ULTRACOMPACT, ULTRASHORT COHERENT LIGHT SOURCES OPERATING AT UV TO X-RAY WAVELENGTHS

Abstract

Systems and methods for generating longitudinally modulated (micro-bunched) electron bunches and for generating coherent radiation by the emission from relativistic electrons with a density that is longitudinally modulated (micro-bunched) with a spatial dimension that is significantly below the wavelength of the emitted radiation. The light source includes a high-brightness relativistic electron beam that interacts in a magnetic structure (linear or helical undulator or wiggler) or an electromagnetic structure with a pulse of high-power electro-magnetic wave (modulation laser pulse). The interaction leads to a large energy-modulation of the electron bunch which is transformed into a spatial modulation by an energy-dispersive element that can be the same undulator.

Description

FIELD AND SUMMARY

The present disclosure provides systems and methods for producing coherent light operating from UV to hard X-ray wavelengths with high average power.

The embodiments described herein provide light sources that enable the generation of ultrashort, high-brilliance, short-wavelength radiation pulses with a high average power from a compact setup. The photon energy of the emitted radiation can range from ultraviolet (UV) to hard X-ray wavelengths, including extreme ultraviolet (EUV) and soft X-ray wavelengths. According to an embodiment, a light source device generates pulses of coherent radiation with an ultrahigh peak brilliance, and with a high average power that ranges from a few Watts to more than tens of kiloWatts. The dimensions of the light source device are ultra-compact ranging from sub-meter to a few tens of meters. The duration of the light pulses is extremely short ranging from sub-attosecond (las=10⁻¹⁸ s) to picoseconds (Ips=10⁻¹² s) or longer. It should be appreciated that “light source” and “light source device” may be used interchangeably herein.

According to certain embodiments, coherent radiation is generated by the emission from relativistic electrons with a density that is longitudinally modulated (micro-bunched) with a spatial dimension that is significantly below the wavelength of the emitted radiation. The light source includes a high-brightness relativistic electron beam that interacts in a magnetic structure (linear or helical undulator or wiggler) or an electromagnetic structure with a pulse of high-power electro-magnetic wave (modulation laser pulse). The interaction leads to a large energy-modulation of the electron bunch which is transformed into a spatial modulation by an energy-dispersive element that can be the same undulator.

In an embodiment, coherent emission with a wavelength that is significantly shorter (by approximately a factor of 100 or more) than that of the incoming high-power modulation laser pulse is generated. The generated radiation has an ultra-high peak brilliance. The source can be operated at high repetition rates with currently available technologies, resulting in a light source with high average brilliance and power.

The wavelength of the incoming laser pulse can range from sub-THz to X-ray wavelengths, including infrared, optical and UV wavelengths. The interaction of the modulation light pulse with the electron bunch inside the undulator leads to a strong periodic energy-modulation of the electron beam energy (see FIG. 1 and FIG. 2). This energy modulation is converted into a spatial density modulation (microbunches) through an energy-dispersive element, which can include the (electro-) magnetic structure used to induce the energy modulation described above or can be an external component.

Certain embodiments are based on the largest energy modulation of the electron bunch possible (a few tens percent), such that microbunches with very short duration that are ultimately limited by repelling space-charge forces between the electrons are generated.

In certain embodiments the radiation is generated while the microbunching occurs inside the undulator where the space charge repulsion is suppressed compared to a free drifting electron bunch. The electromagnetic field pulses can be generated by fresh laser pulses for each repetition or can be provided through recycling the previous laser pulse in a laser cavity that can be an enhancement cavity.

Advantages of the present embodiments compared to currently existing technology include that electron bunches with a much lower beam energy than other electron-beam based approaches, such as free-electron lasers (FELs) can be used to generate coherent short wavelength radiation and that the spatial dimensions of the present embodiments are significantly more compact.

The radiation is generated through coherent superradiant emission from the micro-bunched electron bunch at a wavelength longer than the dimension of the microbunches. This includes emission of spontaneous superradiance, including but not limited to coherent transition radiation (CTR), edge radiation or diffraction radiation or stimulated superradiant emission, including but not limited to coherent inverse Compton radiation, coherent Thomson scattering, coherent synchrotron radiation or coherent undulator radiation.

