A beam conditioning device includes a coherence-breaking module and a beam transforming module. The coherence-breaking module is configured to break a spatial coherence between beam components of the light beam and may include coherence-breaking mirrors having a structured pattern on their reflective surfaces. The beam transforming module may include a primary optical element and a secondary optical element and is configured to transform the spatial energy distribution and the footprint of the light beam. The beam conditioning device may be used to transform a Gaussian light beam into a flat-top light beam suitable for terahertz imaging applications, although other initial and/or final energy distributions may be considered.