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We report the generation of a zero-order Bessel beam of continuously variable spot size using a simple optical setup. We have used a pair of metal axicon mirrors to generate a hollow beam of variable dark diameter. This beam was subsequently focused by a convex lens to get a Bessel beam of variable spot size. We also studied the effect of a hollow-beam ring width on nondiffracting propagation range of the generated beam.

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An experimental study on the radiography of various metallic and biological plant samples with a minimum resolution of ∼75 μm using relativistic electron beams from the laser plasma accelerator is presented. Electron beams were generated from the interaction of Ti:sapphire laser pulses of 120 fs duration with underdense plasma of 4 mm length, created using Ar and He gas jets, with two different parameters, i.e., a maximum energy of ∼50 MeV (broad spectrum) and a quasimonoenergetic beam with a peak energy of ∼150 MeV. GEANT4 Monte Carlo simulations were performed to reconstruct the radiographic images and were found to be consistent with the experimental results. Radiography of biological plant samples was also performed, and in this regard penetration depths of two types of electron beams in adipose tissue were estimated through a simulation. The effect of different electron beam parameters on the quality of the radiograph has been discussed.