Mid-infrared Supercontinuum light sources For food control applications

The advent of spectroscopy by Sir Isaac Newton by observing that white light from the sun can be separated into its constituent colors has found many applications in Scientific research. This observation has been so crucial in fields like color vision and thus, we can say color discrimination and vision is a crude form of spectroscopy. Spectroscopy can simply be described as the absorption of electromagnetic spectral components after interaction with a sample. The inception of spectroscopy has mostly been used to study absorption, scattering, and emission of a limited portion (ultraviolet, visible, infrared) of the broad electromagnetic spectrum but has been expanded to include other components (X-rays, microwaves radio waves) as well as energetic particles like electrons and ions. The infrared part of the electromagnetic spectrum offers a unique advantage as most molecules exhibit distinct absorption fingerprints in this region. The current configuration to probe such absorption fingerprints require broadband thermal light sources whose brightness is much lower especially in the infrared region and also not being spatially coherent. These two disadvantages limit the manipulation of light from these emitters for applications that require simple but efficient instrumentation. This dissertation presents a much more convenient technique of generating broadband, high power, compact light source from the tip of an optical fiber in a process known as supercontinuum generation.
Supercontinuum generation relies on an intense narrow linewidth laser to generate new colors of light after propagation through an optical fiber. This novel process relies on complex nonlinear processes as well as absorption emission processes provided by the specialty fibers used in the generation. Scaling the bandwidth, making an all compact, and improving the noise dynamics of supercontinuum sources has been a major challenge due to the complex processes leading to the generation and inherent limitations of the medium in which the spectrum is being generated. In this work, we present the theory of supercontinuum generation as well as a novel cascading technique to scale up the bandwidth and average power whiles we reduce the relative intensity noise of the spectrum generated. We find the appropriate pumping scheme relevant for improving the supercontinuum light generated. We also show a compact supercontinuum light source which extends the spectrum far into the mid-infrared to approximately 10 µm. The supercontinuum source is finally applied in spectroscopy to monitor food adulteration.