Automated Spotsize Measurements Calley Hardin Chris Baughman Advisor: Duco Jansen

Objectives Measure the FEL laser spotsize within constraint values and find focal point of FEL Improve current design Automate measurements with computer using LabView instrumentation software Perform accurate data analysis within LabView and eliminate outside software Addition of the second dimension to measurements Incorporate current design and new design to accurately output focal point value graphically

Constraints Spotsize is accurate within 10 microns without the use of software outside of LabView Suitable for 0.3-.25mm diameter beam Fully automated system which outputs graphical representation of spotsize so focal point can be determined

Why measure spotsize? Quantify energy delivered during tissue ablation Maximize energy delivered per unit area Minimize damage to surrounding tissue Better understanding of beam intensity profile and beam transport

Current Design:

Alternate Methods: Manually: visual approximation with ruler human error inconsistent CCD camera: image the beam, then measure spotsize camera usual effective at 2-4 or 8-10 microns extremely expensive, $20,000 vs. $5,000

Curve Fitting: Spotsize can be determined by Beam Profile ð Knife-edge technique Spotsize can be determined by Beam Profile Old Design required external use of MatLab and Origin Goal: Incorporate sigmoidal curve fit into LabView 90%and 10% Values????

Curve Fitting Algorithm Fit the data to the standard sigmoidal equation: y=a/(b+e-cx) Made use of the Levenberg-Marquardt method to determine a nonlinear set of coefficients that minimize a chi-square quantity Accurately approximates the curve only if a reasonable guess of the constants a, b, and c is made

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. As shown by previous research the FEL does have a Gaussian profile like shown to the right

Implementation of Curve-Fit

The 2nd Dimension Current Design measures spotsize in one dimension only Goal: To automate the determination of the focal point of the laser by incorporating the second dimension Specific Task: Program MM3000 and add necessary components to current LabView program

Progress In depth understanding of LabView Upgrade to LabView 5.1 Built FEL simulation apparatus which uses a Helium laser to eliminate FEL scheduling constraints Performed spotsize measurements and evaluated error Completed SubVI’s for new program Currently debugging individual programs

Final Steps: Incorporate both SubVI’s Run tests with complete program error analysis Customize program to user’s preferences “smart program” change spotsize estimation choices