Quantum Free-electron Laser Research Articles

Harmonics in a Quantum Free Electron Laser: Towards a compact, coherent γ-ray source

Short-wavelength Free Electron Lasers (FELs), which have recently produced intense, hard X-rays are currently based on the concept of classical Self-Amplified Spontaneous Emission (SASE). In order to extend the production of intense, coherent radiation to sub-Å wavelengths then an alternative to the conventional SASE-FEL concept will be necessary, as conventional SASE-FELs require long wigglers (~ 100 m) and large accelerators (~ km) and produce radiation which has poor temporal coherence. Recently, we have introduced the concept of the Quantum Free Electron Laser (QFEL). The QFEL is characterised by quantised electron momentum recoil and the emission of monochromatic, coherent radiation from a compact apparatus. This makes it appealing for applications requiring a high degree of temporal coherence. We show that a SASE-QFEL may offer the possibility to produce intense, coherent γ-rays via harmonic generation. This has the potential to open up new applications e.g. coherent interactions involving nuclear transitions.

Quantum plasma fluid model for high-gain free-electron lasers

Starting from the eikonal approximation (geometrical optics), a set of nonlinear quantum plasma fluid equations to describe the quantum free-electron laser (FEL) is presented. Subsequently, by using these fluid equations for a relativistic electron beam, interacting with stimulated radiation and an optical wiggler field, a general dispersion relation for quantum FEL instability is derived taking into account the beam space-charge mode modulated by the ponderomotive potential well. It is shown that the saturation time for the quantum FEL instability can be estimated from the solutions of three-wave coupled equations which describe the FEL dynamics in the fluid model.

The quantum free electron laser: A new source of coherent, short‐wavelength radiation

AbstractA Free Electron Laser (FEL) operating in the quantum regime can provide a compact and monochromatic X‐ray source. Here we review the basic principles of a high‐gain quantum FEL starting from noise, with special emphasis on the self‐amplified spontaneous emission (SASE) mode of operation. In the first part of the paper, a condition for the neglect of the fermionic character of the electrons is derived and the full quantum theory of the N‐particle and single‐radiation‐mode FEL Hamiltonian is presented. Quantum effects such as cooperative gain, discrete spectrum and line narrowing are described, both in the multi‐particle and in the second quantization formalism. In the second part, propagation effects (i.e. slippage) are described and the main features of the quantum SASE regime are discussed. The broad and spiky radiation spectrum observed in classical SASE reduces in the quantum regime to a series of narrow lines, associated with sequential transitions between adjacent momentum states. A simple interpretation of the discrete nature of the spectrum and of the linewidth of the single spike observed in the quantum regime is presented.

Quantum-fluid description of the free-electron laser

Using the Madelung transformation we show that in a quantum Free Electron Laser (QFEL) the beam obeys the equations of a quantum fluid in which the potential is the classical potential plus a quantum potential. The classical limit is shown explicitly.

The quantum free-electron laser

The quantum free-electron laser

Dispersion relations for electromagnetic waves in a dense magnetized plasma

AbstractDispersion relations for elliptically polarized extraordinary as well as linearly polarized ordinary electromagnetic waves propagating across an external magnetic field in a dense magnetoplasma are derived, taking into account the combined effects of the quantum electrodynamical (QED) field, as well as the quantum forces associated with the Bohm potential and the magnetization energy of the electrons due to the electron-1/2 spin effect. The QED (vacuum polarization) effects, which contribute to the nonlinear electron current density, modify the refractive index. Our results concern the propagation characteristics of perpendicularly propagating high-frequency electromagnetic waves in dense astrophysical objects (e.g. neutron stars and magnetars), as well as the next-generation intense laser–solid density plasma interaction experiments and quantum free-electron laser schemes.

Wide-field imaging using a tunable terahertz free electron laser and a thermal image plate

The appearance of intense terahertz sources such as quantum cascade laser and free electron laser opens up new opportunities for 2D imaging. Though microbolometer and pyroelectric arrays are promising recorders, they are of small size and cannot be used when wide-field imaging in the longwave region is required. We applied for terahertz imaging 3″ × 3″ and 6″ × 6″ Macken Instruments Inc. “thermal image plates”, a set of thermal sensitive phosphor screens operating in a room temperature environment. The Novosibirsk free electron laser was used as a source of radiation. We have found that the response of thermal image plate is linear until the relative quenching is less than 60% of the initial luminescence intensity. The response curve follows the Seitz–Mott law. The threshold sensitivity was found to be 100 mW/cm 2 at 1.5 THz and 40 mW/cm 2 at 2.3 THz. Interferograms, holograms, and terahertz beam spatial distributions recorded in the spectral range of 1.2–2.5 THz are given as examples.

