Faster Imaging Using Duoscan

In the early days of commercial Raman spectrometers acquisition time for a single spectrum was a matter of hours. Innovations and developments in laser technology and other fields like sensitive CCD detectors, optimized gratings and spectrometers with high photonic throughput led to a reduction of measurement times to within milliseconds. Therefore Raman imaging by mapping of areas and three dimensional structures became feasible and grew more and more important. Since thousands of single spectra have to be recorded for high-resolution images these short acquisition times are essential. However pure time-reduction reaches its limits when it comes to analysis of either component distribution or contamination of larger areas. This is particularly the case for weak Raman scatterers where certain acquisition times are absolutely needed. Mapping these within a realistic time frame is mainly accomplished by increasing the step-width between different measurement points. Simultaneously this also leads to the danger of losing information if the grid used for scanning is too wide.

HORIBA has provided a solution to this problem: DuoScanTM. This is a new technique based on a combination of scanning mirrors. Depending on the objective used the laser spot size (ranging from sub micrometer to micrometer dimensions) is distributed over an area between 1µm2 and 900 µm2 while staying fully confocal within axial direction. This so called DuoScanTM macro-mode realizes step-widths of up to 300 µm without losing information. In addition, DuoScanTM can be used for safe measurements on photosensitive samples by distributing the laser energy while conserving the Raman intensity gain from objectives of high numerical aperture. Imaging of highly structured samples also benefits from DuoScanTM as mapping in 50 nm steps is made possible without even moving the sample. A detailed description of DuoScanTM technology is now available in the latest technical note.