Experimental setup. The IR probe beam (CO2/FEL, red) is divided into two branches using a geometrical beam splitter (BS) (Au-evaporated Si wafer), which redirects part of the beam towards the s-SNOM Credit: http://www.nature.com/srep/2015/150728/srep12582/full/srep12582.html
Computer-assisted technology developed especially for this purpose combines the advantages of both methods and suppresses unwanted noise. This makes highly precise filming of dynamic processes at the nanometer scale possible eg photosynthesis or high-temperature superconductivity.
The new camera from Dresden enables unaltered optical measurements of extremely small, dynamic changes in biological, chemical or physical processes. The instrument is compact in size and can be used for spectroscopic studies in a large area of the electromagnetic spectrum. Time increments from femtoseconds up to the second range can be selected for individual images. “This makes our nanoscope suitable for viewing ultra-fast physical processes as well as for biological process, which are often very slow,” says the HZDR’s Dr. Michael Gensch.
Combining 2 methods guarantees high spatial and temporal resolution. The nanoscope is based on the further development of near-field microscopy, in which laser light is irradiated on an ultra-thin metal point. This creates highly bundled light – 100X smaller than wavelength of light. “In principle, we can use the entire wavelength spectrum of near-field microscopy, from UV to the THz range,” says Dr. Susanne Kehr . “The focused light delivers energy to the sample, creating a special interaction between the point and the sample in what is known as the near-field. By observing the back-scattered portion of the laser light, one can achieve a spatial resolution in the order of the near-field magnitude, that is, in the nanometer range.” This technology, SNOM (Scanning Near-Field Optical Microscopy), is typically only utilized for imaging static conditions.
Sample sketch of a 80 nm Si(23%)-Ge(77%) film on Silicon (100) http://www.nature.com/srep/2015/150728/srep12582/full/srep12582.html
Using ultra-fast spectroscopy can study #dynamic processes on short timescales and with extreme sensitivity. The spatial resolution has, until now, been limited to the #micrometer range. While a 1st pulse excites the sample, a 2nd pulse monitors the change in the sample. If the time between them is varied, snapshots can be taken at different times, and a movie can be assembled. A clever #correction of the #measurement #errors leads to #high #sensitivity of spectroscopic procedure. #Noise is #eliminated by probing the unperturbed sample with a 2nd reference pulse directly before the excitation. This particular technology could not be combined with near-field optical microscopy until now.
“We have developed software with a special demodulation technology with which – in addition to the outstanding resolution of near-field optical microscopy that is at least three orders of magnitude better than the resolution of common ultra-fast spectroscopy – we can now also measure dynamic changes in the sample with high sensitivity,” explains Kehr. The clever electronic method enables the nanoscope to exclusively #record #only the #changes actually occurring in the sample’s properties due to the excitation. http://www.alphagalileo.org/ViewItem.aspx?ItemId=155331&CultureCode=en
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