Advanced Gouy phase high harmonics interferometer

Abstract

We describe an extreme ultraviolet (XUV) interferometric technique that can resolve ∼100 zeptoseconds (10 −21 s) delay between high harmonic emissions from two successive sources separated spatially along the laser propagation in a single Gaussian beam focus. Several improvements on our earlier work have been implemented in the advanced interferometer. In this paper, we report on the design, characterization and optimization of the advanced Gouy phase interferometer. Temporal coherence for both atomic argon and molecular hydrogen gases has been observed for several harmonic orders. It has been shown that phase shift of XUV pulses mainly originates from the emission time delay due to the Gouy phase in the laser focus and the observed interference is independent of the generating medium. This interferometer can be a useful tool for measuring the relative phase shift between any two gas species and for studying ultrafast dynamics of their electronic and nuclear motion.

Attosecond delays of high harmonic emissions from isotopes of molecular hydrogen measured by Gouy phase XUV interferometer

“…Synchronization of microvalve opening delay with the laser pulse reduces the background pressure in the HHG generation and detection chambers, which facilitates better signal to noise ratio (for details, see [10]). The switching of gases in the jets allows about the instrumentation can be found in [10].…”

“…The two mutually coherent XUV pulses are generated by exploiting the inherent properties (Gouy phase) of a single Gaussian focused laser beam. Its unprecedented resolution of ∼ 300 µrad (∼ 100 zeptoseconds) is a result of any instability in the distance between the two arms (the gas jets in this case) of the interferometer is determined relative to the Rayleigh length, z R of the fundamental laser beam as opposed to the XUV wavelength in a conventional optical interferometer [10].…”

“…However, measurement of the harmonic phase is a daunting task. Here we present a precise measurement of HHG phase difference between two isotopes of molecular hydrogen using the advanced extreme-ultraviolet (XUV) Gouy phase interferometer [10]. The measured phase difference is about 200 mrad, corresponding to ∼ 3 attoseconds…”

“…Building an interferometer in the XUV region is quite challenging for two reasons: firstly, it is challenging to control the delay of the XUV pulses precisely between the two arms with sub-cycle precision; secondly, the highly reflective XUV optics is yet to be developed. Our passively stabilized Gouy phase interferometer [10,21], on the other hand, is an all-optical direct XUV interferometric technique. It does not require calibration the parent ion at a certain recollision time.…”

High complexity femtosecond pulse duplicator

“…Experimental schemes providing two XUV pulses of adjustable delays are also central in ultrafast spectroscopy, may it be attosecond-pump/attosecond-probe [8] or attosecond interferometry experiments [15]. In the absence of beam splitters in the XUV spectral range, several experimental arrangements were developed [16][17][18][19][20][21][22][23], some of which consist in splitting a mid-infrared laser pulse in two replicas used to generate attosecond pulses from two spatially separated sources through High order Harmonic Generation (HHG) in gas [24,25] . In this case, the delay between the two XUV pulses is directly controlled by the delay between the two replicas of the HHG driver field.…”