Enhancement of the design of a pulsed UV laser system for a laser-desorption mass spectrometer on Mars

Abstract

Abstract-A laser-desorption mass spectrometer will be part of the ESA-led ExoMars mission with the objective of identifying organic molecules on planet Mars. A UV laser source emitting nanosecond pulses with pulse energy of about 250 μJ at a wavelength of 266 nm is required for the ionization of nonvolatile soil constituents. A passively q-switched, diode-pumped Nd:YAG laser oscillator with external frequency quadrupling has been developed. The basic optical concept and a previously developed flight-near prototype are redesigned for the engineering qualification model of the laser, mainly due to requirements updated during the development process and necessary system adaptations. Performance issues like pulse energy stability, pulse energy adjustment, and burst mode operation are presented in this paper.

Optical design and characterization of the MOMA laser head flight model for the ExoMars 2020 mission

“…Compared to early prototype models, the FM oscillator design has been optimized with respect to pulse energy stability. Wedged components, namely laser crystal and output coupler, reduce sub-resonator effects from multiple plane-parallel surfaces inside the oscillator [5]. Furthermore, the oscillator sub-assembly is temperature stabilized in order to achieve reproducible output parameters under varying environmental temperatures.…”

“…The initial MOMA oscillator design [5] was capable of delivering IR pulses with approximately 2 mJ of pulse energy with a pulse release time of typically 150-200 µs (time delay measured from the beginning of the pump pulse to the emission of the laser pulse; 100-120 W peak pump power; 1 or 2 Hz operation during assembly and testing). After a reduction of the required UV output energy of the LH the oscillator design was adapted by the use of a saturable absorber with a higher initial transmission.…”

Mechanical design and testing of the MOMA flight model laser head for the EXOMARS 2020 mission

“…The influence is quite slow depends on environmental temperature. To improve the unwanted coupling between both subassemblies, later models are realized with two additional independent heaters on the oscillator to reach the set temperature fast and to reduce the dependency from the frequency conversion stage and environmental conditions [3].…”

Energy scaling of passively Q-switched lasers In the Mj-range

“…However, in most cases passive Q-switching is implemented in microchip lasers usually emitting several tens of µJ at a repetition rate of several kHz. For passively Q-switched lasers at low repetition rates of several tens of Hz and good beam quality usually 1-3mJ are achieved [1][2][3][4]. At higher repetition rates the heat dissipation in the laser rods can lead to thermal effects resulting in a bad beam quality or even to stressinduced fracture of the laser crystals.…”

“…To keep the diameter of the beam small over a large distance and to consequently achieve a good lateral resolution, a good beam propagation factor M² is required. Moreover, Q-switched lasers can be used directly on the planetary surface for exploration by laser-induced breakdown spectroscopy [1] or laser desorption mass spectrometry [2].…”