Joint Institute for High Temperatures Russian Academy of Sciences, - PowerPoint PPT Presentation

Joint Institute for High Temperatures Russian Academy of Sciences, Moscow JIHT of RAS Shock, ablation and formation of nanostructures in metals induced by femtosecond laser S.I. Ashitkov, P.S.Komarov, N.A. Inogamov, V.V. Zhakhovsky, M.B. Agranat, G.I. Kanel Santa Fe, NM, USA, April 21-25, 2014

MOTIVATION JIHT of RAS � Laser matter interaction/ experiment and modeling � Materials behavior near the theoretical limit of shear and bulk strength � Development of a theory of plasticity and fracture � Femtosecond laser surface nanostructuring OUTLINE � � Shock compression of aluminum and iron in picosecond range. - - super elastic shock waves at submicron scale - - achievement of ultimate values of the shear and bulk strength - - - possibility of α→ε polymorphic phase transition in iron � Frontal ablation and rear side spallation of aluminum. � Formation of nanostructures: MD simulations and experiment 2

Shock compression of metals. Appearance of material JIHT of RAS properties in a free surface history. Shock wave structure. Diagnostics of shock phenomena are performed by measuring a free surface Free surface velocity history velocity profile of a tested sample. In plate impact experiment*. Reflection of shock compression pulse from the Free Surface Velocity u fs , km/s ∆ u fs free surface leads to appearance of the tensile stresses inside of the sample causing fracture. 13 GPa Value of spall strength is determined from: σ = ρ ∆ + δ U ( u ) / 2 spall 0 S fs α→ε polymorphic phase transition in iron: Armco-iron 2.46 mm (bcc → hcp crystal structure transition) Transition stress ≈ 13GPa in a microsecond range Time t, µs Splitting of shock wave into elastic precursor (HEL) and plastic compression wave makes it possible to σ = ρ U ∆ e e u / 2 determine the plasticflow stress of the material . HEL 0 S fs * G.I. Kanel', V. E. Fortov,S.V. Razorenov Physics-Uspekhi 50, (8) (2007) 2

Ultrafast Chirped Pulse Interferometry JIHT of RAS Femtosecond Ti:S laser (Legend, Coherent, USA) -Detected range 0 ÷ 240 ps Stretcher -Temporal resolution 1ps Oscillator Amplifier Compress о r -Lateral spatial resolution 2 µm -Displacement accuracy 1÷2 nm Probe wavelength, nm Probe wavelength, nm 770 770 810 810 790 790 -Measurements in a single shot 1 , 0 0 , 5 0 , 0 C - 0 , 5 - 1 , 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0 1 8 0 2 0 0 A Probe 300 ps In contrast to multipulse pump–probe 80 80 160 160 240 240 0 0 Time t, ps Time t, ps methods the single-pulse technique Sample ensures much higherreliability of the Imaging CCD measurements and can be used to Spectrometer Acton 2300i Pump 100 fs analyze the reproducibility and statistics of shock wave phenomena in thin film Imaging Michelson samples. interferometr Phase shift, rad 2.0 2.5 1.5 1 0.5 0 Application of Fourier processing of 0 Position y, µm interference patterns and comparison 2D Fourier processing of phase distributions obtained before of interference patterns 100 and during shock wave arrival ensure measurement of surface displacement Spatial-temporal phase with nanometric accuracy. 200 distribution 0 100 200 Time, ps

Time and spatial resolved diagnostics of JIHT of RAS a rear surface displacement Samples: metallic films, deposited Phase distributions at the rear d 1 ∆ ϕ ( y , t ) by magnetron spattering onto glass surface of iron targets of different thicknesses Metal film substrates after shock breakout of 150 µ m in thick Glass substrate 250 Fe, 250 nm 2 200 chirped probe Phase shift, rad Position y, a.u. 1.5 Ti:S laser 150 300 ps 100 1 pump 50 0.5 1 100 fs 0 0,5 0 250 Fe, 540 nm C Gaussian 2 -0,5 200 spot Ø=40 µm 1.5 - 150 80 100 120 140 160 180 200 1 100 0.5 50 d 2 0 0 0 100 200 Time t , ps ∆ = λ ∆ ϕ π Free surface displacement histories z ( y , t ) ( t ) ( y , t ) / 4 150 Al 500 nm Displacement, nm 100 1200 nm 50 0 0 50 100 150 200 250 Time t, ps

Elastic-plastic shock wave in iron Free surface displacement and Ti:S laser: 100fs, 3 J/cm velocity history at different stress Sample: 99.9 purity iron film 540 nm in thick 100 Fe , Shot#8 deposited on glass substrate 80 540 nm Displacement z , nm 60 Splitting of shock into elastic-plastic two-wave configuration at propagation distance of 540 nm 40 20 0 0 50 100 150 200 Time t, ps 1,4 Free Surface Velocity, km/s Fe Shot # 8 1,2 540 nm 1,0 PSW 0,8 0,6 0,4 HEL 0,2 0,0 0 50 100 150 200 Time, ps 2

Evolution of laser driven shock waves in Al and Fe at a submicron scale. Elastic Hugoniout JIHT of RAS Free surface velocity histories 2,0 2,0 Al, 3J/cm2 Fe, 3 J/cm2 Free Surface Velocity, km/s Free Surface Velocity, km/s 500 nm 250 nm 1,6 1,5 HEL 14 GPa 27 GPa 1,2 1,0 8 GPa 0,8 540 nm 0,5 1200 nm HEL 0,4 13 GPa 7.1 km/s 6.4 km/s 0,0 0,0 50 100 150 200 0 50 100 150 200 250 Time, ps Time, ps U S – u p diagrams. Elastic Hugoniout . - In iron splitting of shock 8 wave into two-zone elastic-plastic configuration was observed 7 - In aluminum pure elastic wave U S , km/s U SE = 6.44 + 1.4 u p was detected at stress up to 14 GPa 6 with parameters rise time of 1-2 ps U S = 5.35 + 1.34 u p 5 0,00 0,25 0,50 0,75 1,00 u p , km/s

