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Presentation at sensors expo (pdf files) | |
 Authors and title Outline of the presentation Bipolar vs unipolarHere is presented the difference between a bipolar laser where the light emission results from a recombination of an electron with a hole across the gap of the semiconductor and a unipolar laser where the light emitting transition occures between two subbands in the conduction band. It is possible to manufacture lasers emitting in wide wavelength range, namely 3.5 to 12 mm, because the energy difference between the two electronic states involved in the lasing transition which determines the emission wavelength is defined by the geometry of the layers.  Moduli square of the wavefunction in the active regionOne can notice that the two red electronic states are centered in two adjacent wells which makes the transition sensitive to electric field i.e. Stark effect. The energy of the transition increases with the voltage applied making the ligth bluer.  Peltier cooled QCLLight versus intensity for a Fabry-Pérot laser cooled at -30°C with 9% duty cycle.  High temperature operationDemonstration of operation of a Fabry-Pérot QCL up to 90°C.  Illustration of the Stark effect in a Fabry-Pérot QCL Demonstration of electrical tuning at constant power Emission spectra of a DFB-QCL vs Temperature Chemical SetupIn this experiment, we perform a PH modulation of a sample containing phosphate. This experiment has been performed in collaboration with the Techniche Universität Wien.  Optical setup A flow cell is built by placing close to eachother two silver-halide fibre optics and having the fluid inbetween. One can inject either from a ftir or from a QCL. The detection is performed by MCT detector. One has to note that we had to either use the laser at very low power or disallign it to avoide burning the MCT element. Spectra recorder with a FTIR during a PH cycle compared with the QCL measurement. Photo acoustic measurement principleThe Photoacoustic cell is provided by Orbisphere laboratories, the QCL replaces a black body source with filtre and chopper.  Measurement results with Methanol (Huge file) Conclusion
The proceedings of this presentation at sensors expo in cleaveland is also available. |
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