The device ascertains existence of a small inkdrop to be ejected from a thermal-inkjet pen. It includes a light source (preferably a nonpoint source with extended threadlike form perpendicular to the light path), detector, and optical element--preferably a cylindrical lens--for passing light from source...http://www.google.com.au/patents/US5430306?utm_source=gb-gplus-sharePatent US5430306 - Optoelectronic detector with high, uniform sensitivity and large field of view, for thermal-inkjet inkdrops
