Compression of Nonamplified Femtosecond Laser Pulses by an Organic Crystalline Fiber

Abstract

Compression of femtosecond optical pulses using a single-mode fused silica fiber (glass fiber) always needs high amplification of laser output pulses because of a low nonlinear refractive index of its fiber1). This leads to some problems such as the pulse stability in time and space, the pulse repetition rate, and the precise adjustment of a big amplifier system. In order to solve these problems we developed a femtosecond-response, highly third-order nonlinear 4-(N,N-dimethylamino)-3-acetamidonitrobenzene (DAN) crystal-cored fiber21 . We found that a nonlinear refractive index of the DAN fiber is 1.7 × 104 times as large as that of the glass fiber. Furthermore, we have demonstrated that the DAN fiber has enabled us to compress 39 fs output pulses from a CPMdye laser to 22 fs without any amplification3). This result suggests that , the application of the DAN fiber for direct compression of femtosecond output pulses from a mode-locked Ti:sapphire laser which generates the higher peak power, will generate shorter pulses. Moreover, the application for compression of semiconductor laser pulses will bring the more interesting results. We have calculated in details the dependence of the compressed pulse duration on the output peak power from a picosecond semiconductor laser using a nonlinear Shrodinger equation. The computer calculation shows that, a 200 mWpeak power pulse with a 20 ps duration, which is easily available, can be compressed directly to 500 fs.