Study of sub-mJ-excited laser-induced plasma combined with Raman spectroscopy under Mars atmosphere-simulated conditions

Emission features and expansion dynamics of nanosecond laser ablation plumes at different ambient pressures

“…26,27 Hence, the observed plasma emission intensity dependence on background pressure is extremely complicated because of the changes in laser-target and laserplasma coupling in the presence of an ambient. 28 It has been reported that at particular pressures, the plasma plumes emit profoundly in the presence of Ar compared to He or air. 29 The excitation temperature of the plasma plume has also a strong dependence on nature and pressure of the ambient gas.…”

Development and optical testing of the camera, hand lens, and microscope probe with scannable laser spectroscopy (CHAMP-SLS)

“…Because of the nature in which the geometric rays were incident on the original MIDP CHAMP focal plane, a laser, if focused on the focal plane, could not effectively be scanned across the two-dimensional object plane beyond <10% of the field-of-view of the MIDP CHAMP without significantly degrading the beam modal shape beyond the point where a micro-LIBS or Raman spectroscopic measurement could realistically be acquired through the CHAMP optical system [6]. As a result, a derived optical requirement for the geometric rays incident on the CHAMP-SLS focal plane were constrained to be normal to the focal plane within <3° for any laser wavelength that fell within the spectral bandpass identified below.…”

“…Attribute (2) allows one to conduct high resolution microscopy over a wide array of surfaces without sample preparation. [1,6].…”

“…In independent optical spectroscopic analysis and instrument development conducted under NASA's Astrobiology Science and Technology Instrument Development (ASTID) program, optical coupling ‡ onto microscopic features for conducting Raman § and micro-LIBS ** laser spectroscopies of unimproved geologic surfaces was identified [6]. For the case of tightly-focused laser ablation techniques (e.g.…”

“…This variation in flux causes a corresponding large variation in gas/plasma temperature which typically degrades the quality of an instrument measurement utilizing ablation. In the case of micro-LIBS, the large variation in plasma temperature causes a corresponding larger variation in micro-LIBS emission signal complicating the accurate interpretation of relative elemental abundances [6,7]. For Raman spectroscopy, the coupling is less sensitive, but still important for ensuring that the precious few laser photons that have been frequency shifted and contain chemical signature information are not lost, but rather efficiently collected into the optical system and ultimately into a spectrometer for spectral analysis.…”