Filamentation of femtosecond nondiffracting beams Applications to laser ablation

Transcription

1 Filamentation of femtosecond nondiffracting beams Applications to laser ablation F. Courvoisier, C. Xie, A. Mathis, J. Zhang, L. Froehly, V. Jukna, L. Furfaro, M. Jacquot, R. Giust, P.-A. Lacourt, A. Couairon, J. M. Dudley FEMTO-ST Institute University of Franche-Comté Besançon, France Center for Theoretical Physics Ecole Polytechnique Palaiseau, France

2 Femtosecond laser ablation is not a direct process. I~10 12 to W/cm^2 Energy deposition via ionization Material coupling Gatass,R and Mazur,E. Nature Photonics,2,219 (2008) 2

3 Motivations Femtosecond lasers have enabled significant progresses for precision micro and nanofabrication with ablation accuracy down to ~ nm. But the extent of laser ablation with high accuracy is limited to surface nanocraters or spherical nanovoids in the bulk of transparent materials. 2 µm 1 µm McLeod and Arnold, Nature Nanotech. 3, 413 (2008) Juodkazis et al, Phys. Rev. Lett (2006) 3

4 Motivations We aim at fabricating much deeper structures. Nanofluidics Glass panels Nanophotonics Precision mechanisms The control of the longitudinal profile of ablation structures during drilling and dicing is a key technological issue. 4

5 Motivations - drilling in transparent materials Need to control the beam propagation and energy deposition Need to deal with the nonlinear propagation. 5

6 Deep drilling with Gaussian beams Weakly focused Gaussian beams yield pulse spatio-temporal distorsions (filamentation, splitting ). Self-focusing Plasma Absorption & Diffraction Sudrie et al, Phys. Rev. Lett. 89, (2002) 6

7 Outline Main Objective: we show that the use of stationary regimes of filamentation allows a higher degree of control of the energy deposition process. Non diffracting Bessel beams for high aspect ratio drilling Conical structure Accelerating beams for laser machining of curved profiles Caustic structure 7

8 Beam shaping toolbox Bessel beams SLM Fourier filtering 800 nm 5 KHz 100 fs SLM image Accelerating beams High-quality beams 1-2 µm spot size High angles (up to 50 ) 8

9 Outline Non diffracting Bessel beams for high aspect ratio drilling Conical structure 9

10 Diffraction-free Bessel beams Longitudinally extended Bessel beams are an invariant solution to the wave equation Generated from a superposition of plane waves by an axicon 10

11 What matters is not the intensity distribution The conical structure can be a stationary solution of the nonlinear propagation AND an attractor of the filamentation regime. 2 filamentation regimes at high intensity Plasma density Plasma density Non-stationary (periodic peaks) Polesana et al, Phys. Rev. A. 77, (2008) Stationary (absence of pulse dynamics) 11

12 What matters is not the intensity distribution The conical structure can be a stationary solution of the nonlinear propagation AND an attractor. Water assisted drilling in glass with fs Bessel beams 2 µm Bhuyan et al,opt. Express 18, 566 (2010) Plasma density Plasma density 3µm Non-stationary (periodic peaks) Polesana et al, Phys. Rev. A. 77, (2008) Stationary (absence of pulse dynamics) 12

13 Experimental setup High conical angles allow us to maintain a stationary regime Virtual axicon Bhuyan et al, Appl. Phys. Lett., 97, (2010) Courvoisier et al, Opt. Lett., 34, 3163 (2009) 13

14 Single shot machining of glass (Corning 0211) Result 0.65 µj 0.85 µj aspect ratio =100:1 200 nm 330 nm 14

15 Through-channel with a single laser shot 3 µj single pulse Bhuyan et al, Appl. Phys. Lett., 97, (2010) Unexpectedly deep material extraction. Origin? 15

16 Numerical simulations (NLSE+plasma equation) We accurately reproduce our experimental results with 2 numerical models (NLSE or UPPE) Sudrie et al, Phys. Rev. Lett. 89, (2002) Couairon et al, Eur. Phys. J. Special Topics, 199,1 (2011) Zhang et al, in preparation Fluence Plasma density 16

17 Dense plasma formation Plasma densities are close to those observed during fs laser induced micro-explosions. This time on much longer propagation distances. 17

18 Potential practical applications Nanofluidics Nanophotonics Pitch: 0.8 µm Pitch: 1.6 µm Bhuyan et al, Appl. Phys. Lett., 97, (2010) 18

19 Outline Accelerating beams for laser machining of curved profiles Caustic structure 19

20 Accelerating beams Airy beams are (nondiffracting) solutions of the paraxial wave equation. Propagation Intensity Transverse dimension Siviloglou et al, Phys. Rev. Lett. 99, (2007) Airy beams follow a parabolic trajectory: they are one example of accelerating beam. 20

21 Accelerating beams Airy beams sustain curved & stationary filaments. BUT: paraxial trajectories, parabolic only Polynkin et al, Science 324, 229 (2009) Lotti et al, Phys. Rev. A 84, (2011) 21

22 Accelerating beams are caustics Accelerating beams can be viewed as caustics the boundary of an envelope of rays that forms a curve of concentrated light. The amplitude distribution is accurately described with catastrophe theory and allows us to calculate the phase mask. L. Froehly et al, Opt. Express (2011) E. Greenfield et al. Phys. Rev. Lett (2011) 22

23 Setup Beams are generated from the Fourier space 23

24 Arbitrary accelerating beams-nonparaxial regime Bending over more than 95 degrees Numeric Experiment Mathis et al, Opt. Lett., 38, 2218 (2013) 24

25 Arbitrary accelerating beams-nonparaxial regime The caustic approach allows us to design the phase mask to generate an accelerating beam with an arbitrary trajectory. Mathis et al, Opt. Lett., 38, 2218 (2013) 25

26 Spherical light Half-sphere with 50 µm radius 26

27 Setup Experimental 50% Propagation Transverse distance (µm) Beam cross section 3D View 27

28 Edge profiling 3D processing concept 28

29 Edge profiling 3D processing concept 29

30 Results on silicon 100 µm thick silicon slide initially cut squared 100 µm R=120 µm Mathis et al, Appl. Phys. Lett. 101, (2012) 30

31 Results on silicon quartic profile 100 µm R=120 µm Mathis et al, Appl. Phys. Lett. 101, (2012) 31

32 It also works for transparent materials diamond 100 µm 50 µm R=120 µm R=70 µm Mathis et al, Appl. Phys. Lett. 101, (2012) 32

33 Direct trench machining in silicon Mathis et al, Appl. Phys. Lett. 101, (2012) Debris distribution is highly asymmetric. 33

34 Analysis in terms of light propagation direction Surface trench opening determines the depth of the trench along the caustic trajectory. Intensity on top surface Mathis et al, JEOS:RP, (2013) 34

35 Analysis in terms of light propagation direction Surface trench opening determines the depth of the trench This is performed by the SIDE lobes, that are more intense on surface Mathis et al, JEOS:RP, (2013) 35

36 Conclusion Shaping light direction and addressing stationary filamentation regimes provides a novel degree of control for ultrafast laser micro and nanomachining. We have reported high aspect ratio drilling and curved edge profiling. Perspectives: - novel tool to create and manipulate plasmas - Curved nanochannels? 36