Methods and systems for generating X-ray illumination from a laser produced plasma (LPP) employing a low atomic number, cryogenic target are presented herein. A highly focused, short duration laser pulse is directed to a low atomic number, cryogenically frozen target, igniting a plasma. In some embodiments, the target material includes one or more elements having an atomic number less than 19. In some embodiments, the low atomic number, cryogenic target material is coated on the surface of a cryogenically cooled drum configured to rotate and translate with respect to incident laser light. In some embodiments, the low atomic number, cryogenic LPP light source generates multiple line or broadband X-ray illumination in a soft X-ray (SXR) spectral range used to measure structural and material characteristics of semiconductor structures. In some embodiments, Reflective, Small-Angle X-ray Scatterometry measurements are performed with a low atomic number, cryogenic LPP illumination source as described herein.