All-fiber mid-IR supercontinuum: a powerful new tool for IR-spectroscopy

spectroscopy has until now been greatly limited by the availability of lightsources. The choice has generally stood between a laser whose narrow spectrum limits flexibility or a globar, whose low brightness limits signal to noise ratio. Mid-IR supercontinuum sources, which can deliver an ultra-broad spectrum with a million times higher brightness than a globar, are now appearing to fill the performance gap between the traditional lightsources. The generation of a supercontinuum is a highly nonlinear process produced by high peak power pulses propagating through a nonlinear medium. Since the underlying processes are fundamentally random there will normally be some pulse to pulse fluctuation in the output light which can cause problems in spectroscopy. Most of the mid-IR supercontinuum sources shown to date have also been limited to pulse repetition rates of only a few tens of kilohertz which makes it difficult to apply them to the popular FTIR spectroscopy techniques. Here we will demonstrate a fully packaged, all-fiber, turn-key, low noise, 4.8W, 1.8-4.2 μm supercontinuum source, which can operate with variable repetition rates of up to 30 MHz. In addition we will discuss ways to reduce and counter the effects of pulse fluctuations and we demonstrate optimization of the output spectrum of the source for various applications. Such a source can give any mid-IR optics lab access to a performance which has previously only been available from dedicated beamlines at huge synchrotron facilities.