Mid-infrared Laser Based on Cascaded Raman Wavelength Shifting in Fibers

Spectral fingerprinting for chemical agent detection or industrial process and analytic chemistry requires a compact, lightweight, tunable mid-infrared (mid-IR) laser. A room temperature, fiber-based mid-IR laser is proposed that starts with a pump laser in the near-IR, and then down-shifts the light based on cascaded Raman wavelength shifting in mid-IR fibers. The laser is widely tunable by simply tuning a seed semiconductor laser, and the power can be scaled up to watts by using larger core size fibers. The mid-IR laser leverages the mature technology base from telecommunications, where our team has considerable experience on Raman technology. We use simulation codes carefully tested in near-IR wavelengths to design the proposed mid-IR lasers, and we show that the Raman wavelength shifting process is extremely efficient. New technical challenges arise from using mid-IR fibers based on chalcogenides or fluorides, but these should be engineering challenges rather than fundamental limitations. The Phase I project has three main objectives. First, prove the accuracy of the simulations and better understand the properties of the mid-IR fibers. Second, demonstrate experimentally cascaded Raman wavelength shifting in the mid-IR fibers. Finally, generate light in the 3-5 micron wavelength range using off-the-shelf telecom technologies and mid-IR fibers.