Abstract
In this paper we study the performance of two complementary short pulse generation schemes as applied to a soft x-ray free electron laser. The first scheme, recently proposed by Saldin et al., makes use of a laser pulse consisting of only a few optical cycles to give an energy chirp to a short section of an electron bunch and tapers the main radiator undulator in order to compensate the chirped region. The second scheme investigated takes a low-charge, high brightness electron bunch and compresses it to $\ensuremath{\sim}1\text{ }\text{ }\mathrm{fs}$ in order to operate in the so-called ``single-spike'' regime. We perform start-to-end simulations of both these schemes, assess the sensitivity of each scheme to realistic jitter sources, and provide a direct comparison of the respective strengths and drawbacks.
Highlights
Ultrashort, high brightness x-ray sources would permit considerable advances to be made in many areas of science, such as in single-shot imaging of biological samples and in measuring structural dynamics on subfemtosecond time scales
We have investigated two complementary short pulse generation schemes applied to a soft x-ray free electron lasers (FELs)
While the tapered undulator scheme has the potential drawback of having a SASE radiation background from the main bunch, the undulator taper means the average background power is 3 orders of magnitude below the peak power of the central spike
Summary
Ultrashort, high brightness x-ray sources would permit considerable advances to be made in many areas of science, such as in single-shot imaging of biological samples and in measuring structural dynamics on subfemtosecond (fs) time scales. Several schemes have recently been proposed for the production of short pulse radiation using high-gain free electron lasers (FELs), the majority of which use a fewcycle optical laser pulse to modulate the electron energy or trajectory in a small section of the bunch. Of all but a small section of the electron bunch by passing it through a slotted foil [10], passing an ultrashort, lowcharge electron bunch through the FEL in order to operate in the single-spike regime [11], or using a monochromator to select a short pulse from the radiation emitted by an energy-chirped electron beam to use as a seed for a second stage undulator [12]. We build on previous studies of these schemes [7,8,19] by performing full start-to-end simulations, assessing the sensitivity of each scheme to realistic jitter sources and providing further understanding of their respective performances and further insight in the complicated dynamics which governs the interaction of the electron beam with the FEL electromagnetic field
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