## 2 Measurement Method and Experimental Setup Design
### M-DLS Measurement Cycle  
After touchdown of the ExoMars-2022 landing platform on the surface of Mars and the rover egression, we prepare for further experiments by deploying the air intake device. Following successful deployment, the instrument is ready to operate. The principal scheme of the whole M-DLS and its internal layout is shown in Figure 8a,b. The experiment begins from the preparation of Martian air sample. This procedure is conducted by both the M-DLS and MGAP instruments. The Martian air preparation system can operate in two regimes: the first is a preparation of air sample at Martian ambient pressure; the second is at higher pressures up to 30 mbar. There are sufficient differences between these modes, therefore, they will be described separately. All operations during the Martian air sample preparation procedure are provided by the SSU under commands from the BIP. The procedure of the Martian air sample preparation begins with the pressure and temperature sensors interrogation to evaluate the current condition of the instrument. Then, the SSU, with the  
Figure 8: Principle scheme (**a**) and internal layout (**b**) of the M-DLS. SSU is service system unit, AMU is atmospheric measurements unit. help of sample preparation electronics, sets the ASR valves position to a configuration which allows pumping out the ICOS resonator volume under the 10\({}^{-4}\) mbar by the MGAP vacuum pump. The next step is to configure valves to provide a Martian air with the path to the ICOS cell. Then the MGAP turns off the pump. After that, the M-DLS configures valves to block the cavity volume from the outside atmosphere and to equalize pressure level in the whole gas system. Thereafter, the heater is turned on to reach a predetermined temperature. The final step of the air sample preparation procedure is pressure and temperature sensor data acquisition. In case we understand the M-DLS sensitivity is not satisfied to our measurement purpose due to lack of information about H\({}_{2}\)O and CO\({}_{2}\) isotopologues content near the surface, there is an opportunity to increase the instrument sensitivity by increasing the pressure of the Martian air sample up to 30 mbar. The main difference of operation in this regime is that after pumping out the cavity volume, the M-DLS closes all valves, while the MGAP turns off the pump and connects the ballast tank with Martian air at a high pressure of 930 mbar to the M-DLS gas system. Then the M-DLS configures valves to fill the cavity with Martian air from the tank. As soon as Martian air sample preparation is over and experiment setup data packet from BIP is received by the SSU, it is relayed to the AMU for spectroscopic measurements initialization. After that, peripherals are set and AMU enters the preparation stage for 3 min, where PD cooling is enabled, selected DL goes to the predefined temperature and laser current modulation is turned on to enter the stable thermal regime. The DL temperature is handled by the PI controller based on thermistor data input. After 3 min a line stabilization is linked up to control DL temperature precisely throughout the experiment. The AMU enters a data acquisition stage after a minute of line stabilization, where spectra are collected for up to 15 s each with averaging of up to 700 times. Following the acquisition of 7 spectra, the AMU enters a hibernation mode at the 6 th minute of the experiment, waiting for packets request from SSU. It is worth to notice that the air preparation procedure is highly dependent from environmental conditions, preparation time can take up to 90 min, including only two invariable parameters: 6 min for one configuration of ASR valves and 1.5 s for the sensor interrogation. In case of malfunction of air sample preparation system, there is a scenario where M-DLS functions in the mode with only diffusion responsible for air sample update. Experiment data volume with the 7 measured spectra for a single laser from the AMU is around 14 Kbyte (7 spectra per 2032 byte). The SSU sensor data volume also is 2032 byte.