@misc{oai:ir.soken.ac.jp:00000197,
 author = {劉, 振林 and リュウ, シンリン and LIU, Zhenlin},
 month = {2016-02-17, 2016-02-17},
 note = {Ultrashort-pulse generation in the ultraviolet (UV) region has been receiving a great deal of interest for high-intensity-field physics and different spectroscopic applications.  All known tunable UV short-pulse laser sources are mode-locked Ti:sapphire lasers or various dye-laser based systems with amplification and subsequent wavelength-conversion stages.  The above systems are extremely complicated and bulky devices with limited tunability, but there were no alternative tunable laser sources.  In fact, direct UV short-pulse generation was reported only for excimer lasers.  On the other hand, solid-state tunable UV-Baser materials such as Ce3+ ion activated LuLiF4 (LLF), LiCaAlF4(LiCAF), and LiSrAlF6 (LiSAF) have recently been developed.  With their broad gain-width, they are attractive for direct ultrashort pulse generation and amplification in the ultraviolet region.  Tunable lasers with tunability centered around 290 nm are of special interest for applications relating to the remote sensing.  The simple, compact, all-solid-state Ce:LiCAF (282-314 nm) laser can generate coherent radiation in this wavelength region.  Ce:LLF has a potential longer-wavelength tuning region of around 305 to 340 nm, so it is especially attractive for use in spectroscopy of wide band-gap semiconductors for blue Baser diodes, such as GaN. Their broad gain bandwidth corresponding to a few femtoseconds is extremely attractive for short-pulse applications.
  The new solid-state, tunable, ultraviolet crystals, Ce:LLF and Ce:LiCAF are proven to be very efficient and reliable to realize UV lasers.  Subnanosecond ultraviolet coherent pulses were generated directly from solid-state lasers simply for the first time using low-Q, short-cavity Ce:fluoride lasers pumped by the fifth [1] and fourth [2] harmonics of Nd:YAG lasers.
  To prove the tunability of these new laser materials, they made a tunable all-solid-state Ce:LLF laser with the fifth harmonic of an Nd:YAG laser as the pumping source [1].  They also demonstrated a tunable Ce:LiCAF laser with broad tuning region from 282 nm to 314 nm [2].  Furthermore, they obtained tunable UV pulses around 230 nm by the sum-frequency mixing of Ce:LiCAF and Nd:YAG lasers [3].
  They have demonstrated the direct generation and efficient amplification of UV short pulses from the simplest, all-solid-state, UV short-pulse MOPA system composed of Ce:LiCAF crystals and conventional Q-switched Nd:YAG lasers [4].  In this way, they have proven that the Ce:LiCAF-based MOPA system is as effective and practical as other UV short-pulse systems.
  Large Ce:LiCAF crystals with 15 mm diameter were successfully grown by the Czochralski method in collaboration with Tohoku University recently [5].  Due to the available large Ce:LiCAF crystal, they obtained 60-mJ output energy from the Ce:LiCAF laser, the highest output directly from a Ce:LiCAF Baser reported until now.  A much higher output can be expected by fully utilizing the crystal cross size while using a larger pumping source.  This suggests that Ce:LiCAF is a promising material for high-energy ultraviolet pulse generation combined with a high-power, Q-switched Nd:YAG laser [6].
  With the development of the new laser media and nonlinear crystals, solid-state unable ultraviolet short-pulse lasers have been realized [7].  It is reasonable to expect the cw solid-state ultraviolet Ce:fluorude lasers in future with the improvement of Ce:fluoride crystal qualities and high power ultraviolet cw pumping sources.
  In conclusion, they believe, with the improvement of the quality and size of UV laser crystals and nonlinear crystals (which are important for the cw UV pumping sources), all-solid-state, compact, ultrashort pulse, ultraviolet, tunable Ce:fluoride lasers will be possible in the near future.  Further development of Baser systems using these new laser media will open up new possibility of simple and compact tunable UV ultrashort-pulse laser light sources.

[1] N. Sarukura, Z. Liu, S. Izumida, M. A. Dubinskii, R. Y. Abdulsabirov, and S. L. Korableva, "All-solid-state tunable ultraviolet sub-nanosecond laser with direct pumping by the fifth harmonic of an Nd:YAG Baser," Appl. Opt.  37, 6446-6448 (1998).
[2] Z. Liu, H. Ohtake, N. Sarukura, M. A. Dubinskii, R. Y. Abdulsabirov, S. L. Korableva, A. K. Naumov, and V V. Semashko, "Subnanosecond tunable ultraviolet pulse generation from a low-Q, short-cavity Ce:LiCAF laser", Jpn. J. Appl. Phys.  36, L1384-L1386 (1997).
[3] Z. Liu, N. Sarukura, M. A. Dubinskii, R. Y. Abdulsabirov, S. L. Korableva, A. K. Naumov, and V. V. Semashko, "Tunable ultraviolet short-pulse generation from a Ce:LiCAF laser amplifier system and its sum-frequency mixing with an Nd:YAG laser", Jpn. J. Appl. Phys.  37, L36-L38 (1998).
[4] N. Sarukura, Z. Liu, H. Ohtake, Y. Segawa, M. A. Dubinskii, R. Y. Abdulsabirov, S. L. Korableva, A. K. Naumov, and V V. Semashko, "Ultraviolet short pulses from an all-solid-state Ce:LiCAF master oscillator and power amplifier system", Opt. Lett.  22, 994-996(1997).
[5] K. Shimamura, N. Mujilatu, K. Nakano, S. L. Baldochi, Z. Liu, H. Ohtake, N. Sarukura, and T. Fukuda, "Growth and characterization of Ce-doped LiCaAlF6 single crystals", J. Crystal Growth 197, 896-900 (1999).
[6] Z. Liu, S. Izumida, H. Ohtake, N. Sarukura, K. Shimamura, N. Mujilatu, S. L. Baldochi, and T. Fukuda, "High-pulse-energy, all-solid-state, ultraviolet Baser oscillator using large Czochralski-grown Ce:LiCAF crystal," Jpn. J. Appl. Phys.  37, L1318-L1319 (1998).
[7] Z. Liu, N. Sarukura, M. A. Dubinskii, R. Y. Abdulsabirov, and S. L. Korableva, "All-solid-state subnanosecond tunable ultraviolet laser sources based on Ce3+-activated fluoride crystals", J. of Nonlinear Optical Physics and Materials 8, 41-54 (1999)., application/pdf, 総研大甲第424号},
 title = {Ce3+ Ion Activated Fluoride Crystals as Prospective Active Media for High-Power All-Solid-StateUltraviolet Tunable Ultrafast Lasers},
 year = {}
}