在近十多年來，由於高功率雷射技術的迅速發展，使得超短脈衝雷射與原子團簇的交互作用成為一個活躍的研究領域。由於原子團簇同時具有局部密度接近固體以及氣體般的平均密度的特性，過去的研究已顯示出個別的奈米原子團簇能夠有效的吸收雷射能量而形成高游離態的奈米電漿球，可產生KeV的電子和MeV的離子、並放射出強烈的輻射其波長範圍可從EUV到硬X光。由雷射加熱的氘原子團簇產生的高能離子碰撞達成核融合也已被成功的示範出來。
過去許多研究已顯示出強場物理的實驗中，許多重要的參數都與原子團簇的大小有著密切的關係，譬如高階諧波產生中奈米電漿球折射率的演化，以及X-ray 雷射中反向制動輻射加熱(inverse bremsstrahlung heating)以及三體碰撞結合(three body recombination)的效率。為了更了解原子團簇形成的機制，以及為了產生更大的原子團簇和產生以往我們所不能產生的某些物種的原子團簇(氫氣及氘氣)，我們發展了低溫冷卻氣流閥的方法，以及量測出緩衝氣體(Buffer gas)對於原子團簇形成的影響。同時藉由量測離噴嘴出口不同高度的原子團簇大小，我們可以知道原子團簇形成的演化過程。這些結果將使得我們能更加廣泛而準確的建立實驗上能夠控制原子團簇大小的參數，同時對我們使用原子團簇作為強場物理實驗的介質提供了一個先期的試驗。

With the rapid progress in high-power laser technology in the past decade, the interaction of ultrashort high-intensity laser pulses with atomic clusters has become an active field of research. As a result of their solid-like local density and gas-like average density, it has been shown that individual nanometer clusters can absorb laser energy efficiently to form highly-charged hot nanoplasmas, eject KeV electrons and MeV ions, and emit strongly from EUV to hard x-ray. Furthermore, nuclear fusion has also been demonstrated by collisions of high-energy ions produced from laser-heated deuterium clusters.
In the past many high field science researches have revealed that many important issues, such as the evolution of refractive index in high harmonic generation and the efficiency of inverse bremstrahlung heating and three body recombination in x-ray laser, are strongly dependent on cluster size.
The development of cryogenically cooled cluster jet system and the investigation of cluster formation with buffer gas are used to (1) get deeper insight into the mechanisms of cluster formation, (2) produce larger clusters, and (3) attain cluster formation of hydrogen or deuterium which cannot form clusters under room temperature. Moreover, by measuring the variation of cluster size with the distance perpendicular to nozzle exit we can investigate the evolution of cluster formation. With these methods we can establish the parameters more extensively and precisely for controlling cluster size, and these provide a preliminary study for utilizing cluster as medium in high field science research.

[1] Thomas, J. M. Michael Faraday and The Royal Institution; AdamHilger: Bistol, (1991).
[2] Coulier, M. J. Pharm. Chim. Paris, 22, 165. (1875)
[3] A. W. Castleman, Jr., K. H. Bowen, Jr.”Clusters- Structure, Energetics, and Dynamics of Intermediate States of Matter”, J. Phys. Chem. 100, 12911 (1996)
[4] A. W. CASTLEMAN, JR. and R. G. KEESEE, “Gas-Phase Clusters: Spanning the States of Matter”, Science, 36, 241(1988)
[5] D. J. Wales, Science,” Structure, Dynamics, and Thermodynamics of
Clusters: Tales from Topographic Potential Surfaces” 271, 925 (1996)
[6] Z. Y. Chen, C. D. Cogley, J. H. Hendricks, B. D. May, and A. W. Castleman, J.Chem. Phys. 93, 3215 (1990).
[7] T. Ditmire, T. Donnelly, A. M. Rubenchik, R. W. Falcone, and M. D. Perry, “Interaction of intense laser pulses with atomic clusters”, Phys. Rev. A., 53, 3379 (1996)
[8] H. M. Milchberg, S. J. McNaught, and E. Parra, ,” Plasma hydrodynamics of the intense laser-cluster interaction” Phys. Rev. E, 64, 056402 (2001).
[9] C.-T. Hsieh, C.-M. Huang, C.-L. Chang, Y.-C. Ho, Y.-S. Chen, J.-Y. Lin, J. Wang, and S.-Y. Chen, “Tomography of the injection and acceleration processes that produce a monoenergetic electron beam in a laser wakefield accelerator”, Phys. Rev. Lett , 96, 095001 (2006).
[10] S.-Y. Chen,, A. Maksimchuk, E. Esarey, and D. Umstadter,.” Observation of Phase-Matched Relativistic Harmonic Generation, Phys. Rev. Lett., 84,5528 (2000)
[11] M.-C. Chou, P.-H. Lin, T.-S. Hung, J.-Y. Lin, J. Wang, and S.-Y. Chen,” Experimental investigation of the parameter space for optical-field-ionization cluster-jet x-ray lasers” Phys. Rev. A, 74, 023804 (2006).
