Review of bremsstrahlung photon dose generated from ultra-intense and ultra-short laser target interactions

Abstract

Radiation protection in ultra-intense and ultra-short laser facilities is becoming increasingly important as both the number and the intensity of the laser facilities increase rapidly with the development of laser technology. Experiments show that bremsstrahlung photon dose is usually dominant in this new type of ionizing radiation source. Therefore, estimation of bremsstrahlung photon dose is essential for radiation protection in ultra-intense and ultra-short laser facilities. This paper reviews the current literature on the bremsstrahlung photon dose level obtained by experiments and photon dose estimation models. The effects of laser-target interaction experiment configuration on the photon dose are also analyzed. Experimental measurements are collected from a total of 18 ultra-intense and ultra-short laser facilities with laser intensities from 1017–1021 W cm−2 μm2. Measured normalized photon dose values are spread over six orders of magnitude from 10−5–1 mSv J−1 shot−1. The widespread range of normalized photon dose suggests that there might be some factors not considered in the photon dose estimation models. In this review, four important electron physical quantities related to the photon dose are introduced, which are hot electron energy distribution (dNe/dEe), characteristic temperature of electron (Th), laser-to-electron conversion efficiency (η), and electron divergence angle (θ). Then, four photon dose estimation models are introduced and discussed. The measurement results in the literature are compared with the predicted values of these models. Predicted values of Th, η and normalized photon dose given by the different scaling laws or dose estimation models are compared with measured data. The diagram of normalized photon dose can be roughly divided into four regions according to different target schemes, namely foil target, solid target, coated target and hybrid target scheme. This review shows that the target scheme is one of the most relevant factors that affect the bremsstrahlung photon dose level. For the radiation shielding of such ultra-intense and ultra-short laser facilities, consideration of different target schemes may help ensure radiation safety and reduce the cost. This review could provide a reference for radiation protection of the Ultra-Intense and Ultra-Short Laser facilities.