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Contribution of the Wigner Institute. Imre F. Barna. Outline. - Our Starting Point , just to Remember - E xperimental Setup & Recent Results - Theoretical Work & Recent Results. Starting Point & Requirement. Figure is taken from Patric Muggli . - PowerPoint PPT Presentation
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Contribution of the Wigner Institute
Imre F. Barna
Outline
- Our Starting Point, just to Remember
- Experimental Setup & Recent Results
- Theoretical Work & Recent Results
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
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)
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
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
The Femtosecond Lab
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
HELIOS 1 – 1 KHz, 4,3 mJ, 31 fs
The Vacuum Chamber
Pressure: 10-6 mbar large enough for the source and the MCP
Rubidium Atom Source
Rb atom beam source (dispenser) Laser
MCP detector
approx 1010 particles/cm3
getter current 4.5 A at 2 V
General Overview of the Experimental Setup
Shutter to cut 5-10 pulses
Mirror
Mirror
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
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
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
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
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
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
Results
The direction of injection
The direction of pulse propagation
Energy gain vs. Initial momentum
ResultsEnergy gain vs. Carrier–envelope phase and laser pulse length
ResultsEnergy gain vs. the chirp parameter and laser intensity
Colleagues & Publication
Published: Nucl. Instr. And Meth. in Phys. Res. A 740, (2014) 203-207arXiv: 1309.2442
Thank you for your attention!