X-ray free-electron lasers, delivering x-ray pulses of femtosecond duration, are available for experiments for more than a decade and allow for hitherto unachievable x-ray intensities on sample, reaching up to 1021 W/cm2 for hard x-rays. At these intensities, the probability of a single atom or molecule to absorb a photon of an impinging x-ray pulse reaches unity. Moreover, several interactions of photons and matter within the duration of the x-ray pulse – nonlinear x-ray matter interactions – become possible, opening the pathway to nonlinear x-ray optics. For a macroscopic ensemble of atoms, molecules, nanometer-sized clusters or a solid, the interaction with a strongly focused x-ray beam can create macroscopic, highly excited states of matter, far from equilibrium. In particular, saturated absorption with a high-intensity x-ray pulse can result in transient states, present for roughly one femtosecond, with the characteristic feature, that every single atom in the interaction region is in a population inverted state with missing population in the innermost electronic shell. This macroscopic population inversion can lead to collective radiative decay mechanisms, such as amplified spontaneous emission or superfluorescence. In this presentation I will give you an overview over our experimental and theoretical investigations of these single-pass x-ray laser amplifiers in the x-ray spectral domain. I will address applications of this phenomenon in the area of chemical x-ray emission spectroscopy, a new concept of an x-ray laser oscillator, and will highlight recent theoretical developments to describe collective spontaneous emission in the x-ray spectral domain.
Nearly four decades ago H-like and He-like resonantly photo-pumped laser schemes were proposed for producing X-ray
lasers. However, demonstrating these schemes in the laboratory has proved to be elusive because of the difficulty of
finding a strong resonant pump line. With the advent of the X-ray free electron laser (X-FEL) at the SLAC Linac
Coherent Light Source (LCLS) we now have a tunable X-ray laser source that can be used to replace the pump line in
previously proposed laser schemes and allow researchers to study the physics and feasibility of resonantly photo-pumped
laser schemes. In this paper we use the X-FEL at 1174 eV to photo-pump the singly excited 1s2p state of Helike
Ne to the doubly excited 2p3p state and model gain on the 2p3p-2p2s transition at 175 eV and the 2p3p-1s3p
transition at 1017 eV. One motivation for studying this scheme is to explore possible quenching of the gain due to strong
non-linear coupling effects from the intense X-FEL beam. We compare this scheme with photo-pumping the He-like Ne
ground state to the 1s3p singly excited state followed by lasing on the 3p-2s and 3d-2p transitions at 158 and 151 eV.
Experiments are being planned at LCLS to study these laser processes and coherent quantum effects.
Focusing an x-ray free electron laser (XFEL) pulse into a gas target, a plasma of transiently core excited ions can
be created within a few fs, building a pathway to an inner-shell keV x-ray laser. Varying the XFEL parameters, a
wide variety of pulse structures can be created with comparable peak-intensities to XFELs: isolated pulses of subfs
duration, trains of pulses with increased temporal coherence, and trains of fs pulses of different wavelengths.
We present self-consistent gain and amplification calculations, tailored to predict first experiments on lasing in
neon pumped by the Linac Coherent Light Source at Stanford.
Conference Committee Involvement (2)
X-Ray Free-Electron Lasers: Beam Diagnostics, Beamline Instrumentation, and Applications II
18 August 2014 | San Diego, California, United States
X-Ray Free-Electron Lasers: Beam Diagnostics, Beamline Instrumentation, and Applications
14 August 2012 | San Diego, California, United States
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