Sub-8 fs Pulses: a Consequence of Compressing White Light Continuum Generated by Hollow Core Fiber

In order to generate high-spectral-irradiance white light continuum (WLC) a hollow fiber with 250 µm inner diameter was used. The hollow fiber was mounted on a V-groove holder inside a chamber filled with Argon gas. The output beam of a Ti:sapphire laser producing 30 fs pulses was focused at the entrance of the hollow fiber using a plano-convex lens. The high intensity of the incident laser beam inside the hollow fiber causes self-phase modulation leading to broadening the spectral of the input light. The broadening strength depends on many parameters such as the energy of the incident pulses, duration of incident pulses, length of hollow fiber, gas pressure inside the hollow fiber and the ratio of the beam waist diameter to inner diameter of the hollow fiber. At optimal conditions of 175 cm length hollow fiber, 500 µJ pulse energy, 150 cm focal length lens and 0,6 bar gas pressure the white light exiting the fiber possesses a spectrum ranging from 600 nm- 950 nm which results in generation of sub-8 fs pulses via compressing by a compressor consisting of 8 chirp mirrors.