Role of Spin-Orbit Coupling in High-Order Harmonic Generation Revealed by Supercycle Rydberg Trajectories.

High-harmonic generation is typically thought of as a sub-laser-cycle process, with the electron's excursion in the continuum lasting a fraction of the optical cycle. However, it was recently suggested that long-lived Rydberg states can play a particularly important role in high harmonic generation by atoms driven by the combination of the counterrotating circularly polarized fundamental light field and its second harmonic. Here we report direct experimental evidence of very long and stable Rydberg trajectories contributing to high-harmonic generation in such fields. We track their dynamics inside the laser pulse using the spin-orbit evolution in the ionic core, utilizing the spin-orbit Larmor clock. We confirm their effect on harmonic emission both via microscopic simulations and by showing how this radiation can lead to a well-collimated macroscopic far-field signal. Our observations contrast sharply with the general view that long-lived Rydberg orbits should generate negligible contribution to the macroscopic far-field high harmonic response of the medium.

Few cycle dynamics of multiphoton double ionization.

In intense field ionization, an electron removed from the atomic core oscillates in the combined fields of the laser and the parent ion. This oscillation forces repeated revivals of its spatial correlation with the bound electrons. The total probability of double ionization depends on the number of returns and therefore on the number of optical periods in the laser pulse. We observed the yield of Ne(2+) relative to Ne(+) with 12 fs pulses to be clearly less compared to 50 fs pulses in qualitative agreement with our theoretical model.

Forced molecular rotation in an optical centrifuge.

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 approximately 420. At the highest spinning rate, the molecular bond is broken and the molecule dissociates.

Predictors of successful radiofrequency catheter ablation of sinoatrial tachycardia.

Predictors of successful elimination of sinoatrial tachycardia (SAT) using radiofrequency current (RFC) were investigated in this report. Within 1991-1996 fourteen patients with SAT were subjected to electrophysiological study and radiofrequency catheter ablation (RFCA). Ten patients had sinoatrial reentrant tachycardia (SART), and four patients had chronic non-paroxysmal sinoatrial tachycardia (CNPSAT). The RFC (15-30 W, duration 10-30 sec) were applied during tachycardia in case of CNPSAT, and during sinus rhythm (SR) in case of SART. In 3 patients with SART RFC were delivered during tachycardia due to failing of RFC application, delivered during SR. During successful RFC attempts were noted: 1). In case of SART-transient development (3-6 sec) of SART (if RFC was delivered during SR), and acceleration of tachycardia rate with following termination of tachycardia (if application of RFC was performed during tachycardia); 2). In case of CNPSAT-transient development (4-7 sec) of low right atrial (3 patients) or junctional (1 patient) rhythm with rapid conversion to SR. All 14 patients have been free of tachycardia and have normal sinus node function during follow-up of 8-60 months. We conclude that predictors of successful elimination of SAT are: 1). In case of SART-acceleration of tachycardia rate before termination during RFC application (delivered during tachycardia), and transient development of SART during RFC application (delivered during SR); 2). In case of CNPSAT-transient development of low right atrial or junction rhythm (during application of RFC) with rapid conversion to SR.

Subfemtosecond processes in strong laser fields.

Strong field atomic and molecular interactions can be understood by following electronic dynamics inside the laser cycle. This quasistatic perspective introduces the subfemtosecond time scale into strong-field dynamics through time-dependent Born-Oppenheimer surfaces. We discuss both theoretical and experimental results in atomic and molecular ionization and dissociation with applications to femtochemistry. An all-optical Coulomb explosion method for determining time-dependent molecular structure and properties is demonstrated. The concept of time-dependent Born-Oppenheimer surfaces is used to study molecular dissociation and exchange reactions in infrared fields.