arXiv subjects

E. Seres

Publications and source records attributed to E. Seres.

7 recordsLinked to original sources

arXiv2026

Cascaded multi-harmonic generation in a \b{eta}-BBO crystal reaching 133 nm from a single 800 nm pump beam

Nonlinear crystals are widely used to efficiently generate second or third harmonics, and also for frequency mixing. Generation of multiple cascaded harmonics simultaneously, however, appears much less studied, although supported by the usually large nonlinearity of these crystals. Here, we demonstrate the generation of multiple harmonics up to 6th order in a \b{eta}-BBO crystal, extending into the vacuum ultraviolet spectral range. Phase matched generation of the second or the third harmonic is directly driven by a single 800 nm Ti:sapphire oscillator beam. Our study reveals that the harmonics are generated by \c{hi}(2):\c{hi}(2) and \c{hi}(2):\c{hi}(3) cascaded processes and intense harmonic signals are obtained even for the 5th and 6th harmonics, where the \b{eta}-BBO crystal is mostly absorbing. While higher order harmonics cannot be phase matched simultaneously, limiting the harmonic amplitudes, even the weakest harmonics are more than three orders of magnitude above the measurement noise limit, making them suitable for many spectroscopic applications.

physics.optics↗

arXiv2022

Probing the surface of silicon and the silicon-silica interface using nonperturbative third and fifth harmonic generation

We examined, in backward (reflection) geometry, the generation of the 3rd and 5th harmonics, located in the deep and vacuum ultraviolet, on the surface of silicon and on the interface between silicon and silica when a thin silica film was grown on a silicon substrate. In both cases, a strong dependence of the harmonic signal on the polarization direction of the driving laser beam was found. The differences observed for both samples, are qualitatively explained. Furthermore, a simplified tensor formalism for the polarization dependence is introduced, which reveals the structural symmetry of the surface and the interface and describes the polarization dependence with high accuracy. The study is an essential step to further understand nonlinear interaction and nonperturbative harmonic generation on the boundaries of materials.

physics.optics↗

arXiv2022

Nonlinear propagation effect in x-ray parametric amplification during high harmonic generation

We report the realization and characterization of parametric amplification in high harmonic generation around 100 eV using He gas in a double gas jet arrangement. The delay of the seed XUV pulse with respect to the amplifier gas jet was scanned by changing the distance between the gas jets. Experiments and numerical calculations show that parametric amplification occurs within a temporal window of several optical cycles. Strong correlation between the seed and amplifier was observed in a shorter, few optical cycles delay range, which appeared as a modulation of the XUV intensity with an unexpected one optical cycle periodicity instead of half optical cycle. Simulations revealed that the strong correlation and also the unusual periodicity was the consequence of the nonlinear effect produced by plasma dispersion on the parametric amplification process during propagation in the amplifier jet.

physics.optics↗

arXiv2021

Group delay dispersion tuned femtosecond Kerr-lens mode-locked Ti:sapphire laser

We report on a new design for a femtosecond Ti:sapphire oscillator in which dispersion compensation is realized exclusively using mirrors, including special mirrors with third order dispersion. This makes the oscillator dynamically tunable over a spectral range of 45 nm using an intracavity wedge-pair; and it delivers 40 fs pulses at 80 MHz repetition rate. Due to the all-mirror design, the oscillator represents an attractive base for a tunable frequency comb for high precision spectroscopy applications.

physics.optics↗

arXiv2020

Parametric attosecond pulse amplification far from the ionization threshold from high order harmonic generation in He$^+$

Parametric amplification of attosecond coherent pulses around 100 eV at the single-atom level is demonstrated for the first time by using the 3D time-dependent Schr{ö}dinger equation in high-harmonic generation processes from excited states of He$^+$. We present the attosecond dynamics of the amplification process far from the ionization threshold and resolve the physics behind it. The amplification of a particular central photon energy requires the seed XUV pulses to be perfectly synchronized in time with the driving laser field for stimulated recombination to the He$^+$ ground state and is only produced in a few specific laser cycles in agreement with the experimental measurements. Our simulations show that the amplified photon energy region can be controlled by varying the peak intensity of the laser field. Our results pave the way to the realization of compact attosecond pulse intense XUV lasers with broad applications.

physics.optics↗

arXiv2018

All-solid-state VUV frequency comb at 160 nm using multi-harmonic generation in a non-linear femtosecond enhancement cavity

We report on the realization of a solid-state-based vacuum ultraviolet frequency comb, using multi-harmonic generation in an external enhancement cavity. Optical conversions in such arrangements were so-far reported only using gaseous media. We present a theory that allows selecting the most suited solid generation medium for specific target harmonics by adapting the bandgap of the material. Consequently, we experimentally use a thin AlN film grown on a sapphire substrate to realize a compact frequency comb multi-harmonic source in the DUV/VUV spectral range. Extending our earlier VUV source [Opt. Exp. 26, 21900 (2018)] with the enhancement cavity, a sub-Watt level Ti:sapphire femtosecond frequency comb is enhanced to 24 W stored average power, its 3rd, 5th and 7th harmonics are generated, and the target harmonic power at 160 nm increased by two orders of magnitude. The emerging non-linear effects in the solid medium together with suitable intra-cavity dispersion management support optimal enhancement and stable locking. To demonstrate the spectroscopic ability of the realized frequency comb, we report on the beat measurement between the 3rd harmonic beam and a 266 nm CW laser reaching about 1 MHz accuracy.

physics.optics↗

arXiv2018

High harmonic generation from surface states of solids

We demonstrate that high-harmonic generation (HHG) in solids dominantly originates from strongly localized surface states through non-perturbative processes. Measurements reveal that HHG from bulk states is suppressed by at least 1-2 orders of magnitude due to the lack of phase matching, when generated perturbatively, or by at least 3-4 orders of magnitude, when generated non-perturbatively. We derive a theory that fully supports this observation and quantitatively describes the generation of harmonics from the surface states as well as from interfaces between solids; it also predicts a much weaker generation of harmonics from the bulk states. Our results pave the way for the development of very high repetition rate high harmonic sources for vacuum ultraviolet spectroscopy and high precision frequency comb metrology using surface states from solids.

physics.optics↗