Generation of 14.8-fs Pulses in a Spatially Dispersive Amplifier

Abstract

The rapid advance of ultrashort amplified laser technology into a mature research tool has inspired its widespread use. Such laser pulses, with durations of less than 10 fs, are exclusively generated by using gas-filled capillaries with subsequent chirped-mirror compression [1]. Direct amplification of ultrabroadband laser pulses to high energies (millijoule region) still poses a challenging problem. Thermally induced lensing, gain-narrowing and phase aberrations during amplification reduce the ability to obain ultrashort pulses at a higher energy level with a good beam quality. These problems have been addressed in a number of variants, such as cryogenic cooling of the gain material, spectral filtering and phase control via adaptive shaping or specially designed mirrors and pulses shorter than 16 fs have been reported [2] [3]. Another promising approach, first proposed by Danailov et al. [4] employs a spatially dispersed seed beam inside an amplifier to decouple the amplification of competing wavelengths from each other. With this an artificial inhomogeneous broadening is induced in the Ti:sapphire, which is normally homogeneously broadenend, which makes it possible to tailor the gain profile. The effective gain factor of each wavelength component is only determined through the dedicated pump intensity profile. As a result, gain-competition between different wavelength components, and red-shifting of the spectrum can be eliminated provided that the individual wavelength channels are sufficiently decoupled from each other inside the gain medium. The implementation of such a dispersive amplifier has been previously reported [5], but compression to yield amplified ultrashort pulses was never demonstrated.