REU Presentation Overview

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I. Introduction

  • Common Theme in Projects

      1. materials interaction with intense focused light

        a. magnifying Sun's irradiance
        b. diffuse reflectance of materials

II. Solar Irradiance

  • Applications

      1. solar furnaces


      2. energy storage / energy sources

  • Indoor Experiments

      1. Thin-Lens Equation

        a. verify
        b. find focal length of lenses
  • Outdoor Experiments

      1. set up

        a. optical table with screen & lenses
      2. irradiance on clear day ~ 1 kW/m2


      3. irradiance at spot increased

        a. ratio of lens area to spot area
        b. magnifying lens ratio ~ 100 x
        c. reading glasses ratio ~ 30 x
             i. didn't burn paper
  • Minimum Irradiance to Burn

      1. found by "defocusing" lens until burning happened

        a. measured spot size
        b. new ratio ~ 40 x
  • Spot Size

      1. differed from predicted values

        a. given by Thin-Lens Equation
      2. reasons

        a. difficult to measure bright spot accurately
        b. lenses spherical aberration

III. Diffuse Reflectance

  • Reflection Types

      1. diffuse

        a. Lambertian
      2. specular
  • Applications

      1. laser drilling, cutting & engraving


      2. measurements of surface properties

        a. roughness
  • Purpose

      1. diffuse reflectance of materials

        a. measure optical absorbency
      2. find material for laser engraving master copy

        a. laser engraving
             i. uses high-powered YAG laser
        b. most absorbent material
             i. power = absorbency + reflectance + transmission

             ii. maximize absorbency, minimize reflectance
  • Experiment

      1. set up

        a. photodetector
        b. bright, white Lambertian sample
      2. illuminate with laser normal to sample

        a. used HeNe laser with power ~ 15 mW
        b. data
             i. power ranged from ~ 5 mW to ~ 0.02 mW
        b. agreed with Lambert's Cosine Law
             i. I (theta) = I0 Cos (theta incident)
  • Future

      1. take more measurements

        a. various angles
        b. various materials