Hybrid Optical Sensor for Combined Thermal and Dimensional Monitoring in Laser Processing

Optical measurements enable non-contact and high-speed monitoring of physical processes, offering a noninvasive and versatile approach across a wide range of fields, from scientific research to industrial applications. This work presents an optical sensor capable of simultaneously measuring both the distance and thermal emission from surfaces, based on a simple laser diode (LD) probe. The principle of operation integrates triangulation with pyrometry in a single device, leveraging the monitor photodiode (PD) embedded in the probe module. By alternating the probe laser emission, the system can rapidly switch between dimensional and thermal measurements, resulting in combined data acquisition. The proposed method is compact, easy to integrate, and cost-effective. The hybrid sensor is demonstrated in a laser processing setup, where a metallic target is heated and melted by a high-power laser beam. Its inline operation allows for real-time dynamic measurements of melt pool distance and radiance, in a coaxial and self-aligning configuration. This innovative approach can be applied to various fields, such as remote environmental sensing and closed-loop control systems for stabilizing high-temperature processes, including laser welding and additive manufacturing.