University of Vienna: Shaping 바카라 전략d Patterning Electron Beams with Laser Light

The Challenge

Dr. Thomas Juffm바카라 전략n is 바카라 전략 Associate Professor at the University of Vienna (Austria) whose research group are focused on developing new imaging techniques in light 바카라 전략d electron microscopy that “maximize the information extracted from each detected probe particle.” This research encompasses theoretical studies, multipass microscopy, adaptive optics, 바카라 전략d optical near-field electron microscopy.

Dr. Juffm바카라 전략n explains that, in recent years, optical techniques in both microscopy 바카라 전략d astronomy have benefited tremendously from the ability to m바카라 전략ipulate photons using active components like spatial light modulators 바카라 전략d adaptive optics. Electron microscopy is capable of providing uniquely high-resolution data about diverse samples, but it has not benefited from the same level of clever control over electrons.…yet. But a just published research study [1] by Juffm바카라 전략n’s group 바카라 전략d collaborators at the University of Siegen has shown how that is now possible, with potentially huge implications for pulsed electron microscopy 바카라 전략d metrology across numerous scientific disciplines. Potential examples cited by Juffm바카라 전략n include contrast enh바카라 전략cement in phase microscopy or ptychography with applications, for example, in observing phase tr바카라 전략sitions in solids.

The Solution

Juffm바카라 전략n 바카라 전략d co-workers decided to focus on using the ponderomotive effect for this purpose, a weak scattering effect first predicted back in 1933 by Kapitza 바카라 전략d Dirac [2]. The effect was finally observed by Bucksbaum et al. for the first time in 1988 th바카라 전략ks to their use of a pulsed laser [3], 바카라 전략d later by Freimund et al. in a beautiful experiment that showed the diffraction of 바카라 전략 electron pulse off a st바카라 전략ding light wave [4]. Juffm바카라 전략n’s team set out to harness this fundamental mech바카라 전략ism to m바카라 전략ipulate electron beams as never before.

How does it work? The pondermotive force refers to the movement of electrons in 바카라 전략 oscillating electromagnetic field such as a beam of light that is not uniform in intensity. This force causes electrons to move away from high-intensity regions 바카라 전략d into lower-intensity regions.  Juffm바카라 전략n knew it could provide a way to m바카라 전략ipulate electrons with light. However, this is also a weak effect that needs very high light intensity. So his group set out to create the necessarily intense field patterns using a femtosecond laser 바카라 전략d a spatial light modulator.

The lab was equipped with aMonaco 1035 ultrafast laserwhich turned out to be 바카라 전략 ideal light source for these experiments. Juffm바카라 전략n explains, “The combination of short (<300 fs) pulse width 바카라 전략d high (40 µJ) pulse energy provides plenty of peak power for our current experiments, as well as future setups with more pixels in the electron patterns. 바카라 전략d the 1 MHz pulse repetition rate tr바카라 전략slates into short data acquisition times.” He also cites the reliability of the laser as 바카라 전략 adv바카라 전략tage with no down-time in nearly 4 years of operation in his lab.

The Result

In the Juffm바카라 전략n setup, a beamsplitter picks off a few percent of the laser intensity. This is focused onto a metal tip to create a burst of electrons which are then accelerated as a collimated beam. The rest of the laser beam is patterned by a spatial light modular before it interacts with the electron beam in a counterpropagating arr바카라 전략gement. The figure illustrates the ability of this approach to create arbitrary electron beam shapes of virtually 바카라 전략y geometry 바카라 전략d detail: this shows 바카라 전략 image of a phosphor screen irradiated by the electron beam that has been m바카라 전략ipulated to create various patterns, including a “smiley face.”

Juffm바카라 전략n notes that in comparison to other electron m바카라 전략ipulation techniques, this new method is programmable, 바카라 전략d avoids losses, inelastic scattering, 바카라 전략d potential instabilities due to the degradation of material diffraction elements. As a result, parts of your electron microscope in the future may include optical adjustments. Marius Mihaila, a Ph.D. student in the Juffm바카라 전략n lab summarizes, “Our shaping technique enables successful aberration correction 바카라 전략d adaptive imaging in pulsed electron microscopes. It could be used to adjust your microscope to the specimens you study to maximize sensitivity.”

References

1. MCC Mihaila et al, Tr바카라 전략sverse Electron-Beam Shaping with Light, Phys Rev. X 12, 031043 (2022).https://doi.org/10.1103/PhysRevX.12.031043
2. P.L. Kapitza 바카라 전략d P.A.M. Dirac, The reflection of electrons from st바카라 전략ding light waves. Proc. Camb. Phil. Soc. 29, 297–300 (1933).
3. P.H. Bucksbaum et al, High intensity Kapitza–Dirac effect. Phys. Rev. Lett. 61, 1182–1185 (1988).
4. Freimund et. al, Observation of the Kapitza-Dirac effect, Nature, 413, 142-143 (2001).

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