  VUV radiation around 159 nm is obtained toward direct excitation of a single
trapped $^{115}$In$^{+}$ ion. An efficient fluoride-based VUV output-coupler is
employed for intracavity high-harmonic generation of a Ti:S oscillator. Using
this coupler, where we measured its reflectance to be about 90%, an average
power reaching $6.4\,\mu$W is coupled out from a modest fundamental power of
650 mW. When a single comb component out of $1.9\times10^{5}$ teeth is resonant
to the atomic transition, hundreds of fluorescence photons per second will be
detectable under a realistic condition.
