Generation of Multi-Wavelength Light Pulses by Femtosecond Bessel Laser Beam in Silica Glass

When the near-infrared femtosecond Bessel laser beam (fs-BLB) is obliquely incident on the silica glass, annular beams (ABs) with bandwidths of several tens of nanometers and different peak wavelengths discretely distributed in a visible and near-infrared range are generated simultaneously. It is considered that four-wave mixing (FWM) and the corresponding cascaded parametric processes are responsible for the generation of multi-wavelength ABs. It is also found that the broken symmetry of the optical setup due to the obliquely oriented silica glass and the absorption band of the sample significantly enhance the generation efficiency of ABs. Since the diffraction angles of these colorful ABs mainly depend on their wavelengths and are insensitive to the input laser energy, this technique may find important applications where multi-wavelength ultrashort pulses are needed. For example, these multi-wavelength ABs can be used as light sources in nonlinear dark-field microscopy and multiphoton imaging to further suppress the background noise and improve resolution. They can also be used in multidimensional multiplexing optical communications.