Control over the product branching ratio in the photodissociation of Na 2 into Na͑3s͒ 1 Na͑3p͒ and Na͑3s͒ 1 Na͑3d͒ is demonstrated using a two-photon incoherent interference control scenario. Ordinary pulsed nanosecond lasers are used and Na 2 is at thermal equilibrium in a heat pipe. Results show a depletion in the Na͑3d͒ product of at least 25% and a concomitant increase in the Na͑3p͒ yield as the relative frequency of the two lasers is scanned.

No abstract

A new optical element, a Fresnel axicon (fraxicon), is proposed. Similar to a Fresnel lens, this element consists of concentric prism-like grooves with an apex angle equal to that of a bulk axicon and whose action relies on refraction. The fraxicon is less chromatic and simpler to manufacture than holographic optical element-based diffractive axicons and, in comparison with regular refractive axicons, is more compact with less absorption loss in the material while allowing significant economy in mass production.

A superresolving three-zone plate is applied to a Fresnel diffractive lens. It is shown that for radial incident polarization this combination produces a focal spot approaching superresolution allowed subdiffractive limit of 0.36lambda/NA for focusing. For media responsive to longitudinal field component only, our phase engineering scheme results in a focal spot size of 0.368lambda/NA. When used with a solid immersion lens, the scheme can generate the smallest focal spot available for passive optics.

In 3D, diffraction-free or Bessel beams are well known and have found applications in diverse fields. An analog in 2D, or pseudonondiffracting (PND) beams, is a nontrivial problem, and existing methods suffer from deficiencies. For example, Airy beams are not highly localized, some PND beams have significant side lobes, and a cosine beam has to be truncated by a very narrow aperture thus discarding most of the energy. We show, both theoretically and experimentally, that it is possible to generate a quasi-nondiffracting 2D light beam in a simple and efficient fashion. This is achieved by placing a mask consisting of a pair of double slits on a cylindrical lens. The applications include light sheet microscopy/optical sectioning and particle manipulation.