This presentation will review the recent results obtained in LP3 on the generation of ultrashort X-ray sources from the interaction of a 20/10 TW fs laser source (ASUR platform) with a Mo massive target. In particular, highest K-alpha energy conversion efficiency (> 10^-4 at 17.4 keV) from laser-produced plasmas will be demonstrated. We will discuss the influence of laser control parameters like the contrast of the laser pulse on the characteristics of the produced X-ray flux. Some insights on the physical driving mechanisms will be also reported