Ozone differential absorption lidar OLS-100

c19_09_bigDifferential absorption lidar based on excimer laser is an important tool for the study of ozone generation and transportation in stratosphere and troposphere.

General information

The main idea behind DIAL is simultaneous lidar sounding at two wavelengths: one is absorbed by the gas of interest (λon), and second (λoff) is not. Ozone absorption spectrum is shown on the figure. The most efficient for ozone sounding is UV spectral region (250-350 nm).

c19_10_big

The higher is ozone differential absorption for chosen wavelengths, the better is measurement accuracy. However high absorption decreases maximal sounding distance, thus for different altitudes different wavelengths should be applied.
The most widespread UV radiation sources for ozone measurements are based on XeCl and KrF excimer lasers with hydrogen or deuterium Raman shifters. The wavelengths of different Stokes orders are summarized in the Table.

Wavelengths of Stokes orders in H2 and D2 for XeCl and KrF excimer laser:

Laser λ, nm H2 (4156 cm-1) D2 (2986 cm-1)
S1 nm S2 nm S3 nm S1 nm S2 nm S2 nm
XeCl 308.0 353.2 414.0 500.0 339.2 377.4 425.4
KrF 248.6 277.2 313.3 360.2 268.5 291.9 319.8

Optimal pairs of wavelengths for ozone sounding:

Height range, km Wavelength, nm Radiation source
0 – 3 277.2 – 313.3 KrF+H2
3 – 12 291.9 – 313.3 KrF+H2+D2
12 – 45 308.0 – 353.2 XeCl+H2

Technical parameters of stratospheric ozone lidar OLS-100S

Configuration of OLS-100S can be varied depending on the task.

Lidar includes:

  • Radiation source based on XeCL laser
  • Receiving telescope
  • Photodetection module
  • Electronic module

Laser source

Laser XeCL laser CL-7000 with hydrogen Raman shifter
Wavelengths 308, 353 nm
Pulse energy 200 / 30 mJ @ 308 / 353 nm
Pulse length 10 ns
Repetition rate 100 Hz
Laser beam aperture (after collimation) 85 mm
Laser beam divergence (after collimation) <0.3 mrad

Receiving telescope

Aperture 600 mm
Focal length 3 m
Field of view 0.25 – 2 mrad

Mechanical chopper in the focal plane of the telescope allows to cut off the radiation scattered from low altitudes.

Photodetection module

4 receiving channels 308 nm (strong, weak)
353 nm (strong, weak)
Detectors PMTs Hamamatsu R1924

Receiving electronics

Four channels photon counter

Technical parameters of tropospheric ozone lidar OLS-100T

Lidar includes:

  • Radiation source based on KrF laser
  • Receiving telescope
  • Photodetection module
  • Electronic module

Laser source

Laser KrF laser CL-7000 with hydrogen and deuterium Raman shifters
Wavelengths 277, 292, 313 nm
Pulse energy 70 / 30 / 30 mJ @ 277 / 292 / 313 nm
Pulse length 10 ns
Repetition rate 100 Hz
Laser beam aperture (after collimation) 85 mm
Laser beam divergence (after collimation) <0.3 mrad

Receiving telescope

Aperture 600 mm
Focal length 3 m
Field of view 0.25 – 2 mrad

Receiving electronics

Four channels ADC 12 bit/ 40 MHz

Examples of the measurements