Appearance
The violet 405 nm laser (whether constructed from GaN or frequency-doubled GaAs laser diodes) is not in fact blue, but appears to the eye as violet, a color for which a human eye has a very limited sensitivity. When pointed at many white objects (such as white paper or white clothes which have been washed in certain washing powders) the visual appearance of the laser dot changes from violet to blue, due actually to fluorescence from brightening dyes.
For display applications which must appear "true blue", a wavelength of 445–450 nm is required. With advances in production, and commercial sales of low-cost laser projectors, 445 nm InGaN laser diodes have dropped in price.
A last challenge in projection laser diodes is related to the construction of a "true green" InGaN laser (around 530 nm). Many companies have demonstrated devices working at only slightly shorter wavelengths: 480–500 nm.
Read more about this topic: Blue Laser
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—Laurence Sterne (1713–1768)