Femtosecond laser microfabrication in. Prof. Dr. Cleber R. Mendonca

Transcription

1 Femtosecond laser microfabrication in polymers Prof. Dr. Cleber R. Mendonca

2 laser microfabrication focus laser beam on material s surface

3 laser microfabrication

4 laser microfabrication

5 laser microfabrication surface microstructuring

6 fs-micromachining photon energy < bandgap nonlinear interaction

7 fs-micromachining nonlinear interaction E gap E f = hν multiphoton absorption

8 introduction short pulse duration high intensity (even at low energy)

9 introduction how short is a femtosecond pulse? 1fs= s

10 introduction how short is a femtosecond pulse?

11 introduction Ti:Sapphire lasers 100 fs 50 fs 20 fs Very intense light Laser intensities ~ 100 GW/cm 2 1x W/cm 2 Laser pointer: 1 mw/cm 2 (1 x10-3 W/ cm 2 )

12 introduction Ti:Sapphire lasers 100 fs 50 fs 20 fs Very intense light

13 Light matter interaction Semiclassical treatment electron on a spring harmonic oscillator k m e oscillation frequency ω 0 = k m e

14 Linear optical processes E << E radiation interatomic Induced polarization P = χe linear response ( ) absorption α = α λ refraction n = n( λ)

15 Nonlinear optical processes high light intensity E rad. ~E inter. How high should be the light intensity?

16 Nonlinear Optics Inter-atomic electric field cw laser 2P πw P = 20 W I = w o = 20 μm 2 0 I = W/m 2 e = C r ~ 4 Å E ~ V/m E o = V/m

17 Nonlinear Optics Inter-atomic electric field pulsed laser I = 10 GW/cm 2 = W/m 2 e = C r ~ 4 Å E ~ V/m E o = V/m

18 Nonlinear Optics high light intensity E rad. ~ E E inter. anharmonic oscillator nonlinear polarization response P = χ ( 1 ) E + χ ( 2 ) E 2 + χ ( 3 ) E

19 Two-photon absorption Third order processes χ ( 3 ) 2ω ω ω orbance abso α = α + βi = 0 wavelength

20 Two-photon absorption Nonlinear interaction provides spatial confinement of the excitation fs-microfabrication α = α 0 α = α 0 + βi

21 Two-photon absorption spatial confinement of excitation

22 fs-laser microfabrication focus laser beam inside material

23 femtosecond pulses Ti:Sapphire lasers 1fs= s 100 fs 50 fs 20 fs Repetition rate 1KHz 1 ms Energy mj 100 fs 12 ns 86 MHz nj 100 fs

24 femtosecond pulses amplified laser oscillator repetitive cumulative

25 fs-micromachining: focusing NA = 0.12 μ = 7 o NA = 0.34 μ = 20 o NA = 0.87 μ = 60 o

26 what is the difference? w λ 0 = 1 NA πna 2

27 very different confocal lenght/interaction length

28 two main techniques fs-laser micromachining microfabrication via two-photon polymerization

29 fs-laser micromaching Surface Volume

30 fs-pulses for micromachining polymers Oscillator: 80 MHz, 5 nj heat diffusion time: t diff ~ 1 μs cumulative

31 Micromachining the conductive polymer MEH-PPV a 0.3 nj atomic force microscopy b 20nJ 2.0

32 Micromachining the conductive polymer MEH-PPV

33 Waveguides in azo-polymers H 2 N N N NO 2 DO3 Cl HO H 2 C H 3 C H 2 C H 2 C N N N NO 2 DR13 HO H 2 C H 2 C H 3 C H 2 C 3 2 N N N NO 2 DR1

34 Waveguides in azo-polymers (a) Optical microscope image of the waveguides micromachined (PMMA/DR1) (b) Cross-sectional view of the waveguides

35 waveguides in azo-polymers (c) Output image of the mode profile of nm light coupled through the waveguide

36 microstructuring polymer: super hydrophobic surface CCD lens mirror Pockels cell ps-laser objective 0.65 NA sample

37 laser microfabrication: super hydrophobic surface examples of fabricated surfaces 20 μm 40 μm

