To measure the concentration of a fluid under consideration by means of tunable diode laser spectroscopy an algorithm
for automatic detection of absorption transitions has been developed. The algorithm consists of a three step process. In
the first step, necessary information is taken from the HITRAN database. Measured data are analyzed in the second step
in order to eliminate the laser characteristics underlying the absorption spectrum, to localize the absorption lines and to
get convenient initial values for fitting the absorption transitions to a Lorentzian line shape profile in step 3. The
concentration is calculated from the best approximation among all parameters from the transitions found on the signal.
The developed algorithm was tested with a set of simulated curves with different concentrations of carbon dioxide
transitions at the 2.004 μm band and it could analyse concentrations with relative error better than 1% for concentrations
down to approximately 200 ppb. Computation time including acquisition time and graphical output display is fast
enough to enable online monitoring of fluid concentrations.
We demonstrate gas sensing in a relatively compact sensor unit in particular for weakly absorbing gases in real time. As
a proof-of-concept, we built an oxygen sensor for the A-Band at 760 nm. A VCSEL laser was used as a laser source due
to its mode stability and reduced cost compared to DFB lasers and Fabry-Perot lasers. In order to reduce as much as
possible the sensor size, a hollow waveguide is used to guide the light and the gas to be analysed in a long path to
enhance the sensitivity of the sensor. Two different types of hollow fibres were characterised with respect to their
suitability for gas sensing, a photonic crystal fibre, also known as micro-structured optical fibre, and hollow metal-coated
capillaries. Characteristics as attenuation, spectral transmission properties and filling time were analysed. At the end, a
sensor device with coupling and detection unit was developed. The main advantage of our set-up is the possibility of
using the same design for different gases by changing solely the laser, the detector and the coupling lens.
First results for luminescence-based dual sensing of environmental parameters with a multicolor LED are presented.
With this method, cross-sensitivities of the luminescence material between such environmental properties can be
eliminated. A very compact and inexpensive sensor setup is possible by use of an LED as excitation source and another
LED simultaneously as luminescence detector. The parametrization of the cross-sensitivity will be discussed and
possible further simplifications of the sensor will be pointed out.
We present a compact and cheap sensor device based on the combination of a standard RGB-LED with a luminescence
material. The multicolor LED acts as the exciting light source, the luminescence light detector and simultaneously as an
optical filter. As luminescence material various phosphor materials or crystals can be used, depending on the physical
property to be sensed. Possible applications will be discussed.
We present a compact oxygen sensor based on hollow-core photonic crystal fibres (PCF). The compact design requires only a very small amount of gas. Both ends of the fibre are inserted into miniaturized vacuum adapters, which should result in an increased gas exchange and prevent fibre contamination. The detection of oxygen could be verified. Proper choice of the specific components (PCF, laser source) allows the detection of other gases.