The world’s first x-ray laser is not only a true laser, but it’s an extremely good one, according to measurements reported 30 September in Physical Review Letters. Researchers studying the Linac Coherent Light Source (LCLS) characterized the coherence of the laser–the degree to which the light waves are synchronized–and found that it produces the most coherent x-ray radiation ever measured.
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The coherence length is 150 nm? That strikes me as incredibly crappy for a laser. The article doesn’t say what the center wavelength is, so I’ll assume it’s something like an Angstrom, which puts the linewidth at roughly 1 part in 10^3.
I suppose that must be super-awesome for an x-ray laser or they wouldn’t write the article, but a linewidth of 1 part in 10^3 strikes me as in the running for one of the LEAST coherent lasers ever made. Heck, even your average q-switched YAG probably has a better fractional linewidth than that.
You’re thinking CW land but this is attosecond pulse land, where a the shorter the coherence length the better.