A Method For Measuring The Width Of A Focused Laser Beam In Reflection

We present a simple method to measure the width of a focused laser beam, where we define the width as the radius of the beam at which the intensity is 1/e(2) of its on-axis value. Our method is based on measuring the power of light reflected off a metallized microstructure patterned on a oxidized silicon substrate that is placed on a tri-dimensional positioner. As the boundary between the microstructure and the substrate is scanned across the beam, changes in reflected power provide a quantitative measurement of the width of the beam. Our method is a useful alternative to the knife edge technique if optical measurements in transmission are not possible.