Temporal coherent control of superfluorescent pulses

We demonstrate that collective atomic interferences can be investigated by measuring the superfluorescence (SF) time delay. A pair of broadband (≈20 nm), ultrashort (≈80 fs), collinear pulses with a variable delay coherently excites rubidium (Rb) atoms. The generated superfluorescent pulses at 420 nm on the cascade transition are recorded by a picosecond streak camera. Both intensity and SF time delay of the 420 nm pulse are altered as the delay between input pulses varies. In particular, the SF time delay of the normalized 420 nm pulse exhibits oscillations with different periods. This can be understood in terms of atomic and quantum interferences due to two possible two-photon excitation pathways through the intermediate levels (Rb D-lines).     

Temporal compression of nanosecond laser pulses using coherent control

We present a study of the temporal compression of nanosecond laser pulses resulting from the coherent control peculiarities of the propagation dynamics in a regime of electromagnetically induced transparency. We describe the general theoretical framework and discuss the crucial conditions required in order to experimentally realize such a temporal compression scheme. A proof-of-concept experimental realization of a scheme of this type in a sample of hot sodium vapors is currently being implemented: we describe in detail the experimental setup designed for this purpose.     

Resonance offset tailored composite pulses

We describe novel composite pulse sequences which act as general rotors and thus are particularly suitable for nuclear magnetic resonance quantum computation. The resonance offset tailoring to enhance nutations approach permits perfect compensation of off-resonance errors at two selected frequencies placed symmetrically around the frequency of the radiofrequency source.     

Femtosecond strong-field coherent control of nonresonant ionization with shaped pulses

The strong-field coherent control of the nonresonant ionization of nitrous oxide using shaped pulses is investigated.We study the dependence of periodic coherent oscillation of the total ionization yield on the variation of laser phase parameters. The physical mechanism of the strong-field coherent control is investigated experimentally and theoretically by the nonresonant spectral phase interferences in the frequency domain. We show that the intense shaped pulses with broadband and off-resonance can be used as a robust strong-field coherent control method.     

Self-focusing of coherent pulses

Numerical integration of the coupled field-material system equations shows self-focusing when coherent pulses propagate through resonant absorbers. The effect appears to be distinct from self-focusing associated with adiabatic following.     

Space-time analogy for partially coherent plane-wave-type pulses

In this Letter we extend the well-known space-time duality to partially coherent wave fields and, as a limit case, to incoherent sources. We show that there is a general analogy between the paraxial diffraction of quasi-monochromatic beams of limited spatial coherence and the temporal distortion of partially coherent plane-wave pulses in parabolic dispersive media. Next, coherence-dependent effects in the propagation of Gaussian Schell-model pulses are retrieved from that of their spatial counterpart, the Gaussian Schell-model beam. Finally, the last result allows us to present a source linewidth analysis in an optical fiber communication system operating around the 1.55 microm wavelength window.     

Laser pulse design for coherent control of Rydberg lithium atoms

<正>Using the time-dependent multilevel approach(TDML),this paper studies the dynamics of coherent control of Rydberg lithium atoms and demonstrates that Rydberg lithium atoms can be transferred to states of higher principal quantum number by exposing them to specially designed frequency-chirped laser pulses.The population transfer from n= 70 to n= 75 states of lithium atoms with efficiency of more than 90%is achieved by means of the sequential adiabatic rapid passages.The results agree well with the experimental ones and show that the coherent control of the population transfer from the lower n to the higher n states can be accomplished by the optimization of the chirping parameters and the intensity of laser field.     

Laser pulse design for coherent laser control of potassium atoms

In this paper, the dynamics of coherent laser control of potassium atoms is studied by using the time-dependent multilevel approach (TDMA). The calculation results of population transfer are presented with different laser fields. The results show that the population can be transferred to target state completely by a specially designed laser field.     

Temporal compression of short-wavelength laser pulses by coherent control in rare gases

We present a theoretical study of temporal compression of a short-wavelength laser pulse predicted in a real, Doppler-broadened, atomic system. The compression is the result of the coherent control peculiarities of electromagnetically induced transparency-propagation dynamics. Numerical results are reported and discussed, showing a temporal compression of 2 orders of magnitude (from 10 ns to 100 ps) of a 106.7-nm laser pulse in argon atoms at room temperature.     

Transient sum-frequency mixing with temporally tailored laser pulses

We discuss the possibility of using temporally tailored pump laser pulses to control the temporal width and shape of optical pulses generated in a process of transient sum-frequency mixing in crystals with second-order nonlinearity. Specific calculations performed in a model crystal in the case of fifth-harmonic generation are presented.     

