Title: Cross-polarized common-path temporal interferometry for high-sensitivity strong-field ionization measurements
Absolute density measurements of low-ionization-degree or low-density plasmas ionized by lasers are very important for understanding strong-field physics, atmospheric propagation of intense laser pulses, Lidar etc. A cross-polarized common-path temporal interferometer using balanced detection was developed for measuring plasma density with a sensitivity of ∼0.6 mrad, equivalent to a plasma density-length product of ∼2.6 × 1013cm−2if using an 800 nm probe laser. By using this interferometer, we have investigated strong-field ionization yield versus intensity for various noble gases (Ar, Kr, and Xe) using 800 nm, 55 fs laser pulses with both linear (LP) and circular (CP) polarization. The experimental results were compared to the theoretical models of Ammosov-Delone-Krainov (ADK) and Perelomov-Popov-Terent’ev (PPT). We find that the measured phase change induced by plasma formation can be explained by the ADK theory in the adiabatic tunneling ionization regime, while PPT model can be applied to all different regimes. We have also measured the photoionization and fractional photodissociation of molecular (MO) hydrogen. By comparing our experimental results with PPT and MO-PPT models, we have determined the likely ionization pathways when using three different pump laser wavelengths of 800 nm, 400 nm, and 267 nm.
Blackman, David R.; Adak, Amitava; Singh, Prashant K.; Lad, Amit D.; Chatterjee, Gourab; Ridgers, Christopher P.; Del Sorbo, Dario; Trines, Raoul M. G. M.; Robinson, A. P. L.; Nazarov, Wigen; et al(
, Plasma Physics and Controlled Fusion)
Abstract
The formation and evolution of post-solitons has been discussed for quite some time both analytically and through the use of particle-in-cell (PIC) codes. It is however only recently that they have been directly observed in laser-plasma experiments. Relativistic electromagnetic (EM) solitons are localised structures that can occur in collisionless plasmas. They consist of a low-frequency EM wave trapped in a low electron number-density cavity surrounded by a shell with a higher electron number-density. Here we describe the results of an experiment in which a 100 TW Ti:sapphire laser (30 fs, 800 nm) irradiates aTMPTA foam target with a focused intensity. A third harmonic (nm) probe is employed to diagnose plasma motion for 25 ps after the main pulse interaction via Doppler-Spectroscopy. Both radiation-hydrodynamics and 2D PIC simulations are performed to aid in the interpretation of the experimental results. We show that the rapid motion of the probe critical-surface observed in the experiment might be a signature of post-soliton wall motion.
Britton, Mathew; McCracken, Gregory A.; Howard, Andrew J.; Peard, Nolan; Forbes, Ruaridh; Bucksbaum, Philip H.(
, 52nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics)
null
(Ed.)
It has recently been shown that strong field multiple ionization of water depends on the duration and intensity of the laser pulse. While the polarizability of neutral water is isotropic, the polarizability of the molecular ions can be significant and evolve in time. If the molecular ions spend enough time in the field, dynamic alignment can reorient them and modify the yield of dissociating fragments as a function of angle relative to the polarization of the laser. Unbending motion is one way that the polarizability of the molecular ions increases. Here, we study strong field ionization of water in the long pulse regime where dynamic alignment and unbending are known to contribute at 800 nm, and we tune the laser wavelength to modify coupling between the states of the monocation. A resonance between the X and A states at 660 nm should excite the monocation and initiate unbending motion, but our results cannot be explained without considering the dynamics and structure of the dication and trication. To conduct these measurements, we utilize laser pulses with a duration of 40 fs and central wavelengths of 660 nm, 800 nm, and 1330 nm to multiply-ionize an effusive molecular beam of water. The resulting charged fragments are detected using a velocity map imaging apparatus. Our results provide additional clues about the strong field ionization of water.
*M.B., G.A.M., A.J.H., N.P., and P.H.B. were supported by the National Science Foundation. A.J.H. was additionally supported under a Stanford Graduate Fellowship as the 2019 Albion Walter Hewlett Fellow. N.P. was additionally supported by the Hertz Foundation. R.F. was supported by the Department of Energy office of Basic Energy Science, Facilities Division.
Using the improved quantitative rescattering (QRS) model, we simulate the correlated two-electron momentum distributions (CMD) for nonsequential double ionization (NSDI) of Ar by near-single-cycle laser pulses with a wavelength of 750 nm at an intensity of 2.8 × 1014W/cm2. With the accurate cross sections obtained from fully quantum mechanical calculations for both electron impact excitation and electron impact ionization of Ar+, we unambiguously identify the contributions from recollision direct ionization (RDI) and recollision excitation with subsequent ionization (RESI). Our analysis reveals that RESI constitutes the main contribution to NSDI of Ar under the conditions considered here. The simulated results are directly compared with experimental measurements [Bergueset al.,Nat. Commun.3,813(2012)10.1038/ncomms1807] in which each NSDI event is tagged with the carrier-envelope phase (CEP). It is found that the overall pattern of both the CEP-resolved and the CEP-averaged CMDs measured in experiment are well reproduced by the QRS model, and the cross-shaped structure in the CEP-averaged CMD is attributed to the strong forward scattering of the recolliding electron as well as the depletion effect in tunneling ionization of the electron from an excited state of the parent ion.
