Laser-based contrast control in transmission electron microscopy.

Abstract

According to the present disclosure, a novel system or method for electron beam imaging or electron beam spectroscopy is provided, the system includes a transmission electron microscope (TEM) including an electron source configured to provide an electron beam, at least one laser-based device configured to provide at least one laser beam, the laser beam being configured to shift a predetermined portion of the electron beam to an energy spectrum different from the original energy spectrum provided by the electron source, and an electron energy filter configured to pass the electron beam having the original energy spectrum but not pass the electron beam having the energy spectrum different from the original energy spectrum.

Description

[Technical field]

[0001] The present invention relates to laser-based contrast control in transmission electron microscopes. [Background technology]

[0002] Transmission electron microscopes (TEMs) are essential tools in materials and life sciences. In particular, the development of cryo-electron microscopes (cryo-EM) has led to rapid advances in structural biology and was awarded the Nobel Prize in Chemistry in 2018.

[0003] The rapid progress of cryo-electron microscopy (cryo-EM) has been driven by the development of direct electron detectors, sample preparation and handling techniques, and incremental improvements in data processing software. At the same time, the electron optics of the TEM have also evolved incrementally. Apart from the development of aberration correctors (which are not widely used in cryo-EM), the optical design of TEMs has changed only slowly over the past 10-20 years.

[0004] A key feature of cryo-electron microscopy, as with any TEM imaging of samples made of light elements, is that the sample is nearly transparent to the electron beam. The structure of the sample is imprinted in the phase of the electron beam passing through the sample, but because the detector is only sensitive to the electron flux and not the phase, a focused image of a phase object contains very little information about the sample. The traditional solution to this is to take most images with a defocused imaging system that converts some of the phase information into detectable amplitude modulation. However, while this works efficiently for high spatial frequency information, low frequency information remains unavailable. In addition, the contrast transfer function (CTF) is oscillatory and less than half of all information can be recovered.

[0005] A better solution, widely used in optical microscopy, is known as the Zernike phase contrast method (received the Nobel Prize in 1953). This approach is based on changing the relative phase between the scattered wave (containing information about the sample) scattered by the sample and the part of the illuminating wave that passes through the sample unchanged (the unscattered wave). This requires a phase shift of 90 degrees for the unscattered wave, which can be easily achieved in optical microscopes using optical phase retardation plates (or simply phase plates). Development of phase plates for electron microscopes has been going on since 1947.

[0006] A major advance was the development of a Volta phase plate based on thin carbon foils, but this presents practical difficulties because the phase shift changes with accumulated electron exposure, and it was also found to attenuate the useful signal to some extent.

[0007] Recently, a group at the University of California, Berkeley, demonstrated the implementation of a phase plate for electron microscopy based on electron interaction with a laser field. In this approach, ponderomotive delay of unscattered waves is used to provide in-focus phase-contrast imaging. In this work, the required high laser intensity was achieved by using a highly fine optical resonator that resonantly enhances the laser power. The type of optical resonator (cavity) used was a nearly concentric resonator that supports modes at a tight focus. This system reached sufficient laser intensity to phase-shift a 300 keV electron beam by 90 degrees. The TEM used in this experiment was equipped with a special transformation (magnetic) lens, which formed an additional plane conjugate to the back focal plane of the TEM objective lens, with an additional magnification of 6 times. The optical resonator was integrated with the microscope by suspending it so that the focal point of the optical resonator was located at the center of the conjugate back focal plane.

[0008] However, even with optimal phase shifting, the contrast of cryo-EM images is extremely low. Whether the image is obtained using defocus-based phase contrast or a phase plate, the variation in grey levels across the image remains small relative to the average value. This is a consequence of the fact that cryo-EM samples are weak phase objects, i.e., they contribute little phase to the electron beam.

[0009] This low contrast, for example, places a significant constraint on the data acquisition speed. This is crucial for cryo-electron microscopes, which are operated as multi-user facilities and require the allocation of imaging time. The state-of-the-art electron detection technology, direct electron cameras, works in an electron counting manner and can process a limited number of electrons per unit time. Since the majority of detected electrons are background electrons, the acquisition time of a micrograph represents a major bottleneck in throughput. Another major drawback of low contrast is that it hinders the development of proportional detectors in TEM. The high background means that only a small part of the dynamic range of the detector can be used. Summary of the Invention [Means for solving the problem]

[0010] In some embodiments of the present invention, a novel system for electron beam imaging or spectroscopy is provided, comprising: a transmission electron microscope (TEM) including an electron source configured to provide an electron beam; at least one laser-based device configured to provide at least one laser beam, the laser beam configured to shift a predetermined portion of the electron beam to an energy spectrum different from the original energy spectrum provided by the electron source; An electron energy filter configured to pass an electron beam having an original energy spectrum but not pass an electron beam having an energy spectrum different from the original energy spectrum is provided.

[0011] In some embodiments of the present invention, the laser-based device is placed near the back focal plane of a transmission electron microscope (TEM) or near a plane that is conjugate to the back focal plane.

[0012] In some embodiments of the present invention, the laser beam provided from the laser-based device is a continuous wave laser beam.

[0013] In some embodiments of the present invention, the predetermined portion of the electron beam is a predetermined portion of the unscattered electron wave of the electron beam.

[0014] In some embodiments of the present invention, the laser beam is further configured to impart a predetermined phase shift to a portion of the electron beam.

[0015] In some embodiments of the present invention, a laser-based device is configured to form a laser focus and position the laser focus near a back focal plane or near a conjugate plane of a transmission electron microscope (TEM), and the laser-based device is positioned such that unscattered electron waves of the electron beam pass through the laser focus.

[0016] In some embodiments of the invention, the material structure of the laser-based device is constructed and arranged such that the electron beam of a transmission electron microscope (TEM) is at least 0.1 mm, at least 1 mm, or at least 10 mm away from any material element of the laser-based device.

[0017] In some embodiments of the present invention, the laser-based device and electron energy filter are configured to attenuate an electron beam in a transmission electron microscope (TEM) to a predetermined beam current and / or to attenuate an electron beam in a transmission electron microscope (TEM) by a predetermined attenuation factor.

[0018] In some embodiments of the invention, the laser-based device and electron energy filter are configured to attenuate unscattered electron waves of an electron beam in a transmission electron microscope (TEM) to a predetermined amplitude and / or to attenuate unscattered electron waves of an electron beam in a transmission electron microscope (TEM) by a predetermined attenuation factor.

