Develop novel optical elements and holographic methods for beam-shaping and imaging
Holograms are often designed to reconstruct the phase and amplitude of an object. In conventional holography, the reference beam (recording beam) and the sample beam (object beam) are led to interfere at an angle to produce off-axis holograms. If the light field are temporally coherent, the interference patterns would result in a sinusoidal wave pattern (grating) that is imposed on to the holographic element. The grating pattern on the hologram acts as a diffractive element. This means that when the recording beam illuminates the hologram, the image would reappear at an angle to the recording beam. This type of off-axis hologram aids in the clear separation of the image (first diffraction order) and recording beam (zeroth diffraction order). In most case, the zeroth diffraction order possesses higher intensity amplitude than the rest of the diffracting orders.On the other hand, it is also possible to carry out the interference without an angle: on axis hologram. The on axis separation can be made by using a reference beam with a spherical or conical wavefront. However, the co-propagating zeroth and first diffracting orders could overlap and interfere, which would cause poor reconstruction of the image. With modern day computer and programming scripts, it is possible to “virtually” interfere the reference beam and the object beam while directly recording it onto a light sensitive display i.e. spatial light modulators.
Beam shaping, Spatial Light modulator