Use of a LiNbO3Modulator Gate in Amplification of Femtosecond Optical Pulses Generated by a Passively-Mode-Locked Erbium-Doped Fiber Laser

127-fs, 4-kW pulses by a mode-locked fiber laser were gated to reduce the repetition by a modulator and amplified by an EDFA. The net gain of 50 was 11 times that without a modulator.

1. Introduction

Femtosecond lasers are suitable for mircoprocessing of materials as they have a high peak power and thus nonlinear absorption or breakdown in the material can be used. Ti³⁺ sapphire lasers have been used for this purpose. Although fiber lasers are also suitable for ultrashort-pulse generation and have merits of relatively low cost and a compact structure, they have not been used. In this study we generated femtosecond pulses with a passively mode-locked fiber laser¹⁾and amplified the pulses using an erbium-doped fiber amplifier (EDFA). Various femtosecond-pulse amplification systems have been studied,^{2, 3)} and some of them employ an acousto-optic modulator gate. Here, we inserted a LiNbO₃ (LN) modulator as a gate to reduce the repetition rate and to achieve high pulse energy.