[0019] In some embodiments of the present invention, the transmission electron microscope (TEM) further includes an electron detector disposed at an image plane of the transmission electron microscope (TEM) and configured to receive the electron beam.

[0020] In some embodiments of the present invention, the laser-based device further comprises at least one optical resonator.

[0021] In some embodiments of the present invention, Each of the at least one optical resonator comprises: Having two or more mirrors, A laser beam is configured to be incident thereon, Located near the back focal plane of a transmission electron microscope (TEM) or near a conjugate plane that is conjugate with the back focal plane of a transmission electron microscope (TEM), and It is configured to pass an electron beam provided by a transmission electron microscope (TEM).

[0022] In some embodiments of the present invention, at least one optical resonator is an aspheric nearly concentric resonator having an aspheric mirror.

[0023] In some embodiments of the present invention, the laser beam provided by the laser-based device is a non-monochromatic laser beam.

[0024] In some embodiments of the present invention, a non-monochromatic laser beam is provided by combining two or more laser beams having different wavelengths into an optical cavity.

[0025] In some embodiments of the present invention, the non-monochromatic laser beam is provided by a structure of two or more optical resonators whose foci overlap one another.

[0026] In some embodiments of the present invention, The optical cavity is tilted with respect to the optical axis of the transmission electron microscope (TEM), The optical axis of the optical cavity is tilted with respect to the optical axis of the transmission electron microscope (TEM), or The laser beam propagation direction of the optical cavity is tilted with respect to the optical axis of the transmission electron microscope (TEM).

[0027] In some embodiments of the present invention, a novel method for electron beam imaging or spectroscopy is provided, comprising the steps of: Providing a system according to any of the above embodiments; Attenuating a predetermined portion of the electron beam to a predetermined beam current and / or attenuating the electron beam by a predetermined attenuation factor with a laser-based device and an electron energy filter.

[0028] In some embodiments of the present invention, there is provided another novel system for electron beam imaging or spectroscopy, comprising: a transmission electron microscope (TEM) including an electron source configured to provide an electron beam; at least one laser-based device configured to provide at least one laser beam, the laser beam configured to shift a predetermined portion of the electron beam to a momentum different than an original momentum provided to the predetermined portion of the electron beam by a transmission electron microscope (TEM); and an aperture configured to pass an electron beam having an original momentum provided by a transmission electron microscope (TEM) but not pass an electron beam that has been shifted to a momentum different from the original momentum by a laser-based device.

[0029] In some embodiments of the present invention, the laser-based device is placed near the back focal plane of a transmission electron microscope (TEM) or near a plane that is conjugate to the back focal plane.

[0030] In some embodiments of the present invention, the predetermined portion of the electron beam is a predetermined portion of the unscattered electron wave of the electron beam.

[0031] In some embodiments of the present invention, there is provided another novel method for electron beam imaging or spectroscopy, comprising: Providing a system according to any of the above embodiments; A method is provided that includes attenuating unscattered electron waves of an electron beam in a transmission electron microscope (TEM) to a predetermined amplitude and / or attenuating unscattered electron waves of an electron beam in a transmission electron microscope (TEM) by a predetermined attenuation factor using a laser-based device and an aperture. [Brief description of the drawings]

[0032] The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification, however, the invention, both as to organization and method of operation, together with its objects, features, and advantages, may best be understood by reading the following detailed description when read in conjunction with the accompanying drawings.

[0033] [Figure 1] FIG. 1 is a schematic diagram of a system for electron beam imaging or spectroscopy according to some embodiments of the present invention. [Diagram 2] FIG. 2 is a schematic diagram illustrating the relationship between an illuminating electron beam, unscattered waves, and scattered waves according to some embodiments of the present invention. [Diagram 3] 3(A) and (B) are schematic diagrams of a nearly concentric resonator with a spherical mirror, according to some embodiments of the present invention. [Figure 4] 4(A) and (B) are schematic diagrams of a nearly concentric resonator with an aspheric mirror, according to some embodiments of the present invention. [Figure 5A] FIG. 5A is a schematic diagram of a portion of a system having an optical cavity orthogonal to the optical axis of the TEM, according to some embodiments of the present invention. [Figure 5B] FIG. 5B is a schematic diagram of a portion of a system having an optical cavity tilted relative to the optical axis of the TEM, according to some alternative embodiments of the present invention. [Figure 6] FIG. 6 is a schematic diagram of a TEM system, according to some embodiments of the present invention. [Figure 7] FIG. 7 is a schematic diagram of a dichroic optical resonator according to some embodiments of the present invention. [Figure 8] 8(A)-(D) are schematic diagrams showing the temporal profile (FIGS. 8(A) and 8(B)) and energy spectrum (FIGS. 8(C) and 8(D)) of an electron beam before and after interaction with a dual-frequency laser beam in an optical resonator according to some embodiments of the present invention. [Figure 9] FIG. 9 is a schematic diagram of another system for electron beam imaging or spectroscopy, according to some embodiments of the present invention.

[0034] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale, and reference numerals may be repeated among the figures to indicate corresponding or similar elements. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] The present invention may be more readily understood by reading the following detailed description of exemplary embodiments, which form a part of this disclosure. The present invention is not limited to the specific products, methods, conditions, or parameters described and / or illustrated herein. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments by way of example only, and is not intended to limit the invention as described in the appended claims. Further, unless otherwise required by context, singular terms shall include the plural and plural terms shall include the singular.

[0036] Embodiments of the presently disclosed subject matter relate, inter alia, to laser-based control of electron beams / waves, aimed at improving various aspects of electron-based microscopy and spectroscopy.

[0037] As used herein, in some embodiments, the terms "cavity," "optical cavity," "resonator," and "optical resonator" all have the same meaning and nature and are used interchangeably.

[0038] As used herein, in some embodiments, the terms "wave" and "beam" have the same meaning and properties and are used interchangeably.

[0039] As used herein, in some embodiments, the terms "electron gun" and "electron source" have the same meaning and nature and are used interchangeably.

[0040] As used herein, in some embodiments, the terms "object" and "sample" have the same meaning and nature and are used interchangeably.

[0041] In optical phase-contrast microscopy, in addition to applying a phase shift, the problem of low contrast is addressed by attenuating the unscattered waves with a Zernike plate (the unscattered waves form the image background). High-contrast images are obtained when the unscattered waves are attenuated to a level where they have a similar amplitude to the scattered waves. This attenuation transforms the microscope from an unbalanced imaging interferometer to a balanced one. However, no effective attenuators exist for TEM.

