Diode-pumped Alexandrite laser instrument for next generation satellite-based Earth observation

Abstract

In this work the first diode-pumped Alexandrite ring laser in Q-switched single-longitudinal mode (SLM) operation is presented. A carefully designed and complex ring resonator with several functional components is combined with an innovative pumping scheme with high-power red laser diodes.The spectral and energetic suitability of a first laser was demonstrated in hundreds of operating hours and, with a novel mobile lidar system, by the first measurements in the atmosphere by means of a diode-pumped Alexandrite laser, yielding data from the stratosphere to the mesosphere.An improved laser yields a pulse energy of 1.7 mJ at a repetition rate of 500 Hz with an excellent beam quality of M 2 < 1.1. By seeding the resonator with a narrow-band diode laser, SLM operation with a linewidth below 4 MHz is achieved. The electro-optical efficiency of 2 % is the highest archived for all Alexandrite lasers in SLM operation and reasonable for space-operation.The performance analysis as well as benchmarking with the space-qualified mounting technology point out the TRL and the remaining effort of development of the technology. INTRODUCTIONUnderstanding temperature distributions and wind fields in the atmosphere at altitudes between 80 and 110 km, i.e. the mesosphere and lower thermosphere (MLT), is crucial for performing numerical simulations of the Earth's climate. The effects of gravity waves on the global wind system and atmospheric dynamics are hardly understood and item of research of space agencies and ground-based observations [1-6]. One well-established approach to provide such data is to measure the Doppler-broadened and -shifted resonance line of metal atoms, e.g. potassium (770 nm or 772 nm) [6,7], iron (386 nm) [8,9] and sodium (589 nm) [10][11][12], by means of a Doppler lidar.While localized measurements have been performed over the last 20 years from the ground and revealed fundamental deviations from the predicted conditions, there is no coverage of global scale by lidar. The development of a spaceborne resonance lidar instrument is deferred by the lack of laser sources at the demanded wavelengths that are suitable for spaceborne operation.The currently used Alexandrite (Cr 3+ :BeAl2O4) lasers with their broad tunability (700-800 nm) [13] are well suited for the generation of several interesting wavelengths, either operating at their fundamental wavelength or intra-cavity frequency-doubled. The flashlamp-pumped Alexandrite ring lasers operating in Q-switched single-longitudinal mode (SLM) operation are commonly used as beam sources in resonance potassium and iron resonance lidar systems [6][7][8][9].However the usage of flashlamps as pump source makes them unsuitable for spaceborne operation, due to the poor efficiency and limited lifetime. One hopeful approach to overcome these drawbacks is by replacing the flashlamps with diode lasers [14,15]. Recently, new basic investigations in the field of diode-pumped Alexandrite lasers have been conducted with focus on altimetry lidar and vegetation monitoring (red-edge) [...

Diode-pumped Alexandrite laser for next generation satellite-based earth observation lidar

“…Details on the theoretical basis of the tolerance analysis can be found in [18]. The results of this analysis verify the results from the measurement of the susceptibility to misalignment.…”

“…One hopeful approach to overcome these drawbacks is by replacing the flashlamps with diode lasers [14,15]. Recently, new basic investigations in the field of diode-pumped Alexandrite lasers have been conducted with focus on altimetry lidar and vegetation monitoring (red edge) [16] and resonance lidar [17][18][19][20][21].…”