ABSTRACT
I will report on the likelihood, methods for making and some applications of short wavelength x-ray lasers. The recipe for making robust <4.4 nm x-ray lasers is not clear. Currently, n=3p to n=3s, Ne-like and n=4d to n=4p, Ni-like collisional excitation lasers are capable of reaching down to 3.5 nm, with x-ray laser output power dropping precipitously at the shorter wavelengths and only when using large pump lasers operating at high irradiance. In any case, scaling below ∼2 nm is simply not possible using these systems. Scaling to shorter wavelengths using other collisionally pumped transitions (e.g, n=4 to 3 in nickel-like ions) may be possible but no demonstrations have been observed. Pumping H-like or He-like recombination schemes is also a possibility but no conclusive evidence exists for short wavelength lasing when using 3-body recombination as the pump modality. This brings us to the possibility of using ultrashort pulse lasers for creating the inversion using either multiphoton ionization followed by recombination or by fast x-ray photoionization. In my opinion, the best route to short wavelengths is to use < 50 fsec, 100 TW pump lasers which efficiently convert to broad-band x-rays. Successful implementation of the short pulse x-ray pumping should lead to < 1 nm or even shorter wavelength laser schemes. I will elaborate on the status of efforts at achieving these pump conditions and what x-ray laser schemes can be pumped. Concerning applications, the short wavelength xray laser continues to be the “holy grail” of a source. Biological imaging will benefit greatly from <100 fsec duration x-ray laser at wavelengths from 2.4 to 4.4 nm. Even shorter wavelengths could be useful for semiconductor device imaging, studies of non-linear x-ray phenomena, as well as applications to solid state physics and atomic physics.
