The exact wavelength of 300 nm laser is not very common for lasers. There are several approaches to get laser radiation at 300 nm. Here are some examples of UV lasers:
Excimer lasers. Typically, combination of noble gas (Argon, Krypton, Xenon) and reactive gas (Fluorine, Chlorine) is used as gain medium. Emitted wavelengths lay in UV and visible spectral ranges roughly from 126 nm to 531 nm (for different gas mixtures). The closest wavelength to 300 nm provide XeCl laser (308 nm) and XeBr laser (282 nm). Excimer lasers are used for high resolution photolithography and for medical applications, e.g. eye surgery.
