The vacuum ultraviolet (VUV) light source has been used for soft ionization in many applications. A simple method to get VUV light is by tripling the third harmonic of a Neodymium doped laser (1064 nm) in xenon gas. In order to get more fluence, higher repetition rate and conversion efficiency to enable more applications, we have investigated using a picosecond laser with a 50 kHz repetition rate as our 1064 nm light source. By using two lithium triborate (LBO) crystals, we obtained 354.7 nm UV light with >50% conversion efficiency from the fundamental. Taking this UV light and tripling it in a cell filled with a mixture of xenon and argon gases, the overall VUV power is expected to reach ~100 μW before optical loss. We tried to improve this conversion efficiency of VUV generation with a hollow waveguide. We used a quartz hollow waveguide that has a 100 μm inner diameter, 1200 μm outer diameter and is 10.5 cm long. Under the same focusing condition (32 μm beam-waist) and input average power (1 W) as in the gas mixing case, VUV output is enhanced by 1.4~2 times compared to free focusing with gas mixing. This conversion efficiency is not as high as we had expected. We attribute this low enhancement to scattering and propagation losses in the waveguide and to two-photon ionization. This means that if one wants to have a better conversion efficiency, one shall need to use a waveguide that has a larger inner diameter to reduce waveguide loss and two-photon ionization loss. We suggest that the hollow waveguide (capillary) shall be used when the laser peak power is large enough (for example 20 MW). On the other hand, if the laser peak power is small, we suggest to employ tight-focusing to generate VUV photons at an intensity just below the level where Kerr effect is induced.

[1] Joan B. Pallix, Udo Schuhle, Christopher H. Becker, and David L. Huestis, "Advantages of Single-Photon Ionization over Multiphoton Ionization for Mass Spectrometric Surface Analysis of Bulk Organic Polymers," Anal. Chem., vol. 61, pp. 805-811, 1989.
[2] F. Mühlberger, R. Zimmermann, and A. Kettrup, "A Mobile Mass Spectrometer for Comprehensive On-Line Analysis of Trace and Bulk Components of Complex Gas Mixtures: Parallel Application of the Laser-Based Ionization Methods VUV Single-Photon Ionization, Resonant Multiphoton Ioniza-tion, and Laser-Induce," Anal. Chem., vol. 73, pp. 3590-3604, 2001.
[3] Y. J. Shi, S. Consta, A. K. Das, B. Mallik, D. Lacey, and R. H. Lipson, "A 118 nm vacuum ultraviolet laser/time-of-flight mass spectroscopic study of methanol and ethanol clusters in the vapor phase," JOURNAL OF CHEMICAL PHYSICS, vol. 116, no. 16, pp. 6990-6999, 22 APRIL 2002.
[4] F. Mühlberger, K. Hafner, S. Kaesdorf, T. Ferge, and R. Zimmermann, "Comprehensive On-Line Characterization of Complex Gas Mixtures by Quasi-Simultaneous Resonance-Enhanced Multiphoton Ionization, Vacuum-UV Single-Photon Ionization, and Electron Impact Ionization in a Time-of-Flight Mass Spectrometer...," Anal. Chem., vol. 76, pp. 6753-6764, 2004.
[5] JEFFREY BOKOR AND N. J. HALAS, "Time-Resolved Study of Silicon Surface Recombination," IEEE JOURNAL OF QUANTUM ELECTRONICS, vol. 25, no. 12, DECEMBER 1989.
[6] M. Wittmann, M.T. Wick, O. Steinkellner, P. Farmanara, V. Stert, W. Radloff, G. Korn, I.V. Hertel, "Generation of femtosecond VUV pulses and their application to time resolved spectroscopy in the gas phase," Optics Communications, vol. 173, pp. 323-331, 1 January 2000.
[7] A. Mank, M. Drescher, A. Brockhinke, N. Biiwering, U. Heinzmann, "Angle- and spin-resolved photoelectron spectroscopy in rotationally resolved photoionization of HI," ZEITSCHRIFT FUR PHYSIK D-ATOMS MOLECULES AND CLUSTERS, vol. 29, pp. 275-289, 1994.
[8] M. HENRY R. HUTCHINSON AND KENNETH J. THOMAS, "High-Efficiency Generation of Narrow Bandwidth Tunable VUV Radiation," IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. QE-19, no. 12, pp. 1823-1826, DECEMBER 1983.
[9] A. H. Kung, "Third-harmonic generation in a pulsed supersonic jet of xenon," OPTICS LETTERS, vol. 8, no. 1, pp. 24-26, January 1983.
[10] F. Mühlberger, J. Wieser, A. Ulrich, and R. Zimmermann, "Single Photon Ionization (SPI) via Incoherent VUV-Excimer Light: Robust and Compact Time-of-Flight Mass Spectrometer for On-Line, Real-Time Process Gas Analysis," Anal Chem., vol. 74, no. 15, pp. 3790-3801, 1 Aug 2002.
[11] R. Hilbig and R. Wallenstein, "Narrowband tunable VUV radiation generated by nonresonant sum- and difference-frequency mixing in xenon and krypton," APPLIED OPTICS., vol. 21, no. 5, pp. 913-917, 1 March 1982.
[12] A. H. Kung, J. F. Young, G. C. Bjorklund, and S. E. Harris, "Generation of Vacuum Ultraviolet Radiation in Phase-Matched Cd Vapor," Phys. Rev. Lett, vol. 29, no. 15, pp. 985-988, 9 October 1972.
