Dynamic balance of heat and mass in high power density laser welding.

An experimental system to observe the inner phenomenon of keyhole and molten pool through glass plate by high speed camera and spectrometer in high power density laser welding was set up. Two circular flows in the molten pool were observed by high speed camera, which transferred the mass from the front to the rear of the keyhole to keep the mass balance. Temperature distribution in the molten pool was firstly detected by spectrometer, which indicated that the circular flows acted as the cooling system to take heat away from the keyhole. The porosity formation process was also observed and the mechanism was discussed.

Development of a high-power blue laser (445 nm) for material processing.

A blue diode laser has a higher absorption rate than a traditional laser, while the maximum power is limited. We report the structure and laser beam profile of a 250 W high-power blue laser (445 nm) for material processing. The absorption rate of the blue laser system for the steel was 2.75 times that of a single-mode fiber laser system (1070 nm). The characteristics of the steel after laser irradiation were determined, validating the potential of this high-power blue laser for material processing, such as heat treatment and cladding. The cost of the developed laser system was lower than that of the existing one. To the best of our knowledge, this is the first blue laser with a power as high as 250 W.

Non-destructive real-time monitoring of underground root development with distributed fiber optic sensing.

Crop genetic engineering for better root systems can offer practical solutions for food security and carbon sequestration; however, soil layers prevent the direct visualization of plant roots, thus posing a challenge to effective phenotyping. Here, we demonstrate an original device with a distributed fiber-optic sensor for fully automated, real-time monitoring of underground root development. We show that spatially encoding an optical fiber with a flexible and durable polymer film in a spiral pattern can significantly enhance sensor detection. After signal processing, the resulting device can detect the penetration of a submillimeter-diameter object in the soil, indicating more than a magnitude higher spatiotemporal resolution than previously reported with underground monitoring techniques. Additionally, we also developed computational models to visualize the roots of tuber crops and monocotyledons and then applied them to radish and rice to compare the results with those of X-ray computed tomography. The device's groundbreaking sensitivity and spatiotemporal resolution enable seamless and laborless phenotyping of root systems that are otherwise invisible underground.