TY - JOUR

T1 - Time dependent Doppler shifts in high-order harmonic generation in intense laser interactions with solid density plasma and frequency chirped pulses

AU - Welch, E. C.

AU - Zhang, P.

AU - Dollar, F.

AU - He, Z. -H.

AU - Krushelnick, K.

AU - Thomas, A. G. R.

PY - 2015/5

Y1 - 2015/5

N2 - High order harmonic generation from solid targets is a compelling route to generating intense attosecond or even zeptosecond pulses. However, the effects of ion motion on the generation of harmonics have only recently started to be considered. Here, we study the effects of ion motion in harmonics production at ultrahigh laser intensities interacting with solid density plasma. Using particle-in-cell simulations, we find that there is an optimum density for harmonic production that depends on laser intensity, which scales linearly with a(0) with no ion motion but with a reduced scaling if ion motion is included. We derive a scaling for this optimum density with ion motion and also find that the background ion motion induces Doppler red-shifts in the harmonic structures of the reflected pulse. The temporal structure of the Doppler shifts is correlated to the envelope of the incident laser pulse. We demonstrate that by introducing a frequency chirp in the incident pulse we are able to eliminate these Doppler shifts almost completely. (C) 2015 AIP Publishing LLC.

AB - High order harmonic generation from solid targets is a compelling route to generating intense attosecond or even zeptosecond pulses. However, the effects of ion motion on the generation of harmonics have only recently started to be considered. Here, we study the effects of ion motion in harmonics production at ultrahigh laser intensities interacting with solid density plasma. Using particle-in-cell simulations, we find that there is an optimum density for harmonic production that depends on laser intensity, which scales linearly with a(0) with no ion motion but with a reduced scaling if ion motion is included. We derive a scaling for this optimum density with ion motion and also find that the background ion motion induces Doppler red-shifts in the harmonic structures of the reflected pulse. The temporal structure of the Doppler shifts is correlated to the envelope of the incident laser pulse. We demonstrate that by introducing a frequency chirp in the incident pulse we are able to eliminate these Doppler shifts almost completely. (C) 2015 AIP Publishing LLC.

KW - OVERDENSE PLASMAS

KW - TRANSPARENCY

KW - ABSORPTION

KW - SURFACES

KW - TARGETS

U2 - 10.1063/1.4919857

DO - 10.1063/1.4919857

M3 - Journal article

VL - 22

JO - Physics of Plasmas

JF - Physics of Plasmas

SN - 1070-664X

IS - 5

M1 - 053104

ER -