Nano antenna converges laser light

What do you get when you combine ' cascade ' quantum lasers with an optical antenna? The answer, according to US researchers, is a device that creates a tiny spot of light that can be used to capture images of viruses or DNA circuits with a much higher resolution. with current microscopes.

The gray structure on the background is the electron microscope image of the ' cascade ' quantum laser surface with the inserted antenna nano (black rectangle). The color image in the center of the image above is the received antenna topology using atomic force microscopy. The color image on the left side of the image above is an optical image obtained using the near field scanning optical microscope, showing a highly limited bright spot in the antenna gap. . ( Appl. Phys. Lett. 91 173113 ).

Many structures in living cells are smaller than 1 µm in size and so biologists want a desktop microscope that can analyze samples with a resolution of several hundred nm or less. However, the spatial resolution of traditional microscopes is often greater than the wavelength of light used - typically several hundred µm in modern Fourier transform infrared microscope (Fourier transform infrared microscope).

Currently Federico Capasso and his colleagues at Harvard University and the Agilent Laboratories have found a way to focus infrared light from ' cascade ' quantum lasers into a point of size 100 nm or smaller. In principle, this bright spot can be scanned through the specimen to form nano-resolution images.

' Cascade ' quantum lasers use multiple semiconductor layers with alternating low and high energetic regions to create a series of electron traps or quantum wells. The energy levels of these quantum wells are like electrons on each floor, each passing through the device, releasing a photon at each step. Unlike other traditional semiconductor lasers, ' cascade ' quantum lasers can be adjusted in a wide range of wavelengths, and are a very suitable medium for pink wavelength biochemical applications. Average foreign.

A technical solution according to Capasso, co-inventor of the ' cascade ' quantum laser, is to focus light by adding an optical antenna to the laser. An antenna like this contains two small gold rods and two ends separated by an extremely small slot (almost touching). The electric field of the laser light causes the electrons in these two nanorods to vibrate and accumulate at the tip of the small slot. This creates a point of light that has a strong intensity in the slot and, in principle, this light can be projected onto the specimen.

The team placed the antennas into two ' cascade ' quantum lasers with emission wavelengths of 7 µm and 5 µm. In each case, microscopic optical points have been detected, each of which is the same size as the antennas of the antenna (100 nm and 70 nm respectively). ' This typical Fourier transform interference microscope has a spatial resolution of 10 - 20 µm . We can achieve a resolution as low as 102 times, ' Capasso said.

Building a microscope from this modified ' cascade ' quantum laser is the next step, Capasso told physicsworld.com. The localization of light in the gap is a 'field near' ('near-field' effect) effect. To use light for receiving images or for spectra, samples should be brought very close to the gap.

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