Coherent spontaneous THz undulator radiation from dense electron bunches formed in laser-driven photo-injectorsV.L. Bratman, N. Balal, I.V. Bandurkin, A. Friedman, Yu. Lurie and A.V. SavilovEPJ Web Conf., 149 (2017) 05002DOI: https://doi.org/10.1051/epjconf/201714905002