Laser spot measurement using simple devices

We have designed and tested an automated simple setup for measuring the profile and spot size of a Gaussian laser beam, which exhibits a similar performance to ready-made optical devices, using three light sensors. We use a light dependent resistor as a novel instrument in this approach with good accuracy. We provide the setup in detail in order to be reproduced with the current technology at a standard laboratory. Two profiling techniques were implemented: the imaging technique for the CMOS 2D array (webcam) and scanning knife-edge-like technique using a single photodiode and a light dependent resistor. We apply up-to-date devices, such as a Raspberry Pi, for automation. The methods and sensors were compared to determine their accuracy using lasers of two different wavelengths and technologies. We verify that it is possible to use a webcam to determine the profile of a laser with 1% uncertainty on the beam waist, 1.5% error on the waistline position, and less than 3% error in determining the minimum spot radius. We show that it is possible to use a light dependent resistor to estimate the laser spot size with an 11% error. The photodiode measurement is the most stable since it is not affected by the change in laser intensity. © 2021 Author(s).The authors gratefully acknowledge the Dirección de Gestión de la Investigación (DGI-PUCP) for funding under Grant No. DGI-2019-3-0044. C.S. acknowledges support from the Peruvian National Council for Science, Technology and Technological Innovation scholarship under Grant No. 236-2015-FONDECyT. We would also wish to thank R. Sanchez from the Applied Optics Group and the Quantum Optics Group for letting us use their lasers and equipment, as well as Y. Coello for the photodiode. We also thank J. A. Guerra for useful discussions and suggestions