Measurements characterizing spatial mode filtering of mid-infrared (mid-IR) laser beams using hollow core fiber optics
are presented. The mode filtering depends strongly on the fiber diameter, with effective mode filtering demonstrated
with bore diameters of d = 200 μm and 300 μm. In addition to mode filtering, beam profile measurements also
demonstrate the strong dependence of the mode quality on the fiber coupling conditions. As predicted, optimal coupling
is achieved using relatively slow optics that produce focused spots that nearly fill the fiber diameter. Examples of the
utility of using hollow fibers for mode-filtering to improve molecular spectroscopy experiments are also discussed.