Generalized coherent state for soft gluon emission

By using a recursive soft insertion technique, many gluon emission amplitudes are computed to all orders in α_s and leading infrared accuracy. The resulting correlation structure is systematically exponentiated to yield a generalized coherent state operator which satisfies an integral equation where virtual corrections occur as a Sudakov matrix for many parton states. Infrared cancellations for physical quantities, including Drell-Yan processes, are derived on the basis of the unitarity relation for the coherent state. By further assuming strong ordering in emission angles, all known results on coherent effects and multiplicity distributions are easily recovered.     

Multiplex coherent anti-Stokes Raman microspectroscopy with tailored Stokes spectrum

We combined the ultrabroadband supercontinuum of a photonic crystal fiber with a pulse shaper, resulting in a highly flexible light source for multiplex coherent anti-Stokes Raman microscopy. Implemented as the Stokes pulse, it provides tailored selection of the relevant Raman transitions, resulting in a reduced photon load and partial suppression of the nonresonant background. This experiment exploits the advantages of multiplex excitation with the increased acquisition speed of single-channel detection. The molecule-specific Stokes pulses are demonstrated for chemical mapping of a polymer blend.     

Complex area correlation theorem for statistical pulses in coherent linear absorbers

We derive a complex area correlation theorem describing global second-order statistical properties of pulses propagating in coherent linear absorbers. We also illustrate temporal evolution of a generic partially coherent pulse in a coherent linear absorber by discussing the behavior of its temporal intensity profile and degree of coherence.     

Silicon surface morphology study after exposure to tailored femtosecond pulses

Temporal pulse shaping of ultrashort laser pulses has been used for laser ablation of semiconductors. Even the simplest double pulse sequence with a delay of several picoseconds shows remarkable differences in the interaction process, compared to a single pulse of the same total energy. We discuss the interaction of double pulses with single crystal silicon sample in the context of crater morphology for multiple pulses on the same spot. The growth of the typical columnar structures in helium at atmospheric pressure is suppressed and the crater bottom is flat despite the Gaussian beam profile. The influence of the temporal pulse shape has to be treated in conjunction with the influence of the other ablation parameters.     

Narrow-band coherent anti-stokes Raman signals from broad-band pulses

By tailoring the phase of a 100 femtosecond probe pulse we are able to obtain a narrow-band coherent anti-Stokes Raman spectroscopy (CARS) resonant signal with a width of less than 15 cm(-1), which is an order of magnitude narrower than the CARS signal from a transform limited pulse. Thus, by measuring the spectrum of the CARS signal we are able to obtain a high-resolution energy level diagram of the probed sample in spite of the broad femtosecond pulse spectrum.     

Shaping quantum pulses of light via coherent atomic memory

We describe proof-of-principle experiments demonstrating a novel approach for generating pulses of light with controllable photon numbers, propagation direction, timing, and pulse shapes. The approach is based on preparation of an atomic ensemble in a state with a desired number of atomic spin excitations, which is later converted into a photon pulse. Spatiotemporal control over the pulses is obtained by exploiting long-lived coherent memory for photon states and Electromagnetically Induced Transparency in an optically dense atomic medium. Using photon counting experiments, we observe Electromagnetically Induced Transparency based generation and shaping of few-photon sub-Poissonian light pulses.     

Application of optimal control theory to the design of broadband excitation pulses for high-resolution NMR

Optimal control theory is considered as a methodology for pulse sequence design in NMR. It provides the flexibility for systematically imposing desirable constraints on spin system evolution and therefore has a wealth of applications. We have chosen an elementary example to illustrate the capabilities of the optimal control formalism: broadband, constant phase excitation which tolerates miscalibration of RF power and variations in RF homogeneity relevant for standard high-resolution probes. The chosen design criteria were transformation of I(z)-->I(x) over resonance offsets of +/- 20 kHz and RF variability of +/-5%, with a pulse length of 2 ms. Simulations of the resulting pulse transform I(z)-->0.995I(x) over the target ranges in resonance offset and RF variability. Acceptably uniform excitation is obtained over a much larger range of RF variability (approximately 45%) than the strict design limits. The pulse performs well in simulations that include homonuclear and heteronuclear J-couplings. Experimental spectra obtained from 100% 13C-labeled lysine show only minimal coupling effects, in excellent agreement with the simulations. By increasing pulse power and reducing pulse length, we demonstrate experimental excitation of 1H over +/-32 kHz, with phase variations in the spectra <8 degrees and peak amplitudes >93% of maximum. Further improvements in broadband excitation by optimized pulses (BEBOP) may be possible by applying more sophisticated implementations of the optimal control formalism.