38 Microfabrication Novel concept: build microstructures using fs-laser and nonlinear optical processes

39 Two-photon polymerization Photopolymerization Monomer + Photoinitiator Polymer light

40 Two-photon polymerization Monomer + Photoinitiator Polymer light Photoinitiator is excited by two-photon absorption R2 PA I The polymerization is confined to the focal volume. 2 High spatial resolution

41 Two-photon polymerization bellow the diffraction limit

42 Two-photon polymerization setup Beam Expansion y x Scanning Mirror Laser Ti:sapphire laser oscillator 130 fs 800 nm 76 MHz 20 mw CCD camera glass (150 micron) Objective Objective z spacer resin glass (150 micron) 40 x 0.65 NA Illumination

43 Resin preparation Monomers Monomer A Monomer B reduces the shrinkage upon polymerization gives hardness to the polymeric structure Photoinitiator iti t Lucirin TPO-L Appl. Phys. A, 90, (2008)

44 Two-photon polymerization 30 µm x 30 µm x 12 µm cube polymer glass

45 Two-photon polymerization After the fabrication, the sample is immersed in ethanol to wash away any unsolidified resin and then dried

46 photonic crystal J. W. Perry two-photon polymerization 20 µm

47 Two-photon polymerization Microstructures fabricated by two-photon polymerization 50 μm 20 µm 20 μm 20 µm

48 Microstructures containing active compounds monomer monomer Optical active dye Active Polymer

49 two-photon polymerization applications micromechanics waveguides microfluidics biology optical devices

50 Other studies microstructures for optical storage birefringence p r dye p r dye φ N N E r Light Relax trans cis trans N N N N φ E r J. Appl. Phys., 102, (2007)

51 Other studies microstructures for optical storage birefringence Ar + ion laser irradiation nm one minute intensity it of 600 mw/cm 2

52 Other studies microstructures for optical storage birefringence The sample was placed under an optical microscope between crossed polarizers and its angle was varied with respect to the polarizer angle

53 Other studies microstructures for optical storage birefringence J. Appl. Phys., 102, (2007)

54 Microstructures containing MEH-PPV MEH-PPV Fluorescence Electro Luminescent Conductive

55 Microstructure containing MEH-PPV Appl. Phys. Lett., (2009)

56 Microstructure containing MEH-PPV

57 Microstructure containing MEH-PPV

58 Microstructure containing MEH-PPV

59 Microstructure containing MEH-PPV (a) Scanning electron microscopy (b,c) Fluorescence microscopy of the microstructure t with the excitation ti OFF (b) and ON (c) (d) Emission of the microstructure (black line) and of a film with the same composition (red line) Appl. Phys. Lett., (2009)

60 Microstructure containing MEH-PPV Fluorescent confocal microscopy images in planes separated by 16 μm in the pyramidal microstructure.

61 Microstructure containing MEH-PPV Do we have waveguiding in the microstructure t?

62 Microstructure containing MEH-PPV Do we have waveguiding in the microstructure t?

63 Microstructure containing MEH-PPV

64 Microstructure containing MEH-PPV waveguiding of the microstructure fabricated on porous silica substrate (n= 1.185) Applications: micro-laser; fluorescent microstructures; conductive microstructures

65 3D cell migration 3D cell migration studies in micro-scaffolds SEM of the scaffolds 110 µm pore size 52 µm pore size Top view 110, 52, 25, 12 µm pore size Side view 25, 52 µm pore size

66 3D cell migration 3D cell migration studies in micro-scaffolds Advanced Materials, 20, (2008)

67 Optical circuit

68 Optical circuit microfabrication silica nanowires coupling microstructures 50 μm

69 Silica nanowires nanowires fabrication process

70 Silica nanowires

71 Silica nanowires 70 μm 1 μm

72 Silica nanowires

73 Silica nanowires coupling light into nanowires

74 Silica nanowires coupling light into nanowires

75 Outline microfabrication silica nanowires coupling microstructures 50 μm

76 Coupling microstructures

77 Coupling microstructures

78 Coupling microstructures

79 Coupling microstructures

80 Coupling microstructures

81 Coupling microstructures

82 Summary

83 Acknowledgments FAPESP CAPES CNPq US AirForce NSF ARO

84 for a copy of this presentation presentations