In an embodiment, the light source can be cascaded to generate shorter wavelength radiation. In an example the radiation generated in a first stage can be used as short-wavelength radiation input into a second stage to generate pulses with even shorter wavelength, either from the same spatially- and energy-modulated electron bunch or a fresh (unmodulated) bunch. Multiple cascades can be used.

According to an embodiment, a coherent light source device is provided that comprises a magnetic or an electromagnetic undulator structure configured to produce a linearly or helically polarized magnetic or an electromagnetic field having three or more alternating electromagnetic periods and defining an axis within an interaction region; a modulation laser source configured to emit one or multiple pulses of linearly or circularly polarized electromagnetic radiation that co-propagate with an electron beam bunch along the axis of the magnetic or electromagnetic undulator within the magnetic or electromagnetic undulator; an electron beam source configured to generate the electron beam bunch that traverses the interaction region of the magnetic or electromagnetic undulator along the axis, wherein interaction of the electron beam bunch with the electromagnetic field of the one or multiple pulses of the modulation laser source in the interaction region of the magnetic or electromagnetic undulator structure induces the formation of electron microbunches within the electron beam bunch; and an undulation laser source configured to emit one or multiple pulses of electromagnetic undulation radiation that traverse the interaction region of the electromagnetic undulator at an interaction angle with respect to the axis, or a second magnetic undulator, or a dielectric discontinuity, wherein interaction of the one or multiple pulses of electromagnetic undulation radiation or the second magnetic undulator or the dielectric discontinuity with the electron microbunches induces spontaneous or stimulated coherent emission of radiation by the electron microbunches at an emission wavelength, wherein the emission wavelength is shorter than a wavelength of the one or more or multiple pulses of electromagnetic undulation radiation or is shorter than the period of the second magnetic undulator or is shorter than the thickness of the dielectric discontinuity.

According to an embodiment, the electron microbunches include electron bunches having a longitudinal charge distribution with periodic density spikes that are separated by a distance equal to the wavelength or harmonics of the wavelength of the one or multiple pulses of electromagnetic radiation emitted by the modulation laser source.

According to an embodiment, the one or multiple pulses of electromagnetic radiation are circularly polarized or polarized in a plane of electron deflection of electrons in the electron beam bunch within the interaction region.

According to an embodiment, a method of generating coherent light is provided. The method typically includes generating an electron beam bunch that traverses an axis in an interaction region of a magnetic or an electromagnetic undulator that produces a magnetic or electromagnetic field having three or more alternating electromagnetic periods along the axis within the interaction region, wherein interaction of the electron beam bunch with an additional electromagnetic field induces the formation of electron microbunches within the electron beam bunch; generating one or multiple pulses of electromagnetic radiation that co-propagate with the electron beam bunch along the axis of the electromagnetic undulator within the magnetic or electromagnetic undulator; and generating one or multiple pulses of electromagnetic undulation radiation that traverse the interaction region of the magnetic or electromagnetic undulator at a first interaction angle with respect to the axis, wherein interaction of the one or multiple pulses of electromagnetic undulation radiation with the electron microbunches induces stimulated coherent emission of radiation by the electron microbunches at an emission wavelength that is shorter than a wavelength of the one or more or multiple pulses of electromagnetic undulation radiation, or generating a magnetic undulator, wherein interaction of the magnetic undulator with the electron microbunches induces stimulated coherent emission of radiation by the electron microbunches at an emission wavelength that is shorter than the period of the magnetic undulator, or generating a single or periodic dielectric discontinuity, wherein interaction of the electron microbunches with the dielectric discontinuity induces coherent emission of radiation by the electron microbunches at an emission wavelength that is shorter than the width of the periodic structure.

According to an embodiment, the electron microbunches include electron bunches having a longitudinal charge distribution with periodic density spikes that are separated by a distance equal to the wavelength of the one or multiple pulses of electromagnetic radiation.

According to an embodiment, the one or multiple pulses of electromagnetic radiation are circularly polarized or polarized perpendicular to or in a plane of electron deflection of electrons in the electron beam bunch within the interaction region.

According to an embodiment, the method further includes steering or guiding the electron beam bunch to traverse the interaction region of the electromagnetic undulator along the axis.

