Spatially resolved fourier transform interferometry in the extreme ultraviolet

Through generation of coherent extreme ultraviolet (XUV) radiation, high-harmonic generation (HHG) has opened up a wealth of possibilities for table-top research, ranging from attosecond dynamics to high resolution coherent imaging. The ability to perform interferometry with HHG sources would enable powerful coherent optical techniques such as Fourier transform spectroscopy in the XUV spectral range. However, interferometry and Fourier transform spectroscopy (FTS) remain challenging, due to the need for a pulse pair with a controllable, yet stable, attosecond delay. To overcome this challenge we have developed a method to produce such ultrastable XUV pulse pairs, using a birefringence-based common path interferometer. This interferometer is suitable for high-intensity laser pulses, which enables the generation of fully coherent XUV pulse pairs through HHG. The resulting pulse pairs have sub-attosecond timing variation, a tunable time delay and a clean Gaussian spatial mode profile, as shown in Figure 1 [1].