Particle Imaging Diagnostics

Transcription

1 An Introduction to Particle Imaging Diagnostics Greifswald,

2 Outline 2D Video Microscopy Image Analysis Scanning Video Microscopy 3D Color Gradient Method Stereoscopic Imaging Digital Holography Recent Developments and Outlook

3 Basic Setup of a Video Microscope camera ca. 100 fps Mpixel resolution 1 ms exposure time dust particles filter 1-20 m diameter made of MF, PS, PMMF or SiO2 laser electrode typ. 20mW width ~ 2 cm, thickness ~100 m

4 Mie - Scattering dp = 20 m dp = 4 m [ Bohren and Huffmann, Absorption and scattering of light by small particles, Wiley 1998 ] See for codes (Fortran, C, Matlab, etc.)

5 Light Pressure cross section A light with intensity I particle = IA F rad = c absorption reflection

6 An Example for Laser Manipulation [ Nosenko et al., Phys. Plamas 13, , 2006 ]

7 An Example for Laser Manipulation P av 20 mw

8 Basic Setup of a Video Microscope camera ca. 100 fps Mpixel resolution 1 ms exposure time dust particles filter 1-20 m diameter made of MF, PS, PMMF or SiO2 laser electrode typ. 20mW width ~ 2 cm, thickness ~100 m

9 Depth of Field depth of field for close ups: DOF 2Nc m 1 m 2 N = lens f-number (typ. 8-22) c = circle of confusion (pixel size, i.e. 10 m) m = magnification (typ ) DOF = 0,1 13,2 mm [see for details on depth of field]

10 2D Video Microscopy Image Analysis Scanning Video Microscopy 3D Color Gradient Method Stereoscopic Imaging Digital Holography Recent Developments and Outlook

11 Image of a Particle particle diameter interparticle distance peak intensity detection threshold background intensity

12 Particle Detection with Subpixel Resolution raw image threshold method moment method estimation of center of intensity: X k I k I th X c= I k I th

13 Advanced Algorithms (a) (b) (a) Moment Method with Gaussian bandpass filter (b) Least Quadratic Kernel Method [ Ivanov et al., Rev. Sci. Instr. 78, (2007) ]

14 Subpixel Resolution ~ 0.1 a

15 Subpixel Resolution

16 Pixel Locking

17 Pixel Locking [ Feng et al., Rev. Sci. Instr. 78, , 2007 ]

18 How to avoid pixel locking? avoid saturation increase particle image size by slight defocussing subtract background choose a low threshold value use at least the moment method make particle image big to minimize pixel locking [ Feng et al., Rev. Sci. Instr. 78, , 2007 ] [ Ivanov et al., Rev. Sci. Instr. 78, (2007) ]

19 2D Video Microscopy Image Analysis Scanning Video Microscopy 3D Color Gradient Method Stereoscopic Imaging Digital Holography Recent Developments and Outlook

20 Scanning Video Microscopy [ DIH Lab, Kiel in 2008 ] [ Pieper et al. PRE 54, 5636, 1996 ]

21 Limitations of Scanning Video Microscopy z x Intensity determine positions in each frame y-axis y-position is given by moment method in 3D

22 Limitations of Scanning Video Microscopy z x no instantaneous position recording scan speed mechanically limited determine positions in each frame resolution relies on frame distance Intensity frame distance has to be much smaller than interparticle distance y-axis y-position is given by moment method in 3D

23 Limitations of Scanning Video Microscopy z x no instantaneous position recording scan speed mechanically limited determine positions in each frame resolution relies on frame distance Intensity frame distance has to be much smaller than interparticle distance y-axis y-position is given by moment method in 3D well suited for static particle distributions

24 2D Video Microscopy Image Analysis Scanning Video Microscopy 3D Color Gradient Method Stereoscopic Imaging Digital Holography Recent Developments and Outlook

25 Color Gradient Method

26 Color Gradient Method [ Annaratone et al., PPCF 46 B495, 2004 ] [ Goldbeck, Phd thesis, LMU Munich, 2003 ]

27 2D Video Microscopy Image Analysis Scanning Video Microscopy 3D Color Gradient Method Stereoscopic Imaging Digital Holography Recent Developments and Outlook

28 Stereoscopic Imaging AG Melzer, EMAU Greifswald

29 3D Reconstruction front view side view top view 3D coordinates

30 Alignment and Magnification

31 Line of Sight

32 Line of Sight Calibration needed!

33 Shadowing

34 Number of detected shadow positions Relevance of Shadowing number of particles

35 Results obtained with Stereoscopy

36 Limitations of Stereoscopic Imaging Well suited for small particle clouds, but Quality of the camera model is very important Beware of laser manipulation! Shadowing is a serious problem in larger clouds Transparency of dusty plasmas is limited!

37 2D Video Microscopy Image Analysis Scanning Video Microscopy 3D Color Gradient Method Stereoscopic Imaging Digital Holography Recent Developments and Outlook

38 Digital Inline Holography object wave huge depth of field particle no lenses, no calibration no shadowing reference wave interference pattern

39 Reconstruction Scheme 2 exp i i i Ui,,di = h x, z R x, z dxdz i 2 2 i= x y d2i R(x,z) Fresnel Kirchhoff Integral h(x,z) hologram plane reconstruction planes [ Schnars and Jueptner, Digital Holography, Springer 2005 ]

40 Limitations of DIH high computational efforts, i.e. no real-time monitoring. works only for large particles (rp > 5 m) accuracy in depth not sufficient for high precision measurements?

41 Benchmark of DIH video microscope VM trigger 1 Hz z x y DIH Nd:YAG λ = 532 nm P = 250 mw PCO bit 7,4 µm Pixel 15 4 Mpixel

42 Benchmark of DIH average particle position O DIH + VM y / mm standard dev. x =19µm y =69µm x / mm

43 Benchmark of DIH DIH VM y / mm x / mm DIH VM time / s time / s x =1,6µm y =17µm

44 Aligned Particles average particle positions O DIH + VM y / mm standard dev. x =19µm y =69µm x / mm

45 Limitations of DIH high computational efforts, i.e. no real-time monitoring. works only for large particles (rp > 5 m) accuracy in depth sufficient for high precision measurements!

46 2D Video Microscopy Image Analysis Scanning Video Microscopy 3D Color Gradient Method Stereoscopic Imaging Digital Holography Recent Developments and Outlook

47 High Speed Scanning Video Microscopy Photron ultima apx 10-Bit CMOS camera with Mpixel [Samsonov et al. Rev. Sci. Instr. 79, , 2008 ]

48 Stereoscopic Imaging CAM3 CAM2 observable volume optical axis CAM1 CAM1 optical axis CAM2 [see next talk by Birger Buttenschön ]

49 Stereo - DIH B benefits: A high resolution in all directions B faster reconstruction ( > 1000 holograms per night ) higher temporal resolution ( up to 150 fps ) A

50 Rotating Electrode 0 Hz f(z) 7 Hz z J. Carstensen et al., PoP. 16 (2009)

51

52 top view side view

53 top view side view

54 top view side view

55 Take home messages diagnostics in 2D are well understood and developed diagnostics in 3D are now available and ready for application but particle imaging diagnostic is not that simple as it seems to be

56 Most of this talk will be published as a chapter in Introduction to Complex Plasmas Eds. Michael Bonitz, Norman Horing, Jürgen Meichsner, and Patrick Ludwig Springer Series Atomic, Optical and Plasma Physics. (to appear very soon)