Patent ID: 7830928

Claim:
The method of generating coherent x-ray emissions within a desired spectral region comprising the steps of: (a) providing a hollow waveguide filled with a gas, the waveguide having a first end and a second end; (b) focusing a forward-going femtosecond pump pulse into one end of the waveguide to cause high-harmonic generation (HHG) upconversion of the light to shorter wavelengths within the gas; (c) focusing a counterpropagating pulse train into the other end of the waveguide; wherein the counterpropagating pulse train modulates the optical phase of the HHG signal within the waveguide; and (d) adjusting the timing and duration of the pulses of the counterpropagating pulse train to achieve effective quasi-phase matching (QPM) within the gas by interrupting the HHG process in areas where the HHG signal buildup is undergoing destructive interference, wherein effective QPM is defined as increased conversion into the desired spectral region compared to the maximum attained where the same total energy is in an optimized forward-going pulse.