16-fs, 1-microJ ultraviolet pulses generated by third-harmonic conversion in air.

We describe a simple method for generating sub-20-fs ultraviolet light pulses with useful average powers, using a kilohertz Ti:sapphire laser system. By focusing a 22-fs, 1-mJ laser pulse in air, we obtain ultraviolet pulses with an energy of 1 microJ and at a wavelength of 266 nm and with an average power of 1 mW. The pulse duration of the ultraviolet pulses was measured to be 16 fs with frequency-resolved optical gating.

Molecular engineering of polymer films for amplitude and phase measurements of Ti:sapphire femtosecond pulses.

Using second-harmonic frequency-resolved optical gating and a tricyanovinylaniline polymer thin film, we have measured the amplitude and the phase of mode-locked Ti:sapphire laser pulses as short as 13 fs. These thin films are ideally suited for ultrashort-pulse diagnostics because they eliminate the angle tuning associated with birefringent phase-matched crystals, minimize pulse distortions introduced by group-velocity dispersion, and exhibit excellent photochemical stability.

Ultrashort optical waveform measurements using frequency-resolved optical gating.

We measure the intensity and phase of ultrashort pulses from a self-mode-locked Ti:sapphire laser using the recently developed technique of frequency-resolved optical gating. These results represent to our knowledge the shortest complete optical waveform characterization measurements performed to date. We also verify recent theoretical calculations that predict that the main limitation on the pulse duration from these lasers is the presence of uncompensated higher-order dispersion.

Pulse evolution in a broad-bandwidth Ti:sapphire laser.

We demonstrate that by operating near the zero second- and third-order dispersion point in a self-mode-locked Ti:sapphire laser we can generate sub-10-fs pulses. Our numerical simulations show that the pulse duration is limited by fourth-order dispersion and that shorter pulses will be possible if this can be reduced. Also, by inserting a pellicle in various positions in a Ti:sapphire cavity, we have measured the intracavity pulse duration and chirp of the circulating pulse in the laser. Our results demonstrate that the pulse is shortest near the middle of the laser crystal, in one direction of propagation. In the other direction of propagation, the pulse is positively chirped and several times longer.

Diagnosis and treatment of the hemiplegic patient with brachial plexus injury.

Brachial plexus injury was observed as a complication in 5 of 12 hemiplegic patients admitted over a 5-week period to an inpatient unit of the Rehabilitation Institute of Chicago. These patients exhibited unusual patterns of muscle atrophy and return of function in the impaired upper extremity. Occupational therapists may play an important part in the diagnosis and treatment of this complication of hemiplegia by promptly recognizing its subtle clinical signs and instituting appropriate therapy. Electromyography may be recommended to confirm this diagnosis. The treatment of choice is to maintain correct positioning of the limb both day and night, to use facilitation techniques for specific muscles in order to prevent atrophy, and to maintain passive range of motion as much as possible. Prevention of brachial plexus injury depends largely on the education of patient, family, and staff as to the potential hazards to a frail extremity that has no protective responses.

Stroke and brachial plexus injury: a difficult problem.

Five patients are presented, all of whom had middle cerebral artery syndrome with hemiplegia on the contralateral side. All five had electromyographic evidence consistent with neuropathy involving the upper trunk of the brachial plexus on the side affected by the stroke. All patients were exposed to intensive rehabilitation team effort involving range of motion, strengthening exercises, positioning, splinting, coordination exercises and exercises designed to increase ability at arm placement. Three patients regained EMG evidence of innervation of the shoulder girdle muscles after more than eight months, during which time a rehabilitative effort was made. The other two patients have not yet regained control over the muscles of the shoulder girdle by EMG or clinical criteria. The EMG evidence of brachial plexus injury in those patients who eventually showed reinnervation took 8 to 12 months to resolve. The rehabilitation of the patients with stroke involving the upper extremity may have been set back significantly as a result of the neuropathy. It is suggested that patients with stroke and brachial plexus injury probably will have a more arduous and prolonged course in rehabilitation of the upper extremity as a result.