1. Effect of Beam Steering
on Optical Measurements
and the MAET Technique
Aanish Patel Sikora
August 21, 2014

2. Introduction
• Aanish Patel Sikora
•Pursuing BS in MAE at UCLA (June 2015)
•ERC Summer Intern
•Vishal Parikh Memorial Scholarship
•Mentor: Ed Coy
!
!
!

3. Personal Goals and
Expectations
•Supplement education
•Solidify interest in Rocket Propulsion for Graduate
School and Future Career
•Gain Experience in Work/Research Environment

4. Project Goals
•Use and develop beam steering model in order to
design an optical layout that minimizes effects of
beam steering
•Optimize lens & fibers positions and parameters
•Increase data acquisition rate
•Implement new super luminescent diode light
source

5. Theoretical Background

6. Modulated Absorption
Emission Thermometry (MAET)
• Line-of-sight average temperature
• Non-intrusive, radiometric technique
• Alternating emission and transmission
measurements
• Plank function:
• No measurement of spectral features
• Updated to utilize new optical technology

7. Beam Steering
• Negatively impacts MAET
• Scattering of light due to index of refraction gradients
• Increased diameter and divergence angle of light beam
• Loss of intensity
• Redesign optical setup to minimize beam steering
• Characterized by parameter K

8. Experimental Work

9. • Test Environment (EC-1)
• Hydrogen / RP-2 + Oxygen (range of MR)
• Pressures: 13-50 atm
• Tungsten Halogen Light Source (500 Hz w/ mechanical wheel)
• InGaAs diode (60 dB gain)
• Conclusion:
• MAET valid for hydrogen (within CEA limits)
• MAET invalid for RP-2 (50% off CEA code predictions)
• Reason: Beam Steering
METHOD 1: Demonstration of the MAET Technique at
Conditions Simulative of a LRE Thrust Chamber.

10. METHOD 2: A Method for Eliminating Beam Steering
Error for the MAET Technique.
• 2 detectors on adjacent spectral bands (1.3 & 1.35 μm)
• Absorption coefficients are different but scattering coefficients are the same
• β = α + κ = (-1 / L) * ln (( I2 - I1 ) / I0 )
• Plank Function
• Test Environment (EC-1)
• RP-2 + Oxygen (MR: 2-3.4)
• Pressures: 25-75 atm
• Gas Temperatures: 3000-3700 K
• Tungsten Halogen Light Source (500 Hz w/ mechanical wheel)
• InGaAs diode (60 dB gain)

11. Results
5 5.5 6 6.5 7 7.5 8
0
1000
2000
3000
4000
5000
6000
Time (sec)
Temperature(K)
Run030
5 5.5 6 6.5 7 7.5 8
0
500
1000
1500
2000
2500
3000
3500
4000
Time (sec)
Temperature(K)
Figure: Final Calculation of Figure: Calculation of Temperature using original MAET algorithm

12. Analytical model
• Implements Kranendonk’s model of beam
steering
• Equations:
• Goals:
A. Obtain visual understanding of the
propagation of light through test
article
B. Minimize beam steering by
manipulating parameters
(f1, space1, ,…)

13. Physical Demonstration
Blue: Turbulence Transmission Loss
Green: No Turbulence Transmission Loss

14. Detector
Transmission Loss
at Detector

15. Blue: Turbulence Transmission Loss
Green: No Transmission Loss
Red: Transmission Loss at Detector

16. Light Propagation
L = 0.025 m

17. Extent Growth
• Extent is the product of the square of the spatial and angular
parameters of the light at a position
• Extent = 2 (π*d*NA)^2

18. Light Transmission
More Beam Steering
• Beam steering characterized by K

19. Space1
K﹦0.1K﹦0.0001
↓ INCREASING space1(m)

20. Pin Length
K﹦0.1K﹦0.0001
↓ INCREASING pin length (m)

21. space2 pin diameter
↓ DECREASING pin diameter (m)↓ INCREASING space2 (m)
Other Parameters

22. Extinction Coefficient
Beam Steering Coefficent vs. Chamber Pressure
K(1/m)
0
0.01
Chamber Pressure (PSIA)
100 1000 10000

23. Experimental Progress

24. Light Source
SOURCES FEATURES
SLD
• Can be pulsed at high frequencies
• Power output dependent on wavelength (peak
wavelength)
• High power and brightness (like laser diode)
• Small divergence angle of light
• High coupling efficiency (50% of power coupled into
single-mode fiber)
• Output intensity increases gradually with current
Tungsten
Halogen
• Frequency is limited by mechanical chopper wheel
• Power output not dependent on wavelength
Laser
Diode
• Easily modulated
• Easily coupled

25. SLD Characteristics
Ideal Operation Ideal Operation
1250 nm 1350 nm
Dashed -> 30 C
Straight -> 20 C
!
Green -> 3.6 V
Blue -> 2.6 V
Red -> 1.6 V

26. % of Light Recorded
• Comparison with analytical model
• Experimental value depends on SLD current & temperature and the driving
voltage
• Range from 17.58% to 18.63%
• Values on par with predictions from analytical model

27. Data Acquisition Rate
• Increased data acquisition rate to 50 kHz (from 10 kHz)
• Calculation involved using average gas velocity (120 m/s) & window size
• Absorption/transmission measurements consider the same sample of gas
• Amplifier, (gain = 5)
• InGaAs detector gain = 40 dB (was 60 dB)
• Re-calibrated detectors w/ hi-temp blackbody

28. Calibration

29. Acknowledgments

30. Questions?

31. References
• S.T. Sanders and L.A. Kranendonk,“Optical design in beam steering with emphasis
on laser transmission measurements,” in Applied Optics (November 2005)
• E. Coy, “A method for eliminating beam steering error for the MAET technique.”
• E. Coy, “Demonstration of the modulated absorption-emission thermometry
technique at conditions simulative of a liquid rocket engine thrust chamber.”