Papers by Keyword: Holographic Optical Elements

Abstract: This paper reports a combined, Hartmann/Digital Holographic interferometry inspection system for inspecting optical components that do not easily lend themselves to conventional interferometric or Hartmann inspection. A programmable holographic optical element (HOE) preconditions wavefronts to extend the dynamic range of interferometry measurements and also transforms the same system into a scanning Hartmann operation, which has lower resolution but higher dynamic range. Inspecting aspherical surfaces with existing interferometers requires special, computer generated holographic optical elements to transform the wavefront to within the dynamic range of the interferometer. The Hartmann measurement provides the information required to precondition a reference wave that avails the measurement process to the more precise phase shifting interferometry. The SLM offers yet other benefits including a method for minimizing the effects of speckle on the measurement. The paper provides example measurements, discusses the limitations, and suggests other potential applications.

Abstract: The peculiar property of reversible change of the refractive index (Δn) of photochromic systems, is suitably exploited to realize volume phase holographic gratings (VPHGs), which are finding applications in optics and in spectroscopic instrumentations. A large modulation of the refractive index between the two photochromic states and a relatively thick layer of good optical quality are the fundamental requirements for the materials to achieve a good diffraction efficiency. A backbone diarylethene polymer which combines good processing properties with a proper photochromic sensitivity is synthesised and studied. The large Δn between the two isomer states (i.e. Δn=0.03 measured at 1500 nm and the value is even higher at shorter wavelengths, approaching 0.1 near the visible) and the high transparency in the near infrared range make it a promising substrate for the realization of efficient VPHGs. First prototype of VPHGs based on photochromic diarylethene polymer films has been written by transferring the pattern of lines from a master and its functionality is shown.