Semra Bekele - 2004 REU Participant 

          My name is Semra Bekele.  I attend the University of Arizona  majoring in electrical engineering.  This summer I am lucky enough to participate in the  REU               program.  I'm  working in the Optical Sciences Center  at the University of Arizona in Dr. Nasser Peyghambarian's group.  He is the  chair of  Photonics and              lasers, professor of optical sciences and  professor of material sciences and engineering.
          I'm working closely under Dr. Jayan Thomas who is an assistant research professor.  His main area of research is photorefractive polymers that are organic. 
         Optical technology is expected to contribute a great deal to the future electronic information processing networks since current communication systems are
          becoming more powerful and complex.   To make the emerging optical  technology viable, the search for novel optical materials is of crucial importance.
          Advances in materials are focusing on the development  of optical materials with high optical quality, hight efficiency, high sensitivity, long lifetime, low cost
          and good processing capabilities.
          Among the most sensitive materials for nonlinear optical applications, photorefractive (PR) materials have been the subject  active research for the last 25   
          years.  
          Recently, a new generation of organic photorefractive materials have been introduced.  Dr. Thomas is trying to develop composites with  high diffraction
          efficiency with these materials.
   
          Weekly Progress Reports

           Week 1   (06/14/04 - 06/18/04)
            This was my first week at Dr. Thomas' s lab.  I spent the first two days looking at the lab instruments, going over the lab safety guidelines, and reading the                  theory behind his research. 
            On the third day, I was shown the cleaning procedures of contaminated spatulas, beakers, and slides.  I was also shown the different chemical disposing                     containers.  I correctly marked sample slides of Indium Tin Oxide, which are used as transparent conductive electrodes.
            On the forht day, I was preparing samples by measuring and mixing  polymers, chromophores, plasticizers, and sensitezers together.  We dissolved these    
            in tolune.  Then the solution is passed through a filter before further processing.  We decided to use dichloromethane to dissolve the mixture instead of  
            tolune, since it has a low boiling point (below 40 degrees) due to its water retention characteristics.  It was necessary for us to pass the dichloromethane
            through aluminum oxide to extract the water from it.  We put the sample in a vaccum drying oven setting the temprature to 70 degree celcius for 7 hours.

             Week 2  (06/21/04 - 06/25/04)
             This week, I made Photorefractive Polymer devices using different materials as chromophores, polymers, plasticizers, and sensitizers.  We measured the
             absorption of the sensitizers using spectrophotometer. Fabricating these devices needs very careful and precise steps.  Great care has to be given to make
             sure that no impurities or dust get into the materials. If these impurities come in contact with the materials, they can lead to incorrect measurements.
             I also cleaned the labware that were used.  This process is very critical.  Since we are trying to avoid dust and impurites, I had to thoroughly clean them and
             cover them with aluminum foil. 

              Week 3 (06/29/04 - 07/02/04)
              This week I made more PR(PhotoRefractive) devices to be tested for absorption, photoconductivity and photorefractivity.
              I went to the lab where characterization of the devices was done.  The lab room was occupied  with an optical instrument that has different lenses, devices,
              amplifiers, voltage sources and other optical components.  Labview software was being used to plot the data.
              Two experiments named, Two Beam Coupling (2BC)  and Four Way Mixing (4WM) are used to measure the photoconductivity and photorefractivity of                   the devices.    
              In case of the 4WM experiment , two coherent writing beams are overlapped on the sample to create a fringe pattern.  The intensity of the transmitted      
              and the diffracted light is monitered and the diffraction efficiency is determined. 
              In the 2BC experiment the reading beam is absent and the transmission of the two writing beams is measured. 

              Week 4 (07/06/04 - 07/09/04)
              This week I have been making more PR devices. I also learned how to clean new glass slides using the Ultrasonic Bath and the whole cleaning process in                   detail.
              I learned how to cut ITO(Indium Tin Oxide) conductive glass electrodes for the PR devices.
              I did more of the cleaning of the labware to prepare the PR devices.