[0042] FIG. 1 is a schematic diagram of a novel system for electron beam imaging and / or electron beam spectroscopy of a sample, according to some embodiments of the present invention. The system 100 includes: a transmission electron microscope (TEM) 101 including an electron gun 102 (electron source) configured to provide an electron beam 104; at least one laser-based device 115 configured to provide at least one laser beam 114, the laser beam 114 being configured to shift a predetermined portion of the electron beam 104 to an energy spectrum different from the original energy spectrum provided by the electron gun 102 of the TEM 101; an electron energy filter 116 configured to pass the electron beam having the original energy spectrum provided by the electron gun 102 of the TEM 101 but not the electron beam having the energy spectrum shifted by the laser-based device 115, thereby attenuating the unscattered wave 107 of the received electron beam 117; Note that beam 117 shows the scattered wave 108 and the unscattered wave 107 recombined by lens 103D in this example.

[0043] In some embodiments, where the laser-based device provides multiple laser beams, their combined action is configured to change the energy spectrum of a given portion of the electron beam.

[0044] In some embodiments, the predetermined portion of the electron beam is a predetermined percentage of a component of the electron beam. In some embodiments, the component of the electron beam is ·Unscattered electron waves, ·Scattered electron waves, ·Scattered electron wave group, A set of electron waves that can be selected from the electron beam by spatial filtering, and At least one of any combination of them. In some embodiments, the predetermined percentage is selected from 0.01% to 1%, 1% to 10%, 10% to 50%, 50% to 90%, between 90% to 99%, 99% to 99.99%, and any combination thereof.

[0045] In some embodiments, the electron energy filter is configured to remove at least 50%, at least 90.0%, at least 99.0%, or at least 99.9% of the electron beam having the shifted energy spectrum.

[0046] In some embodiments, the TEM 101 comprises a number of lenses 103A-103D configured to condition and direct the electron beam 104 to illuminate an object or sample 105 being imaged, the object / sample 105 being supported and / or positioned by a sample holder 106. In some embodiments, the number of lenses are magnetic lenses.

[0047] 1 and 2 show that interaction of the illumination electron beam 104 with the object or sample 105 causes some of the illumination electron beam to be scattered to form a number of scattered waves 108, while other portions of the illumination electron beam that are not scattered by interaction with the object or sample 105 form an unscattered wave 107.

[0048] Figure 1 further shows that in some embodiments, the unscattered wave 107 is focused by the magnetic lenses 103B, 103C at the center 110C of the back focal plane 110. Figure 1 also shows that the scattered wave 108 is focused at a location 110S other than the center 110C of the back focal plane 110.

[0049] In some embodiments, the laser-based device 115 includes: Near the back focal plane 110 of the TEM 101, i.e., within ±1 mm, ±0.1 mm, ±0.01 mm, or ±0.001 mm of the back focal plane 110, or It is placed near a plane conjugate to the back focal plane 110, that is, at a position within the range of ±1 mm, ±0.1 mm, ±0.01 mm, or ±0.001 mm from the conjugate plane.

[0050] In some embodiments, the laser beam 114 provided by the laser gun (electron gun) is a continuous wave laser beam.

[0051] Embodiments of the present invention show that by extending the concept of continuously operating a spatially selective phase retarder (laser phase plate) for a transmission electron microscope (TEM), a spatially selective attenuator for an electron beam is provided.

[0052] In some embodiments, the shifted predetermined portion of the electron beam 104 is a predetermined portion of the unscattered electron wave 107 of the electron beam 104 .

[0053] In some embodiments, the laser beam 114 is further configured to impart a predetermined phase shift to a portion of the electron beam 104. In some embodiments, the phase shift is applied / provided to the entire unscattered wave 107.

[0054] In some embodiments, as shown in FIG. 1, the laser-based device 115 forms a laser focus 110C and Near the back focal plane 110 of the TEM 101, i.e., at a position within a range of ±1 mm, ±0.1 mm, ±0.01 mm, or ±0.001 mm from the back focal plane, or Configured to be positioned near a conjugate plane of the back focal plane 110, i.e., within a range of ±1 mm, ±0.1 mm, ±0.01 mm, or ±0.001 mm from the conjugate plane. Additionally, the laser-based device 115 is positioned such that the unscattered electron waves 107 of the electron beam 104 pass through the laser focal point 110C.

[0055] In some embodiments, the laser beam 114 is selected to have a wavelength in the range of 350 nm to 2000 nm, or in the range of 2000 nm to 15 μm.

[0056] In some embodiments, the material structure of the laser-based device 115 is constructed and arranged such that the electron beam 104 of the TEM 101 is at least 0.1 mm, at least 1 mm, or at least 10 mm away from any material element of the laser-based device 115 to avoid distortion, scattering, and / or dephasing of the electron beam due to interaction with the physical structure of the laser-based device.

[0057] In some embodiments, the laser-based device 115 and the electron energy filter 116 are configured to attenuate the electron beam 104 in the TEM 101 to a predetermined beam current and / or to attenuate the electron beam 104 in the TEM 101 by a predetermined attenuation factor.

[0058] In some embodiments, the predetermined beam current attenuation factor is selected from the range of 1-3, the range of 3-10, the range of 10-30, the range of 30-100, the range of 100-300, the range of 300-1000, or 1000 or greater.

[0059] In some embodiments, the laser-based device 115 and the electron energy filter 116 are configured to attenuate the unscattered electron waves 107 of the electron beam 104 in the TEM 101 to a predetermined amplitude and / or to attenuate the unscattered electron waves 107 of the electron beam 104 in the TEM 101 by a predetermined attenuation coefficient.

[0060] In some embodiments, the predetermined amplitude attenuation coefficient is selected from the range of 1-3, the range of 3-10, the range of 10-30, the range of 30-100, the range of 100-300, the range of 300-1000, or 1000 or greater.

[0061] In some embodiments, the predetermined beam current is selected from less than 1 pA, less than 1 nA, less than 1 μA, less than 1 mA, less than 1 A, at least 1 pA, at least 1 nA, at least 1 μA, at least 1 mA, or at least 1 A.

[0062] In some embodiments, the predetermined amplitude of the unscattered wave 107 corresponds to a beam current 104 selected from less than 1 pA, less than 1 nA, less than 1 μA, less than 1 mA, less than 1 A, at least 1 pA, at least 1 nA, at least 1 μA, at least 1 mA, or at least 1 A.

