HERAS: A helium jet to prevent damage on works of art in Raman experiments

Raman spectroscopy is often used for non‐destructive analysis of works of art, polymers and biological materials, but in some cases, the laser beam can cause damages on the surface being studied due to the deposited beam energy. When possible, such damage can be prevented by minimizing laser intensity or acquisition time, but this is usually available only on high sensitivity bench‐top spectrometers. Portable Raman spectrometers are commonly not so flexible and an alternative is needed to ensure the safe study of sensitive works of art and other fragile materials. A helium jet aimed directly at the laser spot may prevent this damage from occurring and, in some cases, helps improving the Raman spectra. We designed a simple system (HERAS, Helium Raman System) consisting of a pinhole collimator, coupled to a helium line and a gas mass flux control and tested it on pyroxylin, vermilion and ochre paint references and pigment samples, using a 785 nm portable Raman spectrometer at various laser powers. Experimental conditions slightly differ for each sample, but small burns on the surface were avoided in all cases and only some ablation was observed on the most sensitive materials. The use of this coupled system allows the non‐destructive application of Raman to a wider variety of materials, while the technique remains portable. This setup may be used in bench‐top apparatus as well. Copyright © 2013 John Wiley & Sons, Ltd. Raman spectroscopy is often used for non‐destructive analysis of works of art, but it can cause damages on the surface being studied. A helium jet aimed directly at the laser spot may prevent this damage and help improving the Raman spectra. A pinhole collimator, coupled to a helium line and a gas mass flux control was tested on paint references and pigment samples. The use of this system allows the non‐destructive application of Raman to a wider variety of materials.