Rugged diode-pumped Alexandrite laser as an emitter in a compact mobile lidar system for atmospheric measurements

We present design and performance data of two diode-pumped Alexandrite lasers developed explicitly as laser emitters in mobile potassium resonance lidar systems. The lasers yield an output power of up to 1.75 mJ at a repetition rate of 500 Hz with a beam quality of $M{{^2}} \lt {1.1}$ in both spatial directions. Reliable single longitudinal mode operation with a unrivaled narrow linewidth of 3.3 MHz at a potassium resonance line at 769.898 nm is achieved. The wavelength can be switched from pulse to pulse in a range of several gigahertz so the potassium line can be scanned. The lasers are finally integrated in highly efficient lidar systems with a power consumption of 500 W for the whole lidar system. The extremely high spectral requirements are investigated and the performance for different working points regarding repetition rates and pump durations is investigated. Several weeks of remotely controlled operation of the prototype in a field campaign were conducted without changes of the output parameters. Approximately 1000 h of reliable single longitudinal mode operation was achieved during the campaign and measurements of Doppler-Mie wind observations in the stratosphere and of the potassium layer in the mesopause were conducted simultaneously even at daytime.

Diode-pumped Q-switched Alexandrite laser in single longitudinal mode operation with Watt-level output power

We present significantly improved performance data of a diode-pumped Q-switched Alexandrite laser in single longitudinal mode operation developed as a beam source for resonance lidar systems. The average output power of the laser-operating at the potassium resonance at 770 nm with a linewidth below 10 MHz-could be increased by a factor of five to the Watt-level by means of an optimized resonator design and pump scheme. The pulse energy is 1.7 mJ with a beam quality of M²≤1.1 in both spatial directions at a repetition rate of 500 Hz.

Diode-pumped alexandrite ring laser in single-longitudinal mode operation for atmospheric lidar measurements

We present, to the best of our knowledge, design and performance data of the first diode-pumped Alexandrite ring laser in Q-switched single-longitudinal mode (SLM) operation. The laser resonator contains two Alexandrite crystals, which are pumped longitudinally by means of two laser diode-bar modules emitting at 636 nm. Single-longitudinal mode operation is achieved by seeding the laser with a diode laser operating in SLM and actively stabilizing the cavity, yielding a linewidth of < 10 MHz at the potassium resonance line at 770 nm. The pulse energy is 1 mJ at a repetition rate of 150 Hz and 0.65 mJ at 320 Hz. The beam quality of M² < 1.2 in both directions remains unchanged for the different repetition rates. After characterization in the laboratory, the laser was implemented in a novel mobile lidar system and first atmospheric measurements were conducted successfully.

Sodium temperature/wind lidar based on laser-diode-pumped Nd:YAG lasers deployed at Tromsø, Norway (69.6°N, 19.2°E)

An Nd:YAG laser-based sodium temperature/wind lidar was developed for the measurement of the northern polar mesosphere and lower thermosphere at Tromsø (69.6N, 19.2E), Norway. Coherent light at 589 nm is produced by sum frequency generation of 1064 nm and 1319 nm from two diode laser end-pumped pulsed Nd:YAG lasers. The output power is as high as 4W, with 4 mJ/pulse at 1000 Hz repetition rate. Five tilting Cassegrain telescopes enable us to make five-direction (zenith, north, south, east, west) observation for temperature and wind simultaneously. This highly stable laser system is first of its kind to operate virtually maintenance-free during the observation season (from late September to March) since 2010.

Solar cycle response and long-term trends in the mesospheric metal layers

The meteoric metal layers (Na, Fe, and K)-which form as a result of the ablation of incoming meteors-act as unique tracers for chemical and dynamical processes that occur within the upper mesosphere/lower thermosphere region. In this work, we examine whether these metal layers are sensitive indicators of decadal long-term changes within the upper atmosphere. Output from a whole-atmosphere climate model is used to assess the response of the Na, K, and Fe layers across a 50 year period (1955-2005). At short timescales, the K layer has previously been shown to exhibit a very different seasonal behavior compared to the other metals. Here we show that this unusual behavior is also exhibited at longer timescales (both the ~11 year solar cycle and 50 year periods), where K displays a much more pronounced response to atmospheric temperature changes than either Na or Fe. The contrasting solar cycle behavior of the K and Na layers predicted by the model is confirmed using satellite and lidar observations for the period 2004-2013.

The near-global mesospheric potassium layer: Observations and modeling

The meteoric metal layers act as unique tracers of chemistry and dynamics in the upper atmosphere. Existing lidar studies from a few locations show that K exhibits a semiannual seasonality (winter and summer maxima), quite unlike the annual seasonality (winter maximum and summer minimum) seen with Na and Fe. This work uses spaceborne observations made with the Optical Spectrograph and InfraRed Imager System instrument on the Odin satellite to retrieve the near-global K layer for the first time. The satellite data (2004 to mid-2013) are used to validate the implementation of a recently proposed potassium chemistry scheme in a whole atmosphere chemistry climate model, which provides a chemical basis for this semiannual seasonal behavior. The satellite and model data show that this semiannual seasonality is near global in extent, with the strongest variation at middle and high latitudes. The column abundance, centroid layer height, and root-mean-square width of the K layer are consistent with the limited available lidar record. The K data set is then used to investigate the impact of polar mesospheric clouds on the metal layers at high latitudes during summer. Finally, the occurrence frequency of sporadic K layers and their possible link to sporadic E layers are examined.

Diurnal variation of the potassium layer in the upper atmosphere

Measurements of the diurnal cycle of potassium (K) atoms between 80 and 110 km have been made during October (for the years 2004-2011) using a Doppler lidar at Kühlungsborn, Germany (54.1°N, 11.7°E). A pronounced diurnal variation is observed in the K number density, which is explored by using a detailed description of the neutral and ionized chemistry of K in a three-dimensional chemistry climate model. The model captures both the amplitude and phase of the diurnal and semidiurnal variability of the layer, although the peak diurnal amplitude around 90 km is overestimated. The model shows that the total potassium density (≈ K + K⁺ + KHCO₃) exhibits little diurnal variation at each altitude, and the diurnal variations are largely driven by photochemical conversion between these reservoir species. In contrast, tidally driven vertical transport has a small effect at this midlatitude location, and diurnal fluctuations in temperature are of little significance because they are small and the chemistry of K is relatively temperature independent.