Quantum control utilizes coherent interactions between molecules and shaped laser pulses for driving nuclearwavepackets to the target of the reaction under investigation. Various theoretical treatments of the quantumcontrol of chemical reaction dynamics are reviewed in this paper. A general optimal control theory isintroduced to provide an understanding of the basis of quantum control of reaction dynamics. Two types ofoptimization methods, global and local are derived from the optimal control theory. An outline of a quantummechanical feedback control method developed by our group, which is a local optimization method, is brieflydescribed. The quantum mechanical feedback control theory can be used not only under weak laser field butalso under intense laser field conditions. The quantum mechanical feedback control theory is applied to simpleunimolecular reaction dynamics: ring puckering isomerization, multiphoton IR-induced dissociation of HFand predissociation of NaI. The optimized pulses are analyzed and explained in terms of π-pulses, pump anddump pulses and chirped pulses.

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Quantum control of chemical reactions was first proposed by Brumer and Shapiro. Since then, various otherideas have been reported, using quantum mechanical interference and manipulation of wave packets. In this review, recent progress of the quantum control is discussed.

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New spectroscopic technique which detects IR transition with high sensitivity is introduced asa tool to study laserreaction control by vibrational excitation. This spectroscopy, nonresonant ionization detectedIR spectroscopy isIR-UV double resonance spectroscopy which detects a vibrationally excited molecule by selective ionizationdue to UV laser. Vibrational transitions of jet-cooled phenol have been detected by Nonresonant IonizationDetected (NID) -IR spectroscopy from 3400 cm^-1 to 14000 cm^-1. The bandwidth of the OH overtone is foundto decrease with increase in the vibrational quantum number. Relaxation of the vibrationally excited moleculeand its application to reaction control are discussed.

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Optical field ionization is potentially useful for molecular analysis. A molecule is efficiently ionized to theparent and multiply charged ions, and eventually atoms in highly charged states are produced. Ultrafast timeresolvedx-ray diffraction techniques are emerging as powerful ways to observe the dynamics and structures ofchemical as well as biological reactions. These two promising applications developed by a terawatt laser arereviewed in brief.

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The light-ellipticity change ψ caused by the off-resonant magnetic birefringence of gases (O₂, N₂, Ar) wasmeasured with a high-sensitivity polarimeter. In order to reduce background noise, we improvedthe extinctionratio of the polarimeter by using high-quality optical elements and adjusting the diameter of the light beam.The extinction ratio of 3×10^-10 was then obtained. The measured value of ψ for Ar, which hadthe smallesteffect of magnetic birefringence among the three gases, was (1.1±0.3) ×10^-9 under the following experimental conditions: light wavelength: 0.79 μm, pressure: 1.3×10⁵ Pa, temperature: 296 K, magnetic field: 7 kG, optical path length: 5 cm. The minimum value of ellipticity change that could be detected was 3×10^-10 at 1-mW incident-light intensity for the quantum efficiency of a light detector of 0.03 and a photon detection time of 16128s. The sensitivity attained in the experiment was in agreement with the theoretical value expected at theshot noise limit.

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Using a laser sheet beam projector combined with a CCD-camera, an efficient technique to recognize thecomplex surfaces of curvature and plane has been demonstrated for the purpose of mobile robotnavigation. In this study, detected pixel images of elliptical arc obtained by laser sheet beam have beenconverted into a corresponding circular arc in the real-world coordinates so that the image processing for theposition and radius measurement became more precise and efficient than conventional techniquesbased ondirect elliptical arc analyses. Advantages of this method includes i) higher measurementaccuracy and shorter processing time, and ii) the capability of distinguishing curvature/planecomplexsurfaces. This technique yields an accuracy less than 2 cm for a 28.5 cm radius column at the distance of 70-250 cm from the robot, the obtained accuracy is significantly small enough to navigate a mobile robotoperating in indoor environments.

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A tunable terahertz-wave source has been realized by Optical Parametric Oscillator (OPO) utilizing the polaritonmode scattering of LiNbO₃. This technique has several advantages such as wide tunability and compactsystem. In this paper, we demonstrate an efficient terahertz-wave radiation by using a new OPOconfigurationwith a trapezoidal LiNbO₃ crystal. A tunable range of 130-310 μm has been achieved without a couplingdevice. This method reduces an influence of the propagation loss in the crystal, so that the shorter wavelengthoscillation is enhanced.

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