Institute Activities

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.

Prof. Nir Davidson, Dr. Oren Raz, and their colleagues have devised a scheme for addressing this difficulty, which they analyzed theoretically and demonstrated experimentally in the October 2020 issue of Nanophotonics. The scheme involves controlling the laser oscillator amplitude through modification of individual laser oscillator loss.

The researchers demonstrated this approach in a classical XY model simulator, based on a digital degenerate cavity laser (the theoretical analysis). They proved that for each XY model energy minimum, there exists a unique, corresponding set of laser loss values that coincide with it, in terms of both oscillation amplitudes and phase values. The researchers also demonstrated an eight-fold improvement in the deviation from the minimal XY energy by employing their proposed solution scheme (the experimental demonstration—see Figure 1). The results are an important step towards perfecting the use of lasers as spin models.

(Image: Schematic illustration of the experimental setup used to support a laser oscillator network and to measure its state. (a) Folded ring degenerate cavity laser supporting the oscillator network. (b) Interferometer for laser network intensity and phase measurement. (c) The detected interference fringes for a house laser network with equal amplitudes. Abbreviations: SLM – spatial light modulator; OC – output coupler; PBS – polarizing beam splitter; RR1 and RR2 – retro reflecting mirrors; λ/2λ/2 – half wave plate; BS – beam splitter; RM – reflector mirrors.)

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.

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.