A novel common-path scheme for fourth harmonic generation by ultrashort laser pulses

A new compact common-path scheme for Fourth-Harmonic Generation (FHG) of femtosecond laser pulses is proposed here. Guidelines for selection of non-linear crystals and birefringent crystals used for delay pre-compensation are derived based on approximation of non-saturated sum-frequency mixing of Gaussian pulses. We experimentally demonstrate the scheme and study its performance for a different combinations of BBO nonlinear crystals for the case of generation of sub-200 nm deep ultraviolet pulses by FHG of pulses delivered by a Ti:Sapphire ultrafast laser. Pulses with duration between 130 fs and 370 fs and pulse energy of 19 to 85 μJ were generated. It is shown, that in addition to its compactness and intrinsic stability, the scheme allows a superior spectrum and pulse quality. •A novel common-path scheme for Fourth-Harmonic Generation by ultrashort pulses in nonlinear crystal sequence is proposed.•The scheme is demonstrated with fundamental pulses from a Ti:Sapphire laser for producing 200 nm range Deep UV pulses.•Excellent FH beam pointing and energy stability intrinsic to the common-path scheme is demonstrated.•Applications in FEL seeding and other fields where compactness of the setup and high stability are a must.