Spot size is an important parameter of the laser, which not only represents the resolution of laser, but is also involved in the calculation of other parameters. Nowadays, CCD imaging systems, scanning imaging systems, and other sensors are used to measure the laser spot size. But they are all lacking flexibility when measuring the spot size in different locations, not to mention their high cost. In this study, a new spot size measurement device based on laser back-injection interferometry was presented. The photodiode integrated with the laser diode was used to collect the feedback laser, then the laser spot size was calculated by the feedback current. A commercial CCD imaging system was used to provide the laser spot size as a reference. Results show that our spot size measurement device could measure the spot size (Full Width Half Maximum) of 5 laser diode modules both in the x (Gaussian-like profile) and y (top-hat-like profile) direction through scanning-slit. Though there are variations between the scanning-slit results and spot sizes from the CCD imaging system due to the diffuse and specular reflection, the accuracy of the spot size measurement device ranges from 96.07 % to 99.46 %, which proves the reliability of our device. It is believed that our device could provide an alternate method for laser spot size measurement, which is cost-effective, easy to operate, and accurate.
Laser is widely used in industry, biomedical and other kinds of fields. Beam size is the most important parameter among the laser variables. Typical state-of-the-art profiling techniques employ either a scanning-based or camera-based system, using photodiodes or image sensors as the signal receiver. Despite their profiling capabilities, these systems do not tend to be budget-friendly and easy to operate. In this paper, a novel cost-effective beam profiling prototype based on self-mixing interference was developed to measure the Full Width Half Maximum (FWHM) of a range of laser diodes by the knifeedge approach. The difference between our prototype and other systems is that the photodiode is placed behind the laser source, and beam size is calculated by analyzing the feedback signal. A commercial camera beam profiler was used to benchmark our prototype. Results show that though there is a variation of 45.29% between the measured beam size and the integrated beam size in the x directions due to diffuse and specular reflection, our USD 200 prototype has a high accuracy on the prediction of laser beam sizes. Our prototype could provide accurate predicted beam size for Gaussianalike beam. This is the very first study to explore the application of self-mixing interference in laser beam profiling. It is believed that our proposed approach has contributed to the on-going development of laser beam profiling methodology.
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