arXiv subjects

L. Kazak

Publications and source records attributed to L. Kazak.

5 recordsLinked to original sources

arXiv2026

High yield creation of germanium vacancy centers in diamond by focused ion beam implantation and high temperature annealing

Negatively charged germanium vacancy centers (GeV) in diamond are a promising platform for quantum computing and quantum communication. However, these applications require the precise incorporation of GeV centers with good optical properties inside of nanophotonic structures. In this work, we demonstrate the highly efficient local creation of GeV centers in diamond via focused-ion-beam implantation, followed by high-temperature annealing. We report the successful creation of GeV centers over the depth range of 5.5 - 30 nm. Implantation at low fluence enables the creation of single GeV centers. The formation yield strongly depends on implantation energy and fluence, reaching up to 33% at energies of 35 and 70 keV. This method, therefore, enables the efficient creation of GeV centers within a small, well-defined local sample volume and offers a potential means of incorporating them into photonic structures.

quant-ph↗

arXiv2026

Phonon-assisted charge-cycling of nitrogen-vacancy centres in diamond

The nitrogen-vacancy (NV) centre in diamond is a leading platform for room-temperature quantum sensing. Improvements in sensitivity require precise control of the NV charge state. Transitions from the neutral NV$^0$ charge state to the negative NV$^-$ charge state can occur during excitation with photon energies below the ZPL transition of NV$^0$. These sub-resonant charge transitions limit modern initialisation protocols and have not been studied in full detail. In this paper we show that sub-resonant charge cycling arises from phonon-assisted anti-Stokes excitation. We further uncover the phonon states which contribute most strongly to the anti-Stokes transition via the development of novel quantitative models. The models indicate that low energy acoustic phonons strongly contribute to the transition close to the ZPL. At longer wavelengths a 43\,meV mode additionally impacts the charge cycling dynamics.

quant-ph↗

arXiv2022

Phase-of-the-phase electron momentum spectroscopy on single metal atoms in helium nanodroplets

Magnesium atoms fully embedded in helium nanodroplets are exposed to two-color laser pulses, which trigger multiphoton above-threshold ionization (ATI). This allows to exemplarily study the contribution of a dense, neutral and finite medium on single electron propagation. The angular-resolved photoelectron spectra show striking differences with respect to results obtained on free atoms. Scattering of the individual Mg photoelectrons, when traversing the neutral helium environment, causes the angular distribution to become almost isotropic. Furthermore, the appearance of higher energy electrons is observed, pointing out the impact of the droplet on the concerted emission process. Phase-of-the-phase spectroscopy, however, reveals a marked loss in the \2ww phase dependence of the electron signal. Taking into account sideband formation on a quantitative level, a Monte-Carlo simulation which includes laser-assisted electron scattering can reproduce the experimental spectra and give insights into the strong-field-induced electron emission from disordered systems.

physics.atm-clus↗

arXiv2021

Development of ion recoil energy distributions in the Coulomb explosion of argon clusters resolved by charge-state selective ion energy spectroscopy

The laser intensity dependence of the recoil energies from the Coulomb explosion of small argon clusters has been investigated by resolving the contributions of the individual charge states to the ion recoil energy spectra. Between $10^{14}$ and $10^{15}$ W/cm$^2$ the high-energy tail of the ion energy spectra changes its shape and develops into the well-known knee feature, which results from the cluster size distribution, laser focal averaging, and ionization saturation. Resolving the contributions of the different charge states to the recoil energies, the experimental data reveal that the basic assumption of an exploding homogeneously charged sphere cannot be maintained in general. In fact, the energy spectra of the high-$q$ show distinct gaps in the yields at low kinetic energies, which hints at more complex radial ion charge distributions developing during the laser pulse impact.

physics.atom-ph↗

arXiv2017

The interaction of intense femtosecond laser pulses with argon microdroplets studied near the soft x-ray emission threshold

The extreme ultraviolet plasma emission from liquid microsized argon droplets exposed to intense near-infrared laser pulses has been investigated. Emission from the warm dense matter targets is recorded in a spectral range in between 16 and 30 nm at laser intensities of 10^14 W/cm^2. Above the emission threshold, soft x-ray radiation exponentially increases with the pulse energy whereby a strong dependence of the yields on the pulse duration is observed, which points at an effective electron collisional heating of the microplasma by inverse bremsstrahlung. Accompanying hydrodynamic simulations reveal the temporal and spatial development of the microplasma conditions. The good agreement in between the measured and calculated emission spectra as well as the extracted electron temperatures confirm that hydrodynamic simulations can be applied in the analysis of strongly excited droplets.

physics.atm-clus↗