According to an embodiment, the emission wavelength λ_r is given by the equation:

${\lambda }_r={\lambda }_{\mathrm{las}}\left(\frac{1+\frac{a_l^2}{2}+{\gamma }^2{\theta }^2}{2{\gamma }^2\left(1-\cos \varphi \right)}\right),$

where λ_las is the wavelength of the one or more or multiple pulses of electromagnetic undulation radiation, a_l is the normalized field of the modulation laser source, θ is the emission angle of the radiation generated by the electron beam bunch, ϕ the interaction angle between the electron beam bunch and the electromagnetic undulator radiation, and γ is the energy of the electron beam bunch normalized to the electron rest mass mc².

According to an embodiment, the emission wavelength λ_r is given by the equation:

${\lambda }_r=\frac{{\lambda }_u}{2n{\gamma }^2}\left(1+\frac{K_x^2}{2}+\frac{K_y^2}{2}+{\gamma }^2{\theta }^2\right),$

where λ_u is the undulator period of the magnetic or electromagnetic undulator structure, n the harmonic number, γ the electron beam bunch energy normalized to the electron rest mass mc², θ the angle of the radiation generated by the electron beam bunch, and

$K_{x,y}=\frac{e{\hat{B}}_{x,y}{\lambda }_u}{2\pi {\mathrm{mc}}^2}$

is a horizontal/vertical undulator deflection parameter with the undulator peak magnetic field {circumflex over (B)}_x,y.

According to an embodiment, the interaction of the one or more pulses of linearly or circularly polarized electromagnetic radiation with the electron beam bunch inside the linearly or helically polarized magnetic or electromagnetic undulator structure leads to a longitudinally modulated or micro bunched density of the electron beam density of the electron bunch with density spikes that have a length significantly below a wavelength of the one or multiple pulses of electromagnetic radiation when the resonance condition given by the equation:

${\lambda }_l=\frac{{\lambda }_u}{2n{\gamma }^2}\left(1+\frac{K_x^2}{2}+\frac{K_y^2}{2}+\frac{a_l^2}{2}{\gamma }^2{\theta }_x^2+{\gamma }^2{\theta }_z^2\right)$

is fulfilled, where λ_l is the wavelength of the modulation laser source, λ_u the undulator period of the magnetic or electromagnetic undulator structure, n the harmonic number, γ the electron beam bunch energy normalized to the electron rest mass mc², θ_x and θ_y the electron beam bunch divergence in x and y direction, respectively and the horizontal/vertical undulator deflection parameter K_x,y=e{circumflex over (B)}_x,yλ_u/(2πmc²)=0.0934 {circumflex over (B)}_x,y[T]λ_u [mm] with the undulator peak magnetic field {circumflex over (B)}_x,y and the normalized laser field a_l=eE_lλ_l/(2πmc²) λ_l [μm] √{square root over (I_l[W/cm²]/1.4×10¹⁸)}.

According to an embodiment, propagation of the electron microbunches through or near a single or periodic dielectric discontinuity leads to the emission of coherent radiation.

According to an embodiment, the electron beam source includes electron optics components configured to steer or guide the electron beam bunch to traverse the interaction region of the electromagnetic undulator along the axis, and wherein the modulation laser source, the undulation radiation source, the second magnetic undulator and the dielectric discontinuity each include optical components configured to condition and/or direct emitted radiation.

According to an embodiment, the one or multiple pulses of electromagnetic radiation have a pulse duration of between 1 fs-100 ps and a wavelength of between 100-3,000 nm and an intensity of 1-1,000 TW/cm², wherein the one or multiple pulses of electromagnetic undulation radiation have a pulse duration of between 1 fs-100 ps and a wavelength of between 100-3,000 nm and an intensity of 1×10¹⁵-1×10²⁰ W/cm², wherein the electron bunch has an energy of between 50-1,000 MeV, wherein the three or more alternating periods of the magnetic or electromagnetic undulator structure have a period of 0.1-50 cm, and wherein the dielectric discontinuity has a thickness of 50 nm-100 μm or a periodic discontinuity with a period of 1-500 μm.

