1. High-power semiconductor lasers for in-situ sensing of atmospheric gases Carl Borgentun Microdevices laboratory (MDL), JPL/Caltech Copyright 2013 California Institute of Technology. Government sponsorship acknowledged.

2. Outline Background Laser design and fabrication Performance Next target 2013-04-04 Postdoc seminar – Carl Borgentun2

3. Background 2013-04-04 Postdoc seminar – Carl Borgentun3

4. Gas sensing 2013-04-04 Postdoc seminar – Carl Borgentun4 Earth science Planetary science Safety Credit: NASA

5. Credit: Richard W. Pogge, Ohio state university Absorption spectroscopy basics Credit: David Sayres, Harvard 2013-04-04 Postdoc seminar – Carl Borgentun5 http://www.astronomy.ohio- state.edu/~pogge/Ast161/Unit5/atmos.html

6. Laser spectroscopy basics Laser Detector Gas 1980s Liquid helium-cooled lasers (1000kg) 1990s Liquid nitrogen-cooled lasers (70 kg) 2000s Thermoelectrically cooled lasers (0.1 kg) 2013-04-04 Postdoc seminar – Carl Borgentun6

7. Example application – Earth science Carnegie airborne observatory Credit: Carnegie institute of science 2013-04-04 Postdoc seminar – Carl Borgentun7 Earth science

8. Example application – Planetary science Mars polar lander Mars science laboratory Credit: NASA 2013-04-04 Postdoc seminar – Carl Borgentun8 Planetary science

9. Example application – Safety Carbon monoxide monitoring instrument Credit: NASA 2013-04-04 Postdoc seminar – Carl Borgentun9 Safety

10. Ozone depletion Chlorine compounds destroy ozone, but only at cold temperatures. Water vapor in the stratosphere increases the threshold temperature, at which ozone destruction can take place. Risk of thinner ozone layer not only at the poles, but also at lower latitudes where people, animals, and plants live. 2013-04-04 Postdoc seminar – Carl Borgentun10 James G. Anderson et al., Science, 337 (6096), 835-839, 2012. Various explanations for high mixing ratios of water vapor, distinguishable by measuring water isotopologues.

11. Traditional absorption techniques are not sensitive enough for the simultaneous measurement of water and its less abundant isotopologues. Jim Anderson’s group at Harvard are developing a cavity- enhanced instrument. A high-power laser source at the right wavelength is needed. In this case: Right wavelength ~ 3777 cm-1 (2.65 µm) In this case: High-power > 10 mW Need for more sensitive instrument Credit: NASA; Jim Anderson, Harvard 2013-04-04 Postdoc seminar – Carl Borgentun11

12. Laser design and fabrication 2013-04-04 Postdoc seminar – Carl Borgentun12

13. Two criteria: Optical gain Cavity Laser crash course 2013-04-04 Postdoc seminar – Carl Borgentun13 Active medium Cavity Pumping Mirror Output beam

14. Molecular Beam Epitaxy Credit: JPL 2013-04-04 Postdoc seminar – Carl Borgentun14 Active region 215 nm 66 Å

15. Processing 2013-04-04 Postdoc seminar – Carl Borgentun15 Etch ridge Insulate and contact Etch grating

16. Single-mode emission 2013-04-04 Postdoc seminar – Carl Borgentun16 Wavelength [µm]

17. Grating Distributed feedback (DFB) laser using a Bragg grating => single-mode emission. Etched, i.e. non-metal => less loss. Laterally coupled => no epitaxial re- growth necessary. Credit: JPL 2013-04-04 Postdoc seminar – Carl Borgentun17 Wavelength [µm]

18. SEM pictures Credit: Cliff Frez 2013-04-04 Postdoc seminar – Carl Borgentun18

19. Coating, cleaving, and bonding Credit: Cliff Frez 2013-04-04 Postdoc seminar – Carl Borgentun19 Wavelength: 2.0 – 3.5 µm Wavelength: 2.0 – 3.5 µm

20. Performance 2013-04-04 Postdoc seminar – Carl Borgentun20

21. Power characteristics Output power at 35 mW @ 10C, 600 mA. Still more than 20 mW @ 30C, 600 mA. No sign of thermal roll-over. Dips in LI curves are due to absorption of ambient water (feature, not a bug!). 2013-04-04 Postdoc seminar – Carl Borgentun21

22. Spectral performance Wavelength is tunable by temperature and/or drive current. 2013-04-04 Postdoc seminar – Carl Borgentun22

23. Reliability and life-time Reliability and life-time test: devices submitted to elevated drive currents and mount temperatures. Over 3000 hours of accumulated testing has been performed, without a single failure. Peak wavenumber stabilizes after 100-200 hours. The change in peak wavenumber is less than 2 cm -1. The output power is not reduced. 2013-04-04 Postdoc seminar – Carl Borgentun23

24. Lasers integrated into TO-3 packages. No significant degradation in performance noticed after packaging.Packaging Before After 2013-04-04 Postdoc seminar – Carl Borgentun24

25. Shape of output beam Divergent and highly elliptical, normal for edge-emitters. Divergence angles: ~ 110 and 40 degrees. 2013-04-04 Postdoc seminar – Carl Borgentun25

26. Instrument aperture Collimating the beam 2013-04-04 Postdoc seminar – Carl Borgentun26 Laser Laser package

27. Package with internal lens TO-3 header TEC Tilted, coated, sapphire window Black housing Coated lens (XYZ active alignment) Precision spacer Laser Cu submount 2013-04-04 Postdoc seminar – Carl Borgentun27

28. Next target: CH4 2013-04-04 Postdoc seminar – Carl Borgentun28

29. Initial results 2013-04-04 Postdoc seminar – Carl Borgentun29 Hit target wavelength (3058 cm-1). Increase in output power (6 mW vs 1.5 mW)

30. Summary Successfully delivered 2 laser modules emitting more than 10 mW at 3777 cm-1 to Harvard for water detection. Developing laser package complete with collimating optics. Initial results show promising outlook for future methane detection missions like TLS. 2013-04-04 Postdoc seminar – Carl Borgentun30

31. Acknowledgements Supervisor: Siamak Forouhar Colleagues: Cliff Frez, Ryan Briggs, Mahmood Bagheri 2013-04-04 Postdoc seminar – Carl Borgentun31

32. Thanks for the attention! 2013-04-04 Postdoc seminar – Carl Borgentun32

33. High-power semiconductor lasers for in-situ sensing of atmospheric gases Carl Borgentun, Microdevices laboratory (MDL)