Аннотация:On-line diagnostics of hot plasma induced by superintense femtosecond laser pulses in a cavity during the deep hole drilling of solid target has been developed. Such a plasma is characterized by higher values of hard X-ray yield and hot electron temperature in comparison with the same parameters measured for flat nearsurface plasma. Dynamics of X-rays yield in the cavity during the deep hole drilling demonstrates several repetitive stages. The yield and energy of X-rays from plasma ignited in a cavity depend on the beam waist position respect to the target surface plane, i.e. focusing regime. We have detected strong second harmonic signal that correlated with hard X-Ray yield in the time of cavity formation. Depth resolved elemental analysis of compound targets, based on this diagnostics technique, has been proposed.