Is a spectrometer with six tunable diode lasers dedicated to in situ measurements of trace compounds in the upper troposphere and the stratosphere up to 35 km altitude.
The 6 laser beams circulate in a multipass HERRIOTT cell located below the gondola. The lower mirror of the two-mirror cell is fixed at the top of a deployable mast. The distance between mirror is about 3.50 m. Given the curvature of the two identical mirrors, two stable optical configuration can be used : first 86 reflections and 300 m optical path, second 156 reflections and 554 m optical path, by moving the lower mirror 5 mm up.
The mast is deployed during the flight to have the first measurements at the tropopause. Around the instrument, a rigid metal frame encompasses it, in order to have a instrument-safe landing.
Inside the instrument, three liquid nitrogen cryostats, hold the six diode lasers and the 12 detectors.
Vertical profiles of concentrations of a great number of species like O3, CH4, CO, CO2, N2O, HNO3, NO2, NO, HCl, HOCl, H2O2, and COF2, are measured with a very high vertical resolution, a high sensitivity and a high precision.