Highly efficient, low-noise Yb femtosecond fiber source

Summary form only given. With the recent availability of Raman-shifted, widely tunable Er fiber laser pulse sources, the direct injection of Yb fiber amplifiers with femtosecond pulses from a frequency-converted Er-fiber laser has become possible. The exploitation of the unique efficiency and large bandwidth of Yb fiber amplifiers thus allows the construction of highly compact ultrafast laser sources operating at W-level average powers. However, in most applications very low noise levels from such systems are needed, which may seem challenging due to the nonlinear processes involved from transferring the output of an Er fiber laser at 1.56 /spl mu/m to the 1 /spl mu/m region. We demonstrate for the first lime to our knowledge that a femtosecond Yb fiber source can be operated in an extremely low noise regime. Injected with a Raman-shifted and frequency doubled Er femtosecond fiber laser low noise performance is achieved by exploiting self-limiting nonlinear frequency conversion in both the Raman shifting stage as well as the frequency doubling stage. Reliable operation of the Yb-amplifier is obtained by employing side-pumping and polarization maintaining (PM) fibers.