Nonlinear optics in the extreme ultraviolet

Abstract

Nonlinear responses to an optical field are universal in nature but have been difficult to observe in the extreme ultraviolet (XUV) and soft X-ray regions owing to a lack of coherent intense light sources. High harmonic generation is a well-known nonlinear optical phenomenon and is now drawing much attention in attosecond pulse generation. For the application of high harmonics to nonlinear optics in the XUV and soft X-ray regime, optical pulses should have both large pulse energy and short pulse duration to achieve a high optical electric field. Here we show the generation of intense isolated pulses from a single harmonic (photon energy 27.9 eV) by using a sub-10-femtosecond blue laser pulse, producing a large dipole moment at the relatively low (ninth) harmonic order nonadiabatically. The XUV pulses with pulse durations of 950 attoseconds and 1.3 femtoseconds were characterized by an autocorrelation technique, based on two-photon above-threshold ionization of helium atoms. Because of the small cross-section for above-threshold ionization, such an autocorrelation measurement of XUV pulses with photon energy larger than the ionization energy of helium has not hitherto been demonstrated. The technique can be extended to the characterization of higher harmonics at shorter wavelengths.

Impact of multichannel and multipole effects on the Cooper minimum in the high-order-harmonic spectrum of argon

“…High-harmonic generation (HHG) is the key physical process underlying the generation of single attosecond pulses [1][2][3] and attosecond pulse trains [4][5][6], which are at the heart of attosecond science [7,8]. In recent years, the rapid progress in HHG has led to applications ranging from atomic systems [9][10][11] over molecular systems [12,13] to solid-state systems [14].…”

MAKING OPTICAL WAVES, TRACING ELECTRONS IN REAL-TIME: THE ONSET OF THE ATTOSECOND REALM (Invited Review)

“…Conventional femtosecond pulse metrology could, in principle, be exploited to characterize the temporal profile of this emission in schemes such as higher order autocorrelations [37,38]. However, the rather moderate photon yields of these sources at the soft x-ray regime, along with the limited nonlinear response of matter in these extreme spectral ranges has so far led to diminishing returns.…”

Wave-packet propagation based calculation of above-threshold ionization in the x-ray regime

“…This process has been studied extensively by now, especially in the range of infrared to visible and XUV light [11][12][13]; however, less work exists for x-ray ATI in the high-intensity regime [14], and mostly on hydrogen or hydrogen-like ions [15][16][17][18].…”