Reference to the remaining portions of the specification, including the drawings and claims, will realize other features and advantages of the present invention. Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with respect to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a schematic of an embodiment of a coherent light source device. The interaction of an electromagnetic wave (modulation laser, blue) with an electron bunch (yellow) in an (electro-) magnetic structure (undulator) causes an energy-modulation of the electron bunch and a modulation of the longitudinal density into spikes (microbunches). A second laser (laser wiggler) is overlapped with the micro-bunched electron bunch to cause emission of coherent short-wavelength radiation (purple). in accordance with an embodiment.

FIG. 2 is a schematic of the laser-electron interaction and bunching mechanism. Top row: a high-power light pulse interacts with a relativisitic electron bunch in a (electro-) magnetic structure. This interaction leads to a strong energy-modulation of the electron bunch and a strong modulation in the spatial electron density. The second row shows the longitudinal electron momentum at the positions along the apparatus indicated by the blue arrows. Rows 2 and 3 show the spatial horizontal (x) and vertical (y) electron distribution at the indicated positions along the interaction.

FIG. 3 shows a simulated spectrum of coherent radiation emission of one microbunch, simulated using the SPECTRA simulation using the parameters shown in Table 1.

DETAILED DESCRIPTION

The present embodiments provide systems and methods for producing coherent light operating from UV to hard X-ray wavelengths with high average power, including light sources that enable the generation of ultrashort, high-brilliance, short-wavelength radiation pulses with a high average power from a compact setup. The photon energy of the emitted radiation can range from ultraviolet (UV) to hard X-ray wavelengths, including extreme ultraviolet (EUV) and soft X-ray wavelengths.

Light Source Properties

The light sources of the present embodiments advantageously require lower, and often significantly lower, electron energies than other electron-beam based approaches. This has the advantage of a compact dimension of the light source, a high conversion efficiency, a lower requirement on the power consumption and lower radiation hazard and shielding requirements.

In certain embodiments, the light sources generate coherent emission that is collimated into a cone in the forward direction, which eases the requirements on subsequent collimation/focusing optics.

The light sources can also generate pulses with ultrahigh brilliance. The extremely short duration of the pulses ensures virtually no motion during exposure, which is of interest for example for high-resolution imaging or lithography applications and can be exploited to investigate atomic dynamics on its natural time scale of interest for the scientific community.

Operated at suitably high repetition rates, the light sources can generate a high average power radiation, which is an essential requirement for lithography and fast imaging. The light sources have a high conversion efficiency of the electron beam power to radiation power.

The wavelength of the emitted radiation is tunable from sub UV to beyond hard X-ray photon energies. The high peak brightness of the radiation can be used to drive nonlinear effects at short wavelengths, for example nonlinear soft X-ray lithography.

Principals and Example Embodiments

In this section, physical principles underlying the process and one example implementation are described (a summary of the light source parameters is given in Table 1, below).

Electron Beam Modulation

The technology described here is based on the interaction of a relativistic electron bunch with a co-propagating linearly or circularly polarized electromagnetic wave (modulation laser pulse) inside a linearly or helically polarized magnetic (or electromagnetic) structure called an undulator or wiggler (see FIG. 1 and FIG. 2). In certain aspects, the undulator or wiggler is not tapered. In an embodiment, using a linear permanent-magnet undulator with a magnetic field B_u={circumflex over (B)}(0, sin(k_uz),0) with an undulator period λ_u and a wavenumber k_u=2π/λ_u, the relativistic electrons are forced onto a transverse sinusoidal trajectory by the magnetic field of the undulator. In this case, the co-propagating electromagnetic wave is polarized in the plane of the electron deflection. The parameters of the undulator and electromagnetic wave or its harmonics are matched to the electron beam, such that the resonance condition

$\begin{array}{cc}{\lambda }_l=\frac{{\lambda }_u}{2n{\gamma }^2}\left(1+\frac{K_x^2}{2}+\frac{K_y^2}{2}+\frac{a_l^2}{2}{\gamma }^2{\theta }_x^2+{\gamma }^2{\theta }_z^2\right)& \left(1\right)\end{array}$

is fulfilled, where λ_l is the wavelength of the electromagnetic wave, λ_u the undulator period, n the harmonic number, γ the electron beam energy normalized to the electron rest mass mc², θ_x and By the electron beam divergence in x and y direction, respectively and the horizontal/vertical undulator deflection parameter K_x,y=e{circumflex over (B)}_x,yλ_u/(2πmc²)=0.0934 {circumflex over (B)}_x,y[T]λ_u [mm] with the undulator peak magnetic field {circumflex over (B)}_x,y and the normalized laser field a_l=eE_lλ_l/(2πmc²)≈λ_l [μm] √{square root over (I_l[W/cm²]/1.4×10¹⁸)}.