[0063] In some embodiments, as shown in FIG. 1, the TEM 101 further includes an electron detector 118 disposed at an image plane of the TEM 101 and configured to receive the electron beam 104.

[0064] In some embodiments, as shown in FIG. 1, the laser-based device 115 includes at least one optical cavity 112 .

[0065] In some embodiments, Each optical cavity 112 has two or more mirrors 112M. Each optical cavity 112 is configured for a laser beam 109 to be incident / coupled therein. Each optical resonator 112 is positioned near the back focal plane 110 of the TEM 101, i.e., at a position within the range of ±1 mm, ±0.1 mm, ±0.01 mm, or ±0.001 mm from the back focal plane 110, or near a plane conjugate to the back focal plane 110 of the TEM 101 (conjugate plane), i.e., at a position within the range of ±1 mm, ±0.1 mm, ±0.01 mm, or ±0.001 mm from the conjugate plane. Each optical cavity 112 is configured to pass an electron beam 104 provided by a TEM 101 .

[0066] In some embodiments, as shown in FIG. 1, the optical cavity 112 is positioned within the TEM 101 such that the laser beam 109 therein has a focus near the center 110C of the back focal plane 110 of the TEM 101, i.e., at a position within a range of ±1 mm, ±0.1 mm, ±0.01 mm, or ±0.001 mm from the center 110C of the back focal plane 110.

[0067] In some embodiments, the laser-based device 115 is configured to provide two or more laser beams 114 having different wavelengths from one another.

[0068] In some embodiments, as shown in FIG. 1, the TEM 101 has a laser port 113 through which a laser beam 114 enters the TEM 101 and is guided or coupled into an optical resonator 112 (cavity).

[0069] In some embodiments, interaction of the unscattered electron wave 107 of the electron beam 104 with the laser beam 114 converts a portion of the unscattered wave 107 into an energy different from the original energy provided by the electron gun 102 (electron source) of the TEM 101.

[0070] 1, after interaction with laser beam 114, unscattered wave 111 includes a portion of unscattered wave 107 having the original energy provided by electron gun 102 and a portion that has been converted to an energy different from the original energy. Both scattered wave 108 and unscattered wave 111 are then directed to electron energy filter 116. Electron energy filter 116 is configured to remove the energy-shifted portion of unscattered wave 111 and to attenuate unscattered wave 111.

[0071] In some embodiments, the energy provided to the electron beam 104 by the electron gun 102 of the TEM 101 is selected to be in the range of 10 keV to 500 keV.

[0072] In some embodiments, as shown in FIG. 1, the scattered wave 108 and the attenuated unscattered wave 107 are then recombined by the TEM 101 and the recombined beam forming an image of the sample / object is then directed to an electron detector 118.

[0073] In some embodiments, as shown in FIGS. 4(A) and (B), at least one optical resonator 400 is an aspheric nearly concentric resonator having an aspheric mirror 430.

[0074] In some embodiments, the laser beam 114 provided by the laser-based device 115 is a non-monochromatic laser beam. In some embodiments, the non-monochromatic laser beam is provided by a configuration in which two or more laser beams having different wavelengths are combined into one optical resonator. In some other embodiments, the non-monochromatic laser beam is provided by a configuration in which two or more optical resonators have overlapping focal points.

[0075] In some embodiments, Whether the optical resonator 535 is tilted with respect to the optical axis of the TEM 560 (see FIG. 5(B)); The optical axis of the optical cavity is tilted with respect to the optical axis of the TEM, or The laser beam propagation direction in the optical cavity is tilted with respect to the optical axis of the TEM.

[0076] 3A is a schematic diagram of a substantially concentric resonator 300 having two spherical mirrors 330 with spherically shaped surfaces, according to some embodiments of the present invention. In this example, the two spherical mirrors 330 have surfaces with the same radius of curvature as each other. In this example, the substantially concentric configuration of the optical resonator 300 is achieved by positioning the two spherical mirrors 330 such that each surface of the two spherical mirrors 330 is located on the surface of a virtual sphere 310 that has the same radius of curvature as the radius of curvature of the surfaces of the spherical mirrors 330. It should be noted that the optical resonator 300 is stable only when each surface of the spherical mirrors 330 is located inside the virtual sphere 310.

[0077] FIG. 3B is a schematic diagram of the same generally concentric resonator 300 shown in FIG. 3A, but in some embodiments of the present invention, a laser beam 350 is shown inside the optical resonator 300.

[0078] FIG. 4(A) is a schematic diagram of an aspherical approximately concentric resonator 400 according to some embodiments of the present invention. The aspherical approximately concentric resonator 400 differs from the conventional approximately concentric resonator shown in FIG. 3(A) in that it has an aspherical mirror 430 with an aspherical surface. In the illustrated example, the two aspherical mirrors 430 have the same shape as each other. In this example, the approximately concentric configuration of the optical resonator 400 is achieved by arranging the two aspherical mirrors 430 such that the central portion of each of the approximately spherical surfaces of the two aspherical mirrors 430 is located on the surface of a virtual sphere 410 having the same radius of curvature as the radius of curvature of the central portion of the surface of the aspherical mirror 430.

[0079] Figure 4(B) is a schematic diagram of the same aspherical quasi-concentric resonator 400 shown in Figure 4(A), but in some embodiments of the present invention, a laser beam 450 is shown inside the optical resonator 400. The main advantage of the aspherical quasi-concentric resonator 400 is that it can achieve a higher numerical aperture and, as a result, a smaller focal spot size than a conventional quasi-concentric resonator with a spherical mirror.

[0080] 5A is a schematic diagram of a portion of a system according to some embodiments of the present invention, showing an optical resonator 530 orthogonal to an optical axis 560 of a TEM 500. In this example, the optical resonator 530 is located in the back focal plane (shown by the thin dashed line) of an objective lens 510 of the TEM 500. The objective lens 510 includes an upper pole piece 510 and a lower pole piece 520. Also shown is a laser beam 550 within the optical resonator 530, having a focal point at the intersection of the optical axis 560 of the TEM 500 and the back focal plane.

[0081] Figure 5B is a schematic diagram of a portion of a system according to some embodiments of the present invention. The system shown in Figure 5B is similar to the system shown in Figure 5A, except that the optical cavity 535 is tilted at an angle to the optical axis 560 of the TEM 500. Thus, in this example, the laser beam 555 in the optical cavity 535 intersects the optical axis 560 of the TEM 500 at an angle.

