Phase Matched Generation of Coherent Soft-X-rays
Nonlinear optical techniques for frequency conversion have played a pivotal role in the development of efficient coherent light sources. Most of these techniques rely on phase matching to obtain high conversion efficiency. Typically, by using birefringence, one can equalize the phase velocity of the pump light with the desired signal light, resulting in constructive interference of the signal produced through a nonlinear interaction. This allows the signal to build up rapidly. However, most techniques rely on crystals. This significantly limits extending nonlinear optics to shorter wavelengths, since no solid material is transparent to wavelengths below 110 nm. Furthermore, dispersion in solid materials makes it difficult to generate extremely short pulses at short wavelengths.
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