Determination of HHG spectrum by measuring the mutual coherence

Abstract

The interference pattern resulting from a double slit (or pinhole pair) is commonly used to measure the spatial coherence properties of a light source in the visible1, as well as in the extreme ultraviolet (EUV)2,3 regions of the spectrum. This interference pattern results from the path difference of the incident light field from each slit to the observation point. In a standard spatial coherence measurement, the incident field is assumed to be quasi-monochromatic, so that temporal coherence effects are isolated from a measurement of spatial coherence. However, under conditions where a broad bandwidth source illuminates a pinhole pair, the interference pattern will contain both temporal and spatial coherence information of the source, as well as the power spectrum. In this talk we show that the spectrum of a beam can be extracted from a measurement of a double-pinhole interference pattern and the geometry of the set-up4. Such a spectral measurement is unique in that it determines the absolute wavelength and relative spectral intensity of the source, which is a great advantage in the EUV region where calibration is very difficult.