The interaction between multiple intense ultrashort laser pulses and solids typically produces a regular nanoscale surface corrugation. A coupled mechanism has been identified that operates in a specific range of fluences in GaAs that exhibits transient loss of the imaginary part of the dielectric function and X2, which produces a unique corrugation known as high spatial frequency laser induced periodic surface structures (HSFL). This mechanism is unique in that the corrugation does not involve melting or ablation.