In a process called inverse free-electron laser (iFEL)^1,2, the interaction of the electromagnetic wave with the electron bunch inside the undulator leads to a sinusoidal longitudinal energy modulation Δγ of the electron bunch (see FIG. 2, panels b-e, first row). The magnitude of the relative energy modulation Δγ/γ is approximately given by²

$\begin{array}{cc}\frac{\Delta \gamma }{\gamma }\approx \frac{a_{l}K}{{\lambda }_l{\gamma }^2}=\left[J_0\left(G\right)-J_1\left(G\right)\right]L_u,& \left(2\right)\end{array}$

with the laser wavenumber k_l=2π/λ_l, the undulator length L_u, J_n are Bessel functions of the first kind and G=k_lK/8k_uγ²≃K²/4(1+K²/2).

The longitudinally modulated electron momentum distribution is given by

p(s)=p₀+A sin(k_ls),  (3)

where s is the longitudinal electron bunch coordinate, p₀ the average initial momentum, k_l the laser wavenumber and A=Δγ/σ_γ is the energy modulation Δγ amplitude normalized to the initial electron bunch RMS energy spread σ_γ (see FIG. 2, panels b-e, first row).

This energy modulation is converted into a longitudinal density modulation using a dispersive element for the electron beam energy, such as the undulator or a separate magnetic chicane (see FIG. 2, panels b-e, 2^nd and 3^rd row). Importantly, the longitudinal charge distribution has periodic density spikes (microbunches) that are spatially separated by λ_l. The longitudinal length of each density spike is approximately for a large relative energy-modulation amplitude A is approximately given by³

$\begin{array}{cc}{\sigma }_s\approx \frac{{\lambda }_l}{2A}.& \left(4\right)\end{array}$

Microbunches with a very short duration can be generated using a large A. These microbunches can generate high-power coherent radiation for a wavelength that is longer than the microbunch duration (see below), even with electron beam energies that is much lower than those conventionally used for example in soft X-ray or hard X-ray FELs.

In one example, an electron bunch with an energy of about 100 MeV (γ≈200) and a small initial RMS slice energy spread of σ_γ/γ=2.5×10⁻⁵ is used. The electron bunch interacts with a modulation laser pulse with a wavelength λ_l=266 nm, 4 mJ pulse energy, 100 fs pulse duration, focused to a spot size of 130 μm. The laser and electron bunch interact in a 3-period undulator with period λ_u=1.1 cm and magnetic field B_u=1.25 T, tuned such that the laser and the electron bunch are resonant according to equation (1). To match the energy-acceptance of the undulator, which is given by Δγ/γ=½ Δλ_u/λ_u=1/nN, where Nis the number of undulator periods, to allow a large energy modulation, an undulator with only a few periods may be used. These interaction leads to an electron beam with a longitudinally modulated momentum with A≈1,600. As there is nearly no net energy transfer from the incoming radiation pulse to the electron bunch, the modulator laser pulses can be generated by fresh laser pulses for each repetition or can be provided through recycling the previous laser pulse in a laser cavity that can be an enhancement cavity.

The interaction may be calculated using a particle-tracking simulation, such as the general particle tracer (GPT). With these parameters, the simulations lead to microbunches, each with an RMS length of σ_s=0.5 nm and a captured charge of 1.5 pC, which is about 50% of the charge. Ultimately, the charge in the microbunches and their duration is limited by space charge repulsion between the electrons, which is implemented in the simulations. In this scheme the radiation is generated during this process, inside the undulator where the space charge repulsion is suppressed compared to a free drift of the electron bunch. Space charge forces are suppressed at higher electron energies due to relativistic effects.

