Burst mode amplification through Yb doped PCF ROD amplifier to generate mJ burst energy with femtosecond multi-micro bunch structure in all fiber laser system

We report generation of burst-mode infrared pulses (1030 nm) with a total energy of approximately 3 mJ, achieved using chirped pulse amplification (CPA) in Yb-doped photonic crystal fiber (PCF) rod amplifiers, seeded with a multi-microbunch pulse structure. The individual pulse energy within the burst ranged from ∼111 μJ (maximum) to ∼14 μJ (minimum). These pulses were successfully compressed to an estimated pulse width of ∼335 fs using a grating-based compressor. The seed source was an in-house developed Yb-doped fiber oscillator, passively mode-locked at 130 MHz using the nonlinear polarization rotation (NPR) technique. A commercial semiconductor optical amplifier (SOA) was employed as a high-efficiency pulse picker, enabling the selection of user-defined multi-micro pulse structures within a 4 μs time window at a 10 Hz burst repetition rate representing a three-time scale burst pulses. The selected pulse structure was amplified through multiple stages, culminating in two Yb-doped PCF rod amplifiers. Through optimization of the pulsed pump configuration, we maximized the gain for the leading pulses within the burst train. The resulting output comprised a multi-MHz repetition rate pulse train with the central lobe compressed to pulse width of ∼335 fs and peak individual pulse energy of ∼111 ± 4 μJ, contributing to a total burst energy of ∼3.1 ± 0.09 mJ. These high-energy, ultrafast burst pulses are currently being utilized to generate high-current electron bursts from photocathode in the Delhi Light Source (DLS), a pre-bunched free electron laser facility under development at IUAC, New Delhi.