Two-Colour Nonlinear Amplification for Mid-infrared Generation by Difference Frequency Generation

Abstract

In this thesis, I discuss the development of a two-colour laser system which uses an all-normal dispersion fiber laser in combination with a gain-managed nonlinear amplifier as its broadband source. The goal is to develop a two-colour laser which can be used for mid-infrared generation through difference frequency generation. Most molecules contain characteristic absorption features in the mid-infrared ”molecular fingerprint” region from 3 - 20 μm. Our goal is to create a high power laser that can access as much of these wavelengths as possible. This requires a wide wavelength separation between colours, along with broad bandwidths in each colour, while attaining high pulse energies. This work shows the use of nonlinear amplification of a two-colour seed in an Yb:fiber in order to combat gain narrowing and maintain broad wavelengths in the two colours through self-phase modulation. Many different experimental setups were implemented, which will be presented, with the most successful results being achieved with the use of a large-mode- area Yb:fiber. We demonstrate a two-colour laser source with colours centered at 1070 nm and 1120 nm with individual bandwidths of 30 nm and 21 nm respectively. This two-colour spectrum was amplified up to a total power of 6.76 W, with a repetition rate of 9.67 MHz, corresponding to a total pulse energy of 700 nJ.