The conversion efficiency from the electron bunch power to radiation power can be increased by increasing the fraction of captured electrons. This can be achieved in an embodiment using a pre-bunched electron beam or through a double buncher including the use of laser harmonics and coupling harmonic coupling to the electron bunch through the harmonic factor n in equation (1).

Generation of Coherent Radiation

Electron bunches can generate intense coherent radiation when the bunch length σ_s is shorter than the wavelength of the generated radiation λ_r, specifically if the condition⁴

$\begin{array}{cc}{\sigma }_s<\frac{{\lambda }_r}{2}& \left(5\right)\end{array}$

is fulfilled.

The intensity of coherent emission scales quadratically with the number of electrons in the bunch N_e, whereas in case of incoherent emission the intensity only scales linearly with N_e. This quadratic scaling leads to a significant increase in the emitted radiation power compared to the incoherent case. The radiation can be generated through spontaneous (superradiant) coherent emission or stimulated coherent emission, which includes but is not limited to coherent synchrotron radiation, coherent undulator radiation, inverse Compton scattering, Thomson scattering, transition radiation, diffraction radiation or Smith-Purcell radiation.

In one embodiment, coherent inverse Compton scattering is used, which can be thought of as coherent undulator radiation with an electromagnetic undulator (laser wiggler) as shown in FIG. 1. In this embodiment a laser pulse interacts with the micro-bunched electron pulse. Due to the dispersion of the electron bunch and space charge repulsion, which results in an increase of the microbunch lengths, the radiation emission occurs inside the undulator that is used to induce the microbunching while the bunch has the shortest micro-bunch length (see FIG. 1). For relativistic electrons, the wavelength that is generated by the electromagnetic undulator is given by

$\begin{array}{cc}{\lambda }_r={\lambda }_{\mathrm{las}}\left(\frac{1+\frac{a_l^2}{2}+{\gamma }^2{\theta }^2}{2{\gamma }^2\left(1-\cos \varphi \right)}\right)& \left(6\right)\end{array}$

where λ_las is the wavelength of the electromagnetic undulator, a_i the normalized field as defined above, θ the emission angle of the generated radiation and ϕ the interaction angle between the electron bunch and the electromagnetic undulator where ϕ=1800 corresponds to a head-on collision (see FIG. 1). The wavelength of the electromagnetic undulator can be tuned by the laser wavelength, the electron energy and the interaction angle ϕ.

In one example embodiment, an electromagnetic undulator is used, which is generated by an 800 nm laser pulse with a normalized field of a_l=0.5 interacting with the electron beam with an angle of ϕ=4.570 (nearly colinear), for a resonant wavelength of λ_r=3.5 nm. The coherent emission may be simulated using the synchrotron radiation calculation code SPECTRA⁵. For the radiation calculation only one microbunch with a charge of 1.5 pC and an RMS bunch length of σ_s=0.5 nm and a relative energy spread of 10% is simulated (see FIG. 3).

The simulation of one microbunch shows a strong emission of approximately 9×10⁸ photons/microbunch/0.1% bandwidth at a photon energy of 307 eV. This is equivalent to a pulse energy 8.8 μJ per 1.5 pC microbunch in a 20% bandwidth. Considering approximately 50% of the charge being trapped in a microbunch and assuming a total bunch charge of 210 pC, this result in an emitted pulse energy of 616 μJ/pulse. For an operation at a 1 MHz repetition rate, this leads to an average power of 616 W.

As can be seen, in an embodiment, the wavelength of the emitted radiation is a factor of approximately 100 smaller than that of the radiation pulse causing the microbunching.

FIG. 3 shows the spectrum of coherent radiation emission of one microbunch simulated using the SPECTRA simulation using the parameters shown in Table 1.

