) (a) (b) Z (mm) Nd:YAG P = 160 mw λ = 808 nm I 9/ F 5/ ; H 9/ L =.1 mm 0.75 at. % Nd 3+ (N = 1.03x10 0 cm -3 )

13 Normalized Transmittance Closed Aperture = 50% Theoretical fit n = 5.6x10-9 cm /W Z (mm) Δα = α ex α g =(6.±0.)x10-6 cm Open aperture = 100% Z (mm) n = -.x10-9 cm /W Theoretical fit Δσ = σ ex σ g = -5.1x10-0 cm σ g ~8x10-0 cm

14 transient response: can clarify the origin of Δn!! 1.0 YAG:Nd YAG:Nd 3+ Normalized signal Closed aperture -> 50% Open aperture -> 100% Exponential fit Time (ms) τ -1 (ms) Closed aperture -> 50% Open aperture -> 100% Linear fit Intensity (KWcm - ) N ex =N o [1- exp(-t/τ)] τ 1 = τ ο 1 (1 + I/I s ) I s = hν/στ I s = 15 KWcm - τ 0 = 30 μs

15 n lineshape in a resonant interaction in ion doped solids? Jamin interferometer anomalous dispersion in Na (vapor) N g N ex λ Korff and Breit Rev. Mod. Phys. (193) Resonant interaction (two-level system) n n A. Siegman book

16 T 1 T resonance in n? BTC Δχ Δα = α ex α g ) T 1 T ~ ns Al O 3 :Cr 3+ (Ruby) BeAl O :Cr 3+ (alexandrite) Energia ( cm E ~ ms 0 A Δν ~ 9 cm -1 FWHM ~ 10 cm -1 E λ ( nm ) λ( nm ) Ruby

17 n spectroscopy in ion doped solids chopper M Tunable laser S L sample aperture S M Pd L L D 1 D L signal Reference signal Closed aperture 50% n Open aperture 100% n

18 Ruby (Al O 3 :Cr 3+ ) Alexandrite (BeAl O :Cr 3+ ) λ ( nm ) λ ( nm ) n ' R 1 R A = 16 A = 0 n R 1m A = 1.9 A = 5 R m n ' n " n " x ν ( cm -1 ) ν (cm -1 ) S. M. Lima et al, Opt. Lett. (00)

19 Yb 3+ doped phosphate glasses Δα= cm 3 F 5/ ν exc ν em F 7/ Yb 3+ Ti:saphire laser QX 6.8wt% Yb 3+ (Kigre ) D.Messias et.al. Opt. Lett 07.

20 n spectroscopy in Nd 3+ :YAG F 3/ (ex) λ ( nm ) nm cm /W n ' I 9/ F 3/ (λ ~ 869nm) I 9/ (g) Δα = 6.0 x10-6 cm 3 n " cm /W ν ( cm -1 )

21 F 3/ (ex) Nd 3+ :YAG 809 nm I 9/ (g) λ ( nm ) A = n n '( δ = 0) "( δ = 0) n (10-9 cm /W) Nd 3+ :YAG T = 300 K A~1 n ' n " ν ( cm -1 )

22 A = n n '( δ = 0) "( δ = 0) Δα σ g temperature linewidth decreases σ g increases resonant effect increases

23 How to improve the discrimination of resonant and nonresonant effects? pump-probe n spectroscopy T 1 T ESA/ESD E E 1 S S chopper L sample Ar+ laser excitation Dye laser probe (tunable) F S Cr 3+ A iris D 3 D 1 Closed aperture 50% n D Open aperture 100% n

24 Alexandrite (BeAl O :Cr 3+ ) 1.1 R 1m 50% 100% Transmittance Transmittance 1.08 R m ν ( cm -1 ) % 50 % Transmittance Proportiona to Δn Linear absorption resonant n ~ resonant n Non-linear absorption Data Fit ν ( cm -1 ) ν ( cm -1 )

25 Pump probe n spectroscopy ( two colors) Nd3+ E 1 S S chopper L sample Ar+ laser excitation Ti:sapphire probe (tunable) F S iris 51nm ~869nm F 3/ I 9/ D 3 D 1 Closed aperture 50% n D Open aperture 100% n

26 Δn (unid. arb.) Nd 3+ crystals 869 nm Δn λ ( nm ) YAG:Nd 3+ Δn Δn Δn YAG F 3/ (ex) I 9/ (g) 100% Curva teórica 50% / 100% Curva teórica ν ( cm -1 ) Δn (arb. units) λ ( nm ) YAP:Nd % Curva teórica 50% / 100% Curva teórica ν ( cm -1 ) Δn (unid. arb.) YAP Δn (arb. units) Kramers-Kronig relations??

27 Non-resonant Resonant δ + i χ = ΔαN ex ( δ) + f. ΔN (1 + δ + s) n A = δ + A(1 + δ ) ' (1 + δ + s) n '( δ = 0) n "( δ = 0) = π λ Δα σ g n ' A = 0 A = 0,3 A = 1 A = 3 n ' -5,0 -,5 0,0,5 5,0 δ -5,0 -,5 0,0,5 5,0 Lima et. al. Opt. Lett. (0); V. S. Butylkin, A. E. Kaplan, and Y. Khronopulo, Sov. Phys. JETP 3, 501 (1971). δ

28 Conclusions Z-scan: theory is made for gaussian beams is a single beam technique and is simple nonlinear refraction spectroscopy (n ): one and two-color experiment Δα(ω) or dispersion effects (?) usually, thermal and electronic contributions can be discriminated Thank you for your attention

29 Richard Jean-Luis Patrice Alain Merci Beaucoup former students: Acácio A. Andrade Sandro M. Lima Djalmir N. Messias