AUTOMATED SPOTSIZE MEASUREMENT

Brian N. LenahanMelisa L. MooreAdvisor: Dr. E. Duco Jansen

BME 273 Senior Design ProjectBME 273 Senior Design ProjectApril 7, 1999

OBJECTIVES

To measure a laser’s spotsize with an accuracy of ±10m for a spotsize range of 100m - 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

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.

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

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.

A detector tracking the decreasing energy of the blocked beam will show the following

profile:

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 -1 = 0.552 (x10-x90) spotsize = 2-1

This algorithm holds true only for lasers with Gaussian profiles.

These images, taken of the FEL’s beam profile, verify its Gaussian nature.

MATERIALS

Energy Meter (EPM 2000)

Motion Controller (MM 3000)

Linear Actuator (Newport 850F)

PC with GPIB card & capabilities

LabVIEW 5.0.1

EXPERIMENTAL SETUP

RESULTS: Beam Profile

Beam Profile of a 1.724 mm Spotsize

0.00E+00

1.00E-03

2.00E-03

3.00E-03

4.00E-03

5.00E-03

6.00E-03

0

0.17

0.33 0.5

0.67

0.83 1

1.17

1.34 1.5

1.67

1.84 2

2.17

2.34 2.5

2.67

2.84 3

3.17

3.34 3.5

3.67

3.84

4.01

4.17

4.34

4.51

4.67

4.84

5.01

5.17

5.34

Distance (mm)

Ener

gy (J

oule

s)

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.

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

ACKNOWLEDGEMENTS

Dr E. Duco Jansen, VU professor

Hans Pratisto, VU post-doc

Stephen Uhlhorn, VU doctorate candidate

National Instruments technical support service