The total number of electrons in a classical microplasma can be non-intrusively measured through elastic in-phase coherent microwave scattering (CMS). Here, we establish a theoretical basis for the CMS diagnostic technique with an emphasis on Thomson and collisional scattering in short, thin unmagnetized plasma media. Experimental validation of the diagnostic is subsequently performed via linearly polarized, variable frequency (10.5–12 GHz) microwave scattering off laser induced 1–760 Torr air-based microplasmas (287.5 nm O2resonant photoionization by ~ 5 ns, < 3 mJ pulses) with diverse ionization and collisional features. Namely, conducted studies include a verification of short-dipole-like radiation behavior, plasma volume imaging via ICCD photography, and measurements of relative phases, total scattering cross-sections, and total number of electrons$$N_{e}$$in the generated plasma filaments following absolute calibration using a dielectric scattering sample. Findings of the paper suggest an ideality of CMS in the Thomson “free-electron” regime—where a detailed knowledge of plasma and collisional properties (which are often difficult to accurately characterize due to the potential influence of inhomogeneities, local temperatures and densities, present species, and so on) is unnecessary to extract$$N_{e}$$from the scattered signal. The Thomson scattering regime of microwaves is further experimentally verified via measurements of the relative phase between the incident electric field and electron displacement.
Adam R Patel; Apoorv Ranjan; Xingxing Wang; Mikhail N Slipchenko; Mikhail N Shneide; Alexey Shashurin(
, Scientific reports)
The total number of electrons in a classical microplasma can be non-intrusively measured through elastic in-phase coherent microwave scattering (CMS). Here, we establish a theoretical basis for the CMS diagnostic technique with an emphasis on Thomson and collisional scattering in short, thin unmagnetized plasma media. Experimental validation of the diagnostic is subsequently performed via linearly polarized, variable frequency (10.5–12 GHz) microwave scattering off laser induced 1–760 Torr air-based microplasmas (287.5 nm O2 resonant photoionization by ~ 5 ns, < 3 mJ pulses) with diverse ionization and collisional features. Namely, conducted studies include a verification of short-dipole-like radiation behavior, plasma volume imaging via ICCD photography, and measurements of relative phases, total scattering cross-sections, and total number of electrons Ne in the generated plasma filaments following absolute calibration using a dielectric scattering sample. Findings of the paper suggest an ideality of CMS in the Thomson “free-electron” regime—where a detailed knowledge of plasma and collisional properties (which are often difficult to accurately characterize due to the potential influence of inhomogeneities, local temperatures and densities, present species, and so on) is unnecessary to extract Ne from the scattered signal. The Thomson scattering regime of microwaves is further experimentally verified via measurements of the relative phase between the incident electric field and electron displacement.
@article{osti_10368280,
place = {Country unknown/Code not available},
title = {Cross-polarized common-path temporal interferometry for high-sensitivity strong-field ionization measurements},
url = {https://par.nsf.gov/biblio/10368280},
DOI = {10.1364/OE.463424},
abstractNote = {Absolute density measurements of low-ionization-degree or low-density plasmas ionized by lasers are very important for understanding strong-field physics, atmospheric propagation of intense laser pulses, Lidar etc. A cross-polarized common-path temporal interferometer using balanced detection was developed for measuring plasma density with a sensitivity of ∼0.6 mrad, equivalent to a plasma density-length product of ∼2.6 × 1013cm−2if using an 800 nm probe laser. By using this interferometer, we have investigated strong-field ionization yield versus intensity for various noble gases (Ar, Kr, and Xe) using 800 nm, 55 fs laser pulses with both linear (LP) and circular (CP) polarization. The experimental results were compared to the theoretical models of Ammosov-Delone-Krainov (ADK) and Perelomov-Popov-Terent’ev (PPT). We find that the measured phase change induced by plasma formation can be explained by the ADK theory in the adiabatic tunneling ionization regime, while PPT model can be applied to all different regimes. We have also measured the photoionization and fractional photodissociation of molecular (MO) hydrogen. By comparing our experimental results with PPT and MO-PPT models, we have determined the likely ionization pathways when using three different pump laser wavelengths of 800 nm, 400 nm, and 267 nm.},
journal = {Optics Express},
volume = {30},
number = {14},
publisher = {Optical Society of America},
author = {Nie, Zan and Nambu, Noa and Marsh, Kenneth A. and Welch, Eric and Matteo, Daniel and Zhang, Chaojie and Wu, Yipeng and Patchkovskii, Serguei and Morales, Felipe and Smirnova, Olga and Joshi, Chan},
}
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