1. A Thermospheric Lidar for He 1083 nm, Density and Doppler Measurements
Chad G. Carlson, Gary Swenson, Lara Waldrop, Peter D. Dragic
Department of Electrical and Computer Engineering
University of Illinois at Urbana-Champaign

2. Introduction
Metastable He atoms, pumped by photo electrons have a large
resonant cross section
Gerrard et al. [1997] modulated and simulated the concept
Resonance between 250 and 700 km
UofI has developed a key enabling element, a 1083 laser, 50 W, CW,
solid state (MOPA), narrow band (< 1 MHz) for Doppler sampling
Simulations for Arecibo, PR and Jicamarca, Peru
Transmitter and Receiver (bistatic)
Summary

4. Metastable He(23S)

5. Resonance Fluorescence Lidar
Number of
transmitted
photons
Probability of
scattering
Probability of
receiving
(z = km)
Number of
photoelectrons
at altitude z
System
efficiency
Noise
Power-aperture product: Seek to maximize system SNR by scaling power and aperture
SNR can also be increased by increasing
the integration time, τ, or range bin size Δz

6. Signal to noise simulations
Bistatic imaging receiver with 1% QE
SNR scales as the square root of power- aperture product, i.e. 3% QE, 100 W of power and Starfire Optical Range telescope (10 m2 aperture) → >10x increase in SNR
Given a CW transmitter in a bistatic configuration
Assuming 50 W, 0.5 m2 aperture, 10 min of integration time, and a range bin of 100 km

7. Measuring temperature
Doppler lidar requires narrow linewidth operation, i.e. delta function sampling of the lineshape function
3 frequency technique can measure winds and temperatures with good SNR and small error -- Requires a tunable transmitter
< 0.02 nm FWHM
~ 4 GHz
Metastable 1083 nm transition consists of three lines that are Doppler broadened by temperature

8. A 1083 nm lidar transmitter
Master oscillator - power amplifier configuration
Overall gain = 36 dB
10 W CW single mode output
Narrow linewidth (~ 150 kHz) and tunable

9. A 1083 nm lidar transmitter

10. 1083 nm transmitter

11. Ref: Price, Personal Communication, 2006
1083 nm master oscillator
2.8 mW
Seed laser is a distributed Bragg reflector (DBR) laser diode provided by J.J. Coleman’s group at U of I
Single frequency and tunable over several nanometers with temperature, gain current, and phase sections
Free-space coupling efficiency of 25% into Hi1060
Ref: Price, Personal Communication, 2006

12. Acousto Optic Modulator

13. Two stage preamplifier
2.8 mW
130 mW
Single-clad Yb198 fiber from INO
Gain = 17.4 dB
Efficiency = 30%
Two stages needed to generate sufficient gain given available seed power and co-propagating configuration

14. Power amplifier
7 m LMA-YDF-10/130 fiber (0.44 NA) provided by Nufern is single mode at 1083 nm
Counter propagating configuration with coupling efficiency of 87%
Beam divergence with 10x telescope is less than 250 μrad
Gain = 18.9 dB
Efficiency = 68%
130 mW
10 W
Talk about etandue matching
Low beam divergence and beam stability -- Important for minimizing pixel spread that lowers SNR

15. 1083 nm imaging receiver
With CW beam, an imaging receiver provides range information
A CCD or InGaAs array is placed at the focal plane of a large telescope
Resolution depends on baseline between receiver and transmitter
Point out green beam in image

16. Image of Bistatic Lidar Sim

17. Recent progress and future work
Pulsed operation at low PRF
Self-phase modulation effects due to pulsed operation
SBS suppressing fiber for higher power with narrow linewidth
Operational lifetime considerations due to photodarkening

18. Low PRF operation Briefly explain pulse pumping experiment
Maintained 170 uJ of output power for measurement

19. Conclusion
Thanks to enabling fiber technology, a thermospheric Doppler lidar to measure temperatures and winds from km has been developed
Work is ongoing to make the first detailed measurements of the 1083 emission in the thermosphere and improve the current system
Thank you!