Extreme Ultraviolet Fourier-Transform Spectroscopy with High Order Harmonics

We demonstrate a new scheme for extreme ultraviolet (xuv) Fourier-transform spectroscopy based on the generation of two phase-locked high-harmonic beams. It allows us to measure for the first time interferograms at wavelengths as short as 90 nm, and open the perspective of performing high-resolution Fourier-transform absorption spectroscopy in the xuv. Our measurements also demonstrate that a precise control of the relative phase of harmonic pulses can be obtained with an accuracy on an attosecond time scale, of importance for future xuv pump-xuv probe attosecond spectroscopy.

Figure 1

Experimental setup for the Fourier-transform spectroscopy of high harmonics.

Figure 2

(a) Experimental trace obtained for the 9th harmonic generated by two collinear laser pulses ($d=0$). (b) Fourier transform of the trace.

Figure 3

Experimental traces of the 9th harmonic (left panels) and corresponding zooms of the first two laser periods (right panels), for different values of the laser foci separation $d$: (a), (b) $d\approx 90\mu \mathrm{m}$, (c), (d) $d\approx 135\mu \mathrm{m}$, (e), (f) $d\approx 300\mu \mathrm{m}$.

Figure 4

(a), (c), (e) Fourier transforms of the experimental traces presented in Fig. 3. (b), (d), (f) Fourier transforms of the corresponding simulated traces. The inset shows enlarged H9 spectra of (e) (white circles) and (f) (black dots).