Laser wakefield acceleration facilitates high-energy gamma ray generation with spot sizes at the microscale

In computed tomography (CT), gamma and X-rays beamed through an object measure radiation absorption and density. A computer then creates images of the cross-sectional area with the data from these scans, revealing the internal components of a dense object. gamma rays with smaller focal spot sizes produce more detailed images and reduce heat dissipation, but smaller spot sizes have historically limited the device’s available energy levels. Using the high fields created in plasma with laser wakefield acceleration, a new experiment reported in the Journal of Applied Physics showed that a high-energy gamma ray beam can be generated with spot size of only 200 micrometers.

In the experiment, femtosecond laser pulses first produce an optimized electron beam via laser wakefield acceleration in a gas jet. The beam then hits a dense conversion target of tungsten, creating high energy Bremsstrahlung radiation with a spot size optimized by varying the distance between the gas jet and target. These findings show that applying laser wakefield acceleration to high-energy X-rays has potential to significantly enhance CT’s spatial resolution in high-areal density objects.

Although high-energy gamma rays of multi-MeV or higher already exist for industrial applications, they have so far relied on the support of electron accelerator facilities. Moreover, these industrial gamma and X-rays suffer from having relatively large spot sizes, usually several millimeters. This group reports that their setup is the first of its kind to achieve high energy levels with such a small spot size, enhancing the spatial resolution of CT imaging in high areal density objects.

Going forward, the researchers plan on further stabilizing the high-power femtosecond laser and improving the overall setup for industrial applications. They are currently preparing a new paper demonstrating the gamma rays’ effectiveness on high areal density objects.

Source: “Micro-spot gamma-ray generation based on laser wakefield acceleration,” by Kegong Dong, Tiankui Zhang, Minghai Yu, Yuchi Wu, Bin Zhu, Fang Tan, Shaoyi Wang, Yonghong Yan, Jing Yang, Yue Yang, Feng Lu, Gang Li, Wei Fan, Wei Hong, Zongqing Zhao, Weimin Zhou, Leifeng Cao, and Yuqiu Gu, Journal of Applied Physics (2018). The article can be accessed at https://doi.org/10.1063/1.4997142 .