Measurement of the intensity profile of a Gaussian baser beam near its focus using an optical fiber

We have designed a new pinhole-scan system to measure the Gaussian intensity distribution of a He-Ne laser beam that passes through a series of lenses. Our detection device uses a single-mode optical fiber as the so-called pinhole. One side of the optical fiber is fixed on the top of a motorized translation stage to capture the laser light, and the other side is connected to an optical power meter. A digital oscilloscope is used to observe the detected light intensity. When the translation stage as well as the fiber tip is moved across the laser beam, the oscilloscope displays the scanned trace of the laser beam intensity. The evolution of the intensity distribution of a focused laser beam is measured and then fitted to distributions predicted from Gaussian optics. The measured beam waist size is compared with the result of Gaussian-beam q-parameter analysis. Using this simple system we can easily observe the transverse intensity profile of a Gaussian laser beam in the (1 + 1)-dimensional plane in the vicinity of the focus. (c) 2007 American Association of Physics Teachers.