Aperture-Sensitive Distal Depth Scanning Raman Spectroscopy

Depth sensitive Raman spectroscopy has shown its advantages in the detection of Raman spectra for layered tissues. However, till now the depth scanning mode in Raman spectroscopy is the proximal scanning mode, which has disadvantages in significant variation of probe-sample contact and the size of the probe. Here, we developed a new Raman system with an axicon lens and a graduated ring-activated zero aperture. The focal range of the system was about 35 mm and nearly two orders of magnitude higher than that of the traditional Raman system. The Raman spectrum obtained from different materials at a fixed depth was demodulated with two Raman spectra from two adjacent depth ranges. Two and three-layer models were used to demonstrate the effectiveness of the proposed Raman system. The Raman spectra of polyvinyl chloride, polyphenylene ether and silica gel were demodulated successfully from overlapped Raman spectra. The new Raman system used the distal scanning mode and offered the following advantages. First, the Raman spectra of full range and a fixed depth can be obtained simultaneously. Second, depth scanning is performed far from the sample. Third, the method can be used in endoscopic applications to reduce the size of the probe.