3D Wigner model for a quantum free electron laser with a laser wiggler

A three dimensional, time dependent, quantum model for an FEL with a laser wiggler, based on a discrete Wigner function formalism taking into account the longitudinal momentum quantization, is presented. Starting from the exact quantum treatment, a motion equation for the Wigner function coupled to the self-consistent radiation field is derived in the realistic limit in which the normalized electron beam emittance is much larger than the Compton wavelength quantum limit. The model describes the three-dimensional spatial and temporal evolution of the electron and radiation beams, including diffraction, propagation, laser wiggler, emittance and quantum recoil effects. It can be solved numerically and reduces to the three-dimensional Maxwell–Vlasov model in the classical limit. We discuss the experimental requirements for a quantum X-ray FEL with a laser wiggler, presenting preliminary numerical results and parameters for a possible future experiment.

Three-dimensional free electron laser numerical simulations for a laser wiggler in the quantum regime

A compact tunable source of soft X-rays could be realized combining a state-of-the-art electron source with an intense counter-propagating laser pulse. If the source is operated in the quantum regime, the theoretical model predicts high monochromaticity (single-spike) and unprecedented temporal coherence for the emitted radiation. Here we present numerical simulations of the complete quantum model for an Free Electron Laser (FEL) with a laser wiggler in three spatial dimensions, based on a discrete Wigner function formalism taking into account the longitudinal momentum quantization. The numerical model includes the complete spatial and temporal evolution of the electron and radiation beams, with an explicit description of diffraction, propagation, laser wiggler profile and emittance effects. The contribution of each interaction term is studied independently, and the 3D results are contrasted with the 1D quantum FEL model neglecting transverse effects. Finally the parameter space for possible experiments is characterized, and a particular experimental case is discussed in detail.

The quantum free-electron laser

A Free-Electron Laser (FEL) operating in the quantum regime can provide a compact and monochromatic X-ray source. Here we review the basic principles of a high-gain quantum FEL starting from noise, with special emphasis on the self-amplified spontaneous emission (SASE) mode operation. In the first part, the full quantum theory of the N-particle and single-radiation-mode FEL Hamiltonian is presented. Quantum effects such as cooperative gain, discrete spectrum and line narrowing are described, both in the multi-particle and in the second quantization formalism. In the second part, propagation effects (i.e. slippage) are described and the main features of the quantum SASE regime are discussed. The broad and spiky radiation spectrum observed in the classical SASE reduces in the quantum regime to a series of narrow lines, associated to sequential transitions between adjacent momentum states. A simple interpretation of the discrete nature of the spectrum and of the line width of the single spike observed in the quantum regime is presented.

Quantum wave kinetics of high-gain free-electron lasers

A wave kinetic equation equivalent to the Schrodinger-like equation for the electrons is derived from relativistic theory in the eikonal approximation. This equation is used to study the interaction of the relativistic electron beam in a wiggler field in the quantum regime, i.e., when the normalized quantum free-electron laser parameter ρ¯⩽1. A general quantum dispersion relation and an expression for free-electron laser instabilities are derived. Conditions for kinetic instability, which takes into account the Landau damping effect, are established.

Pulse propagation solution for a quantum free electron laser

We calculate the exact solution of the propagation equations describing a quantum free electron laser. The solution is obtained by evaluating the residue in the essential singularities of the Fourier-Laplace transformed optical field, and is expressed as a complete series of special functions. The classical and quantum limits of the solution are discussed and an asymptotic form, valid in the high-gain regime, is obtained.

Inhomogeneous effects in the quantum free electron laser

We include inhomogeneous effects in the quantum model of a free electron laser taking into account the initial energy spread of the electron beam. From a linear analysis, we obtain a generalized dispersion relation, from which the exponential gain can be explicitly calculated. We determine the maximum allowed initial energy spread in the quantum exponential regime and we discuss the limit of large energy spread.

Many-body effects in a quantum free-electron laser model

We study N-body effects on the coherence properties of the light emitted spontaneously by a free-electron laser working in the Compton regime. In particular, antibunching, present in a one-electron model, disappears as soon as one introduces more than one electron into the model. We also study quantum versus classical (shot) noise.

A bloch-like model of the free electron laser

The free electron laser (FEL)(~) operation has been the subject of a number of theoretical investigations (2-4), dealing with a possible interpretation of the process. At first glance, the above approaches can be put in two main categories, concerned, respectively, with a collective (2) and a single-particle interpretation {3,4). Both the analyses have been worked out under completely classical hypotheses, i.e. the laser field was assumed strong enough to allow a classical treatment. A quantum analysis of FEL has been undertaken in (5.6), in the framework of the single-particle theory in a inoving frame (a). A remarkable result of such an approach is that it is possible to recover, by means of the density matrix formalism, an equivalence between the approaches of (2) and (4), by deriving quasi-Bloch equations which in the classical limit coincide with those used by the authors of (o) (.). Indeed in (6) ]3ONIFAC10 and SCELLY have presented an elegant formulation of the quantum FEL theory, by defining suitably the Bloch-vector relevant to the interaction. The aim of the present note is to reconsider the Bonifacio and Sculty approach to the FEL and show that the slightlyredefined Bloch-veetor components have, as classical counterparts, the recently introduced (x, y) interaction variables, in dealing with the nmltilnode FEL theory (7).