TABLE 1
Soft X-ray simulation case
Electron microbunch
Electron microbunch charge      1.5 pC
                                (50% charge trapped in microbunch)
Electron microbunch length, σs  0.5 nm
Radiated pulse energy           8.8 μJ in 20% bandwidth @
per microbunch                  4 nm central
                                wavelength
Full electron bunch
Total electron bunch charge     210 pC (70 microbunches in full bunch)
Total electron bunch length     62 fs (RMS)
Radiated pulse energy per bunch 616 μJ in 20% bandwidth @ 4 nm
                                central wavelength
Radiated pulse duration         62 fs (RMS)
Radiation power
Repetition rate                 1 MHz
Average power                   616 W
Electron-to-radiation power     3%
conversion efficiency

In an embodiment, this approach can be cascaded to generate even shorter, hard X-ray wavelengths. In this case the radiation emission of a first stage is overlapped either with the same or a fresh electron bunch in a second undulator that is tuned to the corresponding resonance condition. This causes microbunching on a shorter scale and the emission of coherent radiation at a shorter wavelength.

REFERENCES

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All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

The use of the terms “a” and “an” and “the” and “at least one” and similar referents in the context of describing the disclosed subject matter (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of the term “at least one” followed by a list of one or more items (for example, “at least one of A and B”) is to be construed to mean one item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B), unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or example language (e.g., “such as”) provided herein, is intended merely to better illuminate the disclosed subject matter and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

Certain embodiments are described herein. Variations of those embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the embodiments to be practiced otherwise than as specifically described herein. Accordingly, this disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

1. A coherent light source device, comprising: a magnetic or an electromagnetic undulator structure configured to produce a linearly or helically polarized magnetic or an electromagnetic field having three or more alternating electromagnetic periods and defining an axis within an interaction region;a modulation laser source configured to emit one or multiple pulses of linearly or circularly polarized electromagnetic radiation that co-propagate with an electron beam bunch along the axis of the magnetic or electromagnetic undulator within the magnetic or electromagnetic undulator;an electron beam source configured to generate the electron beam bunch that traverses the interaction region of the magnetic or electromagnetic undulator along the axis, wherein interaction of the electron beam bunch with the electromagnetic field of the one or multiple pulses of the modulation laser source in the interaction region of the magnetic or electromagnetic undulator structure induces the formation of electron microbunches within the electron beam bunch; andan undulation laser source configured to emit one or multiple pulses of electromagnetic undulation radiation that traverse the interaction region of the electromagnetic undulator at an interaction angle with respect to the axis, ora second magnetic undulator, ora dielectric discontinuity,wherein interaction of the one or multiple pulses of electromagnetic undulation radiation or the second magnetic undulator or the dielectric discontinuity with the electron microbunches induces spontaneous or stimulated coherent emission of radiation by the electron microbunches at an emission wavelength, wherein the emission wavelength is shorter than a wavelength of the one or more or multiple pulses of electromagnetic undulation radiation or is shorter than the period of the second magnetic undulator or is shorter than the thickness of the dielectric discontinuity.

2. The coherent light source device of claim 1, wherein the electron microbunches include electron bunches having a longitudinal charge distribution with periodic density spikes that are separated by a distance equal to the wavelength or harmonics of the wavelength of the one or multiple pulses of electromagnetic radiation emitted by the modulation laser source.

3. The coherent light source device of claim 1, wherein the one or multiple pulses of electromagnetic radiation are circularly polarized or polarized perpendicular to or in a plane of electron deflection of electrons in the electron beam bunch within the interaction region.

4. The coherent light source device of claim 1, wherein the emission wavelength λr is given by the equation:

5. The coherent light source device of claim 1, wherein the emission wavelength λr is given by the equation:

6. The coherent light source device of claim 1, wherein propagation of the electron microbunches through or near a single or periodic dielectric discontinuity leads to the emission of coherent radiation.

7. The coherent light source device of claim 1, wherein the electron beam source includes electron optics components configured to steer or guide the electron beam bunch to traverse the interaction region of the electromagnetic undulator along the axis, and wherein the modulation laser source, the undulation radiation source, the second magnetic undulator and the dielectric discontinuity each include optical components configured to condition and/or direct emitted radiation.

8. The coherent light source device of claim 1, wherein the one or multiple pulses of electromagnetic radiation have a pulse duration of between 1 fs-100 ps and a wavelength of between 100-3,000 nm and an intensity of 1-1,000 TW/cm2, wherein the one or multiple pulses of electromagnetic undulation radiation have a pulse duration of between 1 fs-100 ps and a wavelength of between 100-3,000 nm and an intensity of 1×1015-1×1020 W/cm2, wherein the electron bunch has an energy of between 50-1,000 MeV, wherein the three or more alternating periods of the magnetic or electromagnetic undulator structure have a period of 0.1-50 cm, and wherein the dielectric discontinuity has a thickness of 50 nm-100 μm or a periodic discontinuity with a period of 1-500 μm.

