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LE-1300 Iodine Raman Laser

The Iodine Raman laser belongs to the class of molecular laser. However, the laser transition starts from the same level as the pump laser forming a so called Λ system. Due to this coupling a variety of coherent phenomena occur. One of it is the Raman gain which leads to an asymmetrical gain distribution favouring the direction of the pump laser. This effect causes spontaneous and unidirectional propagation inside a ring laser and has been firstly observed and explained by Wellegehausen et. al. in 1979. So far known experiments have been carried out with expensive pump laser. The invention of inexpensive laser pointer like DPSSL emitting laser radiation at 532 nm which is ideal to excite the iodine molecule allowing new affordable exciting new experiments for education. However, the underlying generation of the green radiation is based on the frequency doubling of a diode pumped Nd:VO4 laser. Such a laser has a gain bandwidth of about 1 nm. Due to thermal drift of the cavity also the frequency doubled radiation is drifting in a range of 0.5 nm. The absorption width of the Iodine molecule is much smaller compared to the thermal drift of the excitation laser. Therefore the cavity of the “green laser” must be thermally stabilised by controlling the temperature of the pump laser with an accuracy of 0.01°C and the injection current of 0.1 mA. In such a way it is possible to tune the pump laser to the resonance of the transition indicated by the appearance of strong fluorescence light of the excited Iodine.