In this proposal, we propose to demonstrate and build high pulse energy near 1.55 micron wavelength single frequency fiber laser by developing an innovative polarization maintaining Er-doped gain fiber with extremely large mode field diameter. Such a single frequency high energy and high peak power fiber laser is needed for coherent lidar and sensing. We will enhance the radiation resistance of the gain fiber in order to make it suitable for NASA's applications. In Phase I, we will design and fabricate Er-doped glasses, fiber preforms, and fibers. High pulse energy will be demonstrated. This proposed system will be all-fiber based, which offers excellent reliability. Successful demonstration of such a fiber laser can enable many new NASA and commercial applications.