Time-Domain Raman Spectroscopy for Space Exploration

Raman spectroscopy is an established technique for identifying planetary materials through their unique vibrational fingerprints, which also reveal information about their structure and composition [1]. Accordingly, Raman instruments have been proposed for space missions [2-4] and are by now operational, e.g., on the Perseverance rover [5]. With the advent of space-qualified femtosecond lasers [6, 7], techniques such as Time-Domain Raman spectroscopy (TDRS) and Rotational Coherent Raman Scattering (RCRS) have become viable alternatives to detect the Raman-active vibrational fingerprints of solids and gases in space applications. Since these techniques can intrinsically be much more compact, robust, and performant (e.g., because they are not affected by photoluminescence or background illumination), their merits will be discussed in this contribution.

In TDRS, ultrafast lasers with pulse durations shorter than the phonon period are used to excite coherent lattice vibrations. Coherent phonons subsequently induce measurable changes in the optical properties of the sample, which are probed subsequently by probe laser pulses in the femtosecond time-domain. In this work, we show that, for different planetary-relevant materials, the Raman-active fingerprints can be detected in transmission, reflection, or scattering geometries (see Figure 1).

In RCRS, one utilizes the fact that ultrashort pulses can excite coherent rotational wavepackets of molecules. The RCRS response manifests as periodic bursts called “rotational revivals.” As revivals have periodicities that depend on the molecular constant B, the excited molecules can be clearly identified. In this work, with essentially the same instrumentation as TDRS, we demonstrate that N₂ and O₂ in air at 295 K and 1 bar can be easily detected in good agreement with simulations [8] (Figure 2).  

As a result of our work, we envision a novel instrument design that enables the detection of Raman-active fingerprints of planetary materials and atmospheres based on a single ultra-compact femtosecond laser [9].

Figure 1. TDRS measurement on α-Quartz. (a) Time-domain changes with isotropic detection in the top panel. (b) Time-domain changes with anisotropic detection in the top. In both figures, the bottom panel shows the corresponding Fourier transform of the time-domain signal with the expected Raman modes marked with an asterisk (*).

 

Figure 2. RCRS measurement in laboratory air at 295 K and 1 bar. Experimental time-domain signal showing rotational revivals of N₂ and O₂ compared to the simulations (top panel). Corresponding Fourier transformation with rotational level transitions of N₂ and O_2, shown in green and orange vertical lines, respectively.

References   

[1] J. Blacksberg, G. Rossman, and A. Gleckler, "Time-resolved Raman spectroscopy for in situ planetary mineralogy", Applied Optics 49, 4951-4962 (2010).

[2] F. Rull, S. Maurice, I. Hutchinson et. al., "The Raman laser spectrometer for the ExoMars rover mission to Mars", Astrobiology, 17, 627–654 (2017).

[3] Y. Cho, U. Böttger, F. Rull et. al., "In situ science on Phobos with the Raman spectrometer for MMX (RAX): preliminary design and feasibility of Raman measurements", Earth Planets Space, 73, 232 (2021).

[4] E.A. Cloutis, C. Caudill, E.A. Lalla et. al., "LunaR: Overview of a versatile Raman spectrometer for lunar exploration", Frontiers in Astronomy and Space Sciences, 9, 1016359 (2022).

[5] R. Bhartia, L. W. Beegle, L. DeFlores, et al., “Perseverance’s Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) Investigation”, Space Science Reviews 217, 58 (2021).

[6] J. Lee, K. Lee, Y.S. Jang et. al., "Testing of a femtosecond pulse laser in outer space", Scientific Reports, 4, 5134 (2014).

[7] M. Lezius, T. Wilken, C. Deutsch et. al., "Space-borne frequency comb metrology", Optica, 3, 1381 (2016).

[8] T. Szidarovszky, M. Jono, K. Yamanouchi, “LIMAO: Cross-platform software for simulating laser-induced alignment and orientation dynamics of linear-, symmetric- and asymmetric tops”, In: Computer Physics Communications 228, pp. 219–228 (2018).

[9] Y. Ha, S.G. Pavlov, G. Rabasovic et. al., "Time-Domain Raman Spectroscopy: An Emerging Technique in Space Exploration?", Journal of Raman Spectroscopy, 56, 9 (2025).