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We can force an ensemble of molecules to rotate coherently at an accelerating rate, using tailored femtosecond laser pulses. The maximum rotational rate of 6 THz is sufficient to dissociate chlorine into its constituent atoms.

From a recent study of the growth and optical properties of quantum dots (QD's), we demonstrated that artificial atoms with sharp electronic shells can be fabricated with good control, using self-assembled QD's grown by molecular beam epitaxy. Size and shape engineering of the QD's during growth permits the tailoring of their intersublevel energy spacings. We demonstrate a much improved uniformity of the macroscopic ensembles of QD's, with well-resolved electronic shells. In addition to size and shape engineering of the QDS's in the case of single-layer samples, we demonstrate significant improvements in the uniformity of the vertically self-aligned stacked QD's. State-filling spectroscopy of the zero-dimensional transitions between confined electrons and holes demonstrates that the energy levels are readily tunable. One to five confined levels, with an inter-level energy spacing between 25 and 90 meV, are obtained by adjusting the growth temperature or with post-growth annealings. Such QD's having well-defined excited-states have been grown in the active region of devices and results will be presented for lasers, detectors, or for structures displaying optical memory effects. For example, QD laser diodes with well-defined electronic shells are fabricated, and shape-engineered stacks of self-aligned QD's are used to increase the gain in the active region. Lasing is observed in the upper QD shells for small gain media, and progresses towards the QD ground states for longer cavity lengths. We obtained at 77K thresholds for Jth=15 A/cm2 for a 2 mm cavity lasing in the first excited state (p-shell), and at 300K for a 5 mm cavity, Jth is ~430A/cm2 with lasing in the d-shell. For an increased QD density, Jth is smaller than 100A/cm2 at room temperature. For inter- sublevel transitions, we demonstrated broadband normal incidence detection with responsivity approaching 1A/W at a detection wavelength of 5 microns. For interband detection, the photoluminescence decay time of p-i-n diode can be changed from ~3nsec to ~0.3nsec (3Ghz) with a reverse bias. For Qds capped with less than ~10 nm, remarkable charge transfers between QD and surface states lead to optical memory effects lasting over time-scales of several minutes.

Intense linearly polarized light induces a dipole force that aligns an anisotropic molecule to the direction of the field polarization. Rotating the polarization causes the molecule to rotate. Using femtosecond laser technology, we accelerate the rate of rotation from 0 to 6 THz in 50 ps, spinning chlorine molecules from near rest up to angular momentum states $J\ensuremath{\sim}420$. At the highest spinning rate, the molecular bond is broken and the molecule dissociates.

Artificial molecules are studied using coupled quantum-dot (QD) ensembles with well-defined electronic shells. The coupling strength between the zero-dimensional states is varied by changing the distance between two layers of stacked self-assembled InAs/GaAs QDs. For strongly coupled QDs grown with a 4 nm spacer, state-filling spectroscopy reveals a shift of the QD symmetric state to lower energies by ∼23 meV. The wetting layer states are also strongly coupled because of the shallow confinement, resulting in a redshift of its symmetric state by ∼26 meV.

Large non-resonant laser fields leads to a large, controllable AC Stark shift. Such shift can ensure a strong torque for molecules with anisotropic polarizability. Our experiment on alignment (angular trapping) of molecular axis is described. Molecules can be even spun to high angular momentum if a polarization of laser field rotates with increasing angular velocity in a controllable manner. The outlook on this future experiment is given in the manuscript.

Artificial atoms with up to five well-defined electronic shells are fabricated using self-assembled quantum dots (QD's) grown by molecular-beam epitaxy. State-filling spectroscopy of the zero-dimensional transitions between confined electrons and holes demonstrates that the energy levels are readily tunable. One to five confined levels, with an interlevel energy spacing between 25 and 90 meV, are obtained by adjusting the growth temperature or with post growth annealings. The uniformity and reproducibility of InAs/GaAs QD's are optimized by adjusting growth parameters affecting the evolution and the equilibrium shape of the QD's: the amount of strained material deposited, and the annealing time following the InAs deposition. Well-defined excited states are also obtained with stacked layers of vertically self-assembled QD's.

Random number sequences are a critical resource in modern information processing systems, with applications in cryptography, numerical simulation, and data sampling. We introduce a quantum random number generator based on the measurement of pulse energy quantum fluctuations in Stokes light generated by spontaneously-initiated stimulated Raman scattering. Bright Stokes pulse energy fluctuations up to five times the mean energy are measured with fast photodiodes and converted to unbiased random binary strings. Since the pulse energy is a continuous variable, multiple bits can be extracted from a single measurement. Our approach can be generalized to a wide range of Raman active materials; here we demonstrate a prototype using the optical phonon line in bulk diamond.

We present a systematic study of the molecular-frame photo-electron angular distributions produced by multiphoton double ionization of H2 using circularly polarized 800 nm, femtosecond laser pulses. We compare experimental results to numerical results obtained from a reduced-dimensionality time-dependent Schr¨ odinger equation (TDSE) model. In addition, we implement a TDSE-like version of the strong-field approximation to isolate the effect of the parent ion’s Coulomb potential on the continuum electron in our simulations. Thereby we identify the contributions of the parent ion potential, and light induced sub-optical cycle electron dynamics on the observable energy and angular distributions.

