Multi-wavelength annular optical pulses generated by double interferent femtosecond Bessel laser beams in silica glass

Abstract Double femtosecond Bessel laser beams (fs-BLBs) are used to interact with UV-visible silica glass and ultrashort annular beams (ABs) with six different peak wavelengths in the visible and near-infrared range are simultaneously generated while the super-continuum emission is totally suppressed. Experimental results show that as the time interval Δt between double fs-BLBs gradually approaches zero, the generation efficiency of the ABs increases and reaches the maximum at Δt = 0. When Δt equals ±18 fs, the intensity of the annular beam with a central wavelength of 605 nm decreases to half of its maximum. Compared with the case using single femtosecond Bessel laser beam, the ABs’ generation efficiency can be greatly enhanced due to the interference of double fs-BLBs. It is considered that the four-wave mixing (FWM) and corresponding cascaded parametric processes are responsible for the generation of these ABs, which can be confirmed by the numerical simulations. The colorful ABs have important applications in the imaging and communication fields, such as the stimulated emission depletion microscopy (STED), the high speed 3D live fluorescence imaging, and the multiplexing optical communications.