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William R. Evans Benjamin J. McCall Takamasa Momose

Toward a Continuous-Wave Solid para -Hydrogen Raman Laser for Molecular Spectroscopy Applications. William R. Evans Benjamin J. McCall Takamasa Momose. Department of Physics University of Illinois at Urbana-Champaign Departments of Chemistry, Astronomy and Physics

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William R. Evans Benjamin J. McCall Takamasa Momose

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  1. Toward a Continuous-Wave Solid para-Hydrogen Raman Laser for Molecular Spectroscopy Applications William R. Evans Benjamin J. McCall TakamasaMomose Department of Physics University of Illinois at Urbana-Champaign Departments of Chemistry, Astronomy and Physics University of Illinois at Urbana-Champaign Department of Chemistry The University of British Columbia

  2. Outline • Motivation for the Project • Stimulated Raman Scattering • Hydrogen as a Raman Medium • Measuring the Index of Refraction of Solid para-Hydrogen • Current Progress Toward a cw Solid para-Hydrogen Raman Laser in the Visible • Future Plans and Summary

  3. Mid-Infrared Spectroscopy • Many Attractive Targets in 5 – 10 μm Range • Few Available Laser Sources • Astrochemistry need sub-MHzlinewidth • Need for cwsources

  4. Possible Solution: Solid para-H2 Raman Laser • Transparent for most of 100 nm to 10 μm • Enormous frequency shift • 4155.2 cm-1 in gas • 4149.7 cm-1 in solid M. Fushitani, S. Kuma, Y. Miyamoto, H. Katsuki, T. Wakabayashi, T. Momose, and A.F. Vilesov, Optics Letters, 28, 1, 37 (2003) M. Mengel, B.P. Winnewisser, and M. Winnewisser, Canadian Journal of Physics, 78, 317 (2000)

  5. Brief Review of Raman Scattering • Pump photon scatters inelastically with an atom  Redshiftedto a “Stokes” photon.

  6. Stimulated Raman Scattering • Two-photon process • Incoming Stokes stimulates transition • Outgoing photons emitted coherently • Efficiency of SRS depends on intracavity power and Raman gain coefficient

  7. Previous Work with Hydrogen Pulsed Continuous

  8. Previous Work with Hydrogen Pulsed Continuous A. DeMartino, R. Frey, and F. Pradere, IEEE J. QUANT. ELEC., VOL. QE-16, 11 (1980) P. Rabinowitz, B. N. Perry, and N. Levinos, IEEE J. Quantum Electron. 22, 797 (1986)

  9. Previous Work with Hydrogen Pulsed Continuous M. Fushitani, S. Kuma, Y. Miyamoto, H. Katsuki, T. Wakabayashi, T. Momose, and A.F. Vilesov, Optics Letters, 28, 1, 37 (2003) B.J. McCall, A.J. Huneycutt, R.J. Saykally, C.M. Lindsay, T. Oka, M. Fushitani, Y. Miyamoto, and T. Momose, Applied Physics Letters, 82, 9, 1350 (2003) K.E. Kuyanov, T. Momose, and A.F. Vilesov, Applied Optics, 43, 32, 6023 (2004)

  10. Previous Work with Hydrogen Pulsed Continuous J.K. Brasseur, K.S. Repasky, and J.L. Carlsten, Optics Letters, 23, 5, 367 (1998) J.K. Brasseur, P.A. Roos, K.S. Repasky, and J.L. Carlsten, Journal of the Optical Society of America B, 16, 8, 1305 (1999) L.S. Meng, K.S. Repasky, P.A. Roos, and J.L. Carlsten, Optics Letters, 25, 7, 472 (2000) L.S. Meng, P.A. Roos, K.S. Repasky, and J.L. Carlsten, Optics Letters, 26, 7, 426 (2001) (and others)

  11. Previous Work with Hydrogen Pulsed Continuous

  12. Tradeoff • Want: • Narrow linewidth Need cw laser • Not high complexity  Lower finesse cavity • Drawbacks: • CW pump lasers have lower maximumpower • Lower finesse cavity means less power buildup in the cavity • Both of these factors make lasing more difficult • Tradeoff: • Need high Raman gain coefficient  Solid para-H2

  13. Solid para-H2 Raman Gain Coefficient • Solid para-H2 Raman gain coefficient measured by Katsuragawa and Hakuta • ~ 7,000x that of gaseous hydrogen • Narrow linewidth because solid para-H2 is a quantum crystal M. Katsuragawa and K. Hakuta, Optics Letters, 25, 3, 177 (2000)

  14. Index of Refraction of Solid para-H2 • To design a solid para-H2 Raman laser, we needed to know the index of refraction of solid para-H2. • Surprisingly, this quantity had never been reported before. M. Perera, et al, Optics Letters, 36, 6, 840 (March 15, 2011)

  15. Index of Refraction of Solid para-H2Measurement Setup • Incoming laser is refracted at slanted window. • By measuring the exit angle of the laser, we can determine the index of the solid para-H2 using Snell’s law. OFHC copper connected to cold head Stainless steel cell Laser Sapphire windows M. Perera, et al, Optics Letters, 36, 6, 840 (March 15, 2011)

  16. Index of Refraction of Solid para-H2Results M. Perera, et al, Optics Letters, 36, 6, 840 (March 15, 2011)

  17. Solid para-H2 Raman LaserExperimental Setup • With the index of refraction of solid para-H2 in hand, we can design the setup for our laser. • 1st Stage of Project: • Raman shifting in the visible: 514 nm  654 nm • Multi-mode pump laser • Singly-resonant cavity (only building up Stokes radiation) • No active cavity locking

  18. Solid para-H2 Raman LaserExperimental Setup

  19. Solid para-H2 Raman LaserExperimental Setup

  20. Solid para-H2 Raman LaserExperimental Setup

  21. Solid para-H2 Raman LaserCell Design • Interfaces designed to be at Brewster’s angle. • Minimize reflective scattering losses inside cavity. • Because np-H2 is greater than 1, the windows on the cell need to be wedged.

  22. Solid para-H2 Raman LaserExperimental Setup

  23. Solid para-H2 Raman LaserExperimental Setup

  24. Solid para-H2 Raman LaserCavity Design • Specialty coated cavity mirrors • 1 m Radius of Curvature • High transmitting at pump wavelength(T ~ 98% at 514 nm) • High reflecting at Stokes wavelength(R = 99.5% at 654 nm) • Cavity length 50 cm • Diffraction grating used to separate pump beam from Stokes beam after the cavity

  25. Solid para-H2 Raman LaserCurrent Progress • Solid para-H2 crystal grown in new cell • Pump laser through the crystal  windows properly aligned • Raman output within the next few weeks

  26. Solid para-H2 Raman LaserFuture Plans • Active cavity locking • Single-mode pump laser • Doubly-resonant cavity • Raman lasing in the infrared

  27. Summary • Solid para-H2 is an attractive material for use as a Raman gain medium. • A fully-optimized solid para-H2 Raman laser could potentially provide the first widely tunable laser source for ultra high resolution spectroscopy in the 5-10 μm range. • We have made the first ever measurements of the index of refraction of solid para-H2. • We have successfully designed and built a system that should be able to achieve Stokes output using solid para-H2within the next few weeks.

  28. Acknowledgments • Benjamin McCall • TakamasaMomose • ManoriPerera • Michael Porambo • Heather Hanson • Preston Buscay • Kristin Evans The McCall Research Group

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