Limits...
The interaction of excited atoms and few-cycle laser pulses

View Article: PubMed Central - PubMed

ABSTRACT

This work describes the first observations of the ionisation of neon in a metastable atomic state utilising a strong-field, few-cycle light pulse. We compare the observations to theoretical predictions based on the Ammosov-Delone-Krainov (ADK) theory and a solution to the time-dependent Schrödinger equation (TDSE). The TDSE provides better agreement with the experimental data than the ADK theory. We optically pump the target atomic species and measure the ionisation rate as the a function of different steady-state populations in the fine structure of the target state which shows significant ionisation rate dependence on populations of spin-polarised states. The physical mechanism for this effect is unknown.

No MeSH data available.


Related in: MedlinePlus

Part (a) is a schematic visualisation of the interaction region of the COLTRIMS. The atomic beam is travelling in the plane made with the z-axis and the θ = 0 angular coordinate. As the system is solved symmetrically in θ, the axis along the θ = 0 coordinate is labelled the r axis as the solution requires knowledge of the displacement along the radial coordinate. The laser beam is propagating in the z direction. Part (b) is a modelled 2D ionisation yield map for Ne* interacting with a laser pulse with the following parameters: Ipk = 9.6 × 1013 W/cm2; w0 = 7.25 μm; Tpul = 6.3 fs; atomic beam width = 1.5 mm; average atomic beam speed = 1000 m/s; atomic beam flux = 1.4 × 1014 atoms/sr/s. These parameters, with the exception of Ipk, were held constant throughout the modelling.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5035976&req=5

f5: Part (a) is a schematic visualisation of the interaction region of the COLTRIMS. The atomic beam is travelling in the plane made with the z-axis and the θ = 0 angular coordinate. As the system is solved symmetrically in θ, the axis along the θ = 0 coordinate is labelled the r axis as the solution requires knowledge of the displacement along the radial coordinate. The laser beam is propagating in the z direction. Part (b) is a modelled 2D ionisation yield map for Ne* interacting with a laser pulse with the following parameters: Ipk = 9.6 × 1013 W/cm2; w0 = 7.25 μm; Tpul = 6.3 fs; atomic beam width = 1.5 mm; average atomic beam speed = 1000 m/s; atomic beam flux = 1.4 × 1014 atoms/sr/s. These parameters, with the exception of Ipk, were held constant throughout the modelling.

Mentions: In order to provide comparison to theory, a 3D focal-volume-averaged model was created and implemented through Matlab. It is important to correctly model the interaction region, since the low ionisation potential of metastable neon causes the ionisation probability to quickly reach unity at the centre of the pulse at relatively low intensities. This implies that, as the pulse intensity increases, the outer areas in the interaction region significantly contribute to the total ion yield when compared to the ionisation of ground-state neon. The model made the assumptions that the laser pulse was Gaussian, the divergence of the atomic beam was negligible over the interaction region, the laser pulse was completely linearly polarised, and all ions generated by the interaction were detected by the COLTRIMS. Smoothing functions based on the work of Kielpinski et al.28 were employed. A representation of the interaction region is displayed in Fig. 5, with axes labelled according to a cylindrical coordinate system.


The interaction of excited atoms and few-cycle laser pulses
Part (a) is a schematic visualisation of the interaction region of the COLTRIMS. The atomic beam is travelling in the plane made with the z-axis and the θ = 0 angular coordinate. As the system is solved symmetrically in θ, the axis along the θ = 0 coordinate is labelled the r axis as the solution requires knowledge of the displacement along the radial coordinate. The laser beam is propagating in the z direction. Part (b) is a modelled 2D ionisation yield map for Ne* interacting with a laser pulse with the following parameters: Ipk = 9.6 × 1013 W/cm2; w0 = 7.25 μm; Tpul = 6.3 fs; atomic beam width = 1.5 mm; average atomic beam speed = 1000 m/s; atomic beam flux = 1.4 × 1014 atoms/sr/s. These parameters, with the exception of Ipk, were held constant throughout the modelling.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5035976&req=5

f5: Part (a) is a schematic visualisation of the interaction region of the COLTRIMS. The atomic beam is travelling in the plane made with the z-axis and the θ = 0 angular coordinate. As the system is solved symmetrically in θ, the axis along the θ = 0 coordinate is labelled the r axis as the solution requires knowledge of the displacement along the radial coordinate. The laser beam is propagating in the z direction. Part (b) is a modelled 2D ionisation yield map for Ne* interacting with a laser pulse with the following parameters: Ipk = 9.6 × 1013 W/cm2; w0 = 7.25 μm; Tpul = 6.3 fs; atomic beam width = 1.5 mm; average atomic beam speed = 1000 m/s; atomic beam flux = 1.4 × 1014 atoms/sr/s. These parameters, with the exception of Ipk, were held constant throughout the modelling.
Mentions: In order to provide comparison to theory, a 3D focal-volume-averaged model was created and implemented through Matlab. It is important to correctly model the interaction region, since the low ionisation potential of metastable neon causes the ionisation probability to quickly reach unity at the centre of the pulse at relatively low intensities. This implies that, as the pulse intensity increases, the outer areas in the interaction region significantly contribute to the total ion yield when compared to the ionisation of ground-state neon. The model made the assumptions that the laser pulse was Gaussian, the divergence of the atomic beam was negligible over the interaction region, the laser pulse was completely linearly polarised, and all ions generated by the interaction were detected by the COLTRIMS. Smoothing functions based on the work of Kielpinski et al.28 were employed. A representation of the interaction region is displayed in Fig. 5, with axes labelled according to a cylindrical coordinate system.

View Article: PubMed Central - PubMed

ABSTRACT

This work describes the first observations of the ionisation of neon in a metastable atomic state utilising a strong-field, few-cycle light pulse. We compare the observations to theoretical predictions based on the Ammosov-Delone-Krainov (ADK) theory and a solution to the time-dependent Schrödinger equation (TDSE). The TDSE provides better agreement with the experimental data than the ADK theory. We optically pump the target atomic species and measure the ionisation rate as the a function of different steady-state populations in the fine structure of the target state which shows significant ionisation rate dependence on populations of spin-polarised states. The physical mechanism for this effect is unknown.

No MeSH data available.


Related in: MedlinePlus