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The interaction of excited atoms and few-cycle laser pulses

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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.


Comparison of experimental data with theoretical predictions.The theories are scaled using a spline fitting procedure. For the ADK fit, A = 0.18 and η = 3.89, with Ο‡2 = 0.41. For the TDSE fit, A = 0.42 and η = 1.59, with Ο‡2 = 0.25. Inset: A comparison of the probability of ionisation for a single atom using the ADK theory against the focal volume averaged (FVA) ADK application as described in the main plot. It is observed that the sharp change in ionisation rate at ~1.5 × 1013 W/cm2 observed in the FVA data corresponds to the point where the ionisation probability of a single atom is approximately 80%. The black dashed line is provided as a guide for the eye.
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f1: Comparison of experimental data with theoretical predictions.The theories are scaled using a spline fitting procedure. For the ADK fit, A = 0.18 and η = 3.89, with Ο‡2 = 0.41. For the TDSE fit, A = 0.42 and η = 1.59, with Ο‡2 = 0.25. Inset: A comparison of the probability of ionisation for a single atom using the ADK theory against the focal volume averaged (FVA) ADK application as described in the main plot. It is observed that the sharp change in ionisation rate at ~1.5 × 1013 W/cm2 observed in the FVA data corresponds to the point where the ionisation probability of a single atom is approximately 80%. The black dashed line is provided as a guide for the eye.

Mentions: The theoretical results were obtained as described in the Methods section. In order to compare the predictions to experiment, the theoretical results were scaled to fit the experimental intensity dependence using a Matlab two-parameter spline fitting procedure. The scaling was done for both the ion yield and the laser intensity using the equation y = A × spline(Ξ·x). Here spline is the spline function that is fit to the theoretical predictions, A is the ion yield scaling factor, and Ξ· is the laser intensity scaling factor. The method has been used in previous work to compare theory to experiment in the case of atomic hydrogen2728. The uncertainty presented in the experimental section is given by the Poissonian counting error. Uncertainties in the laser intensity calibration include measurement error as well as systematic power measurement to intensity calculation errors. The latter is corrected with the intensity scaling. The experimental results and theoretical comparison are shown in Fig. 1.


The interaction of excited atoms and few-cycle laser pulses
Comparison of experimental data with theoretical predictions.The theories are scaled using a spline fitting procedure. For the ADK fit, A = 0.18 and η = 3.89, with Ο‡2 = 0.41. For the TDSE fit, A = 0.42 and η = 1.59, with Ο‡2 = 0.25. Inset: A comparison of the probability of ionisation for a single atom using the ADK theory against the focal volume averaged (FVA) ADK application as described in the main plot. It is observed that the sharp change in ionisation rate at ~1.5 × 1013 W/cm2 observed in the FVA data corresponds to the point where the ionisation probability of a single atom is approximately 80%. The black dashed line is provided as a guide for the eye.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: Comparison of experimental data with theoretical predictions.The theories are scaled using a spline fitting procedure. For the ADK fit, A = 0.18 and η = 3.89, with Ο‡2 = 0.41. For the TDSE fit, A = 0.42 and η = 1.59, with Ο‡2 = 0.25. Inset: A comparison of the probability of ionisation for a single atom using the ADK theory against the focal volume averaged (FVA) ADK application as described in the main plot. It is observed that the sharp change in ionisation rate at ~1.5 × 1013 W/cm2 observed in the FVA data corresponds to the point where the ionisation probability of a single atom is approximately 80%. The black dashed line is provided as a guide for the eye.
Mentions: The theoretical results were obtained as described in the Methods section. In order to compare the predictions to experiment, the theoretical results were scaled to fit the experimental intensity dependence using a Matlab two-parameter spline fitting procedure. The scaling was done for both the ion yield and the laser intensity using the equation y = A × spline(Ξ·x). Here spline is the spline function that is fit to the theoretical predictions, A is the ion yield scaling factor, and Ξ· is the laser intensity scaling factor. The method has been used in previous work to compare theory to experiment in the case of atomic hydrogen2728. The uncertainty presented in the experimental section is given by the Poissonian counting error. Uncertainties in the laser intensity calibration include measurement error as well as systematic power measurement to intensity calculation errors. The latter is corrected with the intensity scaling. The experimental results and theoretical comparison are shown in Fig. 1.

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.