Absolute determination of the wavelength and spectrum of an extreme-ultraviolet beam by a Young's double-slit measurement

Includes bibliographical references (page 709).The interference pattern produced by irradiation of a pair of pinholes with a beam contains information on both the spatial and the temporal coherence properties of the beam, as well as its power spectrum. We demonstrate experimentally for what is believed to be the first time that the spectrum of an extreme-ultraviolet (EUV) beam can be obtained from a measurement of the interference pattern produced by a pinhole pair. This approach offers a convenient method of making absolute wavelength and relative spectral intensity calibrations in the EUV

Quasi-phase-matched generation of coherent extreme-ultraviolet light

Includes bibliographical references (page 54).High-harmonic generation is a well-known method of producing coherent extreme-ultraviolet (EUV) light, with photon energies up to about 0.5 keV. This is achieved by focusing a femtosecond laser into a gas, and high harmonics of the fundamental laser frequency are radiated in the forward direction. However, although this process can generate high-energy photons, efficient high-harmonic generation has been demonstrated only for photon energies of the order 50-100 eV. Ionization of the gas prevents the laser and the EUV light from propagating at the same speed, which severely limits the conversion efficiency. Here we report a technique to overcome this problem, and demonstrate quasi-phase-matched frequency conversion of laser light into EUV. Using a modulated hollow-core waveguide to periodically vary the intensity of the laser light driving the conversion, we efficiently generate EUV light even in the presence of substantial ionization. The use of a modulated fibre shifts the energy spectrum of the high-harmonic light to significantly higher photon energies than would otherwise be possible. We expect that this technique could form the basis of coherent EUV sources for advanced lithography and high-resolution imaging applications. In future work, it might also be possible to generate isolated attosecond pulses