Temporal Structure of Attosecond Pulses from Laser-Driven Coherent Synchrotron Emission

Abstract

The microscopic dynamics of laser-driven coherent synchrotron emission transmitted through thin foils are investigated using particle-in-cell simulations. For normal incidence interactions, we identify the formation of two distinct electron nanobunches from which emission takes place each half-cycle of the driving laser pulse. These emissions are separated temporally by 130 attoseconds and are dominant in different frequency ranges, which is a direct consequence of the distinct characteristics of each electron nanobunch. This may be exploited through spectral filtering to isolate these emissions, generating electromagnetic pulses of duration ∼ 70 as.The generation of attosecond pulses of extremeultraviolet (XUV) radiation via laser-matter interactions has been demonstrated as a powerful tool for the observation of ultrafast atomic and electronic phenomena [1,2]. Experimental and numerical studies have shown that emissions of particularly high XUV photon flux are produced by focusing a laser pulse to relativistic intensities (Iλ18 W cm −2 µm 2 ) onto either a thick solid target [3][4][5][6][7] or a thin nanofoil [8][9][10][11][12][13][14][15]. In either case, a train of attosecond bursts is emitted by nanometer-scale bunches of electrons (nanobunches) which are driven periodically by the laser pulse into curved, synchrotron-like trajectories at the front surface of the resulting plasma [14][15][16][17].However, application of this radiation to time-resolved measurements of ultrafast phenomena requires an isolated pulse, otherwise there will be an uncertainty as to which pulse from the train is probing the process. Polarization gating techniques applied to laser-solid interactions [18][19][20] have shown recent promise in reducing the number of cycles during which emission occurs, while spatially selecting the pulses [21] may provide an alternative or a complement to these methods. If a pulse has been successfully isolated then the potential temporal resolution of this source is only limited by the structure of that pulse. However, for oblique laser incidence, simulation results have shown that the reflected radiation may contain an unavoidable sub-structure which limits the temporal resolution of attosecond pulses produced in this geometry [22].In this Letter we provide the first in-depth numerical study of the temporal structure of coherent synchrotron emission transmitted through nanofoils irradiated at normal incidence. Our particle-in-cell simulation results show that two distinct electron nanobunches contribute to the emission, producing a double-pulse structure separated by 130 as. However, we demonstrate that in this geometry this sub-structure does not necessarily place a strict lower limit on the achievable pulse duration. Our simulation results show that the characteristics of the emitting nanobunches are different, and emit radiation with distinct spectral shapes. We show that the relative intensity of the sub-pulses may be controlled by appropriate spectral filtering, resulting in a single pulse of du...

Electron trajectories associated with laser-driven coherent synchrotron emission at the front surface of overdense plasmas

“…Here, since both CSE bursts originate from the same bunch (corresponding to the primary bunch described in Ref. [22]), the forward emission mechanism is fundamentally different from that associated with wave breaking as discussed in Refs. [27,34].…”

“…Forward CSE, though not as extensively studied as the reflected case, has recently shown great promise as a coherent XUV source, particularly when the target is irradiated by the laser pulse at normal incidence [4,[20][21][22]. Experiments which employ this normal incidence in transmission (NIIT) geometry have shown CSE spectra with a shallow intensity scaling with frequency [4] and a strong ellipticity dependence [21] which can be exploited via polarization gating techniques [21,23] to isolate an attosecond pulse.…”

Theoretical and experimental progress of high-order harmonics and attosecond pulse generation based on solid overdense plasma

“…(b) Result of numerical simulations [14] . The line shows the scaling law of harmonic spectral intensity: I~ω 和理论 [26] 、阿秒 脉冲产生 [27] 、纳米双层薄膜靶 [28] 等研究. 其中, 关于…”

Generation of Attosecond Light Pulses from Gas and Solid State Media

“…Due to its superior properties and predominance at high intensities, the basis for the generation of single asec light pulses [87,119] will most probably be the ROM mechanism. More recently, theoretical work has revealed that, under certain conditions, another mechanism can dominate and produce harmonic radiation with superior efficiency [120][121][122][123][124][125]. In this mechanism dense electron nanobunches are formed at the plasma vacuum boundary giving rise to XUV radiation by coherent synchrotron emission (CSE).…”