Knowledge Bank

A periodically poled LiNbO$3$ waveguide has been used to produce up to 200 $\mu$W of mid-infrared light around 3081 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ with a wide tunability range of $>$33cm$^{-1}$. Two commercial near-infrared diode lasers at 1.064 $\mu$m (pump) and 1.583 $\mu$m (signal) are mixed in a nonlinear optical crystal to achieve difference frequency generation. The 48 mm long direct-bonded quasi-phase matched periodically poled LiNbO$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$ waveguide shows a conversion efficiency of 12.3 %/W. The radiation sits in an important window of the mid-infrared spectral region, where a large number of fundamental vibrations of several hydrocarbons occur. Applications in trace gas detection have been demonstrated for ethene, using multi-pass absorption coupled with wavelength modulation spectroscopy to reach a minimum absorption coefficient of 3 $\times$ 10$\mathrm{<mrow\; data-mjx-texclass="ORD">-7</mrow>}$ cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ Hz$\mathrm{<mrow\; data-mjx-texclass="ORD">-1<mrow\; data-mjx-texclass="ORD">/</mrow>2</mrow>}$. The relatively high power of the mid-infrared idler radiation obtained shows great potential for higher sensitive techniques such as cavity enhanced absorption spectroscopy and cavity ring-down spectroscopy, and preliminary results will be presented. \underline{\textbf{94}}, 517-525, 2009.}