High Power Extremely Narrow Linewidth Diode Laser for Polarizing 3He Target

Polarizing high intensity 3He gas is an extremely important task since polarized 3He is an effective neutron target for a broad nuclear physics programs such as some conducted in Jefferson Lab's Continuous Electron Beam Accelerator facility (CEBAF) and Spallation Neutron Source (SNS) in Oakridge National Lab. The polarized 3He gas has also been used in medical imaging to detect the lung disease. The polarization of 3He strongly relies on the power, linewidth, wavelength stability, and polarization of the pumping laser. Raytum Photonics will develop state of art fiber coupled diode laser system to provide the best and turn-key solution for the production of polarized 3He gas. This system will not only facilitate the polarization of 3He gas, but also improve the polarization efficiency, percentage, and the cost. It will help to achieve the objectives specified in the topic 26e to develop polarized high density 3He gas. During the Phase I effort, we demonstrated on the breadboard a fiber coupled diode laser with output of 180W and wavelength tuning range of more than 0.8nm using a unique modular design. We also demonstrated a diode laser with extremely narrow linewidth of less than 0.06nm and output of more than 50W. The lasing wavelength can be thermally tuned in the range of 0.4 nm, which pave the way for the automatic wavelength locking to the Rb absorption line. The optical modeling work during the Phase I effort also shows the feasibility of making a more than 200W laser module. In the Phase II, we will deliver a fiber coupled diode laser system with output power of more than 200W, linewidth less than 0.1 nm and the lasing wavelength automatically locked to the Rb absorption line. We are also going to engineer a prototype high power laser module to evaluate the concept of kW fiber coupled system for the polarization of 3He. The high power fiber coupled diode laser has also been widely used in the material process industry.