Another presentation made by participants at the recently held Annual Photonics Workshop (APW) 2010 in Cochin, India, was on optical homogeneity nonlinear refractive index of KAP, by the School of Physics, Bharatidasan University, Tiruchirapalli, Tamil Nadu, India. The study concluded that the single KAP crystal was grown by slow evaporation method. The wide bandgap energy (4.05 eV) of KAP will be very much useful in nonlinear optical (NLO) device fabrication. The optical homogeneity of the KAP crystal was studied by forming birefringence and conoscopic pattern. The parallelism, straightness in birefringence pattern and sharpness in the conoscopic pattern reveal the refractive index homogeneity of the KAP crystal. According to the presentation, changes of the nonlinear refractive index can be due to different mechanisms – Kerr effect, thermal self-focusing, defocusing, photorefraction, molecular reorientation, etc. Here, the variation in the refractive index is due to thermal nonlinearity, resulting from the linear absorption of the KAP crystal. This negative nonlinear refractive index leads to negative lensing effect; that is, defocusing. There was another presentation on optical investigations on a metal organic coordinated NLO crystal: tris-allyl thiourea cadmium chloride, also by some participants from the School of Physics. I expect to get more details on this one and will surely share those. Hope to add some more of the presentations made at APW 2010 in the some of the forthcoming posts. Pradeep