Institute Activities

Fast radio bursts are powerful pulses of energy at gigaHertz (GHz) frequencies that last only a few milliseconds. Astronomers and astrophysicists have found many fast radio bursts since they were first discovered in 2007. These bursts of radio-frequency appear to be coming from somewhere beyond our own galaxy and are a tantalizing mystery. While no galactic source has yet been documented to emit such a burst, astrophysicists estimate that FRBs may be appearing at a rate of perhaps 10,000 per day if one could watch the whole sky at once. More intriguingly, they have found a number of them that repeat the bursts from the same point in the sky, but researchers cannot pin down a regular period in the pattern of when the signals arrive.

One of the most fascinating aspects of FRBs is their possible relationship with other high energy phenomena found in the universe, such as super novae, pulsars, quasars, rotating radio transients (RRATs), and gamma ray bursts. Dr. Zackay is developing mathematical tools to test whether any of the repeating patterns could be due to the binary orbits of a pair of neutron stars. He is also creating tools for detecting gamma-ray pulsars in data from NASA’s Fermi Gamma-ray Space Telescope and comparing them to known FRBs. The current methods require tens of thousands of hours of computer time (such as provided by the Einstein@home network of thousands of volunteers who allow the project to use their computer’s idle time to search for weak astrophysical signals from pulsars). Dr. Zackay has ideas for algebraic short cuts for solving for the pulsar parameters and sky positions of a gamma-ray pulsar that could be computed on a laptop in a few seconds.

The scientists worked together to fabricate an extremely thin optical fiber that supports a super-extended mode with a diameter as large as 13 times the optical wavelength, residing almost entirely outside the fiber and guided over thousands of wavelengths (5 mm)—all this to couple guided light to warm atomic vapor. This unique configuration balances between strong confinement of the photons and long interaction times with the thermal atoms, thereby enabling fast and coherent interactions (see Figure 2).

The researchers demonstrated narrow coherent resonances (tens of MHz) of electromagnetically induced transparency for signals at the single-photon level, and long relaxation times (10 nanoseconds) of atoms excited by the guided mode. The resulting platform is particularly suitable for observing quantum nonlinear optics phenomena (Optica 2021).

(Image: Super-extended evanescent field of a nanofiber interacting with atomic vapor. (a) Illustration of the extent of an optical mode surrounding a thin optical fiber. (b) Mode field diameter as a function of fiber diameter. Blue and red circles mark the parameters of the two fibers shown in (a). Dashed black line marks the physical fiber dimensions. (c) Calculated Doppler-free absorption spectra for rubidium (Rb) vapor in the evanescent field silica fibers (n=1.45. The effect of transit-time broadening is apparent.)

Putting their findings into practice, the pair is building the Weizmann Astrophysical Observatory (WAO). Located near Kibbutz Neot Smadar in Israel’s Negev Desert, the WAO is based on a novel, modular approach in which dozens of telescopic components are linked together. The system’s unique potential stems from its modularity—which will allow a steady increase in power as new nodes are added—as well as from original algorithms that allow Weizmann astrophysicists to store and analyze the immense data sets generated by their observations.

Inside the WAO, Dr. Ben-Ami and Prof. Ofek are developing the Large Array Survey Telescope (LAST). The LAST design is an assembly of 48 telescopes on 12 mounts. Each telescope will be equipped with full-frame CMOS detectors, creating a system that supports large‑format, high-

performance distributed camera optimization. Along with its superior imaging capabilities, the LAST can view more volume of the Universe per dollar – by an order of magnitude—than any existing ground-based survey telescope. The researchers assert that, once it is ready—by the end of the year, according to current estimates—LAST will be the largest telescope in Israel and among the leading survey telescopes in the world.

LAST’s advanced capabilities are ideal for identifying signatures of hard-to-track celestial events. When observatory is fully operational, studies by multiple Weizmann research groups are expected to help answer the some of most pressing questions in physics and astrophysics, such as the nature of gravity, the origin of “stuff” of the Universe—from heavy elements like gold, to stars, solar systems, and galaxies, and how to identify massive asteroids that could crash into Earth.

Prostate cancer is one of the most challenging cancers to treat without causing collateral damage to sensitive surrounding regions of the body—often leading to incontinence and/or sexual dysfunction. Using computer modeling, Prof. Malka’s group compared the advantages of photon, proton, and VHEE intensity-modulated radiation therapy (IMRT) for treating prostate cancer. Their results indicated that, compared with conventional X-ray treatment, VHEE would likely be better at sparing the surrounding normal tissue while still delivering the required dose level to the target cancer.

In a clinically approved treatment for prostate cancer, Prof. Malka has already shown that such beams are well-suited for delivering the required dose of radiation, precisely concentrated, and with a deep penetration into tissues, resulting in less damage to collateral and healthy tissues.

However, the possible energy gain in laser wakefield accelerators is limited by dephasing between the driving laser pulse and the highly relativistic electrons in its wake. Most efforts to increase the power of these systems have concentrated on continuous phase-locking in the linear wakefield regime.

Prof. Victor Malka from the Department of Physics of Complex Systems examined an alternative scenario that uses rapid rephasing in sharp density transitions, and was able to demonstrate the possibility experimentally. He estimates that a unique phase reset can lead to a gain in energy in the order of 30 percent.

They noted that the burst-to-burst variations in the efficiency of fireball energy conversion to gamma-rays are small; this implies that deviations from the standard fireball model description, if present, are small. However, one of the variations to the fireball theory is that the fireball is not a spherical burst, but rather jet-like. Their observations also imply that that if fireballs are indeed jets, then the jet opening angle is greater than or equal to 0.1 for most cases.