[0082] 6 shows a TEM system 600 having an optical resonator 612 at the back focal plane of the objective lens, according to some embodiments of the present invention. The optical resonator 612 is configured to partially shift the energy of the unscattered electron wave. An electron energy filter 616 is configured to remove the components of the unscattered wave that have been shifted in energy. In some embodiments, the remaining components of the unscattered wave at their original energy interfere with the scattered wave to form an image in an electron detector 618 with optimized contrast.

[0083] Figure 7 is a schematic diagram of a dichroic optical resonator according to some embodiments of the present invention. In this dichroic optical resonator, two laser beams with different frequencies circulate inside the optical resonator, forming four optical lattices (two standing waves and two propagating waves). In Figure 7, only one optical lattice is shown, and the propagation direction is indicated by the red arrows. An electron beam propagating across the focal point of the optical resonator can be efficiently modulated in time if its velocity satisfies the following condition:

[0084]

number

[0085] In the above formula,

[0086]

number

[0087] is the velocity of the optical lattice, v electron is the velocity of the electron, θ is the angle between them, and ω 1 and ω 2 is the frequency of the two laser beams coupled into the optical cavity.

[0088] The interaction of electrons with a tilted dichroic optical cavity is described by a change in the wavepacket shape from a smooth Gaussian-like wavepacket before the interaction to an oscillating waveform downstream of the interaction region, which arises from the interference of components of the electron beam with different energies.

[0089] 8(A)-(D) are schematic diagrams showing the time profile (FIGS. 8(A) and (B)) and energy spectrum (FIGS. 8(C) and (D)) of an electron wave before and after interaction with a two-frequency laser beam in an optical resonator according to some embodiments of the present invention. As shown, after interaction, the time profile of the electron wave function shows interference of different energy components and the energy spectrum of the electron exhibits sidebands (see FIG. 8(B) and (D)). In some embodiments, the electron wave can be attenuated by spectrally selecting (e.g., using a post-column spectrometer) only those electrons remaining at their original energy. The range of energies selected by the energy filter is circled (dashed) in FIG. 8(C) and (D).

[0090] In some embodiments, the system includes a laser device configured to solve the low contrast problem in cryo-electron microscopy, which simultaneously achieves phase shifting and attenuation of the unscattered waves, such that Zernike phase contrast in transmission electron microscopy can be achieved.

[0091] In some embodiments, the technique of ponderomotive phase manipulation in a continuous free-space electron beam is extended to allow optically controlled deflection, temporal modulation, and damping of the electron wave. Experimental realizations include customized TEMs with cavity-enhanced laser beams positioned to manipulate the electron wave in front of and behind the sample plane.

[0092] In some embodiments, the TEM is configured to allow operation of the enhanced optical cavity at the back focal plane of the objective lens or its conjugate plane, with sufficient space between the lasers to allow insertion of the sample holder and contamination prevention device (cryobox). The TEM can be customized to provide sufficient space for the optical cavity while still allowing operation of the TEM.

[0093] In some embodiments, a unique aspect of the realization of the present invention based on CW lasers (continuous wave lasers) is that it allows ponderomotive manipulation of a continuous electron beam in free space. In some embodiments, the continuous mode of operation is configured to benefit from the high coherence and high average beam current provided by the field emission gun (FEG). At the same time, the interaction of the electrons with the laser in free space allows the electron beam to be kept away from material surfaces where it may cause dephasing and scattering. In some embodiments, the combination of these two factors is configured to allow laser manipulation in state-of-the-art TEMs without compromising the capability of atomic resolution imaging and angstrom-scale focusing of the electron beam.

[0094] In some embodiments, the laser-based device comprises: 12 W / cm 2The optical resonator includes two nearly concentric resonators capable of reaching a focal laser intensity of the order of 1064 nm. In some embodiments, the optical resonator supports two wavelengths, e.g., 1064 nm and 532 nm, and the input beam (laser beam) is provided by a dual output CW (continuous wave) laser system, e.g., a fiber laser system providing a 1064 nm beam and a frequency doubled beam. In some embodiments, the laser system and locking electronics are modeled on existing laser resonator frequency locking techniques. In some embodiments, the optical resonator is equipped with a micropositioning system that allows the optical resonator to be positioned at the back focal plane of the objective lens for electronic phase manipulation before and after interaction with the sample, respectively. Also, in some embodiments, the suspension system (micropositioning system) is configured to allow adjustment of the orientation of the optical resonator relative to the TEM optical axis and velocity matching between the electrons and the optical grating moving within the dichroic optical resonator.

[0095] In some embodiments, a time-dependent ponderomotive potential in an optical cavity excited by two monochromatic laser beams can be used to impart an energy shift to an electron beam in a spatially selective manner.

[0096] In some embodiments, for efficient modulation, the velocity of the electrons must be matched to a moving optical grating formed by a pair of counter-propagating waves with different frequencies. For example, when using wavelengths of 1064 nm and 532 nm (for which high-power CW lasers and optical cavity mirror coatings are readily available), the optical cavity must be tilted with respect to the beam direction at an angle that satisfies the following condition:

[0097]

number

[0098] In the above formula,

[0099]

number

[0100] is the velocity of the optical lattice, v electron is the velocity of the electron, θ is the angle between them, and ω 1 and ω 2 is the frequency of the two laser beams coupled into the optical resonator. Alternatively, in some embodiments, a pair of monochromatic optical resonators at an appropriate angle can be used.

[0101] In some embodiments, the focal point of the laser beam is placed at the center of the back focal plane of the TEM, so that interactions with the laser beam affect only the lowest spatial frequencies, including the unscattered waves and images, up to a cut-on spatial frequency determined by the size of the focal spot and the focal length of the objective lens.

[0102] In some embodiments, attenuation can be combined with an optimal phase shift of the non-scattered wave by adjusting the input power or polarization of the laser beam at the two frequencies. In some embodiments, the product of the two electric fields determines the depth of the time modulation, and the sum of the two intensities determines the phase shift of the non-scattered wave component at its original energy. Thus, in some embodiments, a single dichroic optical resonator acts as a phase adjuster and attenuator of the non-scattered beam, very similar to a Zernike plate in an optical microscope.

[0103] In some embodiments, dark-field microscopy is obtained by completely suppressing the unscattered wave by completely shifting its amplitude to the energy sideband. In some embodiments, in this case, the image is not formed as a result of the interference of the scattered wave with the reference wave (unscattered wave), but instead is proportional to the beam current density of the scattered electron wave arriving at each point in the image plane. In some embodiments, in the ideal case, dark-field microscopy is equivalent to phase-contrast imaging in terms of shot noise, but dark-field probing is motivated, for example, by the fact that this imaging modality is less sensitive to defocusing, making it more practical to operate close to the focus.

