The laser emitting a 405 nm violet beam can be made of GaN (gallium nitride) semiconductor. This is close to ultraviolet light, close to the limit of human vision, and will produce bright blue fluorescence on many white surfaces (including white clothes, white paper, and projection screens), resulting in blue instead of purple spots. This is due to fluorescence. Brighteners are widely used in the manufacture of products designed to appear bright white. On ordinary non-fluorescent materials and fog or dust, the color appears as deep purple, which cannot be reproduced on displays and printed matter.
At the same time, some higher power (120 mW) 404-405 nm "violet" blue laser pointer are already on the market. They are not based on GaN, but DPSS frequency doubler technology using a 1 watt 808 nm GaAlAs infrared diode laser. The absorption capacity of green light is much stronger than that of red light, which is why the green light protective glasses are red and transparent. On the contrary, for penetrating green objects, red light is much inferior.
The biggest difference is that the red laser pointer emits coherent light, while the LED only emits colored light. So the LED illuminates everything like a candle, while the laser emits a beam of light. Semiconductor laser is a kind of laser similar to LED. A specific laser emits a specific wavelength. And there are so many lasers emitting visible and invisible spectra. Compared with LEDs, the emission spectrum is very narrow.
