Realization of a mW-level 10.7-eV (λ=115.6 nm) laser by cascaded third harmonic generation of a Yb:fiber CPA laser at 1-MHz

We demonstrate a 10.7-eV (lambda = 115.6 mn) laser with mW levels of average power and a 1-MHz repetition rate which was driven by the third harmonic radiation (THG), at 347 nm, of an Yb:fiber chirped pulse amplifier (CPA) laser. The 347 nm ultraviolet radiation was obtained by frequency conversion of the high power output of a 1-MHz Yb:fiber CPA, using beta barium borate (BBO) nonlinear crystals. The frequency converted output was focused down into a gas cell filled with a mixture of Ar and Xe, and was subjected to a second THG frequency conversion. The generated 10.7-eV laser was separated from the fundamental beam using a LiF prism and no further separation from other harmonic waves was required. The highest measured output power was similar to 80 mu W. which corresponded to an average power of similar to 1.25 mW inside the gas cell when the transmission coefficients of the LiF optics were taken into account. The corresponding conversion efficiency from 347 nm down to 115.6 nm was similar to 2.5 x 10(-4). (C) 2017 Optical Society of America