Raman spectroscopic detection for liquid and solid targets using a spatial heterodyne spectrometer

Abstract

Spatial heterodyne Raman spectroscopy (SHRS) is a new type of effective method for the analysis of structure and composition of liquid and solid targets with the characteristics of no moving parts, high spectral resolution, high optical throughput and large field of view. The technique is very suitable for detecting the targets from long distances or under the conditions with ambient light, which is essential for the exploration of planetary surface. In order to have a better understanding of the ability of SHRS for the detection of liquid and solid targets, a breadboard was designed, built and calibrated. Signal to noise was estimated at different integration time or laser power for carbon tetrachloride. Pure materials or materials contained in bottles were both tested. The mixture of organic liquids or inorganic solids were tested. In order to test the detection ability for natural targets, some composition-unknown rocks and pebbles were tested. The results have shown that SHRS can meet the requirements for the detection of weak Raman signal scattered from artificial or natural targets. Standoff detection of sulfur from 5-m or 10-m distance without using any telescope or collimation optics was also tried to test the high optical throughput of SHRS. The potential feasibility of standoff detection has been proved.

Spectral restoration method for spatial heterodyne Raman spectrometer

“…All lights were turned off to decrease the ambient light. More detailed introductions to the basic theory of 1D‐SHRS and 2D‐SHRS and our breadboard's setup can be seen in the work of Hu et al …”

“… The detection abilities of one‐dimensional SHRS (1D‐SHRS) or two‐dimensional SHRS (2D‐SHRS) both have been demonstrated by their research . Hu et al has also built a breadboard and achieved the Raman spectra of some natural rocks and artificial chemicals …”

Recent advances in linear and non‐linear Raman spectroscopy. Part XI

“…Spatial heterodyne Raman spectroscopy (SHRS) is a new type of effective method for the analysis of structure and composition of liquid and solid targets with the characteristics of no moving parts, high spectral resolution, high optical throughput, and large field of view. The technique is highly suitable for detecting the targets from long distances or under the conditions with ambient light, which is essential for the exploration of planetary surfaces . Kocisova and co‐workers described thiol‐modified gold‐coated glass as an efficient hydrophobic substrate for the drop coating deposition Raman (DCDR) technique.…”

Standoff spatial heterodyne Raman spectrometer for mineralogical analysis

“…Spatial heterodyne spectrometer was first developed by Harlander's group in order to bring the advantages of interferometry described above into the ultraviolet regime and has since been extended to many other applications that generally fall into two categories. First, SHS has been used to measure various forms of scattering and emission spectra from extreme ultraviolet to the near infrared, including Raman spectra of organics, inorganic salts, pharmaceuticals, and minerals, atomic emission spectra of brass alloys, and emissions by particles in various strata of the atmosphere . The second class of SHS experiments involves measuring the Doppler shift of emission lines in order to estimate velocity distributions, notably wind velocity measurements from ground or satellite‐based instruments.…”

“…Also, the larger spot size at the sample allows use of higher laser power without damaging the sample. So far in the SHRS literature, the Raman spectra of molecules with relatively high Raman scattering efficiencies have been obtained and reported . The goal of the current project is to test the limits of sensitivity of SHRS in measuring minerals over a large area of 1.5‐cm diameter with relatively low Raman scattering efficiency that may be useful in planetary science applications.…”