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Sugita, Akihiro; Yokoyama, Keiichi; Yamada, Hidetaka; Inoue, Norihiro*; Aoyama, Makoto; Yamakawa, Koichi
Japanese Journal of Applied Physics, Part 1, 46(1), p.226 - 228, 2007/01
Times Cited Count：7 Percentile：30.11(Physics, Applied)Generation of broadband mid-infrared (MIR) laser pulses by difference frequency mixing (DFM) is reported. Two-color femtosecond pulses from a Ti: Sapphire laser system is mixed in an AgGaS
crystal utilizing a noncollinear phase matching scheme. The relative bandwidth of the generated MIR pulse has been measured to be 23 % to the central frequency, the broadest in DFM-based MIR sources reported so far. It is found that the type-I crystal can give broader phase matching range of spectrum than the type-II crystal within this scheme.
) and Cs(7
) by femtosecond laser pulsesYamada, Hidetaka; Yokoyama, Keiichi; Teranishi, Yoshiaki*; Sugita, Akihiro; Shirai, Toshizo*; Aoyama, Makoto; Akahane, Yutaka; Inoue, Norihiro*; Ueda, Hideki*; Yamakawa, Koichi; et al.
Physical Review A, 72(6), p.063404_1 - 063404_5, 2005/12
Times Cited Count：6 Percentile：31.21(Optics)A demonstration of coherent quantum control for ultrafast precise selection of closely-lying states is reported. A phase-locked pair of femtosecond laser pulses is generated through a pulse shaper to excite the ground-state cesium atom to the Cs(7) and Cs(7) states by two-photon absorption. The excited state population is measured by detecting fluorescence from each spin-orbit state. By controlling the phase-difference of the pulse pair, an ultrafast precise selection is accomplished. The contrast ratio of the maximal to minimal selection ratio exceeds 10
with the delay less than 400 fs.
Yokoyama, Keiichi; Teranishi, Yoshiaki; Toya, Yukio; Shirai, Toshizo; Fukuda, Yuji; Aoyama, Makoto; Akahane, Yutaka; Inoue, Norihiro*; Ueda, Hideki; Yamakawa, Koichi; et al.
Journal of Chemical Physics, 120(20), p.9446 - 9449, 2004/05
Times Cited Count：6 Percentile：18.77(Chemistry, Physical)Optimal laser control for ultrafast selection of closely-lying excited states, whose energy separation is smaller than the laser bandwidth, is reported on the two-photon transition of atomic cesium; Cs(6S 
7D
, J = 5/2 and 3/2). Selective excitation was carried out by pulse shaping of ultrashort laser pulses which were adaptively modulated in a closed-loop learning system handling eight parameters representing the electric field. Two-color fluorescence from the respective excited states was monitored to measure the selectivity. The fitness used in the learning algorithm was evaluated from the ratio of the fluorescence yield. After fifty generations, a pair of nearly transform-limitted pulses were obtained as an optimal pulse shape, proving the effectiveness of "Ramsey fringes" mechanism. The contrast of the selection ratio was improved by 
30 % from the simple "Ramsey fringes" experiment.
Sugita, Akihiro; Yokoyama, Keiichi; Itakura, Ryuji; Yamada, Hidetaka
no journal, ,
Selective excitation to the closely lying state of potassiium atoms were examined as a fundamental research of a new laser-isotope-separation technique. Using time-resolved photon counting to measure the fluorescence intensity, the scatterd light from the pump beam and the fluorescence of interest were perfectly distinguished. Owing to this experimental setup, a high contrast more than 1000 was obtained for the selectivity. In addition, the excitation behavior when the laser intensity increased was recorded through the laser power dependence of the fluorescence intensity. As a result, it is found that the destructive interference between two excited states becomes incomplete with increasing laser power. Moreover, the relative population of the two states exhibit the power dependence expected by a computer simulation, indicating that the laser power required for the selective complete excitation is achieved.
Yokoyama, Keiichi; Sugita, Akihiro; Teranishi, Yoshiaki*; Itakura, Ryuji; Matsuoka, Leo; Yokoyama, Atsushi
no journal, ,
State-selective excitation of atomic cesium and potassium to their spin-orbit states, Cs(7D-6S) and K(4P-4S), are carried out by a coherent quantum control technique. In the weak field regime, ultrafast and highly selective excitation of cesium atoms has been successfully demonstrated with a pair of identical transform-limited pulses in which the control parameter is the phase difference between the two pulses alone. However, the excitation probability is very small (0.001) due to the weak laser field. To perform the selective excitation with large excitation probability (1), one-photon process of the K(4P-4S) transition is examined. The excitation probability is expected to become large while the selectivity degrades if the control parameter is the phase difference alone. The obtained laser intensity dependence agrees well with the theoretical prediction, indicating the excitation indeed in the non-perturbative regime.
