This SBIR phase II project proposes a single frequency high energy fiber laser system operating at low repetition rate of 10 Hz to 1 kHz for coherent Lidar systems for remote sensing. Current state-of-art technologies can not provide all features of high energy and efficiency, compactness, narrow linewidth, super frequency and power stability, low noise, and high extinction ratio at the same time. PolarOnyx proposes, for the first time, a high energy (100 mJ) single frequency (< 1 KHz) PCF fiber laser transmitter to meet with the requirement of solicitation. This proposal is based on the spectral shaping sub-mJ fiber laser we have achieved in our labs. In the high power amplifier stage, PolarOnyx proposes an innovative PCF fiber based regenerative amplifier approach by employing our patent pending proprietary technologies in fiber lasers, that will be able to operate at low repetition rate (10 Hz to 1 kHz) and reach high energy level of 100 mJ. These will make the fiber laser transmitter system superior in terms of wall plug efficiency (over 30%), energy(100 mJ), noise, size, and cost. Proof of concept experiment has been demonstrated in Phase I time frame. A compact prototype will be delivered in Phase II.