James WISHART1, Rotem KUPFER2, Furong WANG1, Marcus BABZIEN1, Mikhail POLYANSKIY1, Igor POGORELSKY1, William LI1, Triveni RAO1, Luca CULTRERA1, Navid VAFAEI-NAJAFABADI1,3, Mark PALMER1
1Brookhaven National Laboratory, Upton, NY, United States
2Lawrence Livermore National Laboratory, Livermore, CA, United States
3Stony Brook University, Stony Brook, NY, United States
We introduce the use of room-temperature ionic liquids (ILs) as efficient Raman wavelength converters. ILs provide an engineerable framework to design suitable liquids for wavelength conversions over a broad spectral range, through careful selection of the molecular structures of the IL anions and cations so that specific characteristics can be obtained, such as a desirable Raman shift, low Brillouin scattering and good optical transmission in the pump and Stokes wavelengths. Applying such criteria, we demonstrated that 1?ethyl-3-methylimidazolium dicyanamide (EMIM DCA) is an effective medium for conversion of 532 nm pulses from a Q-switched Nd:YAG laser to 603 nm. This corresponds to a ~2200 cm-1 shift, which can be used to generate mid-infrared (MIR) radiation through subsequent difference frequency generation (DFG) for optical pumping of CO2 lasers. Threefold-higher Raman conversion efficiency was obtained in EMIM DCA compared to water under identical conditions in a proof-of-principle, single-pass conversion setup, resulting in an efficient generation of multi-mJ, <6 ns duration, high-quality orange laser pulses, in a wavelength region that is difficult to access at high energies. Consequently, we examined ILs representing two other classes of Raman-active functional groups and obtained conversion up to the fifth-order Stokes shift and first anti-Stokes shift. Through the tunable selection of their components and their useful dynamical properties, ILs provide a platform for efficient, simple, and alignment-tolerant high-energy Raman shifting with numerous industrial and technological applications.