ABSTRACT
INTRODUCTION The development of a broadband photon source spanning the (V)UV range to the infrared is of general interest in many fields. Such a very bright and stable white light source is e.g. extremely useful to perform sensitive absorption spectroscopy. The total light absorption by a sample depends on the optical path length through the sample according to the law of Beer-Lambert. In order to investigate weak absorptions by a sample, it is useful to direct a light beam over a long distance through that sample, enhancing the relative absorption. In the cavity ring down detection scheme, a significant path length increase is achieved by placing two highly reflecting mirrors around a sample. When light is locked between these two mirrors, it traverses the sample many times, before the main part of the light has leaked out of the optical cavity through the mirrors. It is clear that a higher reflectivity of the mirrors results in a longer path length of the light beam through the sample. Because only a small fraction of the incident light is transmitted by the first mirror and subsequently locked in the optical cavity, the tight intensity behind the optical cavity becomes a critical issue in the detection scheme. Another main issue is the stability of the light source. Conventionally, lasers are implemented as the light source in a cavity ring down experiment, which exhibits a very high light output intensity. But using a laser limits the spectral range over which measurements can be performed or complicates the experimental setup, when a broad spectral range is of interest. A very elegant alternative solution is to introduce a cascaded arc as the light source, which is an incoherent, bright and stable light source. Below the cascaded arc will be introduced, followed by the description of an optimisation strategy for the geometry of the active part of the cascaded arc. The optimisation strategy is based on an approximate way of plasma modelling: accurate approximate modelling.