Coherent control of observables using the phase properties of weak light that induces one-photon transitions is considered. Measurable properties are shown to be categorizable as either class A, where control is not possible, or class B, where control is possible. Using formal arguments, we show that phase control in open systems can be environmentally assisted.

Coherent control of observables using the phase properties of weak light that induces one-photon transitions is considered. Measurable properties are shown to be categorizable as either class A, where control is not possible, or class B, where control is possible. Using formal arguments, we show that phase control in open systems can be environmentally assisted., Erratum published in volume 134, issue 5, article 059903, February 2011. DOI: 10.1063/1.3549578

Attosecond science has arisen from intense light pulses interacting with low density gases. We show that the initiating process—sub-cycle ionization—also survives in large band gap condensed media. Using fused SiO2 as an example, we measure the differential nonlinear absorption between the major and minor axis of elliptically polarized light. Through simulations that include ionization and light propagation, we confirm that changes in the ellipticity between the incident beam and the transmitted beam encode sub-cycle absorption dynamics. As the pulse duration is increased, we observe that sub-cycle ionization is masked by collisional processes. We propose a general class of methods for measuring attosecond dynamics in condensed media.

We study the spatial profile of high order harmonics generated by a transient grating of rotational excitation. We show that the phase modulation of the harmonic emission as a function of molecular alignment is encoded in the diffraction pattern. In molecular nitrogen, the phase difference between aligned and isotropic molecules decreases from 1.6 rad for harmonic 19 to less than 0.3 rad for harmonic 27. In CO2 we observe a strong phase jump for the highest harmonics. The position of this phase jump in the harmonic spectrum depends on the laser intensity, reflecting the contribution from multiple molecular orbitals to the harmonic emission.

The utility of the Filinov integral conditioning technique, as implemented in semiclassical initial value representation (SC-IVR) methods, is analyzed for a number of regular and chaotic systems. For nonchaotic systems of low dimensionality, the Filinov technique is found to be quite ineffective at accelerating convergence of semiclassical calculations since, contrary to the conventional wisdom, the semiclassical integrands usually do not exhibit significant phase oscillations in regions of large integrand amplitude. In the case of chaotic dynamics, it is found that the regular component is accurately represented by the SC-IVR, even when using the Filinov integral conditioning technique, but that quantum manifestations of chaotic behavior was easily overdamped by the filtering technique. Finally, it is shown that the level of approximation introduced by the Filinov filter is, in general, comparable to the simpler ad hoc truncation procedure introduced by Kay [J. Chem. Phys. 101, 2250 (1994)].

The aerosol optical depth over the Konza Prairie, near Manhattan, Kansas, was recorded at various locations by five separate teams. These measurements were made in support of the First ISLSCP Field Experiment (FIFE) and used to correct imagery from a variety of satellite and aircraft sensors for the effects of atmospheric scattering and absorption. The results from one instrument are reported here for 26 days in 1987 and for 7 days in 1989. Daily averages span a range of 0.05 to 0.28 in the midvisible wavelengths. In addition, diurnal variations are noted in which the afternoon optical depths are greater than those of the morning by as much as 0.07. A comparison between instruments and processing techniques used to determine these aerosol optical depths is provided. The first comparisons are made using summer 1987 data. Differences of as much as 0.05 (midvisible) are observed. Although these data allow reasonable surface reflectance retrievals, they do not agree to within the performance limits typically associated with these types of instruments. With an accuracy goal of 0.02 a preseason calibration/comparison experiment was conducted at a mountain site prior to the final field campaign in 1989. Good calibration data were obtained, and good agreement (0.01, midvisible) was observed in the retrieved optical depth acquired over the Konza. By comparing data from the surface instruments at different locations, spatial inhomogeneities are determined. Then, data from the airborne tracking sunphotometer allow one to determine variations as a function of altitude. Finally, a technique is proposed for using the in situ data to establish an instrument calibration.

The coherent emission from ionized nitrogen molecules is of interest for remote sensing and astronomical applications. To initiate the lasing process, we used an intense ultrashort near-infrared (NIR) pulse overlapped with a terahertz (THz) single-cycle pulse. We observed that coherent emission could be seeded and modulated by the amplitude of the THz field, which is the result of a combined effective second-order nonlinear polarization and the nonlinear effects induced by the NIR pump. Our results shed light on the role of intense transient fields in the coherent emission from photoexcited gas molecules.

We use linearly polarized 45 fs pulses to create rotational wave packets in ${\mathrm{N}}_{2}$ and ${\mathrm{O}}_{2}.$ We Coulomb explode molecules with a high-intensity circularly polarized pulse and use an ion imaging detector to measure a series of two-dimensional projections of the wave packet's angular distribution in 27 fs increments. We highlight the evolving wave packet near the first, second, sixth, and tenth full revival times and also near the one-eighth, one-quarter, one-half, and three-quarter fractional revivals.

Bright narrowly timed coherent UV emission from molecular Nitrogen cations is explained in terms of transient rotational alignment of the ground and excited electronic states leading to laser gain in absence of population inversion.