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Comparison of laser scanning methods

Comparison of laser scanning methods. Yong-Gu Lee. Beam steering methods. Refraction (reflection) type tilt platform Galvanometer Piezo linear stage motor Piezo Diffraction type Diffraction Optical Element Acousto-optical devices. Beam steering (x-y). Beam steering (x-y).

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Comparison of laser scanning methods

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  1. Comparison of laser scanning methods Yong-Gu Lee

  2. Beam steering methods • Refraction (reflection) type • tilt platform • Galvanometer • Piezo • linear stage • motor • Piezo • Diffraction type • Diffraction Optical Element • Acousto-optical devices

  3. Beam steering (x-y)

  4. Beam steering (x-y) PI Ultrafast piezo tip/tilt platform High resolution

  5. Beam steering (x-y) • An acousto-optics deflector changes the angle of direction of a laser beam and its angular position is linearly proportional to the acoustic frequency, so that the higher the frequency, the larger the diffracted angle. • Where λ is the optical wavelength in air, Va is the acoustic velocity, and f is the frequency Ref. http://www.brimrose.com/aodefl.pdf

  6. AOD: high scanning rate Ref. http://www.brimrose.com/aodefl.pdf

  7. Micro-Tetris

  8. Beam steering (x-y) Ref. http://www.gsilumonics.com/product_data_sheets_en/276.html

  9. Galvanometer: wide scanning range

  10. Beam steering (z)

  11. Beam steering (z)

  12. Motor • Motorized Actuator: 12V DC Servo Motor • Actuator Travel: 25mm • 0.05 µm Minimum Incremental Move • Compatible with Many Standard Controllers/Drivers • Limit Switches Prevents Accidental Actuator Damage • High Precision Rotary Encoder (48 counts per revolution) Ref. http://www.thorlabs.com/

  13. Beam steering (z) PI PIFOC Nanofocusing positioners

  14. Double optical Trap = + Two orthogonally polarized beams

  15. N-optical trap Space sharing Ref. http://www.memsoptical.com/

  16. Scanning optical trap Time sharing

  17. Basic Steerable Tweezers Setup The steering mirror must be made “conjugate” to the back aperture of the objective lens. Ref. Dholakia and Gabriel C. Spalding, 2004 SPIE course on Optical Tweeezers

  18. Diffractive optical element • Diffractive optical elements are computer generated holographic devices which can transform an illuminating laser beam into a specified intensity distribution by diffraction rather than refraction or reflection. The diffractive surface of a beam shaping element is split into an array of cells each designed to transform the phase of the coherent illuminating beam by a specified amount. • In a reflective diffractive optical element the required phase change at each cell is achieved by accurately producing a sub-wavelength depth profile as shown below. • Upon reflection each cell is considered to be emitting a spherical wavefront with a specified phase retardation. These diffracted wavefronts interfere in the reconstruction plane to produce the required intensity profile. • The computer algorithms used to calculate the diffraction patterns incorporate the profile of the illuminating laser beam in order to achieve the optimum reconstruction performance. • A measured intensity profile can be inputted or a mathematical description of the beam shape may be used. As the number of depth levels reproduced in the diffractive surface increases so does the efficiency and quality of the reconstruction. Diffraction efficiencies in excess of 90% are achievable using the fabrication techniques. Ref. www.laseroptical.co.uk

  19. Phase only modulation In fact, phase-only modulation allows for complex optical “ landscapes” [Left-hand Image: Oliver Kreylos Right-hand Image: Brian Lent and Dimitrios Mavroidis, Stanford Computer Graphics Laboratory]

  20. Result of passing light through a phase modulator

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