drakebake's comments

Good question, nobody is sure yet how to do it. Indeed any pulsed laser will result in a broad spectrum (spectrum = inverse of laser pulse time e.g. 1 ns pulse is 1 GHz spectral width). Using frequency combs is a way around this, which are pulsed but the comb teeth are still narrow (approximately 100 Hz). To really go sub Hz one needs to build a continuous wave laser and mostly people are looking towards nonlinear crystals (poled materials, KBBF etc.) to create these using second harmonic generation

It doesn't produce an electron, it just donates its energy to one of the electrons bound to it. This energy is then used to free the electron from its bounds and any extra energy is used to give the electron some speed. Effectively the same energy is consumed when emitting the photon or releasing the electron. If the thorium is sufficiently ionized (the more electrons you strip from an atom, the harder it gets to strip the next one), the binding energy of the electrons is so high that the energy from the nuclear excited state is not enough to free the electron and the process is completely blocked from happening.

One has to first imagine that a photon isn't as immutable as one sometimes believes. Effectively by putting lots of photons together in a medium (the medium makes sure momentum and energy is conserved) one can create all kinds of colors of light. We can already make "lasers" up to x-rays in synchrotrons by using the right means. The definition of laser becomes a bit shady though as the light is coherent and has a small divergence angle, but is not produced through stimulated emission.

Hey, I'm one of the authors on the paper and see that people are curious about things. I'm happy to answer any questions, cool to find this here!