Automated Spotsize Measurements

1
Automated Spotsize Measurements

• Calley Hardin
• Chris Baughman
• Advisor Duco Jansen

2
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

3
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

4
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

5
Current Design
6
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

7
Curve Fitting

• Spotsize can be determined by Beam Profile
• Current Design requires external use of MatLab
  and Origin
• Goal Incorporate sigmoidal curve fit into
  LabView

8
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
9
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

10
Progress

• Basic understanding of LabView
• Attended LabView Seminar
• upgrade to 5.1
• Attended FEL beam shifts in which current system
  was utilized
• Built FEL simulation apparatus which uses a
  Helium laser to eliminate FEL scheduling
  constraints
• Performed spotsize measurements and evaluated
  error

11
Experimental Results

• Took 10 spotsize measurements of HeNe laser with
  simulation set-up
• Average spotsize1.035 cm
• Standard Deviation0.067
• 7 Error!!!
• Sources of Error
• Size of detector relative to spotsize
• unstable mounting components