[13] R.A.Ganeev, I.A.Kulagin, T.Usmanov, and S.T.Khudalberganov, "Investigation of the generation of λ=118.2nm coherent radiation in rare gases," Sov. J. Quantum Electron., vol. 12, pp. 1637-1640, Dec. 1982.
[14] RITA MAHON, THOMAS J. McILRATH, VALERIE P. MYERSCOUGH, AND DAVID W. KOOPMAN, "Third-Harmonic Generation in Argon, Krypton, and Xenon: Bandwidth Limitations in the Vicinity of Lyman-α," IEEE Journal of Quantum Electronics, Vols. QE-15, no. 6, pp. 444-451, June 1979.
[15] L. J. ZYCH AND JAMES F. YOUNG, "Limitation of 3547 to 1182 A Conversion Efficiency in Xe," IEEE JOURNAL OF QUANTUM ELECTRONICS, Vols. QE-14, no. 3, pp. 147-149, MARCH 1978.
[16] M. Castillejo, J. Y. Zhou, and M. H. R. Hutchinson, "Coherent Vacuum Ultraviolet Generation by Frequency Mixing in Glass Hollow Waveguides," Appl. Phys. B, vol. 45, pp. 293-299, 1988.
[17] Charles G. Durfee III, Sterling Backus, Margaret M. Murnane, and Henry C. Kapteyn, "Ultrabroadband phase-matched optical parametric generation in the ultraviolet by use of guided waves," OPTICS LETTERS, vol. 22, no. 20, pp. 1565-1567, 15 October 1997.
[18] C. G. Durfee, "Phase matching in cascaded third-order processes," J. Opt. Soc. Am. B, vol. 19, no. 4, pp. 822-831, April 2002.
[19] Charles G. Durfee III, Andy R. Rundquist, Sterling Backus, Catherine Herne, Margaret M. Murnane, and Henry C. Kapteyn, "Phase Matching of High-Order Harmonics in Hollow Waveguides," PHYSICAL REVIEW LETTERS, vol. 83, no. 11, pp. 2187-2190, 13 SEPTEMBER 1999.
[20] Andy Rundquist, Charles G. Durfee III, Zenghu Chang, Catherine Herne, Sterling Backus, Margaret M. Murnane, Henry C. Kapteyn, "Phase-Matched Generation of Coherent Soft X-rays," Science, vol. 280, pp. 1412-1415, 1988.
[21] R. W. Boyd, Nonlinear Optics 3rd edition.
[22] A. H. Kung, J. F. Young, and S. E. Harris, "Generation of 1182-Å radiation in phase-matched mixtures of inert gases," Appl. Phys. Lett., vol. 22, no. 6, pp. 301-302, March 1973.
[23] A. H. Kung, J. F. Young, and S. E. Harris, "Erratum: Generation of 1182-Å radiation in phase-matched mixtures of inert gases," Appl. Phys. Lett., vol. 28, no. 4, p. 239, 15 February 1976.
[24] G. C. Bjorklund, "Effects of Focusing on third-order nonlinear processes in isotropic media," IEEE Quantum Electronics, Vols. QE-11, no. 6, pp. 287-296, June 1975.
[25] Richard B. Miles and Stephen E. Harris, "Optical Third-Harmonic Generation in Alkali Metal Vapors," IEEE Journal of Quantum Electronics, vol. 9, no. 4, pp. 470-484, April 1973.
[26] J. C. M. GARCIA, "ABSORPTION MEASUREMENTS OF KRYPTON AND XENON RESONANCE LINES," J. Quant. Spectrosc. Radiat. Tramfer, vol. 51, no. 4, pp. 533-550, 1997.
[27] Richard L. Abrams and Arthur N. Chester, "Resonator Theory for Hollow Waveguide Lasers," APPLIED OPTICS, vol. 13, no. 9, pp. 2117-2125, September 1974.
[28] E. A. J. MARCATILI and R. A. SCHMELTZER, "Hollow Metallic and Dielectric Waveguides for Long Distance Optical Transmission and Lasers," The Bell System Technical Journal, pp. 1783-1809, July 1964.
[29] Mitsunori Saito, Shin-ya Sato, and Mitsunobu Miyagi, "Loss characteristics of infrared hollow waveguides in multimode transmission," J. Opt. Soc. Am. A, vol. 10, no. 2, pp. 277-282, February 1993.
[30] Rick K. Nubling and James A. Harrington, "Launch conditions and mode coupling in hollow-glass waveguides," Opt. Eng., vol. 37, no. 9, pp. 2454-2458, September 1988.
[31] V. G. Dmitriev, G. G. Gurzadyan, and D. N. Nikogosyan, Handbook of Nonlinear Optical Crystals, Third ed., Springer.
[32] M. C. CASTEX and N. DAMANY, "ABSORPTION SPECTRUM OF THE XENON MOLECULE IN THE VACUUM ULTRAVIOLET REGION," CHEMICAL PHYSIS LETTERS, vol. 13, no. 2, pp. 158-161, 15 February 1972.
[33] M. P. McCann, C. H. Chen, and M. G. Payne, "Twophoton (vacuum ultraviolet + visible) spectroscopy of argon, krypton, xenon, and molecular hydrogen," J. Chem. Phys., vol. 89, no. 9, pp. 5429-5441, 1 November 1988.
[34] J. H. CARVER and P. MITCHELL, "Ionization chambers for the vacuum ultra-violet," J. SCI. INSTRUM., vol. 41, pp. 555-557, September 1964.