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

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

MOTIVATION uLaser fluence (J/mm 2 ) is dependent on the area of the laser beam. uPhotons focused onto a smaller area have more destructive power. uManual measurements are tedious and time- consuming. uAutomation reduces error caused by laser fluctuations over time.

SPECIFIC TASKS uEstablish communication between the hardware drivers and the computer u Drivers: l Energy meter (EPM 2000) l Motorized translation stage (MM 3000) uSynchronize data from the energy meter and translation stage uProgram an algorithm to find the spotsize measurement using this data

BACKGROUND: Finding beam profile uKnife-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. A detector tracking the decreasing energy of the blocked beam will show the following profile : 

BACKGROUND: Finding numerical spotsize uUsing 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  -1 = (x 10 -x 90 ) spotsize = 2  -1 uThis algorithm holds true only for lasers with Gaussian profiles. These images, taken of the FEL’s beam profile, verify its Gaussian nature.

MATERIALS uEnergy Meter (EPM 2000) uMotion Controller (MM 3000) uLinear Actuator (Newport 850F) uPC with GPIB card & capabilities uLabVIEW 5.0.1

EXPERIMENTAL SETUP

RESULTS: Beam Profile

RESULTS: Beam Divergence uSuccessive spotsize measurements were made to quantitatively measure the path of divergence from the focal point. u Numbers in the diagram below indicate the spotsize measurement in microns. u Sampling occurred in 1 mm increments along the path of divergence. uThis 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 uLearned and mastered LabVIEW uEnhanced our understanding of Laser Optics uSuccessfully used FEL to test our system

ACKNOWLEDGEMENTS uDr E. Duco Jansen, VU professor uHans Pratisto, VU post-doc uStephen Uhlhorn, VU doctorate candidate uNational Instruments technical support service