9. The coherent light source device of claim 1, wherein interaction of the one or more pulses of linearly or circularly polarized electromagnetic radiation with the electron beam bunch inside the linearly or helically polarized magnetic or electromagnetic undulator structure leads to a longitudinally modulated or micro bunched density of the electron beam density of the electron bunch with density spikes that have a length significantly below a wavelength of the one or multiple pulses of electromagnetic radiation when the resonance condition given by the equation:

10. A method of generating coherent light, the method comprising: generating an electron beam bunch that traverses an axis in an interaction region of a magnetic or an electromagnetic undulator that produces a magnetic or electromagnetic field having three or more alternating electromagnetic periods along the axis within the interaction region, wherein interaction of the electron beam bunch with an additional electromagnetic field induces the formation of electron microbunches within the electron beam bunch;generating one or multiple pulses of electromagnetic radiation that co-propagate with the electron beam bunch along the axis of the electromagnetic undulator within the magnetic or electromagnetic undulator; andgenerating one or multiple pulses of electromagnetic undulation radiation that traverse the interaction region of the magnetic or electromagnetic undulator at a first interaction angle with respect to the axis, wherein interaction of the one or multiple pulses of electromagnetic undulation radiation with the electron microbunches induces stimulated coherent emission of radiation by the electron microbunches at an emission wavelength that is shorter than a wavelength of the one or more or multiple pulses of electromagnetic undulation radiation, orgenerating a magnetic undulator, wherein interaction of the magnetic undulator with the electron microbunches induces stimulated coherent emission of radiation by the electron microbunches at an emission wavelength that is shorter than the period of the magnetic undulator, orgenerating a single or periodic dielectric discontinuity, wherein interaction of the electron microbunches with the dielectric discontinuity induces coherent emission of radiation by the electron microbunches at an emission wavelength that is shorter than the width of the periodic structure.

11. The method of claim 10, wherein the electron microbunches include electron bunches having a longitudinal charge distribution with periodic density spikes that are separated by a distance equal to the wavelength of the one or multiple pulses of electromagnetic radiation.

12. The method of claim 10, wherein the one or multiple pulses of electromagnetic radiation are circularly polarized or polarized perpendicular to or in a plane of electron deflection of electrons in the electron beam bunch within the interaction region.

13. The method of claim 10, wherein the emission wavelength λr is given by the equation:

14. The method claim 10, wherein the emission wavelength λr is given by the equation:

15. The method claim 10, wherein propagation of the electron microbunches through or near a single or periodic dielectric discontinuity leads to the emission of coherent radiation.

16. The method of claim 10, further including steering or guiding the electron beam bunch to traverse the interaction region of the magnetic or electromagnetic undulator along the axis.

17. The method of claim 10, wherein the one or multiple pulses of electromagnetic radiation have a pulse duration of between 1 fs-100 ps and a wavelength of between 100-3,000 nm and an intensity of 1-1,000 TW/cm2, wherein the one or multiple pulses of electromagnetic undulation radiation have a pulse duration of between 1 fs-100 ps and a wavelength of between 100-3,000 nm and an intensity of 1×1015-1×1020 W/cm2, wherein the electron bunch has an energy of between 50-1,000 MeV, wherein the three or more alternating periods of the magnetic or electromagnetic undulator have a period of 0.1-50 cm, and wherein the dielectric discontinuity has a thickness of 50 nm-100 μm or a periodic discontinuity with a period of 1-500 μm.

18. The method of claim 10, wherein interaction of the one or more pulses of linearly or circularly polarized electromagnetic radiation with the electron beam bunch inside the linearly or helically polarized magnetic or electromagnetic undulator structure leads to a longitudinally modulated or micro bunched density of the electron beam density of the electron bunch with density spikes that have a length significantly below a wavelength of the one or multiple pulses of electromagnetic radiation when the resonance condition given by the equation: