Nonadiabatic blueshift of high-order harmonics from Ar and Ne atoms in an intense femtosecond laser field

High-order harmonic generation (HHG) is a nonlinear nonperturbative process in ultrashort intense laser-matter interaction. It is the main source of coherent attosecond (1 as = 10 −18 s) laser pulses to investigate ultrafast electron dynamics. HHG has become an important table-top source covering a spectral range from infrared to extreme ultraviolet (XUV). One way to extend the cutoff energy of HHG is to increase the intensity of the laser pulses. A consequence of HHG in such intense short laser fields is the characteristic nonadiabatic red and blue shifts of the spectrum, which are reviewed in the present work. An example of this nonperturbative light-matter interaction is presented for the oneelectron nonsymmetric molecular ion HeH 2+ , as molecular systems allow for the study of the laser-molecule orientation dependence of such new effects including a four-step model of MHOHG (Molecular High-order Harmonic Generation).

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“…This imbalance of HHG will lead to a net blue shift in HHG. This has been experimentally confirmed in [12,19]. (5)).…”

Section: Nonadiabatic Blue Shift In Hhgsupporting

confidence: 56%

Spectral Shifts of Nonadiabatic High-Order Harmonic Generation

Bian

Bandrauk

2013

Applied Sciences

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“…This is indeed the case in our measurements and is consistent with our observation that the relative shift increases with the order. This agrees with the earlier results from [25], where a non-adiabatic blue-shift is reported as well. It can be concluded that the total observed harmonic blue-shift obtained is due to both ionization (adiabatic) and non-adiabatic effects.…”

Section: Resultssupporting

confidence: 93%

“…3 and 4, we clearly observe a shift of the high-harmonic output wavelengths as a function of pressure and drive laser chirp. In comparison with the observations of others [15,25] 2 and P = 40 mbar), the blue-shift may result from three mechanisms. One of the mechanisms is an ionization induced blue-shift of the drive laser.…”

Section: Resultsmentioning

confidence: 40%

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Spectral control of high-harmonic generation via drive laser pulse shaping in a wide-diameter capillary

et al. 2016

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Abstract:We experimentally investigate spectral control of high-harmonic generation in a wide-diameter (508 μm) capillary that allows using significantly lower gas pressures coupled with elevated drive laser energies to achieve higher harmonic energies. Using phase shaping to change the linear chirp of the drive laser pulses, we observe wavelength tuning of the high-harmonic output to both larger and smaller values. Comparing tuning via the gas pressure with the amount of blue shift in the transmitted drive laser spectrum, we conclude that both adiabatic and non-adiabatic effects cause pulse-shaping induced tuning of high harmonics. We obtain a fractional wavelength tuning, Δλ/λ, in the range from −0.007 to + 0.01, which is comparable to what is achieved with standard capillaries of smaller diameter and higher pressures. 752-755 (1996). 32. G. Tempea and T. Brabec, "Nonlinear source for the generation of high-energy few-cycle optical pulses," Opt.Lett. 23(16), 1286-1288 (1998).

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“…Harmonics were generated on the leading edge of the laser pulse, which also experienced self-phase modulation and blue-shifting due to ionization of the gas. Thus, they can shift in energy slightly during the high harmonic generation process (28,29) and must be independently measured. In this work, the energy of 7ω was determined from the photoelectron spectra of known compounds (acetone and methyl azide), while 5ω was measured on a home-built spectrometer.…”

Section: Experimental Methodsmentioning

confidence: 99%

Ultrafast 25-fs relaxation in highly excited states of methyl azide mediated by strong nonadiabatic coupling

Peters

Couch

Mignolet

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Highly excited electronic states are challenging to explore experimentally and theoretically-due to the large density of states and the fact that small structural changes lead to large changes in electronic character with associated strong nonadiabatic dynamics. They can play a key role in astrophysical and ionospheric chemistry, as well as the detonation chemistry of high-energy density materials. Here, we implement ultrafast vacuum-UV (VUV)-driven electron-ion coincidence imaging spectroscopy to directly probe the reaction pathways of highly excited states of energetic molecules-in this case, methyl azide. Our data, combined with advanced theoretical simulations, show that photoexcitation of methyl azide by a 10-fs UV pulse at 8 eV drives fast structural changes and strong nonadiabatic coupling that leads to relaxation to other excited states on a surprisingly fast timescale of 25 fs. This ultrafast relaxation differs from dynamics occurring on lower excited states, where the timescale required for the wavepacket to reach a region of strong nonadiabatic coupling is typically much longer. Moreover, our theoretical calculations show that ultrafast relaxation of the wavepacket to a lower excited state occurs along one of the conical intersection seams before reaching the minimum energy conical intersection. These findings are important for understanding the unique strongly coupled non-Born-Oppenheimer molecular dynamics of VUV-excited energetic molecules. Although such observations have been predicted for many years, this study represents one of the few where such strongly coupled non-Born-Oppenheimer molecular dynamics of VUV-excited energetic molecules have been conclusively observed directly, making it possible to identify the ultrafast reaction pathways.

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Nonadiabatic blueshift of high-order harmonics from Ar and Ne atoms in an intense femtosecond laser field

Cited by 44 publications

References 22 publications

Spectral Shifts of Nonadiabatic High-Order Harmonic Generation

Spectral Shifts of Nonadiabatic High-Order Harmonic Generation

Spectral control of high-harmonic generation via drive laser pulse shaping in a wide-diameter capillary

Ultrafast 25-fs relaxation in highly excited states of methyl azide mediated by strong nonadiabatic coupling

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