Adaptive Nonlinear Phase Compensation in a Femtosecond Hybrid Laser with Varying Pulse Repetition Rate

Luka Černe,Rok Petkovšek,Jaka Petelin

doi:10.3390/photonics8090387

Abstract

In this manuscript, an implementation of a tunable nonlinear phase compensation method is demonstrated on a typical femtosecond hybrid laser consisting of a fiber pre-amplifier and an additional solid-state amplifier. This enables one to achieve constant laser pulse parameters over a wide range of pulse repetition rates in such a laser. As the gain in the solid-state amplifier is inversely proportional to the input power, the shortfall in the solid-state gain at higher repetition rates must be compensated for with fiber pre-amplifier to ensure constant pulse energy. This increases the accumulated nonlinear phase and consequently alters the laser pulse parameters such as pulse duration and Strehl ratio. To overcome this issue, the nonlinear phase must be compensated for, and what is more it should be compensated for to a different extent at different pulse repetition rates. This is achieved with a tunable CFBG, used also as a pulse stretcher. Using this concept, we demonstrate that constant laser pulse parameters such as pulse energy, pulse duration and Strehl ratio can be achieved in a hybrid laser regardless of the pulse repetition rate.

Highlights

Phase Compensation in a FemtosecondIn areas where high-quality laser pulses are desired, such as laser micromachining [1,2,3,4,5,6], ophthalmology [7] and nonlinear microscopy [8,9,10,11], nonlinear optical effects such as self-phase modulation (SPM) often limit the achievable pulse energy of high-energy ultrafast laser systems
We demonstrate an inherent need for a tunable nonlinear phase compensation method in a typical hybrid laser that operates at a broad range of pulse repetition rates and with a constant output pulse energy
We can significantly improve pulse duration and Strehl ratio with nonlinear phase compensation with tunable chirped fiber Bragg grating (TCFBG), we can still see in Figure 3h that we have some broad pedestal left in the pulse temporal profile

Summary

Introduction

Phase Compensation in a FemtosecondIn areas where high-quality laser pulses are desired, such as laser micromachining [1,2,3,4,5,6], ophthalmology [7] and nonlinear microscopy [8,9,10,11], nonlinear optical effects such as self-phase modulation (SPM) often limit the achievable pulse energy of high-energy ultrafast laser systems. Many advanced techniques have been demonstrated, among which is coherent beam combining [14,15], pulse stacking [16], the use of tapered fiber amplifiers [17,18] and the use of optical fibers with large core diameters [19,20] These systems offer some outstanding results in terms of power scaling, their relative complexity hinders their applicability in industrial laser applications. Even with the hybrid laser design, nonlinear optical effects remain a problem that needs to be addressed This is even more crucial with lasers that operate in a broad range of pulse repetition rates while at the same time ensuring constant output pulse energies. This type of laser operation is becoming more and more desired in industrial and scientific applications, especially where the lasers are used in combination with fast scanning mechanism such as polygon or resonant scanners

Methods

Results

Conclusion