An MeV spectrometer for photoelectrons generated by ultrahigh intensity lasers

The development of ultrahigh-intensity lasers provides a measurement challenge. Chirped pulse amplification lasers, awarded the 2018 Nobel Prize in physics, are set to soon reach an intensity of 10²⁴ W/cm², promising fundamental insights into the relativistic regime that will only be realized when detectors can accurately record such experiments.

Luo et al. present such an instrument, a spectrometer to analyze relativistic photoelectrons generated by the interaction of intense photons with matter that is sensitive enough to detect single photoelectrons.

Employing technology from nuclear physics, the device selects electrons of specific energies with magnetic deflection, removing background noise so effectively that they were able to detect a mere one to two electrons over a half-hour scan. Their example argon and chloromethane spectra measure photoelectrons with energies up to 2 MeV at 5% resolution, forward scattered by laser fields into a 2π steradian solid angle.

The spectrometer is the culmination of a decade’s development. It employs a wide range of methods to cut background signal: baffles, selection slits, discrimination at the detector, and time of flight gating of the photoelectron within a 10-nanosecond window.

Co-author Barry Walker hopes the new apparatus will advance intense laser atomic science, enable applications such as coherent X-ray sources, and reveal fundamental quantum electrodynamic phenomena.

“Electron-positron electromagnetic cascades from a laser, like we think happen in supernovas -- that would be a holy grail to observe,” Walker said.

Source: “MeV photoelectron spectrometer for ultraintense laser interactions with atoms and molecules,” Siyu Luo, Patrick Grugan, Zahide Demircioglu, Amylia Hoos, Zachary Germain, Rachael A. McIntyre, Xingyu Shen, Yi Ji (University of Delaware), and Barry C. Walker (University of Delaware Department of Physics and Astronomy), Review of Scientific Instruments (2019). The article can be accessed at https://doi.org/10.1063/1.5116589 .