GaN laser self-mixing velocimeter for measuring slow flows.

The self-mixing (SM) laser sensing technique allows for a simple, self-aligned, and robust system for measuring velocity. Low-cost blue emitting GaN laser diodes have recently become available owing to the high volume requirements for Blu-ray Disc devices such as high-definition video players and gaming consoles. These GaN lasers have a significantly shorter wavelength (around 405 nm) compared with other semiconductor lasers (generally around 800 nm for SM sensors). Therefore, if used in SM flow sensors, they allow measuring of flow rates that would otherwise be too slow to measure. In this Letter we report what we believe to be the world's first SM flow measurement system based on a blue emitting semiconductor laser, demonstrating the ability to measure flow rates down to 26 microm/s.