Convergence of light with nano matrices

An array specially designed by nano holes can focus light into a tiny point, smaller than the wavelength of light used. That's a result just published by British and Spanish physicists, opening up many possibilities for applications in nanoscale optics, such as recording high-density optical, photolithic, or generated optical information. " light pens " that can draw pictures of cells and micrometer objects ( Applied Physics Letters 90 (2007) 091119 ).

Nano cavities and nano cavity matrices on a metal screen have many special optical properties such as the ability to pass high light. Recently, the research team, led by Nikolay Zheludev (University of Southampton, England), and colleagues at Rutherford Appleton Laboratory (Oxfordshire, UK) and the Madrid Institute of Optics (Spain) announced that the The crystal dummy matrix of nano holes on metal screens can focus light at a small distance of several tens of times the wavelength of light from the screen.

Figure 1. Image of nano holes (a) and near-field optical diffraction spectra
(Appl. Phys. Lett. 90 (2007) 091119).

The researchers obtained these results by using a structure called " Penrose-like quasicrystal structure (Penrose-like quasicrystal structure), a complex pattern of nano holes that has both periodicity and circulation. and random. A beam of light shining through the different niches will interfere with each other, creating a bright spot called " hot spot ". This matrix contains about 14000 cavities with a diameter of 200 nm, fabricated by optical etching with electron beam from thin film Al 100 nm thickened on Si substrate (Figure 1).

Using light combined with a wavelength of 660 nm and diaphram optical microscope (scanning aperture optical microscopy), Fu Min Huang (Southampton) and colleagues observed bright spots with a diameter of around 290 nm, at 12.5 mm distance from the matrix. At closer distances, convergent points around 200 nm in diameter are observed (Figure 2).

Figure 2. Images of bright spot lights focused on the screen, the size is just over 200 nm, which is smaller than the limit of normal light convergence (Appl. Phys. Lett. 90 (2007) 091119).

With this result, nano niches can be used in a wide range of applications such as photolithography (lithography) and imaging. We know that the traditional photolithography method uses ultraviolet light to focus on the photoresist to draw the configuration of the membrane to be created, limited to the difficulty of creating the convergence of light at a small size. Furthermore, physicists also said that an isolated hot spot with a mask can be used as a "light pen" to draw images below the wavelength size by scanning objects under the spotlight. capacitor.

These matrices can also be used to focus light in cells and other smaller objects. The relatively large gap between the array and the object will allow for much faster scanning due to the ability to use traditional near-field optical microscopy techniques. And furthermore, because the light is focused from multiple niches on the array, the bright spot will have even greater luminous intensity than the use of diaphram-converged lens systems under the current universal wavelength. . And another possibility is that it can be applied to high-density optical data recording and optical trapping.

Author Fu Min Huang next to research equipment

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