Studies of the energy transfer of ultra-short laser pulses to solid matter Mirela Cerchez, Ralph Jung, Jens Osterholz, Toma Toncian and Oswald Willi Institute of Laser and Plasma Physics, Heinrich-Heine University Düsseldorf Harmut Ruhl Institute for Theoretical Physics, Ruhr University, Bochum Peter Mulser Theoretical Quantum Electronics, Technical University, Darmstadt

Laser energy transfer to the matter: How and with what efficiency ? Motivation Laser energy transfer to the matter: How and with what efficiency ?

Laser energy transfer to the matter: How and with what efficiency ? Motivation Laser energy transfer to the matter: How and with what efficiency ? Ultrashort, high contrast, sub-10 fs laser pulses Overdense targets

Absorption of extremely short laser pulses in overdense targets Interaction regime Experimental results PIC simulations Conclusions Further plans

Ultra-short pulses regime Interaction regime Ultra-short pulses regime

Ultra-short pulses regime Interaction regime Ultra-short pulses regime On the solid target IL = 1-5 ·1016 W/cm2 , λL = 800 nm, τL=8 fs, high contrast >105 on ps time scale

Ultra-short pulses regime Interaction regime Ultra-short pulses regime On the solid target IL = 1-5 ·1016 W/cm2 , λL = 800 nm, τL=8 fs, high contrast >105 on ps time scale

Ultra-short pulses regime Interaction regime Ultra-short pulses regime On the solid target IL = 1-5 ·1016 W/cm2 , λL = 800 nm, τL=8 fs, high contrast >105 on ps time scale no significant preplasma is created before the main pulse (high contrast) no significant hydrodynamic expansion during the interaction (ultra-short pulse) overdense, steep profile of the plasma during the interaction (*) J. Osterholz, PRL, 96, (2006) R. Jung, Dissertation, 2007

Experimental arrangement results A – absorbed fraction

Experimental arrangement results This A dependes on diffrent parameters.... A= f (θ , IL, polarization, target)

Experimental results - angular dependence

Experimental results - angular dependence

Experimental results - angular dependence the collisionless contribution at the absorption level is estimated as Ap-As similar results within the error bars for all three investigated materials

Target surface quality influence on the laser absorption process Experimental results Gold evaporated layer σ << λ (σ=2.5 nm)

Target surface quality influence on the laser absorption process Experimental results Boron Nitride hot pressed ceramic σ ≈ λ (σ=500 nm)

Target surface quality influence on the laser absorption process Experimental results

Target surface quality influence on the laser absorption process Experimental results

Experimental results – absorption vs laser intensity

2D PIC* simulation results Analysis the Poynting flux of the pulse before and after being reflected by the target surface. Binary collisions were included in the PSC and the simulations were performed for p- and s-polarization of the incident laser pulse. The absorption profiles of p and s- polarization were subtracted from each other in order to estimate the collisionless contribution. * PIC-PSC by H. Ruhl, in Introduction to Computational Methods in Many Particle Body Physics (2006)

2D PIC simulation results The computational results are in good agreement with the experiment assuming a profile of L/λ ~ 1%;

2D PIC simulation results at the laser peak, the target is in overdense state, ne≈70 nc

2D PIC simulation results at the laser peak, the target is in overdense state, ne≈70 nc PIC simulation confirm the weak dependence of the collisionless absorbed fraction on the laser intensity

Collisionless absorption mechanisms – validity and contributions Conclusions Overdense, steep plasma profile L/λ ~ 0.01 Resonance absorption the linear regime (small amplitude of plasma waves) validity limited to plasma profiles L/λ > 0.1 Vacuum heating the validity is imposed by the condition xosc=vosc/ω>L and fullfilled for one cycle, at the laser peak; contribution estimated of about 10 %; scalling law AVH ~ (IL *λ2)0.5 not identified experimentally. Collisionless skin effects processes effective when thermal effects of electrons becomes important estimated contribution smaller than 5% at normal incidence Nonlinear regime of resonance absorption recent proposed model of anharmonic resonance absorption - aim to explain the resonant coupling of the laser energy to overdense plasma predics efficient absorption for IL>1015 W/cm2 work in progess

Further plans on absorption of ultra-short, high-contrast laser pulses by solids non-relativistic regime GW laser system (8 fs, IL =1016 W/cm2) circular polarized laser pulses relativistic regime TW laser system (25 fs, IL=1018-1019 W/cm2) linear and circular polarized laser pulses