Volkov transform generalized projection algorithm for attosecond pulse characterization
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| Anzahl der Teile | 51 | |
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| Lizenz | CC-Namensnennung 3.0 Unported: Sie dürfen das Werk bzw. den Inhalt zu jedem legalen Zweck nutzen, verändern und in unveränderter oder veränderter Form vervielfältigen, verbreiten und öffentlich zugänglich machen, sofern Sie den Namen des Autors/Rechteinhabers in der von ihm festgelegten Weise nennen. | |
| Identifikatoren | 10.5446/38836 (DOI) | |
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51
00:00
GleitlagerVideotechnikNiederspannungsnetzGreiffingerComputeranimation
00:03
LichtEdelgasatomPhotoelektrizitätExtremes UltraviolettElektron
00:14
Elektronisches BauelementElektronProfilwalzenRotverschiebungTheodolitHobelInterferenzerscheinungSchwingungsphaseLuftionisationMatrize <Umformen>HalbwellendipolDPSKElektronOptisches Spektrum
01:26
ElektronFließfertigungHobelGate <Elektronik>FehlprägungEmissionsvermögenLuftionisationGreiffingerMessungHobelMatrize <Umformen>ComputeranimationFlussdiagramm
02:05
Satz <Drucktechnik>HobelSchwingungsphaseDomäne <Kristallographie>GreiffingerDreidimensionale IntegrationBrent SparComputeranimationFlussdiagramm
02:34
FlugsimulatorTheodolitHobelSchwächungSchwingungsphaseFehlprägungProfil <Bauelement>Bandbreite <Elektrotechnik>GreiffingerHalbwellendipolScheinbare HelligkeitBegrenzerschaltungFlussdiagramm
03:12
Natürliche RadioaktivitätScheinbare HelligkeitDiagramm
03:20
AmplitudeIntensitätsverteilungOberschwingung
03:31
GasSatz <Drucktechnik>TheodolitExtremes UltraviolettBahnelementMatrize <Umformen>OberschwingungTunerAirbus 300DiagrammTechnische Zeichnung
Transkript: Englisch(automatisch erzeugt)
00:03
An attosecond pulse of extreme ultraviolet light is typically characterized by ionizing a noble gas in the presence of a longer wavelength near IR streaking field. By recording the photoelectron energy spectrum as a function of the delay between the two pulses, it is possible to retrieve complete temporal information about both the IR streaking
00:22
pulse as well as the attosecond UV pulse. This information is recorded through both the momentum shift of the electrons as well as their spectral interference. In this paper, we demonstrate an improved technique for retrieving this information. According to the strong field approximation, the ionization of an electron packet and
00:42
subsequent streaking can be described in the following equation. It can be arranged such that there is a phase modulation term phi resulting from the accumulated phase of the electron during the streaking process as well as the electric field of the UV pulse. The last component of the expression accounts for the dipole transition matrix element describing
01:01
both the probability of ionization and the phase imparted by the atom during ionization. By assuming one can neglect the dipole transition matrix element, and that the momentum term in phi can be approximated by the central momentum of the ionized electron packet, the expression takes on the exact form of a frog spectrogram. One can then use a frog algorithm to retrieve information about the attosecond UV and IR pulses.
01:26
A typical frog retrieval starts with guesses for the pulse and gate function, assembles a time domain matrix, uses an FFT to transform that to the energy domain, projects the measured spectrogram magnitude, and converts this back to the time domain. It then uses a minimization procedure to get an updated guess for both pulses.
01:44
Most of the error in this process results from the FFT steps being inadequate to describe the actual physics of electron emission and streaking. In our paper, we ask a simple question. Why can't we just use the equations that best describe the physics of the ionization and streaking process and do away with the typical frog spectrogram?
02:02
To accomplish this, we devised a process that starts with a guess for the attosecond pulse and vector potential of the streaking pulse. It then numerically integrates to compute the spectrogram in the energy domain. As with any frog technique, it still contains a projection step, however, unlike a typical frog retrieval, it uses a minimization procedure directly in the energy domain to compute
02:24
the next set of pulses. Since this perfectly preserves the Volkov phase accumulated during streaking, we call it the Volkov transform generalized projections algorithm. To test our approach, called VT-GPA for short, we compare it to a standard frog algorithm, the least squares generalized projections algorithm, or LS-GPA.
02:45
The spectrogram from a 200 attosecond chirped EUV pulse with a bandwidth of 120 EV was simulated. At these bandwidths, the error resulting from the central momentum approximation and removal of the dipole transition matrix element prevent the LS-GPA from accurately retrieving
03:01
the EUV pulse profile and phase. Significantly, it retrieves a shorter pulse than in reality. However, the VT-GPA retrieves the pulse and phase without error. Furthermore, we even observe a significant improvement in the VT-GPA's ability to predict the exact magnitude of the IR streaking pulse. Overall, this spectrogram retrieval was improved by around three orders of magnitude.
03:25
Finally, we use our new algorithm with experimental data. The experimental spectrogram was fit using the VT-GPA, indicating a peak streak intensity of around 10 to the 9 watts per centimeter squared, and EUV pulses having a duration of roughly 300 attoseconds.
03:41
These results show no issues when applying VT-GPA to experimental data, as VT-GPA is flexible and works with the same sets of experimental data currently being used. It will be able to immediately impact the field of attosecond science, especially for EUV pulses having large relative bandwidths, and for situations where the transition matrix element of gases must be accounted for.