Intracavity Frequency Doubling Deep-Ultraviolet Ho3+: ZBLAN Fiber Laser with Wavelength Tuning from 269.5 to 275.4 nm

Laser sources emitting in the deep ultraviolet (DUV) spectral region are required by numerous industrial and scientific applications owing to their characteristics of higher photon energy, more strongly scattering than other wavelengths and better absorption in most materials. DUV lasers can be produced by several techniques to date, mainly including free-electron lasers, excimer lasers, and high-order harmonic conversion such as frequency-converted fiber lasers and frequency-converted solid-state lasers, which suffer from a bulky structure and a high cost. For the first time, we successfully demonstrate a compact tunable green-light intracavity frequency-doubled DUV laser. Pumped by the 450 nm laser diode, with the 10 cm length Ho
³⁺
: ZBLAN fiber as gain medium, the maximum power at 272.6 nm is 1.36 mW under the green power of 293 mW. A visible reflective diffraction grating is used to realize the laser tuning output, which acts as a resonator along with a coated plane mirror, and a 7-mm BBO crystal is used for frequency conversion. Stable DUV lasers are obtained at $269.5 \sim 275.4 \mathrm{nm}$ and the minimum linewidth is <0.025 nm with a maximum visible - DUV efficiency of 5.3 %. To our knowledge, it is the first demonstration of tunable DUV laser below 280 nm by visible light fiber laser direct frequency doubling technology.