WORCESTER POLYTECHNIC INSTITUTE

Transcription

1 WORCESTER POLYTECHNIC INSTITUTE MECHANICAL ENGINEERING DEPARTMENT Optical Metrology and NDT ME-593L, C 2018 Lecture 03 January 2018

2 Lasers sources Some operating characteristics: laser modes Schematic diagram of a He-Ne laser Possible longitudinal resonant modes (cavity length = L)

3 Lasers sources Some operating characteristics: laser modes Schematic diagram of a He-Ne laser Laser cavity configurations (cavity length = L) Possible longitudinal resonant modes mode 2 2nL

4 Lasers sources Some operating characteristics: laser modes Possible transversal resonant modes Gaussian TEM 00 Hermite-Gaussian TEM 02 Laguerre-Gaussian

5 Lasers sources Some operating characteristics: continuous & pulsed Near IR continuous laser Output wavelength: narrow bandwidth Line width: FWHM ~ 0.02 nm Transversal mode

6 Lasers sources Some operating characteristics: continuous & pulsed Picosecond pulsed laser Typical pulsetrain Intensity, W/m 2 Time, ps Individual pulse characteristics

7 Lasers sources Some operating characteristics: continuous & pulsed Picosecond pulsed laser Pulse dispersion through media Dispersion in optical fibers Dispersion compensation

8 Lasers sources Some operating characteristics: temporal coherence

9 Lasers sources Some operating characteristics: temporal coherence Packets of emitted light (Coherence time)

10 Lasers sources Some operating characteristics: temporal coherence Coherence time Two emissions side-by-side Laser cavity Emitted packets

11 Lasers sources Some operating characteristics: temporal coherence Temporal coherence length contributes to interference ability Coherence time Two emissions side-by-side Central wavelength: Line width: Coherence length: l c 2 ln(2) 2

12 Lasers sources Some operating characteristics: spatial coherence

13 Lasers sources Some operating characteristics: temporal & spatial coherence Electric fields of focused laser beams Good temporal & Good spatial coherence z (Propagation direction) Poor temporal & Good spatial coherence z Good temporal & Poor spatial coherence z

14 Lenses Snell s law Light ray propagating through two media n 1 and n 2 are refractive indexes v 1 and v 2 are velocities of light Light wavefronts n 1 sin 1 n2 sin sin 1 sin 2 and v1 v 2 n n 2 1 2

15 Lenses Snell s law & total internal reflection Angle of incidence and internal reflections: Fiber optics Laser in fiber

16 Lenses Snell s law: refraction at a spherical interface

17 Lenses Types Convergent lenses Divergent lenses

18 Lenses Types Focal point Virtual focal point

19 Lenses Imaging properties: real image 1 S 1 S f ; Magnification: M S S 2 1 f f S 1

20 Lenses Imaging properties: real image formation

21 Wavefronts of light Lenses Imaging properties: real image formation Microscope objectives f

22 Lenses Imaging properties: virtual image 1 S 1 1 S 2 1 f for S 1 f

23 Lenses Imaging properties: virtual image

24 Lenses Imaging properties: real image formation

25 Lenses Imaging properties: real image formation

26 Lenses Some optical aberrations: spherical No-aberration Spherical aberration Spherical aberration

27 Lenses Some optical aberrations: coma & chromatic Removing chromatic aberrations

28 Lenses Some optical aberrations: distortion (need for camera calibration and software) Barrel Pincushion Mustache

29 Potential Course Projects Overview: lab visit Ultra-high speed imaging: DIC Shearography: NDT Fringe Projection: Shape measurements & NDT MEMS metrology: Shape/deformation measurements & NDT Digital holography

30 Potential Course Projects Overview: shearography Nondestructive testing: standoff detection Internal defect detection & measurements Realized opto-electronic head with pulsed laser Developed holographic system in the field

31 Nondestructive testing: standoff detection Internal defect detection & measurements Hidden object under person s shirt Detected defect an inside object

32 Course Projects Overview: Fringe Projection for Shape measurements & NDT Texas Instrument s DMD Each mirror of the DMD is individually addressable Number of mirrors 480,000 to >2,000,000 Close-up of chip surface 20 mm

33 MEMS in optoelectronic metrology High-speed measurements based on holographic interferometry principles Use of computer generated holograms 1 Fringe 2 Fringes 4 Fringes 8 Fringes 16 Fringes 32 Fringes 64 Fringes

34 MEMS in optoelectronic metrology High-speed measurements based on holographic interferometry principles Shape measurements in 3D inspection applications

35 MEMS in optoelectronic metrology: art-conservation High-speed measurements based on holographic interferometry principles Worcester Art Museum: Sculpture titled Funeral of a Young Maiden Casona, South Italy. Late 4 th Century BCE Representative Measurements A 0 ⁰ A

36 MEMS in optoelectronic metrology: road shape High-speed measurements based on holographic interferometry principles A prototype system has been developed and applied to road surface analysis We are currently designing a robust, low-cost, projection system that can be deployed in the field for measurements at up 60 mph driving speeds Prototype projector on a vehicle Typical surface road measurements

37 Course Projects Overview: MEMS metrology for Shape/deformation measurements & NDT Piezo Mirror Reference Beam CCD or CMOS Beam Splitter Object Beam LED High-power LED s: 470, 520, 620, 680 nm FWHM 25 nm Coherence length: 10 µm (620 nm) Matching of the OPLD within coherence length T and I modulation: rise and fall time of 175 nsec Object Coherence length

38 Course Projects MEMS accelerometers: shape/deformation/ndt Electrostatic combs Folded springs

39 Full-field-of-view characterization of mode shapes of vibration Fundamental frequency is related to the measuring accuracy of the MEMS device Observed fundamental mode at KHz Continuous full-field-of-view measurements Frequency scan: 10 khz 11 khz 100 µm

40 Testing at the wafer level: inspecting an ADXL202 wafer Multi-scale approach Level-3: stitching patches of Level-2 Level-1: measurement of individual dies Level-2: stitching individual die measurements Level- 4: stitching patches of Level-3

41 Announcements Homework distributed soon in class/web Project for this class: list of topics (CF) and teams