  Inference of joule-class THz radiation sources from microchannel targets
driven with hundreds of joule, picosecond lasers is reported. THz sources of
this magnitude are useful for nonlinear pumping of matter and for
charged-particle acceleration and manipulation. Microchannel targets
demonstrate increased laser-THz conversion efficiency compared to planar foil
targets, with laser energy to THz energy conversion up to approximately 0.9% in
the best cases.
