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AUTOMATED SPOTSIZE MEASUREMENT

AUTOMATED SPOTSIZE MEASUREMENT . BME 273 Senior Design Project April 7, 1999. Brian N. Lenahan Melisa L. Moore Advisor: Dr. E. Duco Jansen. OBJECTIVES. To measure a laser’s spotsize with an accuracy of ±10 m m for a spotsize range of 100 m m - 25mm

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AUTOMATED SPOTSIZE MEASUREMENT

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  1. AUTOMATED SPOTSIZE MEASUREMENT BME 273 Senior Design Project April 7, 1999 Brian N. Lenahan Melisa L. Moore Advisor: Dr. E. Duco Jansen

  2. OBJECTIVES • To measure a laser’s spotsize • with an accuracy of ±10mm • for a spotsize range of 100mm - 25mm • To develop a computer-controlled environment capable of taking fully automated, expedient spotsize measurements • To develop a means of saving these beam profiles & spotsize measurements for later reference

  3. MOTIVATION • Laser fluence (J/mm2) is dependent on the area of the laser beam. • Photons focused onto a smaller area have more destructive power. • Manual measurements are tedious and time-consuming. • Automation reduces error caused by laser fluctuations over time.

  4. SPECIFIC TASKS • Establish communication between the hardware drivers and the computer • Drivers: • Energy meter (EPM 2000) • Motorized translation stage (MM 3000) • Synchronize data from the energy meter and translation stage • Program an algorithm to find the spotsize measurement using this data

  5. BACKGROUND: Finding beam profile • Knife-Edge technique to find beam profile: • Using a translational stage, move the knife-edge in slow increments until all the laser beam is blocked. ð ð ð A detector tracking the decreasing energy of the blocked beam will show the following profile:

  6. BACKGROUND: Finding numerical spotsize • Using the beam profile, find the positions along the x - axis at which the knife-edge eclipsed 90% and 10% of the total beam energy. • Plug these values into the following algorithm • b-1 = 0.552 (x10-x90) • spotsize = 2Ö2 b-1 • This algorithm holds true only for lasers with Gaussian profiles. These images, taken of the FEL’s beam profile, verify its Gaussian nature.

  7. MATERIALS • Energy Meter (EPM 2000) • Motion Controller (MM 3000) • Linear Actuator (Newport 850F) • PC with GPIB card & capabilities • LabVIEW 5.0.1

  8. EXPERIMENTAL SETUP

  9. RESULTS: Beam Profile

  10. RESULTS: Beam Divergence • Successive spotsize measurements were made to quantitatively measure the path of divergence from the focal point. • Numbers in the diagram below indicate the spotsize measurement in microns. • Sampling occurred in 1 mm increments along the path of divergence. • This type of measurement can be useful in finding the focal point of a beam for optical fiber coupling.

  11. ACCOMPLISHMENTS • Designed and developed an automated spotsize measurement system • Learned and mastered LabVIEW • Enhanced our understanding of Laser Optics • Successfully used FEL to test our system

  12. ACKNOWLEDGEMENTS • Dr E. Duco Jansen, VU professor • Hans Pratisto, VU post-doc • Stephen Uhlhorn, VU doctorate candidate • National Instruments technical support service

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