Long wavelength mid-infrared from mixing two colors from a fiber amplifier

摘要

At Waterloo, we are developing a high power, short pulse, two-color, Yb:fiber amplifier system to generate the long wavelength (＞15μm) side of the molecular fingerprint spectral region, by difference frequency mixing the two colors. This spectral region is important for trace gas detection of explosives. As an example, it has been shown that the strong spectroscopic signatures of a peroxide-based explosive triacetone triperoxide (TATP) occur between 15 and 20 μm. To date, we have achieved a tuning range from 16 to 20 μm with a maximum average power of 1.7 mW. On the short wavelength side, the two colors would need to be pulled further apart, which requires a higher power seed to beat the amplified spontaneous emission that appears at the gain peak of the amplifiers between the two seed colors. On the long wavelength side, we are limited to 20 μm by the transparency region of the nonlinear crystals. We would like to find new nonlinear materials that have transparency from 1 to 30μm. If we could generate wavelengths from 15 to 30 μm with sufficient power, we could extend the spectral region to also cover 8 to 15μm by frequency doubling the longer wavelengths. We are currently working on replacing bulk optics in the system with fiber based optical elements to select the wavelengths as well as stretch and recompress the pulses in order to make the system compact and stable.