This picture shows a lab demonstration of the measurement chamber inside the Tunable Laser Spectrometer, an instrument that is part of the Sample Analysis at Mars investigation on NASA's Curiosity rover. This demonstration uses visible lasers – rather than the infrared ones on the actual spectrometer – to show how the lasers bounce between the mirrors in the measurement chamber.
The TLS shoots laser beams into a type of measurement chamber that can be filled with Mars air. By measuring the absorption of light at specific wavelengths, the tool can measure concentrations of methane, carbon dioxide and water vapor in the Martian atmosphere and different isotopes of those gases.
Image credit: NASA/JPL-Caltech