[0104] One practical negative effect of low contrast (or high background) is that most of the electrons collected by the electron detector in a TEM are background electrons, so the electron detector must process many electrons to obtain a useful image. Conversely, the benefit of increasing image contrast is that the same amount of useful information can be conveyed with fewer electrons. A representative electron detection technology is the direct electron camera, which operates in an electron counting manner and can process a limited number of electrons per unit time. As many cryo-electron microscopy centers and facilities strive to maximize throughput and eliminate time inefficiencies and overhead, image acquisition time becomes a fundamental bottleneck. In some embodiments, imaging systems with higher contrast are configured to enable faster image acquisition by an order of magnitude or more.

[0105] Also, in some embodiments, such increased throughput can be used to collect image data at high magnification, which means a reduction in effective pixel size. The reduction in pixel size in a cryo-electron microscope leads to an increase in the modulation transfer function at high spatial frequencies, resulting in an improved signal-to-noise ratio and improved data quality. The reduction in pixel size usually comes at the expense of a reduction in TEM throughput, since a smaller field of view is captured. However, the reduction in TEM throughput can be more than compensated for by the increased data acquisition speed enabled by the increased image contrast.

[0106] Embodiments of the presently disclosed subject matter relate, inter alia, to a laser-based device configured to provide electron wave attenuation for a TEM in combination with an electron energy filter.

[0107] In some embodiments, the laser shifts a portion of the electron wave to a different energy, and the portion of the electron wave with the shifted energy is then filtered out by the energy filter.

[0108] In some of the above embodiments, the novel attenuator comprises: · Scattering of electrons (elastic and / or inelastic) is negligibly small; ·Not susceptible to charging and / or damage from the electron beam; · have sufficient spatial selectivity to attenuate non-scattered waves without attenuating information-carrying scattered waves (i.e. the attenuator has a low cut-on frequency); · The attenuation level is controllable (adjustable); Compatible with laser phase plates or functions as a laser phase plate in addition to attenuation: the device can simultaneously apply an optimal phase shift and optimal attenuation to non-scattered waves; · For dark-field imaging, the unscattered waves can be attenuated to zero amplitude (negligible residual amplitude); · Compatible with widely used TEM models with TEM retrofit or minor modifications; · Negligible adverse effects on the imaging system, such as increased aberrations in the CTF or other deleterious features; requiring minimal input laser power; or · configured to provide any combination thereof.

[0109] In some embodiments of the present invention, a system for electron beam imaging or spectroscopy is provided. This system is A transmission electron microscope (TEM) with a back focal plane; one or more optical resonators (i.e. optical cavities) configured to provide continuously adjustable attenuation of an electron wave, each optical resonator having two or more mirrors, a focal point of each optical resonator being located in the back focal plane (or a conjugate plane thereof) of a TEM, each optical resonator being positioned such that unscattered waves provided by the TEM pass through the focal point of the optical resonator, and each optical resonator being operative to receive a laser beam; a laser coupled to the optical resonator and operative to direct a laser beam of a predetermined wavelength into the optical resonator; an electron detector arranged at an image plane of the TEM and configured to receive the electron beam, the unscattered waves being phase shifted and / or attenuated by the laser beam;

[0110] In some embodiments, as shown, for example, in Figures 3(A) and (B), 4(A) and (B), 5A, 5B, and 6, the novel system 600 further comprises one or more of the following:

[0111] A new type of optical resonator: an aspherical nearly concentric resonator 400 configured to allow for a smaller focal spot 450 within the optical resonator. A comparison of a spherical nearly concentric resonator and an aspherical nearly concentric resonator is shown in Figures 3(A and B) and 4(A and B). In some embodiments, the small focal spot size is configured to increase the ability to address a particular portion of the electron beam.

[0112] A configuration of laser beams formed using one or more optical resonators 530, 535 configured to enable spatially selective interaction with the electron beam 560. In some embodiments, the laser beam is configured to impart an energy shift and / or momentum shift to the unscattered wave. More specifically, in some embodiments, the laser beam transforms the unscattered electron wave into a coherent superposition of a small amplitude electron wave of the original energy and momentum and multiple electron waves of different energies and / or momenta.

[0113] In some embodiments, the systems of the present disclosure include an aperture configured to remove (eliminate) the portion of the unscattered wave that has been shifted in momentum as a result of interaction with the laser beam.

[0114] In some embodiments, the system of the present disclosure includes an electron energy filter 616, for example of the type typically used in a TEM to remove inelastically scattered electrons, which in some embodiments removes components of the unscattered wave that have been shifted to a different energy by the laser beam.

[0115] In some embodiments, the transmission electron microscope (TEM) 600 is specially configured to allow for the integration of a laser device in or near the back focal plane of the objective lens or its conjugate plane. The Transmission Electron Microscope (TEM) 600 is an objective lens 510, 520 having a back focal plane located at least a predetermined distance above the top of the lower pole piece 520 and configured to allow placement of a laser device thereat, or in some other embodiments having a back focal plane located at least a predetermined distance below the top of the lower pole piece and having mechanical features (e.g., apertures) configured to allow placement of a laser device thereat; Access to a plane within the microscope conjugate to the back focal plane, with a magnification suitable for placement of the laser device; a contamination prevention device (e.g., a cryobox) having a shape and arrangement configured to ensure sufficient space for the laser device; A port for inserting a laser device or for coupling a laser beam, optical fiber, or electrical cable to the laser device.

[0116] In some embodiments of the present invention, it is possible to reach small mode waists by using nearly concentric resonators, but the manufacturing tolerance requirements are not practical for mode sizes of a few micrometers. In some embodiments, small deviations from a spherical shape (asphericity) result in more stable mode behavior, which allows substantially smaller mode waists to be achieved with current technology compared to conventional (spherical) nearly concentric resonators. In some embodiments, the desired asphericity is rotationally symmetric and has a positive fourth order term. In some embodiments, non-rotationally symmetric surfaces can also be used, in which case the mode waist is narrow in only one of the two lateral directions.

