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AUTOMATED SPOTSIZE MEASUREMENT BME 273 Senior Design Project April 7, 1999 Brian N. Lenahan Melisa L. Moore Advisor: Dr. E. Duco Jansen
OBJECTIVES u. To measure a laser’s spotsize u with an accuracy of ± 10 mm u for a spotsize range of 100 mm - 25 mm u. To develop a computer-controlled environment capable of taking fully automated, expedient spotsize measurements u. To develop a means of saving these beam profiles & spotsize measurements for later reference
MOTIVATION u. Laser fluence (J/mm 2) is dependent on the area of the laser beam. u. Photons focused onto a smaller area have more destructive power. u. Manual measurements are tedious and timeconsuming. u. Automation reduces error caused by laser fluctuations over time.
SPECIFIC TASKS u. Establish communication between the hardware drivers and the computer u Drivers: l l Energy meter (EPM 2000) Motorized translation stage (MM 3000) u. Synchronize data from the energy meter and translation stage u. Program an algorithm to find the spotsize measurement using this data
BACKGROUND: Finding beam profile u Knife-Edge technique to find beam profile: l 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:
BACKGROUND: Finding numerical spotsize u 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. u Plug these values into the following algorithm -1 l b = 0. 552 (x 10 -x 90) -1 l spotsize = 2Ö 2 b u This algorithm holds true only for lasers with Gaussian profiles. These images, taken of the FEL’s beam profile, verify its Gaussian nature.
MATERIALS u. Energy Meter (EPM 2000) u. Motion Controller (MM 3000) u. Linear Actuator (Newport 850 F) u. PC with GPIB card & capabilities u. Lab. VIEW 5. 0. 1
RESULTS: Beam Profile
RESULTS: Beam Divergence u Successive spotsize measurements were made to quantitatively measure the path of divergence from the focal point. u u Numbers in the diagram below indicate the spotsize measurement in microns. Sampling occurred in 1 mm increments along the path of divergence. u This type of measurement can be useful in finding the focal point of a beam for optical fiber coupling.
ACCOMPLISHMENTS u Designed and developed an automated spotsize measurement system u. Learned and mastered Lab. VIEW u. Enhanced our understanding of Laser Optics u. Successfully used FEL to test our system
ACKNOWLEDGEMENTS u. Dr E. Duco Jansen, VU professor u. Hans Pratisto, VU post-doc u. Stephen Uhlhorn, VU doctorate candidate u. National Instruments technical support service