Time of analysis is an important factor for investigations and a determining factor for fast processes. What is the fast and ultra-fast Raman imaging? Everything has to be compared and the terminology doesn’t matter.
Minimal time of acquisition of Raman spectrum for each pixel of an image is basically limited by CCD detector operation speed (about: 760 µs – 1 ms) and makes in practice about 5 ms. In Confotec® NR500 system we apply two modes for Raman imaging. Alongside with CCD detection mode we apply the mode in which PMT is a receiver and the scanning is realized with galvanic mirrors at a fixed sample. We call this mode Fast mapping, rather modestly, considering that the time of acquisition of each pixel of the image is only 3 µs! And the minimal time of 1001 pixels x 1001 pixels Raman image acquisition is only 3 s!
Some capabilities of Fast mapping mode have been shown at its application to the investigation of Granite Gneiss India sample (the sample has been supplied by Brno University of Technology). Fast mapping mode allows imaging both at relatively strong signals and maximal signals which are several orders weaker, if compared with the Raman signal from silicon. Two dry objectives have been applied for the measurements: 100х and 20х.
As an example the confocal (1AU) megapixel (1002001 pixels) images of Granite Gneiss India sample with total measurement time of 3 seconds are shown in Fig.1. The images in Fig.1 have been obtained with the objective 100х by scanning of maximum sample size e for the given objective (150 μm х 150 μm) at scanning step of 150 nm.