Incoherent optical pattern recognition has been demonstrated with a simple setup using photorefractive BaTiO3 crystals. The input patterns to be identified can be transmitted into the system with completely incoherent (both temporal and spatial) light. The setup does not require prefabricated filters for its operation and is thus a real-time system. The working principles of the system involve the photorefractive beam fanning effect and degenerate four-wave mixing.

We have demonstrated experimentally that optical Not-OR (NOR) and Not-AND (NAND) operations can be done with a single setup. The setup is capable of processing parallel inputs. Two barium titanate (BaTiO3) crystals are used in the setup and photorefractive effects are employed. Instead of using the interference between the two input signals to be processed or the so called local incoherent erasing, the setup works on the phenomenon of self-pumped phase conjugation and the suppression of it by the input signals in ordinarily polarized state. In this way, the two input channels can be mutually incoherent.

Using the beam Lanning effect in a BaTi03 crystal, we propose two simple set-ups to perform the function of an optical image combiner and an optical AND gate respectively. The optical image combiner combines two mutually coherent as well as mutually incoherent patterns transmitted to it separately into a single coherent pattern. This set.up can also be used as an optical OR gate. For the AND gate, the two input signals may also be mutually coherent or incoherent. Experimental results showed the response time of these two devices to range from 0.01 second to 2.5 seconds.Key words : optical image combiner, optical OR gate, beam fanning effect, photorefractive crystal IntroductronSince the discovery of photorefractive effect, several 10gic operations have been accomplished by its use. Photorefractive materials are used for making these devices because the effect responsible for the desired Lunctions is fast and it does not require large incident power.Image combiners have also been proposed by several groups.1'2) However, if the input patterns to be combined are mutually incoherent, the resultant combined pattern would not be coherent in general, and thus it is often not possible to treat such cases by the well-developed coherent optical techniques in the subsequent stages of the system.Making use of the fanning phenomenon in BaTi03 crys' tals, we propose here a simple set-up which combines two mutually coherent or incoherent patterns into a single coherent pattern. The device can also function as an optical OR gate. By making use of the sarne phenomenon, color converter and optical AND gate can be fabricated. The former has been discussed elsewhere.3,4) A simple set-up performing the latter function is proposed in this paper. The two input signal beams in this set-up can also be mutually coherent as well as incoherent. Principle of OperationWhen a beam of coherent light penetrates into a piece of photoreLractive crystal, some portion will be scattered by the defects and impurities contained in the crystal, thus producing scattered waves. These scattered waves interfere with the original incident beam locally and lead to the formation of gratings, usually called noise gratings. These gratings can transfer the energy in the original incident waves to the scattered waves, thus amplifying the latter and depleting the energy in the incident beam if the process of writing and reading these noise gratings continues. Since the propagation directions of the scattered waves are in general not too different from the original incident wave and since the two kinds of waves cannot be differentiated from each other, the incident beam phenomenologically fans out. This phenomenon is called "beam fanning" in photorefractive optics. The energy of the incident beam can be transferred to the scattered waves almost completeley if the incident beam is an extraordinary ray and the grating vector of the noise grating is about 45 degrees from the c axis of a high-gain BaTi03 crystal.5,6) Under these conditions, strong beam fanning results. ...

PACS. 68.10 -Fluid surfaces and interfaces with fluids. PACS. 61.10 -X-ray determination of structures.Abstract. -The final stages of the spreading of nonvolatile polymer droplets on smooth solid surfaces have been studied by the technique of X-ray reflectivity. Clean and silanated silicon wafers which are substrates corresponding, respectively, to high and low positive spreading parameters S, have been investigated. In both cases the equilibrium state has been characterized and compared with recent theoretical predictions. We show that for a high S value, the final state cannot be viewed as a dense homogeneous film, whereas for a low S value, the theoretical *pancake* picture could be appropriate.