Chirped pulse amplification (CPA) has enabled the creation of ultrafast lasers with high pulse energies and very short pulse lengths. In CPA, a short seed pulse (which, as a result of the pulse's brevity, has a wide wavelength band) is dispersed by diffraction Illuminated in various ways, a three-level phase grating produces various aerial images: normal incidence (a), symmetric oblique incidence (b), and multipole illuminations (c), which is the combination of (a) and (b). The three-level profile of the phase mask is shown in blue (top); note that the period of the mask is twice that of the aerial image.
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