Download - Contribution of the Wigner Institute
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Contribution of the Wigner Institute
Imre F. Barna
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Outline
- Our Starting Point, just to Remember
- Experimental Setup & Recent Results
- Theoretical Work & Recent Results
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Starting Point & Requirement
Homogenous ionization of Rb gas is needed!!!
How to do it?? This is the coupling point for Wigner Institute
Figure is takenfrom Patric Muggli
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Rubidium-85 energy levels
Our idea to create homogenous plasma
Idea: use the short laser pulse to populatethe 7s and 5d two-photon resonant excited states to enhance the total single-ionization cross sections in the laser-Rb interaction andcreate a homogeneous plasmaJ. S. Bakos et. alEuropean Physical Journal D, 44 (2007), p. 141
(Model: a laser-atom excitation calculation including propagation phenomena)
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The Experimental Setup- A fs laser with high repetition rate - Vacuum chamber with 10-6 mbar - Rb dispenser atomic beam source- MCP detector to detect the ions/electrons- later plasma diganostics - till now approx. 4 KEuro investment - two local grants are for 13 KEuro
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Typical values806 nm 4.1W9 mm (1/e2 ,Gauss)Linear, vertical1 kHz 35 fs 0.25%800nm30nm
ParametersMean wavelengthAverage PowerBeam Diameter:Polarisation:Repetition Rate Pulse duration (FWHM):Energy. stab. rms (%): Medium wavelength:Bandwidth (FWHM):
Output parameters of the laser system
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The Femtosecond Lab
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Primary laser source - fs-duration system:
Ti:sapphire oscillator + regenerative amp.
Clean room: 3000-4000 particles/foot3
P. Dombi, A. Czitrovszky, P. Rácz, Gy. Farkas,N. Kroo, I. Földes use the laboratory forHHG experiments, surface plasmons
The Femtosecond Lab
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HELIOS 1 – 1 KHz, 4,3 mJ, 31 fs
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The Vacuum Chamber
Pressure: 10-6 mbar large enough for the source and the MCP
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Rubidium Atom Source
Rb atom beam source (dispenser) Laser
MCP detector
approx 1010 particles/cm3
getter current 4.5 A at 2 V
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General Overview of the Experimental Setup
Shutter to cut 5-10 pulses
Mirror
Mirror
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Recent experimental results
Laser parameters: Mean wavelength: 800 nm
Beam diameter: 9 mm (1/e2 ,Gauss) NO focusing
Max: Intens 1011 W/cm2
varied via Q-switch Far from being ideal
Polarization: Linear, vertical
Repetition rate: 1 kHz
Pulse duration: 35 – 45 fs
The three photon ionisation proccessis almost measured
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Recent Experimental Results &Direct MCP Signal
The signal of the MCP was closed with 50 Ohm in the oscilloscope, the noise was filtered with a 11 point smoothing algorithm, saturated ionisation current is measured
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Improvements- a polarfillter will be applied- the slit of the ion getter will be enlarged the atom beam
becomes more stable - later a 50 cm long ion-source is planned to use, with 2-3
MCPs to detect ionization currents
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Theoretical Works- Direct relativistic mechanical calculations for
electron acceleration in underdense plasma MSc Thesis, Mr. Pocsai
- Improve the quantum optical calculation, to include ionisation states for the Rb gas
- Quantum optical improvement of PIC simulations for electron acceleration Phd work Mr.
Pocsai
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Electron Acceleration in Underdense Plasma
The relativistic Newtonian equations of motion
Lorentz force
External fields
Chirped pulse
Retarded time in vacuum & underdense plasma
Index of refraction
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Electron Acceleration in Underdense Plasma
Only downchirp causes acceleration, the sharpest edge does the job.Downchirp = a dephasing effect
Laser parameters:
Wavelength: 800 nm
Intensity: 1017 W/cm2
Pulse length: 35 fs
The plasma parameters
at n = 1015 cm-3 nm =0.9999997 basically no diference from vacuum solutions
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Results
The direction of injection
The direction of pulse propagation
Energy gain vs. Initial momentum
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ResultsEnergy gain vs. Carrier–envelope phase and laser pulse length
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ResultsEnergy gain vs. the chirp parameter and laser intensity
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Colleagues & Publication
Published: Nucl. Instr. And Meth. in Phys. Res. A 740, (2014) 203-207arXiv: 1309.2442
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Thank you for your attention!