Samenvatting
We study the feasibility of second harmonic generation (SHG) with spatially incoherent laser radiation. We conduct a thorough literature study entailing the general polarization and susceptibility properties of non-linear media and particularize towards second harmonic generation. Based on this theoretical framework we illustrate angular phase matching for a type I SHG process (840nm-> 420nm) in B-Barium Borate. We calculate phase matching angle, walk-off angle and phase matching bandwidths.Next we have performed several SHG experiments. in the first series of experiments we show how a rotating diffuser and two lenses can be added to the setup to convert a coherent laser beam into a time-averaged spatially incoherent laser beam. We select an optimum configuration for this setup both yielding sufficient power and good focusability. During th second series of experiments we study the focusing properties of our coherent and incoherent sources by means of beam profiling. We show that the incoherent beam has a high M2 value, leading to larger divergence and beam waist. The final series of experiments consist of three second harmonic conversion efficiency measurements. The first two feature a coherent laser source and serve as a frame of reference. In the last ewperiment we explore the conversion efficiency for an incoherent laser beam. We observe that the specific incoherence generated by our diffuser setup leads to conversion efficiency decreasing by order of magnitude 250 times compared to the case of a coherent laser beam. We have thus proven that SHG of a spatially incoherent fundamental beam is indeed possible, albeit with low conversion efficiency.
Finally we explore the possibilities of simulating the incoherent second harmonic generation process. We show that simulation is indeed possible, but that further modeling of the process is required. In conclusion we put forth several improvements that might increase the limited conversion efficiency observed within the scope of this master thesis. Hereby we provide several starting points for future work.
| Datum prijs | 2011 |
|---|---|
| Originele taal | English |
| Begeleider | Jan Danckaert (Promotor), Guy Verschaffelt (Promotor), Gordon Craggs (Advisor) & Simon-Pierre Gorza (Advisor) |