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!