R. R. Jones

Generation of high-power sub-single-cycle 500-fs electromagnetic pulses.

We have generated sub-single-cycle pulses of electromagnetic radiation with pulse energies as high as 0.8 μJ and pulse lengths < 500 fs. The 10-dB width of the spectrum is 1.5 THz. The transmitter is a GaAs wafer illuminated at normal incidence by 120-fs, 770-nm pulses from a Ti:sapphire chirped-pulse amplifier system while a pulsed electric field is applied across the surface. The pulse energy of the far-infrared radiation is found to be a quadratic function of bias field and a nonmonotonic function of laser intensity.

Interferometric characterization of 160 fs far‐infrared light pulses

We report the first interferometric characterization of freely propagating, subpicosecond, far‐infrared (FIR) light pulses. FIR light was generated via short pulse photoexcitation of a semi‐insulating InP wafer. The half width of the intensity interferogram was 230 fs. The FIR light contained frequency components from 3 to 150 cm−1.

Attosecond tracing of correlated electron-emission in non-sequential double ionization

Despite their broad implications for phenomena such as molecular bonding or chemical reactions, our knowledge of multi-electron dynamics is limited and their theoretical modelling remains a most difficult task. From the experimental side, it is highly desirable to study the dynamical evolution and interaction of the electrons over the relevant timescales, which extend into the attosecond regime. Here we use near-single-cycle laser pulses with well-defined electric field evolution to confine the double ionization of argon atoms to a single laser cycle. The measured two-electron momentum spectra, which substantially differ from spectra recorded in all previous experiments using longer pulses, allow us to trace the correlated emission of the two electrons on sub-femtosecond timescales. The experimental results, which are discussed in terms of a semiclassical model, provide strong constraints for the development of theories and lead us to revise common assumptions about the mechanism that governs double ionization.

Alteration of the lifetimes of autoionizing Rydberg states by a circularly polarized microwave field

Autoionizing Rydberg states in zero field exhibit lifetimes scaling as the cube of the principal quantum number, n3, but in a linearly polarized static or microwave field the lifetimes scale as n4 due to l mixing. To mimic the effects of collisions with charged particles we have examined the effect of a circularly polarized field on the decay rate and find longer lifetimes than in a linearly polarized field, but not an n5 dependence.

Probing Rydberg electron dynamics

Recently, the excitation of various types of Rydberg wave packet has become a common method for studying quantum-classical correspondence, internal dynamics in the presence of strong electromagnetic fields, and possibilities for quantum control. This paper reviews several methods for probing the evolution of Rydberg electrons including the basic theory behind each method and what dynamical information can be obtained.

Extracting the polarizability anisotropy from the transient alignment of HBr

We use 40 fs, 780 nm laser pulses to transiently align HBr molecules. We study the temporal dynamics of the resultant rotational wavepacket to gain insight into the electronic properties of the molecule. We show that the HBr polarization anisotropy can be extracted by comparing the time dependence of the HBr alignment with both the analogous alignment behavior of N(2) and the predictions of a rigid-rotor model.

Controlling atom motion through the dipole–dipole force

We describe simulations that illustrate the possibility for manipulating the position correlation of atoms in a magneto-optical trap (MOT) using the dipole–dipole interaction. The control scheme utilizes a narrow band laser that is detuned to the high-frequency side of a single-photon Rydberg transition in an isolated atom. As two atoms move near each other, they can be laser excited to repelling diatomic Rydberg–Rydberg potential energy curves which halt their approach. By chirping the laser from large to small detunings, atoms in a MOT can be pushed apart by dipole–dipole forces, thereby controlling nearest-neighbor interactions. Alternatively, by holding the frequency of the Rydberg excitation laser fixed as the MOT is loaded, it should be possible to limit the minimum distance between atoms to a prescribed value.

Single-shot Detection of Wavepacket Evolution

We have developed a new instrument for monitoring electronic wavepacket dynamics using a single electromagnetic pulse pair. The operation of the device is analogous to that of single-shot cross-correlators commonly used to monitor the temporal evolution of short laser pulses. We have used the instrument to probe wavepacket evolution over time scales ranging from 100 psec to less than 1 fsec. The device reduces the amount of time required to collect pump-probe time delay data by orders of magnitude, greatly reducing the deleterious effects of experimental drifts. In addition, the single-shot feature provides real-time feedback as to the aspect of various experimental parameters on the electron dynamics, allowing us to literally tune-up our equipment to enhance desired behavior at specific times.

Ba 6pjnfj' autoionizing series.

Members of the 6{ital p}{sub {ital j}}nf{sub j{prime}} autoionizing series in barium have been observed experimentally using multistep laser excitation. The recorded spectra exhibit extremely broad profiles for {ital n} values ranging from 7 to 30. We have fitted the spectra using an energy-independent multichannel quantum-defect theory model that reproduces the data reasonably well in spite of the fact that the full widths at half maximum of the excitation profiles are comparable in magnitude to the energy spacings between adjacent states. Experimental quantum defects and autoionization rates are presented along with the parameters determined from the theoretical fit.

Stability of atoms in intense laser fields

Several mechanisms can impede or even eliminate photoionization or photodissociation of bound quantum systems in an intense laser field. This paper reviews recent laboratory studies of these effects.