Controlling the velocity of a femtosecond laser pulse using refractive lenses.

Spencer W Jolly,Fabien Quéré,Antoine Jeandet,Olivier Gobert

doi:10.1364/oe.384512

Abstract

The combination of temporal chirp with a simple chromatic aberration known as longitudinal chromatism leads to extensive control over the velocity of laser intensity in the focal region of an ultrashort laser beam. We present the first implementation of this effect on a femtosecond laser. We demonstrate that by using a specially designed and characterized lens doublet to induce longitudinal chromatism, this velocity control can be implemented independent of the parameters of the focusing optic, thus allowing for great flexibility in experimental applications. Finally, we explain and demonstrate how this spatiotemporal phenomenon evolves when imaging the ultrashort pulse focus with a magnification different from unity.

Highlights

Control and manipulation of laser beams has a broad realm of applications in many different fields
We discuss the so-called flying focus effect whereby the velocity of the light intensity peak formed within the focal region of a broadband laser pulse can be arbitrarily different than the speed of light via very simple spatio-temporal shaping [9,10]
We present here an implementation of this effect more appropriate for femtosecond laser beams, which exploits the chromatic properties of a special lens doublet rather than those of a diffractive lens

Summary

Introduction

Control and manipulation of laser beams has a broad realm of applications in many different fields. We discuss the so-called flying focus effect whereby the velocity of the light intensity peak formed within the focal region of a broadband laser pulse can be arbitrarily different than the speed of light via very simple spatio-temporal shaping [9,10]. This recently identified effect has many potential scientific applications such as ionization waves of arbitrary velocity [11,12,13], Raman amplification in a plasma [14], particle acceleration [15], and photon acceleration [16]. A key advantage of this configuration is that the shaping is induced independently of the focusing optic, allowing for more flexibility in applications of this effect

Overview of the flying focus

Different scenarios for producing the flying focus

Measurement of the chromatic lens system

Measurement of the flying focus

The effect of magnification

Conclusion