[0117] Although it is difficult to manufacture (polish) a mirror substrate with the required high curvature, low roughness, and appropriate aspheric shape, in some embodiments, techniques for manufacturing spherical concave substrates can be used to produce the desired aspheric shape on the polished substrate, such as by: First, the substrate is polished while a stress generated by a compression ring or other method to induce elastic deformation is applied to the substrate. After polishing, the elastic deformation is relieved to obtain the desired aspheric shape. A substrate made of a material with an anisotropic thermal expansion tensor, such as sapphire, is polished at a temperature different from the operating temperature. The anisotropic thermal expansion induces asphericity. Applying mechanically or thermally induced stress fields during operation. Fabricating a mirror substrate by imprinting a shaped sphere into the desired shape by applying mechanically or thermally induced stress during imprinting.

[0118] In some embodiments, the laser device can generate non-monochromatic light, including beams of two or more wavelengths. In some embodiments, the non-monochromatic laser beam generates a time-dependent ponderomotive potential. In some embodiments, the ponderomotive potential can form a moving system of fringes (light lattices) with a velocity matching that of the electrons in the non-scattered wave. The enhanced interaction during the propagation of the non-scattered wave with the ponderomotive potential effectively attenuates (depletes) the amplitude of the non-scattered wave with the original energy or momentum, while generating multiple electron waves with different energies or momentum that can be removed by an aperture or electron energy filter.

[0119] In some embodiments, the desired configuration of the laser beam is formed by coupling two or more different wavelengths of laser beams into one optical resonator, which is designed to support both wavelengths. Alternatively, in some embodiments, two or more optical resonators can be used, with monochromatic or polychromatic light coupled into each optical resonator. In some embodiments, the difference in wavelengths needs to be sufficient so that the energy shift imparted to the non-scatterer is greater than the resolution of the energy spectrometer or the energy spread of the electron gun. In some embodiments, the optical resonator can be tilted to create the electric field configuration required for the function of the laser attenuator.

[0120] In an exemplary embodiment, the laser device includes a seed laser and a fiber amplifier, providing a laser beam with a wavelength of 1064 nm and a frequency-doubled beam with a wavelength of 532 nm. These laser beams are coupled into an optical resonator located in the back focal plane of a TEM operating at an accelerating voltage of 300 keV. The optical resonator is positioned so that its focal point (the position where the laser beam has a maximum intensity) is located at the intersection of the optical axis and the back focal plane of the TEM. The optical resonator is tilted at an angle of about 65° with respect to its optical axis, which allows the electrons to be velocity-matched with one of the moving laser gratings generated in the optical resonator. Due to the interaction of the laser beam with the electrons, the unscattered electron beam is partially converted to an energy different from the original energy of the electrons in the TEM, generating energy sidebands. The energy sidebands are separated from the original energy by the difference in photon energy (and multiples of that energy difference) corresponding to the two wavelengths used. For 532 nm and 1064 nm, the photon energy difference between both wavelengths was 1.17 eV. Correspondingly, the sidebands are separated from the original energy by ±1.17 eV, ±2.33 eV. The energy filter of the TEM can eliminate the portion of the unscattered wave that is transmitted to the sidebands if the sideband separation is greater than the resolution of the energy filter combined with the width of the energy distribution provided by the electron source. In this example, an energy filter slit width corresponding to a spectral width of 1 eV is effective to suppress the sidebands while allowing all or most of the portion of the unscattered wave to remain at the original energy.

[0121] In some embodiments, the laser-based device includes one or more optical resonators that support bidirectional propagation of optical waves (also referred to as standing wave optical resonators), and in some embodiments, the laser-based device includes one or more optical resonators that support unidirectional propagation of optical waves (also referred to as traveling wave optical resonators or ring optical resonators).

[0122] In some embodiments, the laser attenuator is configured to achieve the functionality of a phase plate by creating a field configuration in which the average of the time-dependent ponderomotive potential is adjusted to give an optimal phase shift of the unscattered wave.

[0123] In some embodiments, the use of an optical resonator is configured to minimize the input laser power, although in some embodiments, if a high power laser beam (containing two or more wavelengths of light) is available (e.g., in a pulsed configuration), it can be used to create a suitable laser beam configuration.

[0124] In some embodiments, these developments can have an immediate impact on cryo-electron microscopy (cryo-EM) as an important method in structural biology. Cryo-EM samples tend to be weak phase objects and are therefore best observed using Zernike phase contrast methods, which require phase delay and non-scattered electron wave attenuation. Phase delay allows some embodiments of the invention to improve image contrast in interferometric TEM by tuning the attenuation of the non-scattered waves. In some embodiments, a regime has been demonstrated that completely eliminates the non-scattered waves, allowing dark-field imaging.

[0125] In some embodiments, a method for electron beam imaging or electron beam spectroscopy is provided, comprising providing a system 100 according to any one of the embodiments of system 100 described above and below, and attenuating the unscattered electron wave 107 in the TEM to a predetermined amplitude and / or attenuating the unscattered electron wave 107 by a predetermined attenuation factor using a laser-based device and an energy filter.

[0126] In some embodiments, as shown in FIG. 9, a novel system 900 for electron beam imaging or spectroscopy is provided, comprising: a transmission electron microscope (TEM) 101 including an electron gun 102 (electron source) configured to provide an electron beam 104; at least one laser-based device 915 configured to provide at least one laser beam 914, the laser beam configured to shift a predetermined portion of the electron beam to a momentum different from the original momentum provided to the portion of the electron beam by the TEM 101 (illustrated as a shift to a portion 911 of the unscattered beam 107); and an aperture 916 configured to pass an electron beam having the original momentum provided by the TEM but not an electron beam that has been shifted to a different momentum by the laser-based device.

[0127] In some embodiments, the aperture 916 removes by absorption the electron beam that has been shifted to a different momentum by the laser-based device.

[0128] In some embodiments, the predetermined portion is a predetermined percentage of the component of the electron beam, and in some embodiments, the component of the electron beam is ·Unscattered electron waves, ·Scattered electron waves, ·Scattered electron wave group, A set of electron waves that can be selected from the electron beam by spatial filtering, and At least one of any combination of them. In some embodiments, the predetermined percentage is selected from 0.01% to 1%, 1% to 10%, 10% to 50%, 50% to 90%, between 90% to 99%, 99% to 99.99%, and any combination thereof.

[0129] In some embodiments, the aperture 916 is configured to remove at least 50%, at least 90%, or at least 99% of the electron beam that has been shifted to a different momentum by the laser-based device.

