The stationary and mobile potassium lidar

The IAP operates two similar potassium lidars for temperature, density and NLC profiling in the Mesopause region (about 80 – 105 km). The stationary lidar is located at the IAP (54°N, 12°E) whereas the mobile lidar is operated at remote locations.

Method

The potassium lidar is designed to probe the terrestrial potassium atom layer using the K(D1) resonance wavelength. Over the distance of 80 - 110 km it performs a remote spectroscopy of the potassium layer. Thus, scanning the Doppler broadened hyperfine structure it measures a height resolved picture of the thermal movement of the atoms. From this picture the temperature profile can be calculated.

The heart of the transmitting unit as shown in the right column is a specially developed solid state alexandrite laser, emitting light pulses with the necessary properties. The wavelength is controlled by the seederlaser and measured for every single laser pulse with the spectrumanalyser. Since 2000 the receiving unit is equipped with a daylight filter which allows measurements under full daylight conditions.

Transmitter

Laser active material2 alexandrite crystals, Cr3+ :BeAl2O4
Geometryring resonator, unidirectional
Wavelength770 nm, tunable

Mode structure

TEM00
Bandwidth<< 20MHZ (FWHM)
Polarisationlinear
Repetition rate35 pulses per second
Pulseenergy150 mJ
Energy jitter5% (1σ)
Pulse length250 ns (FWHM)
Beam width2.5 mm, behind AWT 6.7 mm
Beam divergence (full angle)0.45 mrad, behind AWT 0.3 mrad

Receiver

Telescoped = 80 cm, f = 199.5 cm
Field of view192 µrad
Broad band filterIF filter (1nm, Τ=70%)
Narrow band filter2 potassium FADOF (1800 G), 124° C, T = 75%
Transmission50 %
Contrast (FADOF)1:10000
Band width (FWHM)6.7 pm
Temperature shift±0.5 K
DetectorAPD
Photon efficiency68% @ 770 nm

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Contact

Dr. Josef Höffner

5-day run

5-day run of temperature measurements at Kühlungsborn in February 2003

Resonance line

Doppler broadened resonance line at different temperatures

Setup