1. 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

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

3. 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

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

5. Ultra-short pulses regime
Interaction
regime
Ultra-short pulses regime

6. 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

7. 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

8. 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

9. Experimental arrangement
results
A – absorbed fraction

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

11. Experimental results - angular dependence

12. Experimental results - angular dependence

13. 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

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

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

16. Target surface quality influence on the laser absorption process
Experimental
results

17. Target surface quality influence on the laser absorption process
Experimental
results

18. Experimental results – absorption vs laser intensity

19. 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)

20. 2D PIC simulation results
The computational results are in good agreement
with the experiment assuming a profile of L/λ ~ 1%;

21. 2D PIC simulation results
at the laser peak, the target is in overdense state, ne≈70 nc

22. 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

23. 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

24. 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= W/cm2)
linear and circular polarized laser pulses