Validation of a Near-infrared Laser Beam Profiler at 2 µm Using a Rotating Detector

Optical beam profiling is essential for characterizing beam quality and diffraction for the optimization of laser-based systems. However, in wavelength ranges such as near-infrared, commercially available beam profilers are often costly, limiting their accessibility. There is therefore a clear need for low-cost and flexible beam profiling approaches that can operate across a broad wavelength range while maintaining acceptable accuracy and robustness. We present a beam-profiling system based on a rotating photodiode that reconstructs the 1D beam intensity profile via angular scanning. A single photodiode on a motorized stage rotates around the beam's axis with an angular resolution less than 0.1 degrees, corresponding to a spatial resolution of 0.1mm, while a microcontroller with a fast-sampling analog-to-digital converter (ADC) performs real-time data acquisition of the detected signal. We validated the system using a 2 µm laser source. At a propagation distance of 140 mm, the rotating diode profiler measured a beam width of 7.3 mm, compared to 6.5 mm from a commercial Thorlabs profiler. Given the photodiode width of 0.3mm, the step resolution, variations in the fit results from beam asymmetries, and variations in the beam itself, the difference is within the expected tolerances. Reconstructed profiles showed good agreement with a Gaussian distribution, and the measured beam diameters were highly repeatable. Our rotating diode profiler is a cost-effective and scalable alternative to scanning slit and camera-based systems, especially for near-infrared wavelength regimes, making it suitable for research, development and instructional applications. Commercial infrared beam profilers cost 6,000 USD and up, while our rotating photodiode system can be implemented for under 400 USD—representing a greater than 10-fold cost reduction.