[12] T. D. Donnelly,, T. Ditmire, K. Neuman, M. D. Perry, and R. W. Falcone, “High-Order Harmonic Generation in Atom Clusters”, 76, 2472 (1996)
[13] T. Ditmire, J. Zweiback, V. P. Yanovsky, T. E. Cowan, G. Hays& K. B. Wharton,” Nuclear fusion from explosions of femtosecond laser-heated deuterium clusters” NATURE, 298, 489 (1999)
[14] Zweiback, R. A. Smith, T. E. Cowan, G. Hays, K. B. Wharton, V. P. Yanovsky, and T. Ditmire.” Nuclear Fusion Driven by Coulomb Explosions of Large Deuterium Clusters” Phys. Rev. Lett. 84, 2634 (2000)
[15] T. Mocek, C. M. Kim, H. J. Shin, D. G. Lee, Y. H. Cha, K. H. Hong, and C. H. Nam” Enhancement of soft x-ray emission from a cryogenically cooled Ar gas jet irradiated by 25 fs laser pulse” APL, 76,1819 (2000)
[16] 蕭一方, 國立台灣大學物理研究所碩士論文 (2003)
[17] V. Kumarappan, K.Y. Kim, and H. M. Milchberg, “Guiding of Intense Laser Pulse in Plasma Waveguides Produced from Efficient, Femtosecond End Pumped Heating of Clustered Gases” Phys. Rev. Lett. 94, 205004 (2005)
[18] R. A. Smith, T. Ditmire, and J. W. G. Tisch, “Characterization of a cryogenically cooled high-pressure gas jet for laser cluster interaction experiments”,Rev. Sci. Instrum. 69, 3798 (1998)
[19] E. Parra, S. J. McNaught, and H. M. Milchberg, “Characterization of a cryogenic, high-pressure gas jet operated in the droplet regime” ,Rev. Sci. Instrum., 73, 468
[20] E.W.Becker,K.Bier, and W.Henkes, Z.Phys. 146, 333 (1956)
[21] Terry A.Miller “Chemistry and Chemical Intermediates in Supersonic Free Jet Expansions,” Science. 223, 545-553 (1984)
[22] Hellmut Haberland, Clusters of atoms and molecules I, (Springer, 1994)
[23] Giacinto Scoles, Atomic and molecular beam methods, (OXFORD, 1988)
[24] Otto F. Hagena “Cluster ion sources”, Rev. Sci. Instrum. 63, 2374 (1992)
[25] C.H. Yang, H. Qiu,”Theory of homogenous nucleation:A chemical kinetic view”, J.Chem.Phys. 84, 416 (1985)
[26] H.Pauly, Atom, molecule, and cluster beam I, (Springer, 2000)
[27] O.F.Hagena, W.Obert, Cluster Formation in Expanding Supersonic Jets Effect of Pressure, Temperature Nozzle Size and Test Gas, 56, 1793-1802 (1972)
[28] F. Dorchies, F. Blasco, T. Caillaud, J. Stevefelt, C. Stenz, A. S. Boldarev,
and V. A. Gasilov, “Spatial distribution of cluster size and density in supersonic jets as targets for intense laser pulses”, Phys. Rev. A. 68, 023201 (2003)
[29] E. B. Treacy, IEEE J. Quantum Electron. QE-5, 454 (1969).
[30] J. Wörmer, V. Guzielski, J. Stapelfeldt, and T. Möller, Chem. Phys. Lett. 159, 321(1989).
[31] http://www.webelements.com/
[32] T. Auguste, M. Bougeard, E. Caprin, P. D’Oliveira, and P. Monot, “Characterization of a high-density large scale pulsed gas jet for laser–gas interaction experiments”, Rev. Sci. Instrum., 70, 2349 (1999)
[33] K. Y. Kim, V. Kumarappan, and H. M. Milchberg, ”Measurement of the average size and density of clusters in a gas jet” APL, 83, 3210 (2003)
[34] 楊宗憲, 國立中正大學物理研究所碩士論文 (2005)
[35] Richard P. Feynman, Robert B. Leighton, Matthew Sands,”The Feynman Lectures on Physics volume 1”, (Wesley, 1970)
[36] I. Weiner, M. Rust, and T. D. Donnelly “Particle size determination: An undergraduate lab in Mie scattering” Am. J. Phys. 69, 129
[37] A. J. Cox, Alan J. DeWeerd, and Jennifer Linden, “An experiment to measure Mie and Rayleigh total scattering cross sections” Am. J. Phys. 70 , 620 (2002)
[38] Max. Born, Emil Wolf, “Principles of optics 7th”, (Cambridge, 1999)
[39] http://atol.ucsd.edu/scatlib/
[40] A. Ramos, J. M. Fernández, G. Tejeda, and S. Montero, “Quantitative study of cluster growth in free-jet expansions of CO2 by Rayleigh and Raman scattering” Phys. Rev. A., 72, 053204 (2005)