[0130] In some embodiments, the laser-based device 915 includes: Near the back focal plane 110 of the TEM 101, i.e., within ±1 mm, ±0.1 mm, ±0.01 mm, or ±0.001 mm of the back focal plane 110, or It is placed near a plane conjugate to the back focal plane 110, that is, at a position within the range of ±1 mm, ±0.1 mm, ±0.01 mm, or ±0.001 mm from the conjugate plane.

[0131] In some embodiments, the predetermined portion of the electron beam is a predetermined portion of the unscattered electron wave 107 of the electron beam 104 .

[0132] As shown in FIG. 9, the shifted portion of the unscattered beam 107 is indicated at 911, and the scattered wave 108 and the unshifted unscattered wave 107 are recombined (917) by lens 103D in this example.

[0133] Also in accordance with the present disclosure is a method for electron beam imaging or spectroscopy, comprising the steps of: Providing a system 900 according to any one of the embodiments of system 900 described above; Attenuating the unscattered electron wave 107 in the TEM to a predetermined amplitude and / or attenuating the unscattered electron wave 107 by a predetermined attenuation factor using a laser-based device and aperture.

[0134] It is to be understood that embodiments formed from combinations of features described in separate embodiments are also within the scope of the subject matter of the present disclosure.

[0135] Although certain features of the subject matter of the present disclosure have been illustrated and described herein, mutatis mutandis, various modifications, substitutions and equivalents are within the scope of the present disclosure.

Claims

1. 1. A system for electron beam imaging or spectroscopy, comprising: a transmission electron microscope (TEM) including an electron source configured to provide an electron beam; at least one laser-based device configured to provide at least one laser beam, the laser beam configured to shift a predetermined portion of the electron beam to an energy spectrum different from the original energy spectrum provided by the electron source; an electron energy filter configured to pass an electron beam having the original energy spectrum but not pass an electron beam having an energy spectrum different from the original energy spectrum.

2. 2. The system of claim 1, The system, wherein the laser-based device is positioned near a back focal plane of the transmission electron microscope (TEM) or near a conjugate plane conjugate to the back focal plane.

3. 2. The system of claim 1, The system wherein the laser beam is a continuous wave laser beam.

4. 2. The system of claim 1, The system, wherein the predetermined portion of the electron beam is a predetermined portion of an unscattered electron wave of the electron beam.

5. 2. The system of claim 1, The system, wherein the laser beam is further configured to impart a predetermined phase shift to a portion of the electron beam.

6. 3. The system of claim 2, the laser-based device is configured to generate a laser focal spot and position the laser focal spot near the back focal plane or near the conjugate plane of the transmission electron microscope (TEM); and The system, wherein the laser-based device is positioned such that unscattered electron waves of the electron beam pass through the laser focal point.

7. 2. The system of claim 1, A system, wherein the material structures of the laser-based device are constructed and arranged such that the electron beam of the transmission electron microscope (TEM) is at least 0.1 mm, at least 1 mm, or at least 10 mm away from any material elements of the laser-based device.

8. 2. The system of claim 1, The system, wherein the laser-based device and the electron energy filter are configured to attenuate the electron beam in the transmission electron microscope (TEM) to a predetermined beam current and / or to attenuate the electron beam in the transmission electron microscope (TEM) by a predetermined attenuation factor.

9. A system according to claim 4 or claim 6, comprising: The system, wherein the laser-based device and the electron energy filter are configured to attenuate the unscattered electron waves of the electron beam in the transmission electron microscope (TEM) to a predetermined amplitude and / or to attenuate the unscattered electron waves of the electron beam in the transmission electron microscope (TEM) by a predetermined attenuation coefficient.

10. 2. The system of claim 1, The system, wherein the transmission electron microscope (TEM) further includes an electron detector disposed at an image plane of the transmission electron microscope (TEM) and configured to receive the electron beam.

11. 2. The system of claim 1, The system, wherein the laser-based device further comprises at least one optical resonator.

12. 12. The system of claim 11, Each of the at least one optical resonator comprises: having two or more mirrors, The laser beam is configured to be incident thereon, Located near the back focal plane of the transmission electron microscope (TEM) or near a conjugate plane conjugate to the back focal plane of the transmission electron microscope (TEM), A system configured to pass the electron beam provided by the transmission electron microscope (TEM).

13. 12. The system of claim 11, The at least one optical resonator is an aspheric nearly concentric resonator having an aspheric mirror.

14. 2. The system of claim 1, A system wherein the laser beam provided by the laser-based device is a non-monochromatic laser beam.

15. 15. The system of claim 14, The system, wherein the non-monochromatic laser beam is provided by combining two or more laser beams having different wavelengths into an optical cavity.

16. 15. The system of claim 14, The system, wherein the non-monochromatic laser beam is provided by a structure of two or more optical resonators whose foci overlap each other.

17. A system according to any one of claims 11 to 13, the optical resonator is tilted with respect to the optical axis of the transmission electron microscope (TEM); the optical axis of the optical resonator is tilted with respect to the optical axis of the transmission electron microscope (TEM); or A system wherein the laser beam propagation direction of the optical cavity is tilted with respect to the optical axis of the transmission electron microscope (TEM).

18. 1. A method for electron beam imaging or spectroscopy, comprising: Providing a system according to claim 1; and attenuating the predetermined portion of the electron beam to a predetermined beam current and / or attenuating the electron beam by a predetermined attenuation factor with the laser-based device and the electron energy filter.

19. 1. A system for electron beam imaging or spectroscopy, comprising: a transmission electron microscope (TEM) including an electron source configured to provide an electron beam; at least one laser-based device configured to provide at least one laser beam configured to shift a predetermined portion of the electron beam to a momentum different than an original momentum provided to the predetermined portion of the electron beam by the transmission electron microscope (TEM); an aperture configured to pass an electron beam having the original momentum provided by the transmission electron microscope (TEM) but not to pass an electron beam that has been shifted to a momentum different from the original momentum by the laser-based device.

20. 20. The system of claim 19, The system, wherein the laser-based device is positioned near a back focal plane of the transmission electron microscope (TEM) or near a conjugate plane conjugate to the back focal plane.

21. 20. The system of claim 19, The system, wherein the predetermined portion of the electron beam is a predetermined portion of an unscattered electron wave of the electron beam.

22. 1. A method for electron beam imaging or spectroscopy, comprising: Providing a system according to any one of claims 19 to 21; and attenuating, by the laser-based device and the aperture, unscattered electron waves of the electron beam in the transmission electron microscope (TEM) to a predetermined amplitude and / or attenuating unscattered electron waves of the electron beam in the transmission electron microscope (TEM) by a predetermined attenuation factor.

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