Generation of ultrafast user defined multi-micro-pulse burst structure from a femtosecond mode-locked fiber oscillator by using semiconductor optical amplifier for photoinjector.

We demonstrate and present detailed technical insights into the generation of a user-defined multi-micro-pulse burst structure from an in-house developed femtosecond mode-locked fiber oscillator using a standard semiconductor optical amplifier (SOA), which acts as an excellent candidate for an ultrafast fiber-based pulse-picker. An in-house developed 130 MHz mode-locked fiber oscillator followed by a 500 m long optical fiber as the pulse stretcher along with polarization control units was used to achieve a highly stable multi-micro-pulse structure at variable repetition rates by using and adapting a fiber coupled SOA. The timing system with a synchronous trigger setup has been explained in detail to achieve the multi-micro-pulse structure from the fiber laser system, which is being used to generate multi-micro-electron bunches in a photoinjector based free electron laser facility at IUAC named as Delhi Light Source. The technical insights from the detailed experimentation and results help bring out various advantages and challenges in the use of an SOA as an ultrafast pulse-picker for generating a multi-micro-pulse structure, which will be useful for widespread applications of the modern compact femtosecond lasers and in the field of photoinjector based systems for higher electron currents.