P – V diagrams. Shear strength of aluminum and iron JIHT of RAS Recorded states in elastic shock waves (points) in aluminum and iron films 20 Al Elastic: U S = 6.44 + 1.4 u p 15 σ z - p = 4.3 GPa σ , GPa σ z - p = 2.4 GPa 10 3 τ = σ − ( ( V ) p ( V )) τ = 3.2 GPa z τ = 1.8 GPa 4 5 Bulk: US = 5.35 + 1.34 up 0 0,80 0,85 0,90 0,95 1,00 V/V 0 Maximum shear stress at uniaxial compression: 3 τ = σ − ( ( V ) p ( V )) z 4 Experimental value Theoretical limit Al up to 3.2 GPa 3.4 GPa Fe up to 7.9 GPa 7.5 GPa

Decay of the elastic precursor in aluminum and iron JIHT of RAS Ashitkov, et al Al, HEL Ashitkov et al 10 Whitley, et al Crowhurst et al Crowhurst, et al σ HEL , GPa Gupta, et al Smith et al 1 Garkushin, Winey, et al Kanel et al et al 0,1 Arvidsson, et al 0,01 -3 -2 -1 0 1 10 10 10 10 10 Distance h , mm − σ = 0 . 63 σ = − + − 0 . 45 0 . 083 S ( h h 0 ) S ( h h ) S ( h h ) HEL HEL 1 0 2 0 - Super elastic shock waves with the stress >10 GPa were detected at submicron propagation distance γ & - Decay of the elastic precursor is connected with plastic strain rate : γ & σ G d 4 p = − p x dh 3 c HEL l ( G - shear modulus ) S.I.Ashitkov, et al JETP. Lett. 92 , 516 (2010) S.I. Ashitkov, et al JETP Lett . 98 , 384(2013) V. H. Whitley, et al J.Appl. Phys . 109 , 013505 (2011) J.C.Crowhurst, et al J.Appl. Phys . 115 , 113506 (2014) J.C.Crowhurst, et al Phys.Rew.Lett. 107 , 144302 (2011) 2

The α → ε phase transition in iron at strain rate ~10 9 s -1 JIHT of RAS LLNL Livermore, 2013 JIHT of RAS, 2013 Laser, 100 fs Laser, 300 ps Sample: Fe film on a glass substrate Sample: Fe film on a glass substrate Glass Fe, >1 µm Glass Fe, 0.5 µm P x P x 300 ps 50 ps t t Fe Fe Fe 1.2 µm 1.6 µm 100 ps - HEL = 13-14 GPa at propagation distance 0.54 µm - deviatoric stress 4.5 GPa - HEL = 10-12 GPa at propagation distance 1.2-1.6 µm - PSW stress is up to 23GPa - deviatoric stress exceeds 3 GPa - observation of a trend to splitting PSW into two waves - transition stress is up to 25GPa - but α→ε polymorphic transition in iron - α→ε polymorphic transition in iron isn’t realized within 20 ps is realized within 100 ps J.C. Crowhurst et al, J.Appl. Phys. 115 , 113506 (2014) 2

Spall strength of aluminum and iron at strain rate ~ 10 8 - 10 9 s -1 JIHT of RAS Free surface velocity histories Free Surface Velocity, km/s 150 Al indicate spallation at a pure 1,5 760 nm 2 F=2J/cm Displacement z , nm elastic uniaxial compression 100 1200 nm 1,0 in a picosecond range ∆ u fs ∆ u fs 50 0,5 1 σ = ρ − ∆ ∆ ( c b u 2 ) u spall 0 l fs fs 2 0 0,0 0 50 100 150 200 250 Time, ps nonlinearity of compressibility Strain rate & = V / V u fs 2 c & 0 Ideal strength 28 GPa S.I.Ashitkov, et al JETP. Lett. 92, 516 (2010) 2

Formation of nanostructures on metal surface after JIHT of RAS femtosecond laser irradiance above ablation threshold SEM images of ablation crater at a surface of gold sample. Laser: 100 fs; F/Fabl=1.5 1.5 µm 15 µm Result of long large-scale MD simulation of a sample with dimensions LxLyLz = 500x240x24 nm 3 and 172x10 6 atoms. Laser: 100 fs; F/F abl =1.5 Expansion of foam,breaking of membranes, and freezing the remnants of membranes near the transit between foam and continuous metal. (a) - density map (b-e) - atomic order map: solid (green), liquid (red) 2 N.A. Inogamov, et al Contr.Plasma Phys . 53, 796 (2013)

Dynamics of surface layer expansion during femtosecond ablation of aluminum JIHT of RAS Temporal spatial phase distribution Ti:S laser Glass substrate pump 100 fs 0.3 Gaussian Phase shift, rad spot Ø=40 µm 0.2 F 0 = 0.9 J/cm 2 0.1 -0,5 - 0 120 80 100 120 140 160 180 200 Time, ps chirped probe x, a.u. 300 ps 0 Al film Displacement history 760 nm Ablation threshold 0.7 J/cm 2 20 F/ Fa=1.2 Al Displacement z, nm Profile of ablation crater 15 F/ Fa=0.9 50 µm 10 F/ Fa=0.7 5 40 nm 0 Crater 80 100 120 140 160 180 Time t, ps 2