Rasmus Grönlund

Remote imaging laser-induced breakdown spectroscopy and remote cultural heritage ablative cleaning

We report, for what we believe to be the first time, on remote imaging laser-induced breakdown spectroscopy (LIBS). Measurements have been performed by using a tripled Nd:YAG laser working at 355 nm with 170 mJ pulse energy, with an expanded beam that is focused onto a target at 60 m distance. The LIBS signal is detected by using an on-axis Newtonian telescope and an optical multichannel analyzer. The imaging is performed by scanning the laser beam on the target. The same setup is also used in demonstrations of remote laser ablation for cleaning of contaminated objects with applications toward cultural heritage.

Remote Imaging Laser-Induced Breakdown Spectroscopy and Laser-Induced Fluorescence Spectroscopy Using Nanosecond Pulses from a Mobile Lidar System:

A mobile lidar system was used in remote imaging laser-induced breakdown spectroscopy (LIBS) and laser-induced fluorescence (LIF) experiments. Also, computer-controlled remote ablation of a chosen area was demonstrated, relevant to cleaning of cultural heritage items. Nanosecond frequency-tripled Nd:YAG laser pulses at 355 nm were employed in experiments with a stand-off distance of 60 meters using pulse energies of up to 170 mJ. By coaxial transmission and common folding of the transmission and reception optical paths using a large computer-controlled mirror, full elemental imaging capability was achieved on composite targets. Different spectral identification algorithms were compared in producing thematic data based on plasma or fluorescence light.

Hyperspectral fluorescence lidar imaging at the Colosseum, Rome

Fluorescence lidar techniques offer considerable potential for remote, non-invasive diagnostics of stone cultural heritage in the outdoor environment. Here we present the results of a joint Italian-Swedish experiment, deploying two hyperspectral fluorescence lidar imaging systems, for the documentation of past conservation interventions on the Colosseum, Rome. Several portions of the monument were scanned and we show that it was possible to discriminate among masonry materials, reinforcement structures and protective coatings inserted during past conservation interventions, on the basis of their fluorescence signatures, providing useful information for a first quick, large-scale in situ screening of the monument.

Laser spectroscopy of gas in scattering media at scales ranging from kilometers to millimeters

Free gases are characterized by their narrow line width, and they can conveniently be studied by laser spectroscopy. The present paper discusses the monitoring of such ambient pressure gases, which are dispersed in scattering media such as aerosol-laden atmospheres, solids, or liquids. Atmospheric work basically constitutes the well-known field of differential absorption lidar (DIAL), while the study of free gas in solids and liquids was initiated more recently under the name of GASMAS (GAs in Scattering Media Absorption Spectroscopy). We discuss the connections between the two techniques, which are extensively used in our labortory. Thus, we span the field from trace-gas mapping of gases in the lower atmosphere to gas studies in construction materials, food products, and the human body. We show that the basic ideas are very similar, while the spatial and temporal scales vary greatly.

Fungus Covered Insulator Materials Studied with Laser-Induced Fluorescence and Principal Component Analysis

A method combining laser-induced fluorescence and principal component analysis to detect and discriminate between algal and fungal growth on insulator materials has been studied. Eight fungal cultures and four insulator materials have been analyzed. Multivariate classifications were utilized to characterize the insulator material, and fungal growth could readily be distinguished from a clean surface. The results of the principal component analyses make it possible to distinguish between algae infected, fungi infected, and clean silicone rubber materials. The experiments were performed in the laboratory using a fiber-optic fluorosensor that consisted of a nitrogen laser and an optical multi-channel analyzer system.

Remote laser-induced breakdown spectroscopy for the detection and removal of salt on metal and polymeric surfaces

The detection of contamination such as salt in outdoor high-voltage insulator systems and its subsequent removal are vital for a reliable transmission of electric power. Remote detection of salt on a copper metal surface was carried out by using a mobile laser-induced breakdown spectroscopy (LIBS) Lidar system with a laser wavelength of 355 nm. Detection of salt on a polymeric high-voltage insulator was obtained when an additional lens was inserted into the beam path, and the number of photons that was detected could be calculated by using a calibrated white light source. Ablative cleaning could readily be carried out with LIBS and was verified by observing the disappearance of the sodium D-line emission.

Fluorescence lidar multispectral imaging for diagnosis of historical monuments - Övedskloster, a Swedish case study

A fluorescence lidar measurement has been performed on the castle Ovedskloster in Sweden. A mobile system from the Lund University was placed at ~40 m distance from the sandstone facade. The lidar system, which uses a frequency-tripled Nd:YAG laser with a 355-nm pulsed beam, induces fluorescence in each target point. Areas were studied by using whisk-broom scans. The possibility of detecting biodeteriogens on the surface and characterization of materials was confirmed. The method can be a tool for conservation planning and status control of the architectural heritage where fluorescence light can point out features that are not normally visible under natural illumination.

Development of a tool for remote detection of fungi and algae on electrical insulators using laser induced fluorescence combined with principal component analysis

In this study a combination of laser induced fluorescence (LIF) and principal component analysis (PCA) is used in an attempt to develop a method to detect fungal growth on silicone rubber. Field experiments on aged insulators have been carried out to test whether LIF combined with PCA can give useful information about the fungal growth.

Remote Multicolor Excitation Laser-Induced Fluorescence Imaging

Remote laser-induced fluorescence of stone materials was performed with application towards cultural heritage. Fluorescence was induced in targets ∼60 m from a mobile lidar laboratory by ultraviolet laser light, either from a frequency-tripled Nd:YAG laser or from an optical parametric oscillator system. Analysis was performed on combined spectra from the different excitation wavelengths and it was noted that important additional information can be gained when using several excitation wavelengths.

Remote Gas Detection in Solid Scattering Media using Differential Absorption Lidar

Large-scale GASMAS (gas in scattering media absorption spectroscopy) measurement, which resemble multiple-scattering differential absorption lidar (DIAL) is discussed. Preliminary experiments have been performed and limitation and possibilities will be discussed. Potential future applications could include helicopter-born detection of snow avalanche victims (trapped carbon dioxide) or leaking snow-covered natural gas pipe lines.