A system for treatment of biological tissues is provided. The system includes a lens having a hollow, substantially hemispherical shape with an outer surface and an inner surface, the inner surface defining a substantially hemispherical cavity for inserting the biological tissues. The system further includes an antenna assembly for generating and directing electromagnetic radiation towards the outer surface. In the system, the lens is configured to direct the electromagnetic energy to an area in the cavity, a dielectric constant of the lens at the inner surface substantially matches a dielectric constant of the biological tissues, the dielectric constant monotonically increases from the outer surface to the inner surface, and the electromagnetic energy is generated via a series of pulses having a transient of less than about 1 nanosecond.