Trivia Question During the Strategic Defense Initiative (Star Wars Initiative) under President Ronald Reagan, which of the following futuristic weapons systems were developed? (a) Nuclear X-Ray Laser (b) Photon Torpedoes (c) Rail Gun (d) Brilliant Pebbles (e) Neutral Particle Beam

Trivia Question During the Strategic Defense Initiative (Star Wars Initiative) under President Ronald Reagan, which of the following futuristic weapons systems were developed? (a) Nuclear X-Ray Laser (b) Photon Torpedoes (c) Rail Gun (d) Brilliant Pebbles (e) Neutral Particle Beam All of them!

How do you ‘cheat’ nature and get around fundamental limitations of optics? Photon Torpedoes – Go nonlinear with high intensity laser pulses which self-focus in a medium to counteract diffraction. Embrace diffraction, but confine light to define spatial resolution BELOW diffraction limit.

Diffraction: Light does not like to be confined

Examples of Diffraction Knife edge Light passing by a sharp edge

Examples of Diffraction Waves passing through a small hole

Examples of Diffraction Focusing light with a lens Geometric Optics – Wavelength small compared to other dimensions. No Diffraction. Light focuses to a point. Wave Optics – Wavelength can be comparable to other dimensions. Diffraction MUST be considered. Light focuses to a minimum spot size. oo

Diffraction of light through an aperture

Sample Problem

Fresnel Diffraction Fraunhofer Limit

Error in Focusing

Simple demonstrations of Improved Focusing Squinting If you use corrective glasses, take off your glasses. Use your fingers to make a small aperture and look through the aperture. As the aperture gets small, the quality of the image improves! Better in focus. Pin hole camera – for a pin hole, depth of focus is large so that you can generate an image of a scene WITHOUT a lens.

4-f imaging system

Spatial Filters

Image Quality with Wave Optics

Near-Field Imaging

THz Near-Field Imaging John F Federici et al 2002 Phys. Med. Biol

Hints for Problem 4.2-3